Sanders Sound Systems

World Leading ESL - Electrostatic Speakers & Amplifiers
The Electrostatic Specialists -Hand Crafted In Colorardo
ABOUT US
Roger Sanders has been at this for 40 years. His first published article on Electrostatic Speakers was in 1974, followed by another on amplifiers to drive ESL's in 1976.

His contribution to audio include the invention of the curved, free-standing, electrostatic loudspeaker driver the development of extremely compact transmission line woofer systems; integration of electrostatic speakers and transmission line woofer systems; and, several "how to" construction articles in "The Audio Amateur" and "Speaker Builder" magazines.

One of Roger's greatest contribution to the state-of-the-art, is his book, "The Electrostatic Loudspeaker Design Cookbook" , published by The Audio Amateur in 1993.Written for the audiophile craftsman rather than the engineer, this treatise is a definitive set of instructions, explanations, and, arguments for a "The Electrostatic Loudspeaker Design Cookbook"' published by The Audio Amateur in 1993.Written for the audiophile craftsman rather than the engineer, this treatise is a definitive set of instructions, explanations, and, arguments for achieving the most accuracy and realism possible.Throughout all this time, he has been perfecting the hybrid electrostatic loudspeaker, as well as designing amplifiers to effortlessly drive them to maximum effect.
Great listening,
…….Roger Sanders

DESIGN PHILOSOPHY
Roger Sanders built his first ESL (ElectroStatic Loudspeaker) in 1972.  He quickly appreciated the superior performance that a massless electrostatic offered over conventional magnetic speakers with regards to low distortion, lack of resonances, and incredible detail.  But their problems of limited output, inability to produce deep powerful bass, and unreliability have kept him busy improving them over the last 30+ years.

The result of this lifetime of work is that Sanders Sound Systems ESLs are the only ones to have solved all the  problems and limitations of ESLs.  Roger's "Ultrastat" panels will play at ear-bleeding levels, cannot be arced, do not use or need protective circuitry, are immune to humidity, dust, and dirt, and do not need or use dust covers.  They can be driven by multi-thousand watt amplifiers without damage.  They are more rugged than conventional magnetic drivers.  They do not fail and are so robust that they come with a lifetime warranty.

A major part of his work was devoted to dealing with the issue of high frequency "beaming" in large, planar loudspeakers.  To deal with this issue, he invented the free-standing, curved, electrostatic panel.  This made it possible to widely-disperse the high frequencies from a large ESL.  He published this invention in Speaker Builder Magazine in 1980.  The Martin Logan company adopted his technique in their ESLs.

Roger expected that his wide-dispersion, curved panels would perform better than narrow-dispersion, planar speakers. But he discovered that the curved panel was inferior to a planer one with respect to transient response, imaging, frequency response, speaker placement, and output.    These problems caused by wide-dispersion speakers spraying their sound all over the room instead of being directed at the listener.  As a result, in a wide-dispersion speaker, the listener hears the room with all its confused and delayed reflections instead of the superb sound available directly from a planar ESL.   Roger won't compromise the quality of the sound by using his wide-dispersion design, so he abandoned it in favor of planar ESLs.  The sound from his planar speakers are superior to all others with regard to transient response, 3-dimensional imaging, and frequency response.

"Roger Sanders, inventor of the curved electrostatic loudspeaker, will make you rethink everything you always thought you knew about stats. He sure did (rethink everything) to the point of abandoning his own invention for a contradictory philosophy. His logic is irrefutable, his speakers are infallible, and his electronics are unstoppable. Check out this video for a crash course on electrostatic myths and mating." - Audiogon

A major part of his work was devoted to dealing with the issue of high frequency "beaming" in large, planar loudspeakers.  To deal with this issue, he invented the free-standing, curved, electrostatic panel.  This made it possible to widely-disperse the high frequencies from a large ESL.  He published this invention in Speaker Builder Magazine in 1980.  The Martin Logan company adopted his technique in their ESLs.

Roger expected that his wide-dispersion, curved panels would perform better than narrow-dispersion, planar speakers. But he discovered that the curved panel was inferior to a planer one with respect to transient response, imaging, frequency response, speaker placement, and output.    These problems caused by wide-dispersion speakers spraying their sound all over the room instead of being directed at the listener.  As a result, in a wide-dispersion speaker, the listener hears the room with all its confused and delayed reflections instead of the superb sound available directly from a planar ESL.   Roger won't compromise the quality of the sound by using his wide-dispersion design, so he abandoned it in favor of planar ESLs.  The sound from his planar speakers are superior to all others with regard to transient response, 3-dimensional imaging, and frequency response.

Full-range, crossoverless ESLs are widely believed to be the "holy grail" of loudspeakers.  In theory, using a single drive to reproduce the entire audio range, without the problems introduced by crossovers, would be ideal.  Roger has built many such speakers.  But the laws of physics cannot be circumvented.  A full-range ESL simply cannot produce deep, powerful bass or have generally high output and full dynamic range.

Roger spent 17 years developing woofer systems that would blend seamlessly with a massless ESL to produce outstanding bass and end the frustrating limitations of full-range ESLs.  His well-designed, hybrid systems are far superior to a full-range, crossoverless ESL.

While building and selling full-range ESLs is easier and less costly than a hybrid, Roger won't compromise .  Therefore all Sanders speakers are hybrids.

Crossovers are a major limitation in conventional speakers.  The passive crossovers typically used are seriously flawed and cannot be used if you want a speaker with the highest possible performance.  Electronic crossovers and bi-amplified operation are far superior to passive crossover systems and are absolutely essential for spectacular speaker performance.  Therefore, all Sanders' speakers come with electronic crossovers and bi-amplification.  Sanders ESL Panel

We supply an amplifier and electronic crossover with each speaker system.

To eliminate the usual customer complaint about having to buy two amplifiers to operate bi-amped speakers, Sanders supplies a bass amplifier as part of each speaker system.  The customer then only has to provide a single amplifier of his choice just as they would for any conventional speaker system.

These amplifiers are not cheap, underpowered, or Class D switching amplifiers.  They are multi-hundred watt, Class AB amplifiers that are very expensive, offer the finest in performance, come in beautiful chassis, and will drive the speakers with full dynamic range at realistic, concert hall levels.

When a speaker system is put in a room, it will interact with the room and this will have adverse effects on the sound.  Even a "perfect" speaker system will be degraded by the room.  It therefore is essential for all speakers to be adjustable to compensate for room effects.  The electronic crossovers used in Roger's speaker systems have extensive controls to allow the user to adjust the speaker to compensate for the flaws in his listening room.

This adjustability means that the user can make the speakers sound almost any way they wish.  It is no longer necessary to be "stuck" with the particular sound of a room/speaker combination as is the case with conventional speakers.  If you don't like what you hear with Sander's electrostatic speakers, you can adjust them so that they sound the way you like.

In summary, Sanders' speakers use the finest technology and design possible. 

No compromise is made to either to reduce cost or sacrifice any aspect of speaker performance.   The combination of electrostatic mids/highs, transmission line woofers, and fully adjustable electronic crossovers makes it possible finally to have a speaker system that can do it all without compromise.

Sanders Sound Systems Electrostatic Speaker Model 10 in walnutSanders Sound Systems Electrostatic Speaker Model 11 in walnut 

We now have Three Unique ESL models available:

11 -  Smaller version of the 10c; with digital crossover and ESL Mark II Amplifier

10c - Full size speaker with digital crossover and Magtech Amplifier
10d Latest version of Model 10 with new bass driver and revised transmission line digital crossover and Magtech Amplifier 

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Power amplifiers (Stereo & Mono)

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We have 1 left (1 sold) of these awesome Sanders 500w stereo power amps available being sold-on-behalf. Had little use and in perfect condition, guaranteed to get any speaker dancing to it's maximum...
Magtech - the only amplifier with a linear, voltage regulator (Patent Pending) Over 500 watts/...
For some reason there remain relatively undiscovered gems in the audio world. The Sanders Sound...

Reviews

Roger Sanders' new speaker system strikes me as being a remarkable achievement, - I left it on for months, it was always quiet, it drove the crap out of anything I connected to it, and it seemed to have no distortion
Phillip Holmes

Please note: since this review Roger updated the ESL amp to 360w/ch plus other modifications and introducded its bigger brother the Magtech @ 500w/ch, the outcome is for even great enjoyment and power to drive any speaker. 

Summaery:
The Sanders Sound ESL Amp is actually closer sounding to a powerful big-ticket tube amp than a “normal” 60wpc transistor amp. That’s what makes me consider the ESL Amp an enormous success. Outside of the user friendly qualities that Roger has designed into the amp, it does a tremendous job of amplifying a signal without changing its character. Considering the reasonable price, I think it’s an amazing product. If you need power, and most of you need more than you realize, you must hear it if it fits your budget.

Extended review:
I consider this more of an addendum than a proper review. I had the ESL power amp for use with the 10B speaker system. The 10B comes with electronic crossover and built-in bass amp, but you had to supply your own amp for the electrostatic panels. I had some tube amps on hand, but the load presented in the highs would cause high frequency roll-off. The impedance drops to 1.6 ohms at 20 kHz. I had an amp from Plinius, but the combination sounded bright. I wasn’t expecting it to be bright and couldn’t figure out why. Roger suggested it was possibly an oscillation caused by the wrong kind of speaker cable and an unhappy capacitive load for the big Plinius. I tried some video coax for speaker cabling since it was shielded and of very low capacitance. I still had the same tonal balance. I wanted to hear the same combination I had heard at CES 2009, so I contacted Roger about sending the Magtech Amp to complete the system.
 
Outside of a powerful tube amp (at least 120 watts), I can’t imagine a better amp to drive an electrostatic loudspeaker than the ESL Amp. Roger thoroughly addressed every pitfall of driving ESLs, and did so with a transistor design. It would’ve been easier for Roger to design a powerful mono tube amp of generic design, say parallel push-pull sweep tubes for 200 watts. Tube amps don’t oscillate when driving the very high capacitance loads presented by ESLs. They just lose steam in the highs. In the end, Roger’s ESL Amp has flat frequency response, is several orders of magnitude more efficient, generates almost no heat, is housed in one chassis that can be situated almost anywhere and can be left on all the time.
 
What’s more important for this article is how it sounds with other speakers. To wit, how does it sound driving the incredibly inefficient and low impedance Magnepan 2.6R? I’ve had these speakers for years, and after modifications (updates), still enjoy the sound. On the other hand, I always felt as if I needed WAY more power.
 
The ESL is rated at 2000 volt-amps, which is similar to a “normal” 1000-watt amplifier, see here for an explanation. The volt-amp rating applies to capacitive loads. With magnetic speakers, the ratings are more typical, though still quite powerful:
 
· 300 watts/channel into 8 ohms
· 600 watts/channel into 4 ohms
· 1000 watts/channel into 2 ohms (momentary/dynamic output)
 
If this isn’t enough, there is the mono version that delivers 800 watts into 8 ohms and 1200 into 4 ohms.
 
I found out from Roger that the ESL has since been upgraded and uprated:
 
“The latest version is:
- 360 w/c @ 8 ohms,
- 700 w/c @ 4 ohms,
Mono
- 1000 watts at 8 ohms
- 1600 watts at 4 ohms.

I need to update my website! The amp you tested was the original 300w version.”
 
For the sake of saving time, and touching on the technical issues, please refer to the “ESL Amp White Paper” on the Sanders Sound website.
 
I can say that none of the statements are snake-oil ramblings, or marketing hyperbole. I left it on for months, it was always quiet, it drove the crap out of anything I connected to it, and it seemed to have no distortion (that I could hear).
 
There’s no reason to spend a thousand words to describe the music I listened to with the ESL Amp, but if you haven’t read the 10B speaker review, then do so. Whatever I say about the sound of the 10B goes for the ESL Amp. If the ESL Amp weren’t good, the 10B is transparent enough that it would’ve told me it stinks (which it did on cables, amps, tubes, cartridge set-ups….you name it; if you get it wrong, you’ll know with the 10B).
 
What I do want to point out is that this is a primo quality amp for driving power-thirsty Magnepans. Until Roger’s ESL, the most powerful amps I had tried were 150-watt mono tube amps. They could play “loud”, but sounded forced and flustered when trying to recreate the sound and fury of the Beethoven 9th, Saint-Saens “Organ Symphony”, Der Ring Cycle, or anything by Shostakovich. By extension, this meant that I couldn’t rock-the-house with tube amps. No balls when listening to AC/DC, Metallica, The White Stripes, “The King James Version”, “Still Harry After All These Years”, and a lot of good stuff from Basie and Ellington. Sure, they could play Beethoven’s 1-8, any jazz quartet/quintet, “Kind Of Blue” and most pop music. Growing up around music, and having spent years in concert halls, I can tell you that music is often felt as much as heard. Regardless of what it might do to your hearing, a tam-tam at 50’ while the symphony is playing Stravinsky takes your breath away. It requires monumental amounts of power to try to recreate something like that, and 150 watts won’t cut it with the ESL 10B.
 
The ESL Amp delivered the goods when it came to reproducing musical peaks without strain. There’s a hot-rodding saying that applies here: there is no substitute for cubic inches. Even the “tricks” like supercharging are just making the engine hold the same amount of air that a larger displacement normally-aspirated engine would use. With speakers I’ve used, even the high efficiency designs, the use of a healthy power amp allows me to listen to all kinds of music, not just audiophile recordings of pretty girls. The intermodulation distortion of under-powered systems is something that you won’t hear until you get an amp of proper power. Once your ear becomes accustomed to hearing the IM distortion and compression, you can’t go back. I’ve heard 98dB single-driver speakers that compressed and got muddy, and not at what I consider realistic levels. That might mean an 833-based amp instead of a 300B for a horn. Maybe 150 watts for moderately efficient speakers. With the Maggies, it must mean that at least 600 watts is the minimum to sound relaxed. I’ve heard what a system can do with 3,000 tube watts driving 93dB efficient speakers, and the power was only sometimes needed. The ability to play peaks with no effort means less listening fatigue. Less IM and compression means more enjoyment.
 
That’s not to say that just any old, powerful amp is going to be “mission accomplished”. The mantra that power corrupts and absolute power corrupts absolutely is well applied to amplifiers. Few are the powerful amps that sound transparent. Many are the powerful amps that sound downright unmusical. Until the ESL, I’d heard only a couple other designs that had the openness and transparency of the tube designs I like.
 
I think one of, or maybe the thing, that makes the ESL Amp sound the way it does, is that it doesn’t use coupling (DC blocking) capacitors in the signal path. The only transistor amps I’ve heard that I liked were direct-coupled/DC-coupled (no coupling caps). Further, like the other transistor amps I’ve liked, it is balanced/complimentary/push-pull all the way through. This contributes to a dead-quiet nature of the ESL Amp.
 
Roger differs with my opinion and had this to offer: “Truth be told, the main reason that the ESL Amp sounds good has nothing to do with capacitors. It is due to the fact that it has no protective circuitry that ruins the sound when in operation. The output stage of the ESL Amp is so massive that it can never be taxed when driving difficult loads, so I can eliminate the awful audio effects of protective circuitry.”
 
Overall, the ESL Amp is one of the most neutral power amps I’ve had the pleasure of hearing. It’s very transparent. If you have something amiss, you’ll be able to hear it. Recordings have their sound amplified intact. There is no “sterile transistor sound” or pseudo-tube romanticism.
 
Macro-dynamics are very strong. Bass drum whacks are first rate. The plucked string is also very good, but not quite as jumpy as a SEDHT amp. There is some penalty for the extra devices and complexity, that seemed to be one of the trade-offs here: a penalty on microdynamics. Likewise, this amp isn’t as immediate as simple tube amps. It still has immediacy, but not on the level of the finest tube products. I could say the same thing about really big tube amps: not as much immediacy or micro-dynamics—very simple amps can do some things quite well.
 
Soundstage width of the ESL Amp is first rate, imaging well outside the speakers and placing a solid center image. It’s not as deep or dimensional as some competing thermionic designs, but it’s as good as any transistor amp I’ve heard.
 
Many of the stereotypes of tubes-versus-transistors have more to do with execution and design than any inherent weakness of the transistor (or the tube if that’s where you stand). At this level of performance, I am splitting hairs. The Sanders Sound ESL Amp is actually closer sounding to a powerful big-ticket tube amp than a “normal” 60wpc transistor amp. That’s what makes me consider the ESL Amp an enormous success. Outside of the user friendly qualities that Roger has designed into the amp, it does a tremendous job of amplifying a signal without changing its character. Considering the reasonable price, I think it’s an amazing product. If you need power, and most of you need more than you realize, you must hear it if it fits your budget.
 
As a follow-up to the review, I spoke with Roger about his other amps, and his response is in the following:
 
Note that I now have my Magtech amplifier in production. It uses the same outstanding amplifier design as my ESL Amp, but incorporates a linear regulated power supply that is virtually 100% efficient. As a result, it produces much more power than the ESL Amp (500 w/c @ 8 ohms) even though it is in the same chassis.
 
Because the internal voltages are not modulated over a range of 30% (typical of conventional amps that do not have regulated power supplies), the distortion remains extremely low at all times (0.0012% typical).
 
There are virtually no amplifiers on the market that have regulated power supplies (only the Krell monoblocks at $100K are regulated). And the Magtech is the only amp that uses a linear supply that is essentially 100% efficient (patent pending). It would drive your Maggies even better than the ESL Amp.
 
Sounds like Roger isn’t sitting still (pun intended).
The Sanders ESL amplifier can form the heart of a fine reference audio system
Ron Nagle

What can I say, practically all the clean power one could ever want, capable of driving any audiophile loudspeaker, surely the last amplifier you will ever buy? Understand that I believe the ML Vista electrostatic hybrid loudspeaker serves as an excellent test for an amplifiers ability to drive any type of loudspeaker. Most certainly, this amplifier represents the current here and now edge of technology applied with precision without becoming hard or sterile sounding.

Let me premise what follows by saying I am impressed by what I have learned so far. These ESL amplifiers spring from the mind of an audiophile and not just a numbers-crunching paradigm driven techno type. Having said that Mr. Sanders is an interesting story unto himself. Back in 1974, he authored an article in Speaker Builder magazine about electrostatic speakers. Then in 1976, this was followed with an article on amplifiers designed to drive them. In 1980, he wrote about the construction of an electrostatic speaker with a curved diaphragm and he was the first to develop this curved profile. You might remember that a similar Curvilinear electrostatic radiating surface is the hallmark of all of the loudspeakers made by the MartinLogan Company. He is best known for his contribution to the state of the art in his book, "The Electrostatic Loudspeakers Design Cookbook" published by The Audio Amateur in 1993.
 
In 1997 Roger Sanders joined Raj Varma to form the Innersound Company. Their products were a hybrid loudspeaker with a cone woofer and a flat electrostatic panel and the Innersound ESL amplifier designed to drive their loudspeakers. Both products received a lot of good press in the audiophile articles written at that time. Then in 2003, Innersound moved from Georgia to Boulder, Colorado. The year 2004 Roger Sanders left and in 2007 he formed Sanders Sound Systems now located in Conifer, CO. It is important to note that Mr. Sanders has managed to not only continue to make and improve his ESL amplifiers but after a gap of three years, he has resumed production of his innovative electrostatic loudspeakers. The now discontinued Innersound loudspeakers and the new Sanders sound systems loudspeakers abandoned the curved electrostatic panels he developed explaining that the curved surface introduces a new set of problems not inherent with flat electrostatic panels.
 
Facts Of Life
 
It just may be that you need a very special amplifier to get the best performance from an electrostatic loudspeaker. Electrostatic loudspeakers present an amplifier with a very varied and difficult load more complex than conventional cone driven loudspeakers.
 
The designer of a dedicated ESL (Electrostatic Loudspeaker) amplifier has to consider many factors, not only the crazy impedance shifts but also the fact that as frequency increases electrostatic speakers morph into something that looks like a giant capacitor. Basic electronics textbooks will tell you that at high frequencies capacitive current leads voltage by 90 degrees. To make an obvious point such an amplifier must be able to supply enough voltage and current to more than match any demands made by frequency changes and dynamic swings in music. Most importantly, it is necessary to supply this power in an evenhanded manner (low distortion) at all frequencies. All of these factors mandate that the power source be absolutely rock solid stable under any conditions. Normally I would mention only a few salient amplifier stats and leave the rest to the specifications I list at the end of an article. However, some of the specifications that describe the Sanders ESL Amplifier are damn amazing. I wouldn't want these languishing as an unread end of the article after thought. All the same I would like you to understand like must audiophiles I am really not into measurements because experience tells us they usually do not predict how an amplifier will sound, having said that good specs are generally not a bad thing.
 
Amplifier Nomenclature
 
It is important to understand that the Sanders Sound Systems amplifier under review is a different and much improved version of the earlier Innersound design. The chassis is now aluminum and is of a heavier gauge construction. The balanced XLR connectors are Neutrik, and the RCA connectors are Cardas. The more powerful-shielded toroidal power transformer is massive and fills about 75 percent of the chassis interior. This larger transformer has increased the power rating by 60 watts it is now rated at 360 watts per channel into 8 Ohms. A redesigned power supply circuit board now eliminates all wire except for a 2-inch piece connecting it to the speaker binding posts. The low-level input circuitry is redesigned and uses higher-grade transistors. More powerful and more linear bipolar output transistors are now used; this in combination with improved circuitry lowers harmonic distortion from 0.03% in the Innersound version to a vanishing 0.008% for the revised Sanders amplifier.
 
In this newer ESL amplifier there are 18 bipolar hi-power transistors in each channel connected in parallel they have a combined power rating of 4500 watts at 10 MHz. The peak current rating is 135 Amperes. The term damping factor refers to a ratio of amplifier output impedance to loudspeaker load impedance, this computation gives you some idea of the control exerted at bass frequencies. These select hi-capacity power transistors present a total parallel output resistance of only 0.01 Ohm. This translates into a very high damping factor of 800 into an 8-Ohm load. The power rating listed is 360 watts per channel into 8 Ohms and 600 watts per channel into 4 Ohms and the amplifier is stable down to 1 Ohm. The rated power is 1700 VA per channel into capacitive loads with both channels driven from 20Hz to 20kHz. The distortion is listed as 0.03% from 20Hz > 20kHz. Noise less than 100dB below rated output. Last but not least the specifications are for a linear class A/B amplifier. The definition of a linear amplifier is: an amplifier where the output signal is a replica of the input signal and the output is directly proportional to the input. There are many more specifications I could list but you get the idea.
 
There are two ergonomic difficulties that I encountered. The owner's manual suggests that you could leave the amplifier powered on and this would eliminate stress by not cycling the amplifiers power on and off. Naturally, this makes a lot of common sense but I have a tube preamplifier and it needs to be powered down when not in use. In addition, it is not a very good idea to turn on my tube preamplifier while it is plugged into this power amplifier. There should be a way to mute the amplifier output and some indication that it is muted. My last concern is that the power switch is located on the back panel and if you have the amplifier stacked on a shelf in an equipment rack (like I have) than it would be hard to reach.
 
Raison D'etre

Hooked on air, the kind that surrounds me in sound. It is the something that makes music appear on a gossamer fabric of film that energizes the air around. I have owned Quad ESL 63 electrostatic speakers for many years. I love the way they make music that flows effortlessly and naturally in continuous wavelets free from mechanical artifact. While having never stopped trying to squeeze the very last drop of music out of my Quads, over the years I replaced all the panels and upgraded the grills than installed a mod squad resistor capacitor network plus mounted them on dedicated Gradient woofers. So you may understand my abiding interest in Roger Sanders ESL amplifier made specifically for electrostatic loudspeakers. The ESL amplifier arrived just as I was in the process of evaluating a pair of MartinLogan's brand new Vista loudspeakers. This $3995 electrostatic hybrid is the only loudspeaker in the extensive MartinLogan line that does not have a built in 'Class D' woofer amplifier. It stands 57 inches high 40 inches of that is a narrow line source electrostatic panel and below in a ported enclosure is an 8inch metal cone woofer. Common sense will tell you if you want to use these loudspeakers to evaluate audiophile electronics then you best had better not use their built in amplifier to complicate the musical mix. At this point I would love to go off on a tangent and tell you what a mess most switching amplifiers make of high frequencies but that is best left for another time.
 
Amplifier Trials

Using my Marantz DV8400 Universal disc player feeding an Audio Research SP 9 MK3 preamplifier signal from this then routed to my power amplifiers via three meters of Wire World Eclipse 2 unbalanced cables, this was the unchanging reference front end. My in house loudspeakers are called, Strata Mini by AV123.com. These 4 way loudspeakers have a built in woofer amplifier so even though I listened to them they are not part of this report.
 
Initially I powered the ML Vista loudspeakers with a PrimaLuna Prologue 2 this is a 40wpc KT88 integrated amplifier. The bass was less defined and not as agile when compared to the mid range and treble speed but overall it was not at all hard to listen to. Next up was my feature filled OutLaw RR2150 receiver. This 100-wpc receiver has bass and treble controls and a separate EQ control to select bass turnover frequencies. With this EQ control, I was able to limit the amount of bass at a frequency of 55 Hz confirming that without this bass cut the bass sound was, as the British would say a bit "plumy". Next in line was my much-modified 250 wpc Hafler 500 amplifier. The main advantage here was that it has the ability to pump a lot more power into the Vista loudspeakers.
 
At this point what I heard was a lot closer to the musical truth. The Hafler seemed to be able to supply the power necessary to inject life into the performance by way of dynamic contrasts. The Sanders SEL Amplifier arrived at this time and in a manner of speaking it placed all the other amplifiers into a different musical context. What I had been doing was not just switching amplifiers but sampling music through a variety of tinted lenses. My analogy is that in retrospect some of the amplifier characteristics I noted were subtle colorations not inherent to the music. None of these was unpleasant but none of these was quite accurate. In retrospect, there was a suggestion from the tube amplifier of a subdued shade of mauve. The Outlaw amplifier tended more toward a shade of pale blue and the Mosfet Hafler was a pleasant slightly fuzzy light beige. Forgive my imaginative rainbow of a description but that is the best way to convey my subjective impressions.
Aural Aspects
What do you hear when you have all the clean music power you need and limitations have been pushed to a place that is practically unapproachable. Metaphorically speaking, we can experience this (borrowing a worn phrase) as a clearer window on the performance. With the Sanders ESL amplifier driving the MartinLogan Vista loudspeakers the cone bass drivers were now held in a tight grip and became nearly as articulate as the electrostatic panels. (Note: 90 percent of the audio power produced is used to drive the loudspeaker at frequencies below 200Hz) At a manufacturers specified frequency of 20 kHz the Vista loudspeakers become more capacitive and the resistive load drops down too a very difficult 1.3 Ohms.
 
Right now I can't think of a better recording to illustrate the articulation and speed of the ESL amplifier than a wonderful version of "You Were Always On My Mind" by Willy Nelson. I found it on a Sony (CD A21562) it is from an album titled Willie Nelson Yours Always. This is a wonderfully engineered and detailed studio mix with transient speed and studio ambience that highlights the ESL amplifiers resolving ability. At two minutes and forty seconds into this cut there is a brief faint sound of a person in the distant background whistling along with the melody. Meanwhile Willy's vocal resides front and center in all his nasal glory amidst the glisten of steel guitar strings. Backup vocals are etched and clearly delineated and recede in layers from the immediate left center stage. In a strange and unexpected way the metallic reverberation of the guitar strings complements the country twang of Willy's voice.
 
If you want to test low frequency tonal integration than I can think of no better way than to play "Adagio d' Albinoni" as performed by Gary Karr and Harmon Lewis. This was originally on a Japanese Firebird label but it may be available via the Cisco Music catalog (GCD8003). Recorded in a cavernous Japanese cathedral it is a duet of a large sonorous pipe organ and Karr's centuries old Amati bass fiddle. It is not enough to just rattle low bass it is another thing to get all the wooden warmth and rich sad sounding harmonic overtones of this bass instrument correct.
 
The reverberations and echo of the low register organ pipes holds the woofer for a moment on a deep sustained rumble. The resinous bass bowing sighs and breathes a mournful moan that tugs at your heart. The sound is absolutely organic and for a time you forget that it's not flesh and blood calling out to you. Every contributing element of my system and music selections was clear to hear. If I had to pick my best CD it would more than likely be The Look Of Love by "Diana Krall"; it is the Verve [589-597-2] SACD release. She appears on this sound stage warm and made of flesh and blood with a subtle pause and a moist intake of air she seems as real as life. Moreover, if I wasn't happily married and I could just get my; but that's another story. I would like to mention one last recording even though it's not strictly a reference but rather a fun recording I enjoy very much. It is a gathering of famous artists brought together to celebrate the Queen of England on her Golden Jubilee. Recorded live out doors in front of Buckingham Palace it is ever so clean spacious and dynamic with ESL power applied to the Martin Logan Vistas. You can find it on Virgin [7243 8 12833 25] and it is called Party At The Palace. Did you ever hope to hear Brian Wilson performing "GodOnly Knows" backed by The Royal Academy Of Music Symphony Orchestra? Of course there is much more to commend it, like Rod Stewart, Elton John, Paul McCartney and Eric Clapton to name only some of the talent on this disc, it is wonderful music that is wonder filled! 
 
Coda
What can I say, practically all the clean power one could ever want, capable of driving any audiophile loudspeaker, surely the last amplifier you will ever buy? Understand that I believe the ML Vista electrostatic hybrid loudspeaker serves as an excellent test for an amplifiers ability to drive any type of loudspeaker. Most certainly, this amplifier represents the current here and now edge of technology applied with precision without becoming hard or sterile sounding.  One side of my reviewer's brain craves exactitude while the other half soaks in a soft bed of rose petals. What to do?
 
Logic tells me accuracy is undeniably essential to what I need to know. The Sanders ESL amplifier can form the heart of a fine reference audio system. It could serve as a tool to evaluate every type of loudspeaker or even the performance of each separate driver. Our you might use it's purity to hear deeper into a recording and dissect the way it was recorded and mixed down. However, there is a way to have your cake and eat it too. Using its neutrality there are many options that were not available before. You could go upstream and swap in softer sounding interconnects or feed it from a tubed preamplifier, like my Audio research SP9 MK3. Oh! Lest I forget, Mr. Sanders makes a dual mono version of this amplifier and a (what the hell could he be thinking) 1000 watts per channel stereo amplifier! With the permission of the Editor, the boys down at the IRS and my spousal partner I would like to provide a new home for this much deserving amplifier. 
…….Ron Nagle 
Recommendations don't get more specific than this, I think. The Sanders 10B system has the ability to play music in a way that is not often heard at any price and never to my knowledge at NZ$16,995.
JAMES L. DARBY

Note - since this review the 10B has been upgraded significantly to the new 10C but price still remains very competitive considering it comes with a 500w/ch Sanders Magtech power amp for the bass drives and the external active digital crossover.

Summary:
Recommendations don't get more specific than this, I think. The Sanders 10B system has the ability to play music in a way that is not often heard at any price and never to my knowledge at NZ$16,995. In addition, they are the fullest of full range, able to play in the subsonics (some subwoofers do not go as low) which is rarely if ever found at this price point. They will rattle pictures on the wall and flap your pants if you so desire and want to go deaf. You can feel the bass and it even vibrated the chair at times. 
So. A very positive review. If I were not a reviewer, these would never have gone back to Roger. He informed me that he has a new groundbreaking amp (Magtec) ready to go that has a linear power supply. Frankly, after listening to his description and knowing his philosophy and demand for perfection, I paid for it sight unseen and totally unheard. 

Extended review:
The Sanders 10b is a hybrid electrostatic/magnetic speaker with the electrostatic panel handling the mid and treble and a conventional cone/transmission line bass cabinet. The system includes an external 330 wpc stereo amplifier specifically for the bass cabinets that includes an electronically adjustable bass and midrange via the included universal remote control. This review includes an optional separate amplifier for the electrostatic panels that puts out 1700VA/channel or 400 wpc at 8 ohms.
 
A note about his review; it is unusually long. Part of what Stereomojo is all about is education. We believe an informed and educated reader is more likely to make better decisions in regard to his audio purchases, resulting in more enjoyment and less money wasted. True electrostatic speakers are not common (not all planar speakers are ‘stats) and not widely sold on stores. Most people know little about them. The same is true about the specific product in this review and the person behind it. We believe it is important to inform you about all these facets. We also realize that many of you are reading this in your office or some other time sensitive place, so if you just want to read the review and skip most of the background, click here and we’ll take you there.
 
Have you ever heard of Rodger Sanders? Or his speakers? Or amps? He’s only been in the audio industry for about 40 years. He has been making and selling speakers and electronics for almost as long and there are many people who think his products are among the best, if not THE best you can get. Why is he practically invisible? It could be that he is a rebel, and an outspoken one at that. He has very strong opinions born out of four decades of work, study, trial, experimentation, failure and success. His opinions, like ours, go against those that are so deeply entrenched in the audio industry and supported by the audio press. Take this statement for example: “I believe that most high-end, audio products are priced at unconscionably high levels. Not only is this unfair to consumers, it is damaging the reputation of the entire industry”. Ouch. But he doesn’t stop there; “Examples of this include tiny amplifiers selling for prices in excess of $20,000 and speaker cables selling for thousands of dollars. There is no way that the parts, performance, or design costs of these amplifiers or cables justify such prices. This is particularly true in the case of small amplifiers, because they cannot drive loudspeakers in a typical home environment to realistic levels without clipping. I believe in designing and selling products of real value for a reasonable price”. We agree. We don’t want to imply that Roger is the only one who believes the way he does and proves it in his products. We have introduced you to several others. It’s just that people like him don’t get enough exposure in the mainstream audio press and have, in fact, been shunned over the years.
 
One of the main reasons Stereomojo was created and exists today is because of people like Sanders and the products he makes. Stereomojo searches far and wide to find people and products that publications like Stereophile and The Absolute Sound routinely ignore. Small companies don’t have the $20,000 it takes to advertise in them so their products aren’t going to be reviewed for the most part. Yes, they sneak in a few to keep up appearances and give themselves something to point to when the obvious connections are pointed out, but it is a fact that in many print and online publications, reviews are directly tied to advertising money which leaves small companies out in the cold. It’s people and products like Sanders that make the trails and tribulations of publishing Stereomojo worthwhile. 
 
SANDER’S STORY
 
Roger Sanders may be the most knowledgeable person on the planet when it comes to electrostatic loudspeakers – let’s call them ESL’s. His first published article on ESL’s was in 1974, followed by another on amplifiers to drive ESL's in 1976. His contribution to audio include the invention of the curved, free-standing, electrostatic loudspeaker driver, the development of extremely compact transmission line woofer systems, integration of electrostatic speakers and transmission line woofer systems and, several "how to" construction articles in "The Audio Amateur" and "Speaker Builder" magazines.
 
Roger's greatest contribution to the state-of-the-art is his book, "The Electrostatic Loudspeaker Design Cookbook", published by The Audio Amateur in 1993. Written for the audiophile craftsman rather than the engineer, this treatise is a definitive set of instructions, explanations, and, arguments for achieving the most accuracy and realism possible. Since that time, he has never stopped experimenting and improving his driving passion of the consummate speaker and the amplifiers that best drive them to their ultimate goal.
 
WHAT IS AN ELECTROSTATIC SPEAKER?
 
An electrostatic speaker is almost the opposite of a standard electromagnetic speaker; you know, the kind with cones in a box. Roger explains: “Unlike conventional speakers that use magnetic forces to move a relatively heavy cone, electrostatic speakers use high voltages to move an extremely thin, light diaphragm. High voltages produce an attractive force similar to magnetism. You may have discovered this by combing your hair on a dry day. The comb takes on a high voltage charge and you can feel it pull the hair on your arm or watch it pick up dust or small bits of paper. Note that this charge is STATIC (it doesn't move). In an ESL, a small, high-voltage power supply puts a static charge on the speaker's diaphragm. Hence the name, electroSTATIC loudspeaker. This is also why the speaker must be plugged into the wall like any other electronic component. On either side of the speaker's diaphragm is a STATOR, an electrically conductive, acoustically transparent grill. The amplifier is connected to both stators through a high-voltage step-up transformer. The transformer is necessary to raise the voltage of your amplifier from a few tens of volts to the several thousand volts needed to drive the diaphragm. Music causes the amplifier to deliver varying amounts of electricity to the stators.”
 
So how does an ESL actually produce music? “Like north and south magnetic forces, positive and negative electrostatic forces are attracted to each other, while similar polarities are repelled from each other. Music drives the amplifier to produce a positive voltage on one stator and a negative voltage on the other. These voltages alternate back and forth between positive and negative very rapidly to produce a tone. For example, "middle C" on a piano has a frequency of 256 Hz (Hertz). That means the polarity on the stators will alternate 256 times per second. The amplifier also alters the voltage as necessary to make the music a particular loudness.
 
Now, let's look at what is happening inside the speaker to make it produce sound. At a given moment in time, in response to the musical signal, let's say the front stator has a positive voltage. The rear one will be negative. Let's assume that the diaphragm has a negative voltage. Remember that the diaphragm's voltage is static and comes from the little power supply and does not change like the voltages do on the stators. The negatively charged diaphragm will be attracted to the positively charged front stator because opposite charges attract. It will be repelled from the negatively charged rear stator because like-charges repel. A moment later, the amplifier will reverse the voltage polarity on the stators, so the diaphragm will move the other way. As the diaphragm moves, it produces pressure waves in the air that we hear as music”.
 
Like every speaker design, there are advantages and disadvantages. In general, history tells us that an ESL has these advantages:
 
There are no cabinets with an ESL panel, so there is no cabinet resonance. Cabinet resonance is a huge factor in speaker design and much of the cost of a good speaker is sunk into the cost of designing cabinets that minimize resonance. Exotic materials like aluminum and even granite are used. Other costly formulations are devised. Internal bracing is expensive. Once they are designed, building them is very expensive and time intensive as well.
 
Speed. Because there are no big heavy cones to start and stop (or to break up), only a very light, thin mylar-like diaphragm, the very instantaneous beginnings and ends of note and sounds are reproduced in a way standard cones simply cannot. Think of a gazelle being chased by an elephant or a battleship trying to catch a fighter jet. Or Roadrunner vs. Wile E Coyote. Conventional speakers have tried to catch up by using exotics like Kevlar, aluminum and even ceramic cones to lighten them up, making them easier to start and stop and not distort. All have their own colorations and all can be pretty expensive.
 
Midrange purity. Most people who have experience with electrostats will tell you that they do mids better than anything else. Take the Quads for example. Many people, including reviewers, swear by them even though they are very flawed reproducers in many ways, but their midrange, where the majority of music is located, is superlative.
Big image and soundstage. The ESL area that radiates and actually produces sound is much larger in square inches than a speaker of a similar or even much larger size with cones. 
There are only three US companies that make ESL's. So why don’t more people make electrostats and why don’t more people buy them?
 
ELECTRO-BADNESS
 
That’s simple. In the past, electrostats have had some severe limitations and more downsides than upsides and. Among them are:
 
Limited bass response. To fix that, hybrids are necessitated that add a conventional cone woofer for lower frequencies, but they never quite match the sound or speed of the electro panels.
 
They don’t play very loud. They have been rather fragile and prone to damage if overdriven, or underdriven for that matter. Even the newest Quads are notorious for limited output.
 
They have to be plugged in and require a long time to “charge up” before they sound good. Some say as long as an hour. Not conducive for “right now” listening.
They are hard to drive. Their sensitivity is low and their impedance can range from very low to extremely high making them very incompatible with most amplifiers. Conventional speakers present a mostly resistive load to an amplifier while an ESL appears mostly as a capacitor. Most amps are designed to accommodate resistance, not capacitance, so they are two very difference animals. You know that amplifiers are rated in watts, right? An ESL doesn't operate on watts, it operates on voltage. Offering watts to an ESL is like offering a glass of water to a vampire; it’s not really what it wants or needs to live. Literally, a conventional amp that is rated at 500 wpc may not have the juice to effectively drive a pair of ‘stats. That’s why Sanders also makes an amplifiers that are specifically made to drive voltage hungry ESL’s.
 
In addition, ESL’s have been known to be very sensitive to their environment. Humidity is an enemy. So is dust and any other airborne detritus like bugs or dog hairs. Ever notice how your TV screen attracts dust? So do the highly charged ES panels. They have been known to arc like a bug zapper.
 
Then there is the sweet spot. It’s always been small. Tiny. Almost microscopic. Once you locate it, if you move or turn your head it’s gone. Early ESL’s came with neck braces to keep your head precisely in place! No….that’s not true. But in some cases you might have needed one.
 
ESL’s have never been very flexible when it comes to tuning or shaping the sound. There might be a level on the conventional low-end box, but that was it.
 
Then there is the cost. ESL's have never been particularly cheap. They still aren’t, but it may be that you get a lot more for your money now than you did a decade or so ago. That’s what we are about to explore. 
 
ELECTRO-NOW
 
You notice that I started this section saying, “In the past, electrostats have had more downsides than upsides.” That’s because Mr. Sanders’ forty years of research, trial and error has paid some pretty big dividends. Many, but not all, of the “bad” elements noted above have either been eliminated or minimized substantially.
 
According to Roger, with his ESL’s:
 
You can listen cleanly at 100 DB levels with correct amplification
The amplifier cannot damage the panel. No protective circuitry required
Goes down to 20 Hz
Bass and midrange is adjustable – even via remote control from your seat
Panel is arc-proof
Extremely rugged and durable
Immune to dust and dirt. Actually repels it
Immune to humidity
Unaffected by insects, dust, and foreign objects
Higher efficiency – greater than 90 db
Does not require long periods to charge up – can even be left on continuously
 
He does not claim to have a wide sweet spot so that is not solved, but is it any better? And his speakers still require voltage and as such are still not easily driven by some amps. That’s why he makes his own.
 
Speaking of amplifiers, the 10b’s are bi-ampable. Bi-wire, too of course, but they are designed to be driven by two different amps. Rather uniquely, one amp is included in the price. The Sander’s 10B is really a system more than just a speaker. In a separate chassis comes a 330 watt per channel stereo amp. “Hold on”, you say. “Didn’t you just tell me that ESL’s don’t like watts and need more voltage”? Aha! So you were listening! But, the amp included with the speakers is only for the bass bins which are conventional cone speakers, not ESL’s. They like watts, so we are fine. You need to provide your own amp for the ES panels (mids & treble) or buy the optional one used in this review which is designed for the type of loads ESL’s present.
 
The box you get with the speakers is much more than just a bass amp – it is also a very sophisticated fully balanced preamp with separately adjustable bass and mids via the also very spiffy universal remote. Backlit and everything. It can be programmed to operate every component in your system – audio and video. It controls both the internal bass amp and the other amp powering the panels. I cannot tell you how great it is to be able to sit in my chair and make minute adjustments to the low bass or the midrange levels and hear them in real time while the music is playing. A couple of quick tweaks and recordings that usually sound thin are brought to life and/or others that are either too heavy or too weak at the very bottom are transformed. Of course, you are also able to set the speakers so that they match your room almost perfectly for normal play and then make your micro adjustments from there. Just make sure to jot down your settings because if you turn the controller/amp off, it looses its settings and goes back to the defaults.
 
The amp/controller can also be used as a preamp – as long as you only have one input at a time. As much gear as I have, that was never a problem - I just decided beforehand whether I was going to listen to LP’s or disks for that session and moved the one pair of cables. No biggie. I had planned to use other preamps in front of the piece, but I never did.
I told you that this review was unusually lengthy, but I hope you appreciate why all that background was necessary for a thorough review. You are anxious to hear what they sounded like, right? Good. We are anxious to tell you!
 
SANDERS - FINGER LICKIN" GOOD?
 
I have a confession. Full disclosure. I have never cared much for the sound of electrostatic speakers. Also you should know that I have never had a pair in my system. However, I have heard them in various stereo shops and at many audio shows. The local Sound Advice, now shuttered and out of business, used to sell Martin Logan so I heard a lot of them over the years. The only pair that I almost liked were the big Summits – also a hybrid system with a conventional low end. The midrange for vocals was outstanding and it did play pretty loud with excellent dynamics, but solo piano sounded uneven and edgy. The low end did not match the mids and high end well. And, like I have always experienced with ESL’s after a few minutes, I wanted to leave the room. I have developed a very unique, sophisticated test instrument that tells me when a speaker is too bright or too harsh or just plain distorted. It’s called my lower jaw. It always confirms what my ears are telling me when it spontaneously tightens up and begins to ache. That’s usually what happens when I hear ESL’s, even a few Soundlabs.
 
However, something funny happened in Denver at the Rocky Mountain Show. Because of the severe time limitations at audio shows, I always make a list of those rooms, people and products I MUST SEE. Roger Sanders and his ESL’s was NOT on it. But, as I was walking down one of the many crowded, noisy, hot and sticky hotel hallways where every open door vents a blast of hi-fi sound, I went past a room that made me stop in my tracks – something that is not very smart or safe in the teaming traffic.
 
There was something highly unusual wafting from that room. It sounded like real music!
 
The room was rather stark and bare – not stuffed to the gills with gear like most. There was a single pair of speakers set up catawampus in the room on a diagonal with the right rear corner centered between the two tall, semi-transparent panels. A sign said “Sanders” and there was a guy sitting there with a nametag that matched the sign. I was not familiar with the name or the speakers. I handed Roger my card and introduced him to Linda. He sat me in the one chair that was set up as a listening position and started his presentation, extolling his products like everyone else does. He mentioned all of the features listened above, particularly the ability to play loud. He casually toggled the volume to ear splitting levels playing huge scale orchestral. The sound was pristine with enormous dynamics even at that near 100db level. He was not at all concerned about the welfare of his speakers with the fragile looking mylar panels. I handed him my custom Stereomojo evaluation disk. I listened to one track. Then another. I ended up staying in that room for a good thirty minutes – waaay too long for show reporting. And the next day I did something I seldom do. I came back. I listened some more and talked to Roger about his career, experiences and philosophies. I was impressed with his sincerity and no BS demeanor. I asked if his speakers had been reviewed. He said a print magazine had done a review of his older model when he was at Innersound years ago, but the guy didn’t even read the owner’s manual and thought the speakers were defective. Duh. I told him about Stereomojo’s approach, experiences and philosophies and asked if he would be interested in doing a review.
 
He looked me straight in the eyes for a moment before committing to a definite maybe. It was obvious he didn’t have much trust in the audio press.
 
SOME ASSEMBLY REQUIRED
 
The Sanders 10b system plus optional ESL amp arrived in 5 containers; three for the speakers and two for the amps.
Assembly is easy but it takes a good hour. Only one tool is needed and it (an Allen wrench) is included. You have to attach the upright frames to the wood bases and then the panels and wood trim attach via Velcro.
 
I placed the speakers in the standard starting point, an 11-foot equilateral triangle. The instructions are to aim the speaker right at your ears, so a toe in is required. There are four pages of text with pictures to help you position precisely. You will not see a better written, more intelligent and thorough owners manual, further evidence that Roger truly cares about his product and customers. He stresses that they must be equidistant from you.
 
In the manual he asks, “How precise should you be?” The answer; “The wavelength of a 10KHz tone is about 1”. And error of ½” will place this frequency a full 180 degrees out of phase, so ideally the speakers should be within a quarter wave. For 10Khz this would be 1/4” of being equidistant”. I learned this a long time ago. I always measure distance from the back wall exactly for the inside and outside of each speaker. Then Linda helps by holding a long wire firmly in front of her nose while I move the other end to identical positions on each speaker.
 
Precise distance is vital. Aiming the 10b’s at your chair could not be easier because the see-through panels with crosshatches look just like a periscope or an assassin’s long rifle site. To make the finest adjustments, you can use a flashlight because the mylar is reflective. Just sit in your chair and hold the flashlight above your head and get the reflection centered from side to side. Done.
 
I hooked up the bass amp/controller and the special ESL amp he had sent. He includes his own cables to run from the controller to the ESL amp. As usual, Roger throws in his expertise in the manual. “Some speaker cable has high capacitance and can cause high quality amps to oscillate at very high frequencies. You cannot hear this oscillation as it is supersonic, but it will cause the amp to operate at full power and can overheat and damage both the amplifier and the speakers. One brand of cable is notorious for (this) and that is Goertz (Alpha core) cable.”
 
Yikes! Do you have any of that? Also in keeping with his honesty, he goes on to say the he has designed extremely low inductance, moderately low capacitance and moderately high impedance which he says is what ESL’s prefer. BUT, he also declares that most other cables will be ok as long as their inductance is very low. Roger is not a greedy marketing monster. He just says things as he thinks they are. Like the power cables that connect the AC to the speakers. He supplies some and says that you can use any you prefer, but there is no reason to use special cables or power conditioners. How often do you hear something like that? Maybe that’s why Roger is not the most popular kid on the block in the audio press. Too much good sense.
 
I used my reference Kimber Selects running to the ESL posts on the back of the speakers. I went directly in to the controller from my Xindak tube DAC.
 
I did read in the manual where Roger says because his speakers are phase coherent and dipole (sound comes out the back as much as the front), they can be placed much further apart than normal, but I started in the default position. At the show, he had his demo setup pretty close together about like my initial position.
 
As I began listening to the Stereomojo evaluation disk, one thing became very apparent; there was no image beyond the edge of the speakers. Usually we hear sound well beyond the speaker’s outer boundaries as well as in front and way behind. You can see how they were positioned in the picture. I was not surprised; that’s exactly what I expected. But I wrote to Roger to
see what he would say about it; and so I could pass it along to you.
 
“James, there should not be any image beyond the outside edge of any speaker. But since wide dispersion speakers spray highs all over the room, the reflected sound will often cause you to hear sound from beyond the edges of the speakers as it bounces off the walls. Of course, the problem with this is that the sound has been delayed compared to the speaker's direct sound. The result is confused phase information that prevents the speaker from producing a 3-dimensional image. Wide dispersion speakers totally mess up the phase information by having a myriad of delayed room reflections. The image is so confused that you can hardly even tell when you are at the sweet spot. The laws of physics dictate that all stereo speakers have an infinitely small sweet spot (when you are exactly equidistant from both speakers). The idea that you can sit three listeners abreast and all can hear a perfect image is impossible. The fact that some audiophiles believe that some speakers have a wide sweet spot simply proves that wide dispersion speakers do not produce accurate, holographic images.”
 
Well. I’m sure most makers and owners of conventional speakers would disagree as far as not hearing accurate, holographic images. I certainly have as have every visitor to my home in both listening rooms. Now. Having said that, do I think the Sanders 10b is at least as detailed and accurate as any speaker at any price I have had in my system? Yes. Do I think they are possibly more accurate and holographic than any speaker I’ve had in my system? Hmmm. I don’t know about you, but one thing I really despise is when I see each month’s addition of Stereophile or The Absolute Sound and the cover screams “THE BEST (you name it) EVER”.Then you read the reviews and almost every single one ends the same way – “The best I’ve ever heard!” Then next month the cycle starts all over again. Needless to say, we religiously try to avoid such hyperbole. So, when it comes to the Sanders, we’ll just have to wait and see.
 
What I’m hearing with the speakers in a triangle is an image that is very constricted and narrow. There’s minimum depth and minimum width. Not good. The musicians sound like they are performing in a phone booth. So I moved them out. About a foot from the side walls but still precisely equidistant and toed in. This is usually a bad thing to do because it causes a hole in the middle and less precise imaging. Playing the Stereomojo disk again (do a link to a new page) sounded like I had installed a completely new system. The new stage was wide and deep with images so crisp, clean and clear that it was startling. A few minutes in and I began to laugh. Out loud. This only happens when I experience something incredibly and uniquely amazing and joyful. In audio, it’s only happened a couple of times. In live music situations it has happened much more often and I’ve had to do some serious stifling. Apparently every other reviewer in the world has some sort of facial affliction because when they hear something amazing their jaws always drop. Have you noticed that?
 
So the soundstage was outstanding, but imaging alone doesn’t elicit such enthusiasm for me. There must be something else going on.
 
SPEED THRILLS
 
Way back I reviewed a power amp by Luminous badged the KST-150. Its main claim to uniqueness was its speed. Baby, it was fast. Here’s what I said then: “The KST-150 is a stereo power amplifier whose rated output is (surprise) 150W RMS continuous into 8 Ohms, both channels driven over a frequency range of 20 Hz to 20 kHz with less than 0.1% total harmonic distortion. Pretty specific specs. The rest of the specs are also impressive, but the one that stands out the most is one not usually touted or viewed as all that important; slew rate. Slew rate represents the maximum rate of change of signal at any point in a circuit. Limitations in slew rate capability can give rise to non-linear effects in amplifiers.
 
The red trace represents a true square wave, the green the effect of a slow slew rate on its reproduction by an amplifier. I went on, “Slew rate for this amp is a claimed 250 volts per microsecond (vps). Think of that as "miles per hour" in your car. That amounts to near record setting speed in the audio world, and certainly the highest anywhere near this pricepoint. For example, Krell’s best power amp, the Evo 1 lists for $25,000 and has a published slew rate of 100 vps – less than half as fast. How does that 250 vps translate to sound? We’ll find out in a minute.”
 
I cited two cuts from the older version of the Stereomojo Disk: “I must digress for a moment. I am not a drummer, but I have played drums on occasion and I took a course required for my music degree called Class Percussion where one is required to learn to play every orchestra percussion instrument from snare drum to triangle to tympani. Flams and paradiddles. In bands in which I’ve played, I also on occasion sat way to close to the drummer where every chart sounded to me like a drum solo. I say that simply to state that I know first hand what real drums and cymbals sound like, feel like, and sometimes smell like – depending on the drinking/smoking/hygiene of the drummer. Cymbals, like every other instrument have a basic, fundamental pitch. Even on some very expensive amps and speakers, crash cymbals sound more like a short shot of white noise or the sound a wet finger makes when it touches a hot iron. So, it was with a great deal of surprise that the first thing I noticed when listening through the Luminance was that crash cymbals on the Tricycle cut were reproduced with their fundamental pitch intact. Hmmm. Even my Halcro Class D, 400 wpc MC20 didn’t do that as well, and one of the qualities of a Class D amp is supposed to be speed. Through the KST 150, cymbals did not sound like white noise and their long ring-outs were there, too. They had a real body and presence to them that was not an artificial boost in frequency. This seemed to warrant further exploration.”
 
And, “One of the most demanding recordings I know of for speed is “Friday Night Live in San Francisco” by Al DiMeola, John McLaughlin and Paco Deluca (SACD) – three of the best guitarists on the planet. Here they are live and executing some of the most incredibly jaw-droppingly fast acoustic guitar technique ever recorded. The 150 had no problem reproducing the lightening-like pick on strings sound – sometimes all 3 players simultaneously. “Lively” is an understatement. It was remarkable and left me almost breathless just listening to it. This quality was apparent in every recording and every genre I played; drums, plucked strings, anything struck and most thankfully, piano. That fast slew rate was slaying them all. You really need to hear this phenomenon if just once.”
 
I listened to the same two cuts over the Sanders stuff. Better. Much better. I threw in Winston Ma’s amazing Chinese percussion CD using the K2HD mastering from FIM music. “Yim Hok-Man – Master of Chinese Percussion”. When Winston sent me this disc for review, I almost sent it back to him unopened. I knew I wouldn’t like it. It sat in a pile for the longest time. The 10b system made me want to try it. If anything was going to make my jaw ache via the ESL’s, it would be this. Crazy good sonics as well as immense musicianship that made this the first Chinese music release I have not hated. I really like it. And it certainly is a great test CD for speed and frequency response. Winston Ma triumphs again.
 
Working with the Luminous taught me a lot about speed and how important it is to audio reproduction. While slew rate is not strictly a speed measurement (frequency response is part of the equation), working with the Sanders ESL’s I feel like I’ve been given a PhD in speed and how absolutely necessary it is to audio reproduction. Everything else, including horns, now sounds as if it is playing in slow motion. Not having to start and stop those heavy cones really does make a drastic difference. Listening to other very fine conventional speakers makes me feel like something is missing; because it is. It’s like driving your first ultra-high-performance sports car. I laughed out loud the first time I drove a Ferrari. The mylar panels are so responsive it’s ridiculous. And no I did not get that from the Podium panels I reviewed previously. They were not ESL’s. But what about that cone woofer below those mylar panels? Can it keep up with the quick panels? More on that coming up.
 
By the way, we’ve established that the ESL’s are super fast, but what about the amp driving them? Recall that the super fast Luminous had a slew rate of 250 vps compared to the big $25,000 Krell’s of 100 vps . I looked at the Roger’s spec for his amp: Slew rate: 500 vps. Five hundred! Lorda mighty! Is there another amp anywhere with that spec?
 
But speed alone does not make great sound. While the panels are tall and semi-transparent, the 10b’s are sonically totally transparent. There is just no sense of music being emitted by a speaker. Pffft! Disappeared! In the past, my ears have been assaulted by the beaminess of some panel and ESL speakers. It sometimes sounded like I was listening to razor blades. Some regular speakers do that, too. Ugly, very ugly. There was never a hint of glare, shouting, beaming or anything non-musical from the low mids up. But what about that bass cabinet? We’re getting there.
 
While there was complete macro transparency as relates to the overall lack of perceived sound emitters in the room, the macro transparency – that space between, around and during the notes – was as good as if not superior to anything ever in my system. Huh-oh. We’re starting to hear a lot of superlatives here and words like “best ever”. Is Stereomojo selling out?
 
Well just hold on. We haven’t talked about vocals yet. For me, if a speaker can’t do guys and chicks well, it’s worthless no matter how fast or otherwise great it is. The Stereomojo disk as you can see is replete with several vocal tracks. You’re not going to like this. Male and female vocals were so pure and uncolored I had to start digging out older LP’s and CD’s I hadn’t listened to in years. And for me that almost never happens.
 
S-S-S-S-S-S-S-S-S-S-S-S-S-S-s-s-s-s-s-ibilance
 
Sibilance is that nasty hissing, smearing sound you sometimes hear when a singer, usually female, sings and “S”. It is usually not on the recording as such, but a artifact of
playback. And it is not confined to digital, LP’s can do it, too. In an LP it is a misalignment issue or bad tracking for one reason or another. It is related to timing. Same thing with digital. The sound is being smeared. A source, an amp or a speaker can cause it. Cables too to a lesser extent. Here’s the thing. With Roger’s babies…no sibilance. Zero. Sometimes it takes a while to notice something is not there and since the Sanders was causing sensory overload anyway, it took some time to realize what was not happening.
 
I pulled out my sibilance torture track; “So Nice” by Stacy Kent from the “Publisher’s Award” winning “Best Audiophile Voices” CD. There’s a link to my review of it at the end of this one – if we ever get there. Just the title can sound like “S-s-s-s-s-s-o Nic-c-c-c-c-c-c-c-c-e”. I have heard this played back so badly that it hurt like being hung upside down naked and having your testicles tapped by a silver spoon. I know. Somehow the “silver spoon” part of that is the worst. Here’s an “inside the recording studio” secret; for years engineers have been using a device called a “De Esser”. Here are pics of a software plugin and a hardware rackmount I own;
 
A De Esser is really just a compressor tuned to specific frequencies to help reduce sibilance. The problem is, you just can’t take it out without compromising the sound quality. In addition to the threshold parameter used to set the processing level, there is a frequency controller for setting the center frequency of the process. Processing therefore compresses the entire selected range, not just the sibilant or S sounds. So you get things like lisping and a nasal-sounding vocal. And compression that kills dynamics.
 
SO SANDERS SYSTEM SOUNDS SEXY?
 
What I heard was Stacey caressing her S's a little too much and too long and a little peakiness in the recording in the range around 3-4K. But it sounded pretty natural; no silver spoons in sight. No smearing. And that was the case throughout the frequency range; simply the cleanest, smoothest, unsmeared audio imaginable.
 
HOME ON THE (DYNAMIC) RANGE
 
I have had the privilege of evaluating several speakers whose forte was dynamic range - the ability to accurately and fully reproduce the sonic distance between the loudest and softest sounds in a recording. Many if not most speakers constrict dynamic range. Speakers like the ATC 150’s I reviewed do dynamics range superbly. They better – they are home versions of studio monitors used to record and mix many Grammy winning recordings. The powered Salagars were also very adept as well as the Nola’s and a few others. Dynamics have always been a weakness of ESL’s because they just don’t play very loud. The Sanders’ do. I measured 100 db playback without them breaking a sweat. No breakup, no bottoming out, no arcing and no shards of mylar panels exploding in the room. Just pure, clean, undistorted music. It’s a beautiful thing. When the wide dynamics are combined with the speed, things like guitars, drums, brass and pianos are taken to a higher level. Yet another past limitation of ESL’s bites the dust.
 
I guess I might as well go ahead and admit it; the Sander’s 10b system has the best mid and upper ranges I have had the privilege of hearing in my home. I keep saying “in my home” because hearing anything outside of the system and room I know most intimately is not as accurate. However, I can honestly say that what I heard via this system at least competes with anything I have ever heard at any show at any price. I did not say these are better, as good as, or “the best”. There are systems and speakers that do more in the realm of “hifi-ness”, but among the many great audio experiences I have enjoyed I just cannot recall a more musically satisfying experience than the Sanders system in Casa Mojo.
 
ELECTRO-SWEET
 
I had to laugh when I asked Roger about the sweet spot – or lack of it – in electrostats. Being the up front, honest and transparent guy that I am, I told Roger that the main reason I’d never buy ‘stats is because my wife and I like to listen to music together. Being the male chauvinist pig that I am, I hog the center position while she is relegated to just-right-of-center, so we need a wide sweet spot. And there are speakers that where she sits sounds every bit as good as dead center. Sanders would tell me those are bad speakers. He also told me the solution with his speakers would be to place Linda in a chair directly BEHIND me to listen to music! Yeah right. So imagine my surprise when a few minutes into her first listen I ask her how it sounds over there she says, “Not bad. Pretty good actually.” The first thing Linda listens for is left to right balance; is the singer in the middle and the band behind and spread left to right. I thought for sure we say, “I’m only hearing the right speaker”, something that is not unusual. But she didn’t. Something was wrong. Now, in my own defense and being the loving husband that I am, I never truly hog the center chair but always invite her to switch. When I sat in her chair, indeed I was hearing a stereo image and a rather well proportioned soundstage. There was a strong sense of phasiness and the overall presentation was a bit fuzzier, but it was pretty listenable, which was a big surprise.
 
One of my best and oldest friends was in town and came over. I had helped him pick out his current system comprised of Revel speakers and Mark Levinson electronics. The choices had to do more with what brands the local dealer had to offer more than anything else, but he has a very fine sounding system; one which he has upgraded over a period of three decades. He also happens to have great ears. Sitting in the sweet spot, he told me that what he was hearing was far superior to what he had at home. When he scooted over, he said that there was a drop off in the high and low end and detail became more obscure, but he thought it still sounded as if he were listening to live music off to the side and not in a center section. There was still a strong left/right/front/rear presentation.
 
While I cannot declare that the ESL sweet spot challenge had been overcome, it has certainly come a long way under the Sanders regime.
 
BASS FISHING
 
So we have established that the Sanders 10b’s are world class from the midrange up. The vast majority of music lives there so we can all just go home now, right? Not so fast. Music needs a foundation of low frequencies upon which to build and Sanders claims that these go down to 20 Hz. There are not many speakers that come anywhere near to that spec and even if they do they are in a much higher price league. But producing low bass is not the biggest challenge hybrid ESL designers have to contend with. No. Matching the ultra speed and dynamics of the panels with a standard magnetic (slower) cone driver is the problem. Like a bad toupee, the seam between the panel and the cone is the Achilles heel of hybrid ESL’s.
 
If the continuity between the “cone” bass and the ESL panels is such an issue, why not just make a speaker that goes down to 20Hz using all ESL panels? Rogers responds in his inimitable factual, no-nonsense style; “I have built many full-range, crossoverless ESL's. They are much easier and less costly to build that a transmission line hybrid. But you can't beat the laws of physics. A full-range ESL is a severely compromised speaker that cannot produce deep bass or high output. Also, the bass quality is truly awful (flabby, boomy, and wimpy) due to the high "Q" behavior of the diaphragm around its fundamental resonance. An ESL is a drum. That's right -- its tensioned diaphragm is exactly like a drum. And if you operate the ESL near the drum's resonance, it will have massive amounts of overshoot and ringing that totally ruins the sound quality. Also, the magnitude of the resonant peak typically is 16 dB! A full-range ESL will act like an extremely poorly controlled and heavy woofer that will not stop moving when it is supposed to (think bass drum).
 
Bass needs to be clean, tight, and highly damped. In other words, a good woofer system will have very low "Q." Only two types of woofers systems offer this quality -- horns and transmission lines. Bass horns must be huge for good performance, so they are not a practical way to build woofer systems for most homes. Therefore, I use transmission lines. The trick is to get a conventional woofer to integrate well with an ESL, which has an extremely low "Q" (when operated above its fundamental resonance).
 
It has taken me 17 years to solve this problem. But I think you will agree that the Model 10b is very well integrated and sounds like a single speaker is reproducing the music. Its bass performance is vastly superior to a full-range ESL”.
 
Perhaps the folks at Soundlab would dispute Roger's claims since they make several all electrostat (non-hybrid) models that they say go down to the twenties. Their top model, the Majestic, is said to bottom out at 24 Hz without using cone drivers. It retails for $32,000/pair and I have heard them several times at various shows in demos of IsoMike recordings by Ray Kimber. Ray uses 12 of the 200 lb., 8 1/2 foot tall monsters driven by a truckload of Pass amps. The total system was said to cost close to half-a-million bucks. I never heard any flabbiness or drum effect. The sound was pretty spectacular as one would expect for half-a-mil.
 
A closer comparison would be the Millinium 2 model at $12,000/pair that claim a low limit of 30 Hz. I have not heard these but certainly would like to. These do feature variable bass and mids like the Sanders but also ad variable highs. No remote though, so you can't make the changes while listening. There is also no bass amp included nor a preamp function with remote volume control like the Sanders. But, thier existance would seem to contradict his belief that a true full-range ELS is "severely compromised". According to Soundlab, they have patented a principle called "Distributed Bass Resonance" that virtually eliminates the membrane "drum-head" resonance and dipole energy cancellation.
 
Martin Logan also makes a full-range ESL. Roger’s hybrid is spec’d at 20 Hz for a bottom limit. The CLX? 56. Huge difference. At $20,000, they cost more and do not include a 330 wpc bass amp, a preamp with remote and the ability to adjust mids and lows from your chair. They are also much bigger.
 
As you can tell, Roger is very confident in his product. Let’s see if that conviction is deserved or if his self-assuredness is more fiction than fact.
 
ATTACK OF THE NUCLEAR PIANO or PLASTIC SURGERY
 
So far I have attacked the ESL’s main weaknesses. But there was one more big one looming and it may be the most critical; the seam between the ESL panels and the magnetic cone bass. Roger will tell you that physics dictate that they cannot absolutely sound identical. Therefore, the challenge is to make the transition as unnoticeable as possible. The outcome of this review for me and for many others would hinge on how well Roger was able to suture the two divergences together. Not plastic surgery per se, but close – the panels are made of mylar…
 
I ran a couple of cascading frequency response tests but that doesn’t tell me too much other than the linearity of a single sine wave. For me, the true test would be a solo instrument that is difficult to reproduce in the first place and which widely spans the frequency range in the second. Third, it is one with which I am very intimately acquainted. If you’ve been around Stereomojo much, you know that I started playing piano at age 2 and began formal study at age five which continued until I got my degree in music, followed by another 20 or so years in the music profession. I know what piano is supposed to sound like. Especially the recordings I made over the years. Playing these would put the 10b’s under a scanning electron microscope.
 
The 10b’s cross over from ESL panel to the bass cabinets at a rather high 300 Hz. That corresponds roughly to D above Middle C on the piano keyboard or almost smack dab in the middle. There is no place to hide. Needless to say, that is the area on which I concentrated. I should mention that the included preamp/crossover/bass amplifier is analog. It uses Linquitz/Reilly filters with 24 dB/octave slopes. Roger told me that in his opinion the analog route is not the best way. He says his digital crossover is even better, “But my customers sometimes cringe when I even mention the word “digital”, so I make the analog version standard. But I can give them a better digital model”.
 
I continued the bombardment with other favorite piano solo recordings such as “Nojima Plays Liszt” (Reference Recording #25). As a recluse, Nojima makes Howard Hughes look like Howard Stern. This guy could have taught Bobby Fisher how to hide out. His playing is so precise he approaches an almost machine perfection, yet he has the romance and warmth of the old schoolers like Rubinstein and Horowitz. Recorded in 1987 in HDCD at the Oxnard, CA Civic Auditorium, it still stands out as one of the best piano recordings ever. Long out of print, Reference Recordings brought it back in 2006 and is among its top sellers. Of particular interest is the famous Mephisto Waltz – torturous and diabolical to play and to hear, it was one of my favorites to knock around. I wish I could still play the thing.
 
The London (414 600-2) recording of Vladimir Ashkenazy playing Chopin waltzes is dear to me since I have performed most of these waltzes and I like his balanced of technique and passion so critical in their interpretation.
 
Peter McGrath is one of the world’s premiere recording engineers who now happens to be the front man for Wilson speakers. I’ve known him years prior since he used to own a high-end store in Florida I visited frequently. I think it was the Montreal audio show at which he unveiled a live recording he had recently made in Miami of a Spanish pianist named Pietro De Maria. He played it back (over Wilson speakers of course) in hi-rez 24bit. In terms of raw virtuosity, power and expression, the playing was stunning and the recording was superb.
 
As I listened, his style was such that I felt as if I were listening not to him in a formal concert, but to the composers themselves just sitting down casually to toss out a couple of their most beloved compositions for a few friends. The composers were very diverse; Scarlatti, Schubert, Liszt, Mozart and Chopin. Of course, I had to have it. It is on the VAI label (VAIA 1204). This recording is not only great for evaluating how well a system plays back piano but also how well it captures “feelings” and the other intangible “drops of emotion” that Emmanuel Kant thought made up the true path to reason in his “Critique of Pure Reason”. What I mean to say is, this recording will reveal weaknesses in systems if you know what to listen for.
 
I listened to many, many solo piano recordings via CD, SACD and vinyl while concentrating on the continuity of that splice between 300 cycles and lower vs. 300 cycles and higher. How did they compare in terms of speed, texture, sonority, timbre and every other sonic quality I could think of?
 
But that was not punishment enough. I went nuclear and pulled out the pipe organs and listened carefully again. All this was not in one sitting, rather over a period of two weeks; a steady diet of the most arduous recordings in existence. What this verdict? Was there a seam, split, disparity or discrepancy between the top and bottom?
 
Let me phrase this carefully and succinctly; if I put the crossover point under an sonic microscope and focused on it, yes – a small difference in character can be detected. Of course, that can and often does happen in conventional speakers as well. But – under normal listening conditions, the linearity from top to bottom is outstanding and absolutely not a detriment to an extremely high level of musical enjoyment. In short, it didn’t bother me a bit. In fact, the bass in terms of speed, solidity, cleanness, dynamics and detail were nothing short of exemplary. These babies go low. Can I confirm an in-room response down to 20 Hz? No. But I could not care less what the actual number is. At no time did a feel a need for more or better bass. Now there were certain times when a particular recording could use a bit more oomph, but guess what? I just took the remote and dialed up a db or two more via the crossover amp! I loved that feature, and it’s the same for the midrange as well. Now, I wish it were possible to do the same with the top end, but that is not an option with the system I had. And turning UP the bass and mids is not the same as turning down the highs.
 
So here it is friends, something I really loathe to say, but in this case it is unavoidable: the Sanders 10b speaker and amplifier system is THEE best system I have yet to have in my home. This system not only pressed all my musical buttons, it just flat demolished them. Am I saying it is the best in the world? No. I have not heard every speaker in the world and neither has anyone else. So when you see a critic say something like “The best on the planet”, he is lying. Unless, of course, he has actually heard every speaker on the planet. Even if he has, it’s pretty obvious that his “best” might sound like crap in another room or system. Or even to someone else’s ears. Don’t get me started…
The fact is, your buttons might be very different than mine. All we can do is give you our opinions. It’s up to you to take it from there.
 
There is so much more to say about these speakers and the electronics that come with them as well as the optional ESL amp I used, but this is much too long already. Let’s go to the bottom line.
 
Recommendations don't get more specific than this, I think. The Sanders 10B system has the ability to play music in a way that is not often heard at any price and never to my knowledge at NZ$16,995. In addition, they are the fullest of full range, able to play in the subsonics (some subwoofers do not go as low) which is rarely if ever found at this price point. They will rattle pictures on the wall and flap your pants if you so desire and want to go deaf. You can feel the bass and it even vibrated the chair at times. Hmm…that could be a real selling point to many wives come to think of it. You also have to factor in that with the speakers you get a single input preamp and a universal remote to control it. The backlit remote also allows you to adjust the bass and mids levels from your seat so you can hear the changes. What’s more is that a dedicated bass amplifier is also included that puts out 330 watts per channel at a very high quality. You can add your own amp for the mids on up or buy Rodger’s model that is designed specifically for the unique demands of ESL’s. Roger sells direct so there is no middleman to pay. He is supremely confident in his product to the extent that he offers a 30 Day in-home risk free trial as well as an unheard of LIFETIME TRANSFERABLE WARRANTY. Do you now anyone else who does that? And how much does that add to the value quotient.
 
Is this system for everyone? No. The manual says that you do not have to place them out in the room – you can place them against any wall side or back. Mine were about 9 feet from the back wall and we could hear that much depth. I think placing them against a back wall would diminish that, but I didn’t design them or try them that way. Placing them close to a sidewall is fine – a real no-no for conventional speakers. They are designed to have a hard reflecting wall behind them. I did. The sweet spot becomes smaller if the back wall is damped. Remember the sound comes out the back as much as the front of the panels. They must be equidistant from you and pointed right at you.
 
And Roger confessed another factor. “Wives are my biggest problem”, he grimaced. “I don’t know how many times the husband wanted to buy them and the wife said “no way”. Thank God for Linda. These did not bother her at all, but she is used to having speakers out in the room. And they are tall. You just can’t hide ‘em.
 
If your current amplifier is low output tube or solid state that lacks a very hefty gain output – not just watts – you may have to upgrade it. ESL’s use voltage, not watts. I wanted to try a higher output tube amp with them but all I had at the times was a few SET’s. And ESL’s do NOT like “digital” or Class D or T amps. If you have one, it may well blow up with these. It should be noted that both Sanders amps ran surprisingly cool even when pushed hard.
 
The fact that both speakers need to be plugged into AC may be factor for you. Since they are also bi-amped, you could have two sets of speaker wires as well as AC cords for each speaker. I always left them on – they draw very little current – but you may not want to. Same with the controller/amp. I left it on. Each time you turn it off it goes back to zero volume and defined levels for the mids and bass. You’d have to readjust them every time if you turn it off, though there are big number LED’s to make that quick and easy from your chair.
 
There is some assembly required. you do not take these out of the box, connect a wire and juice them up. If you are disabled or otherwise challenged, that may be an issue, but the assembly is very well documented and if I can do, so can you.
 
Lastly, there is that sweet spot issue. It’s not nearly as bad as earlier generations and may be perfectly acceptable to those who mainly listen solo or whose partner is not too particular.
 
So. A very positive review. But would I actually buy these speakers myself? If I were not a reviewer, these would never have gone back to Roger. But because of their unique characteristics in amplifier demands and the default bi-amp set-up, they would just not be versatile enough for the breadth of gear with which I have to work. Sometimes practical trumps preference. I did want to buy the ESL amp, but Roger informed me that he has a new groundbreaking amp (Magtech) ready to go that has a linear power supply. Frankly, after listening to his description and knowing his philosophy and demand for perfection, I paid for it sight unseen and totally unheard. And yes, we will have the world’s first review of it, too.
 
If you are in the least bit interesting in pursuing these speakers or amplifiers, or even if you just want to learn more about audio, you should visit Terry's website: www.audioreference.co.nz. There is more information there than we could ever include here. Roger also tells me that he will soon have a smaller version of the Model 10b called the Model 11a. It will have the same type of electronic crossover and bass amp that he sells with the 10b. However, its price will be less at NZ$14,995.
A Hidden Gem - with the Magtech, the MRTs were rock solid at uncomfortably loud levels, visual confirmation of what I was hearing-"No Distortion".
Don Shaulis

Summary:
Pure Enjoyment on Quad ESL-2805s: -  its brute strength the Magtech showed its sensitive side by gently reproducing each layer as the whole it was meant to be and capturing the surprisingly long, barely audible fadeout that would be lost on most systems. It also faithfully captured Joni Mitchell’s voice, mostly clear as a bell but sometimes exhibiting a slight tobacco-induced haze. 


The Magtech did an excellent job of revealing the nuances in Emmylou Harris’s voice on “Can You Hear Me Now” from Stumble Into Grace [Nonesuch 79805-2]. Again there were layers to be revealed including backup singing and soft guitars. And again the Magtech seemed particularly adept at revealing layers without losing the connectivity between them. Other amplifiers might etch each layer independently or smear them irretrievably. The Magtech made me enjoy this and other music to a level I had not previously experienced. I heard more, but not because I was trying. I heard more because it was presented so effortlessly and without drama. The seduction I previously alluded to. 

For some reason there remain relatively undiscovered gems in the audio world. The Sanders Sound Systems Magtech amplifier is one of them.

Certainly their designer, Roger Sanders, has been around the block several times and mention of the brand name often brings recognition but not familiarity. Someone may have read about Sanders Sound Systems loudspeakers and amplifiers in a show report or magazine but not actually heard them. 

 
I found the Sanders Magtech amplifier somewhat by accident myself. I was searching for an amplifier for my Quad ESL-2805 loudspeakers and I found the Sanders ESL Mark II amplifier designed specifically to handle the more complex load of electrostatic loudspeakers (ESLs). The Sanders Sound Systems website explains that ESLs are driven by voltage in contrast to magnetic speakers that are driven by current. All this occurs because a magnetic speaker is a resistive and inductive load while ESLs are a capacitive load. Since most amplifiers are designed to drive the more common magnetic speakers, Roger Sanders recognized the need for an amplifier more appropriate for driving both his own and other brands of ESLs.
 
Hang in there; I will get to the Magtech amplifier shortly. A little more information on the ESL Mark II amplifier is warranted here since it is the foundation on which the Magtech amplifier is designed and built. While they are designed with different loudspeaker demands in mind, neither amplifier is limited in its final application. Roger Sanders has assured me the ESL Mark II amplifier can perform very well on magnetic speakers as well as on ESLs. He further advises that the Magtech amplifier is the best amplifier for either application but the edge over the ESL Mark II amplifier is not as significant on electrostatic loudspeakers. 
 
To achieve optimum performance Roger has eliminated protective circuitry that causes the harshness frequently associated with solid-state amplifiers. One key to eliminating protective circuitry is the design of an output stage that is so powerful it is never stressed. The ESL Mark II uses twenty large output transistors capable of delivering 7,000 watts (64 volts RMS) into an ESL. The amplifier can drive a 1/3-ohm load. 
 
But there is more to eliminating protective circuitry than just “Tim the Tool Man Taylor” amounts of power. An amplifier must also be designed to prevent thermal runaway and maintain a stable bias at the appropriate level regardless of power-level demands or constantly varying load demands from loudspeakers at different frequencies. Both the Mark II ESL and Magtech amplifiers use Thermal Trak transistors. Thermal Trak transistors have built in temperature sensors to adjust bias much more quickly than conventional amplifiers. Most conventional solid-state amplifiers have temperature sensors mounted on the heat sinks, which results in inaccurate readings due to the time delay. The result is an unstable and inaccurate bias and the possibility of overheating, which ultimately demands protective circuitry. 
 
The above features are also incorporated into the Magtech amplifier, which is essentially a Mark II ESL amplifier with the addition of a linear voltage regulator. Line-level electronics typically use voltage regulated power supplies but regulated power supplies would run too hot for the larger power requirements of amplifiers. To solve this problem Roger Sanders has developed (patent pending) a voltage regulator that he claims is essentially 100% efficient. In addition, the regulator does not employ switching that could create radio frequency problems. Roger further claims the regulator maintains a stable voltage regardless of load or reasonable changes in the line voltage. This enables the maintenance of stable bias and unchanged distortion levels. 
 
After living with the Magtech amplifier for a couple months I spent some more serious time rereading the information on the Sanders Sound System website. A well-written white paper can always sound convincing to me. But what resonated with me as I explored the technical design of the Magtech was how much it confirmed my subjective observations. 
 
At first blush Magtech amplifiers are not that exciting. Seduction is more their style. One reason the Magtech amplifier does not call attention to itself is that it does not excel in (or exaggerate) any specific area. But rather, it performs equally well at all frequencies and never shows strain. Consistency was what I had written in my listening notes. Performance was uniformly good from top to bottom. The figurative light bulb was burning brightly above my head. Finally, something I read in a white paper could be confirmed by my actual experience.
 
It is easy to get Quad speakers to sound good. They are legendary for coherence and an engaging midrange. It is more difficult to get them to sound their best throughout their frequency range. I have tried various tube amplifiers on the Quads and found tube amplification provided extremely enjoyable sound but only within certain frequency range limits. The Quads are not as easy a load as one would be lead to believe by how good they sound with tube amplification. The Magtech further revealed the tube shortcomings (which I had already noticed) by expanding the peak performance range of the Quads. The “sweet region” grew to the limits of the speakers themselves. Meaning they suddenly didn’t have extended bass but what they did have was tighter and more refined. The top end was not more extended, just smoother and less brittle. The Magtech amplifier did not create new loudspeakers; it just let them be all that they could be. 
 
The amplifier also exhibited a rich tonal density with good soundstage depth and imaging. Performers and instruments were not exaggerated in size. Extended harmonic reproduction made piano and stringed instruments more realistic. 
 
While the Magtech is a solid Class-A/B design it provides more power and is more efficient than most A/B designs. It draws approximately 40 watts at idle and up to 2000 watts at full power. The Magtech does generate heat but significantly less than many other Class-A/B amplifiers. The heat sinks are small but effective. I measured the idle and operating temperature using a thermal probe. Operating temperature varied with how hard the amplifier was working. The outside edge of the heat sinks averaged about 82°F at idle and ranged from 89-95°F while operating when ambient temperature was 66°F. The low surface temperature makes Magtech amplifiers kid and kitty friendly.
 
Its size and weight (55 pounds) give it serious attitude but it will easily fit on an audio rack and one healthy male can handle it and bask in a prideful testosterone rush of accomplishment. If you want to feel even more manly, Magtech amplifiers are also available in a monoblock version that produce 1600 watts into an 8-ohm load and 2000 watts into a 4-ohm load. Although they have both XLR and RCA inputs, the stereo Magtech operates in single-ended mode while the monoblock version operates in balanced mode. 
 
I personally found the Magtech amplifier (black faceplate) quite attractive. The entire amplifier has a solid look and feel to it including the thick top and small heat sinks. Fit and finish are excellent. The faceplate was simple but somehow elegant. This is all in keeping with Roger Sanders’ more pragmatic attitude toward design. His intention is to design equipment that brings the best sound in realistically sized and priced packages. I quote Sanders from his website: “I believe in designing and selling products of real value for a reasonable price.” I applaud that attitude. Too many times I have seen equipment that is only available to the 1% with the biggest wallets, listening spaces, and egos. Ego aside, I don’t fit the other two criteria. I very much appreciate the more practical approach.
 
Sanders further stands behind his products (both amplifiers and loudspeakers) like no other manufacturer I am aware of. Sanders Sound Systems offers a 30-day, in-home, risk-free trial. That includes the unbelievable offer of free round-trip shipping anywhere in the world for any Sanders equipment. If that is not enough craziness, Sanders products also carry a lifetime warranty for the original owner. Sanders Sound System products are manufactured in Conifer, Colorado and sold both directly and through selected dealers. 
 
Pure Enjoyment on Quad ESL-2805s:
A consummate artist but not performer, Joni Mitchell was uncomfortable on stage but a master in the studio. She applied multiple layers to “The Tea Leaf Prophecy (Lay Down Your Arms)” from Chalk Mark in a Rain Storm [Geffen 24172-2]. Despite its brute strength the Magtech showed its sensitive side by gently reproducing each layer as the whole it was meant to be and capturing the surprisingly long, barely audible fadeout that would be lost on most systems. It also faithfully captured Joni Mitchell’s voice, mostly clear as a bell but sometimes exhibiting a slight tobacco-induced haze. 
 
The Magtech did an excellent job of revealing the nuances in Emmylou Harris’s voice on “Can You Hear Me Now” from Stumble Into Grace [Nonesuch 79805-2]. Again there were layers to be revealed including backup singing and soft guitars. And again the Magtech seemed particularly adept at revealing layers without losing the connectivity between them. Other amplifiers might etch each layer independently or smear them irretrievably. The Magtech made me enjoy this and other music to a level I had not previously experienced. I heard more, but not because I was trying. I heard more because it was presented so effortlessly and without drama. The seduction I previously alluded to. 
 
No One-Trick Pony:
The Magtech had so much available power I turned down the output of my Laufer Teknik (formerly Nova Physics Group) Memory Player to protect my Quad ESL 2805 loudspeakers. When I rotated my Apogee Stage loudspeakers into service I increased the output slightly but still maintained it at a reduced level. I found the Magtech amplifier was equally at home on electrostatic and planar-magnetic speakers. 
 
Although Apogee Stage loudspeakers are nominally rated at three ohms they can dip much lower. The Magtech appeared to have no care in the world; easily handing everything I threw at it. I was particularly impressed that at loud levels I could detect no discernable movement of the Apogee’s midrange tweeter ribbon (MRT). Lesser amplifiers can clip and cause the ribbons to dance with reckless abandon. Slight MRT motion is either a sign of imminent amplifier clipping or the speakers are being over-driven. With the Magtech, the MRTs were rock solid at uncomfortably loud levels. Visual confirmation of what I was hearing-no distortion.
 
Conclusion:
The Sanders Sound Systems Magtech amplifier deserves more than just name recognition. It is well worthy of consideration in any system where its power would be appropriate for the loudspeakers in use. But don’t take my word for it. Find out for yourself by taking advantage of the unprecedented 30-day, in-home, risk-free trial offer.

Call Terry on +64 21 880 884 or vist his website: www.audioreference.co.nz 

This amp is a keeper, absolutely no doubt about it
Sir Sanders Zingmore - audio forum member
A bit of background
 
A few months ago, after searching high and low for an amp to drive my Sonus Faber Auditor M's I had a flash of insight; the amp may not have been ideal but it was really that the speakers were not for me.
 
A long and enjoyable quest finally saw me buying my Zingalis which I have waxed lyrical about in other posts and some fellow SNAers have heard at my GTG
 
Trouble with the Zingali's is that they are very revealing of weaknesses elsewhere in the system. The dreaded upgrade bug had bitten. At first I felt that my DAC was the weak link in the chain and was tempted to spend a LOT of money upgrading. An expensive gardening project put paid to that but also made me pause and think about amplification.
 
In my initial quest for an amp for my Sonus Fabers, For those not familiar with Sanders Sound, Roger is best known for his electrostatic speakers and the amps he designs to drive them. He also makes Magtech amps for 'traditional speakers. His designs are innovative and although I don't fully understand the technical stuff, Roger very patiently and promptly responded to every email I sent over many many months. I never felt pressured and I certainly felt like I was being educated by someone who has been in the business for a long time and really knows his stuff. His approach is very much no-nonsense and I imagine quite controversial as he doesn't seem to play by the usual rules that encourage audiophiles to spend extraordinary amounts of money. I like this approach a lot. (The same service is now available through Terry at Audio Reference in New Zealand).
 
It took me a long time and many questions to decide to go ahead with this trial - I didn't want to audition unless I was really ready to keep the amp if I liked it.
 
Anyway, a few days ago one of his Magtech amps arrived at my door. This thing is powerful - 500w into 8 ohms, 900 into 4 ohms
 
So am I crazy driving 97dB speakers with 500w of solid state power.............. Not on your life!
This amp is a keeper, absolutely no doubt about it :confused:. It disappears. It gets out of the way and lets the music through. Not sure what else to say about it cos I've spent long enough writing and I want to go back to listening :)
I'm convinced.
Review by cmk - Asylum forum member:

Summary:
One of my key goals was to try to re-create life-like dynamics and impact. How else do you get the sense of a real performance in your room if you cannot feel it? The start of a note should be incisive to give this impact. With this amp, I did not feel any lack of power, compression, driving 93db/w speakers of course made it an easy load. Nevertheless, the Baltics are very reveiling of up stream components so I never felt anything was amiss. Instrumental decay lingered on till the black silence of the "end of track". 

Exrended review of Sanders Sound Systems ESL amplifier Amplifier (SS):

I happen to chance upon this amp one afternoon at the local dealer's showroom, driving a pair of Vandersteen 2CE SigIIs. Initial impressions were that it was physically reminiscent of Coda amps, which was a good start point, I had always liked Coda's purity of treble. Siting down for a brief listen was a "mistake", I was taken back by the amp's ultra clean treble, free of hash, vocals had a palpable presence, and the bass was just amazing, tight fisted control, deep and tuneful. Up till then, I had never heard the 2CEs with such performance, and as a previous owner of the 2CE Sig, I knew what they sounded like. 

 
Upon reaching home, I was haunted by the pure sounds from the Vandies, so pristine and pure. I had to get a home trial/demo to confirm if it was really the amp that was responsible. 
 
Carrying it back, I heard something rocking internally and thought something had come loose. It turned out to be the ultra big transformer, and was told that I could tighten the screw below. After I fired up the unit, it worked fine, so I left it at that. 
 
Having used tube amps for sometime (the more linear sort), I was used to having some body in the music and felt that accurately rendered a performance. Putting the ESL amp in place, it had the same body but gave some further insight into the music, little details popped out, largely due to the dark background that now surrounded each performer. 
 
On the Cabasse Baltics, the treble took on greater clarity, cymbals ringed without sounding harsh or distorted. In the all important midrange, where tonal accuracy is paramount, instruments had body, presence, impact was heightened, and decay seemed to be lengthened. Each instrument seemed to occupy a distinct place, while the soundstage extended beyond the speaker and room boundaries. But the tone of each instrument could be heard as never before...I mean I could tell if it was a grand piano or an upright playing. The sounds were similar to really good SE tube or SS amps, think Lamm and Dartzeel and you get an idea of what I mean. 
 
Bass in my system is reproduced by the powered Thor sub, fed in parallel with the main speakers via Anticable speaker wires. Here I also noticed a distinct tightening up of the entire bass region. Bass notes went deeper, with greater definition and weight. 
 
One of my key goals was to try to re-create life-like dynamics and impact. How else do you get the sense of a real performance in your room if you cannot feel it? The start of a note should be incisive to give this impact. With this amp, I did not feel any lack of power, compression, driving 93db/w speakers of course made it an easy load. Nevertheless, the Baltics are very reveiling of up stream components so I never felt anything was amiss. Instrumental decay lingered on till the black silence of the "end of track". 
 
Does it sound like a tube or SS amp? Well neither, and both. It was the purity of tone so typical of SE tube amps in the treble and mids, while it also possess the tight fisted control of the bass typical of SS amps. Yet the whole musical reproduction sound coherent and altogether musical. This amp is different from typical power amps going before, its neither hot - like class A amps, but sounds cleaner than a typical class A amp. I would suggest a read of the Sanders' white paper on their ESL amps to understand what he has done. I'm convinced. 
THE MAGTECH REGULATED POWER SUPPLY WHITE PAPER
Sanders Sound Systems website

Many audiophiles have asked if the regulator in the Magtech is truly 100% efficient as claimed.  The purpose of this paper is to describe how it works so that you can see that it is, in fact, super efficient.  It actually does run cold and truly solves the heat problems of conventional regulators that prevent their use in power amplifiers.

So how does the Magtech regulator work?  I'll explain, but readers will need to understand the basics in order to appreciate the problems and solutions involved.  Since the technical expertise of readers varies, I will cover the basics.  I apologize in advance if some of what I am about to say is review for some readers.
 
First, what exactly is "efficiency" as applies to a voltage regulator?  Efficiency is the amount of energy put into a system compared to the amount of energy that you get out of it.  Since energy cannot be destroyed and must be accounted for, any losses in efficiency will be reflected as waste heat somewhere in the system.  
 
Or to put it another way, any heat that is produced by the voltage regulator is a loss in efficiency and results in less power being fed to the electronics than would be the case if the regulator was not present.  The exact efficiency percentage can be calculated based on watts in compared to watts out or watts of waste heat produced.  
 
In the Magtech's voltage regulator, you will not find any waste heat.  It will pass virtually all of the watts put into it on to the amplifiers.  
 
To see why, it is necessary to understand exactly how a power supply operates.  Only then will it be possible to see how the Magtech's voltage regulator works and how it can be so efficient.  
 
The purpose of a power supply is to produce smooth DC (Direct Current) at specific voltages to drive the downstream electronics.  A basic, linear power supply consists of three sections, each having different types of output characteristics.     
 
The first section is the power transformer.  This converts the mains voltage to the voltage(s) required by the downstream electronics.  The output is AC (Alternating Current) in the form of a sine wave.  
 
A sine wave is a smooth wave form without any harmonic structure with alternating positive and negative polarity.  There is one positive and one negative wave per mains cycle (60 Hz in North America, 50 Hz in the rest of the world).
 
The second section is a bridge rectifier.  This consists of four diodes.  Diodes are electric check valves that flow current in only one direction.  These diodes flip the phase (polarity) of alternating waves by 180 degrees so that all the waves are in phase.  Therefore the output from the bridge rectifier will be pulsating DC sines at twice the mains frequency. 
 
The third section is capacitance.  This usually takes the form of a bank of large, storage capacitors.  A capacitor bank acts like a rechargeable battery in that it can store a lot of electrons and release them when needed.  
 
The practical difference between a rechargeable battery and a bank of capacitors is speed.  A capacitor bank can be charged and discharged virtually instantly, which is necessary to meet the sudden large current demands of an amplifier.
 
The main purpose of the storage capacitors is to smooth out the current flow from pulsating DC to continuous DC.  The storage capacitors are often called filter capacitors since they "filter out" the DC pulses from reaching the downstream electronics.  If there were no filter capacitors, an amplifier would make a very loud hum come from the speakers.  
 
The storage capacitors are also needed to help the power transformer deliver enough peak current to reproduce dynamic peaks that require more current than the transformer can deliver.  Think of the current that is required to drive the woofer at that moment when a bass drum is struck . . .
 
The current required by a Class B amplifier is directly proportional to the energy in the music.  So at idle (no music), no current is needed or used.  Very loud music will require an equally large amount of current to drive the speakers loudly.  
 
It is this huge difference in current that causes the large voltage changes in the rails (the power supply output voltage) you find in most amplifiers.  The difference in the rail voltage between idle and full power in most amplifiers is around 30%.  This massive voltage drop causes the distortion, the bias, and the output capability of an amplifier to be modulated by the music.  
 
An electronic circuit's distortion can only be optimized at a specific voltage. Any variation of voltage will result in increased distortion.
 
Class AB amplifiers are a bit more complicated than Class B amplifiers as they require a constant bias current that requires some power.  The bias will be optimized at a specific rail voltage.  Therefore, the bias will change directly with changes in the rail voltage.  
 
But the biggest issue is that an amplifier's power will fall as its rail voltages fall.  So unregulated amplifiers suffer significant performance degradation as the music modulates their power supply voltage.
 
The rail voltage fluctuations caused by amplifier load are only part of the problem.  The mains voltage is not stable either.  
 
The mains voltage will vary depending on the load on the power grid and the load on the house wiring.  High load conditions can cause the mains voltage to vary by 10% or more.
 
For example, compare the electrical load and usage in the middle of the night to early evening on a hot summer day.  At night people are sleeping so they are not using electrical equipment and the temperature is cool so air conditioners are not running much.  
 
In the early evening, everybody is home from work, dinner is being cooked, electric washers and clothes dryers are operating, air conditioners are maxed out, people are using power-hungry electronics like big TVs, the lights are on, the water heater is running, etc.  So the load on both the grid and home wiring is great.  
 
And when do you listen to your music system?  Of course, when power demand is the highest and voltage is the lowest.  Murphy is hard at work here.
 
And there is even more bad news.  The amplifier itself can severely tax the capacity of your house wiring to which it is attached.  A powerful amplifier can draw all the power that is available from your wall receptacle, which is limited to about 2,400 watts on a 20 amp circuit.  This will drop the voltage on that line by several percent -- this is in addition to the losses on the grid and in your home from other power uses.
 
Furthermore, the mains frequency has a big effect on the output of a power supply.  This is because a transformer's power is determined by the current it can deliver in its power pulses multiplied by the frequency of those pulses.  
 
This means that a transformer can deliver about 20% more power when operated on a 60 Hz mains than it can when operated on a 50 Hz mains.  Therefore, an amplifier with an unregulated power supply will lose up to 20% of its power supply power when operated on a 50 Hz mains.
 
All this is further complicated by the fact that the relationship between voltage and power in an amplifier is not linear.  Power varies by the square of the voltage.
 
Power is the product of volts times amps.  Ohm's Law says that one volt will drive one amp through one Ohm of resistance.  If you do the math, you will come to realize that the power of an amplifier is determined by the voltage that it can drive into the loudspeaker (assuming it can also deliver the current required).  
 
The formula for calculating amplifier power is the amplifier's RMS output voltage squared and then divided by the speaker's impedance.  As an aside, impedance and resistance are the same thing.  Resistance applies to DC circuits while impedance is used for AC circuits.  This is because the impedance often varies with frequency in AC circuits but there is no frequency in DC circuits.  For calculations, you may use impedance and resistance the same way.
 
To determine the voltage, the formula is the square root of the product of watts times Ohms.
 
Using these formula, you can see that for an amplifier to drive 100 watts into an 8 Ohm speaker, it will have to produce 28.28 volts and deliver about 3.5 amps.  Now what happens if we drop the power supply voltage by half?  The voltage will then be 14.14 volts and the current will drop to 1.76 amps.  
 
How much power will the amplifier now drive into the speakers?  It will be just 25 watts.  This is a huge loss.  
 
So you can see that the typical 30% loss of rail voltage in an amplifier results in a very large loss of power -- about 50%.  If you add an additional loss of mains voltage due to heavy house wire loading, you will lose another big chunk of power.
 
When you add all the above factors together, you can see that an amplifier's performance is severely degraded by power supply voltage fluctuations and that eliminating them will produce substantially better amplifier performance in terms of power, distortion, and optimum bias levels.  So why don't amplifiers have voltage regulated power supplies?
 
The problem is that the poor efficiency of conventional voltage regulators results in vast amounts of waste heat.  Most amplifiers run very hot and adding large amounts of waste heat to an already hot amplifier is intolerable.  It is also expensive in terms of both hardware and electricity usage.  So it is very rare indeed to find any amplifier that is fully voltage regulated.
 
So exactly how does a voltage regulator work and what makes it so wasteful and hot that using it is impractical?  The most common type of voltage regulator is called a "down" regulator.  This means that it pulls down the power supply's voltage so that it remains stable under the worst case conditions.  
 
For example, all quality preamps are voltage regulated so that their power supply voltages will remain stable all the way down to a mains voltage of around 90 volts (using a 120 volt mains).  Only if the mains falls below 90 volts ("brown-out" conditions) will the regulation be insufficient and the power supply voltage will start to fall.
 
The power supply will be driven by a 120 volt mains most of the time, although it might be up to perhaps 125 on occassion.  The difference between 120 and 90 volts is about a 30%.   
 
Let's assume that the preamplifier's electronics operate on 12 volts.  The electronic engineer will design the power supply to deliver at least 30% more voltage than that (typically about 18 volts).  He will then add a "down" regulator to pull the power supply voltage down to 12 volts, which is about the voltage that the power supply would produce using a 90 volt mains.  So for any mains voltage between about 90 and 125, the preamp's power supply voltage will be stable at 12 volts.
 
The regulator actually works by placing a variable load across the power supply in the form of a power transistor that is shunted across the output.  A power transistor can be thought of as a very fast-acting, variable resistor whose resistance can be changed electronically.  By monitoring the rail voltage, the electronics can adjust the resistance of the transistor to alter the voltage.  
 
As the mains voltage rises, the electronics will reduce the resistance of the loading transistor, which will draw more power and drop the power supply voltage.  As the mains voltage falls, the electronics will increase the resistance of the load transistor, which will reduce the power used by the transistor and allow the voltage to rise.
 
Of course, the action of the electronics are nearly instantaneous, so there is no significant rise and fall of the rail voltages with changes in the mains.  The voltage will remain rock stable to within a tiny fraction of a percent.
 
A down regulator is very inefficient.  This is because it operates by feeding a voltage through a resistance.  This causes a voltage drop by converting some of the power supply's current into waste heat.  
 
Remember the above concept because it is extremely important.  To repeat -- anytime you apply voltage across a resistance, there will be a voltage drop.  The loss of current causing the voltage drop will result in waste heat.
 
The circuitry in a preamp uses only a tiny fraction of an amp (typically just a few milliamps).  So the power involved will only be a fraction of a watt or so. 
 
If you waste 30% of a watt in a voltage regulator, the heat produced and the electricity wasted is insignificant.  So nobody cares about the efficiency of down regulators when used in small-signal devices.
 
But now let's look at power amplifiers.  Just how much power do we need to regulate?
 
The typical Class AB amplifier is about 50% efficient.  Why?  Because it applies its power supply voltage to its output transistors and these act as variable resistors that control the voltage being applied to the speaker.  So once again, we have the issue of producing waste heat because we applied voltage across a resistance.
 
This means that for every watt that the amplifier feeds to the speaker, a watt will be injected as heat into its heat sinks, and two watts will be drawn from the mains.   A powerful amplifier like the Magtech will produce 500 watts per channel into 8 Ohms.  With both channels operating at full power, 1,000 watts will be fed to the speakers.  It also means that about 1,000 watts of waste heat will be fed into the heat sinks, and 2,000 watts will be drawn from the mains.  
 
The Magtech's power supply will produce 2,000 watts continuously, so a regulator must be able to control a minimum of 2,000 watts of power (and more to be conservative).  The regulator must be able to regulate at least 30% of the rail voltage in order to eliminate fluctuations in voltage due to the variable music demands.  In addition, it must be able to handle more than that to account for voltage variations in the mains and 50 Hz operation.  
 
All together, we are looking at regulating about half of the power supply's voltage.  This is a daunting task for a down regulator because it means that under worst-case conditions (maximum mains voltage, 60 Hz mains, and with the amp at idle), the regulator will have to dissipate half the power supply's voltage (and hence half its power) as waste heat.  
 
That means that the regulator would produce 1,000 watts of waste heat.  This would turn the amp into a room heater and require truly massive heat sinks.  It would waste enormous amounts of electricity, be very large, and the heat would cause failures of parts over time.  You should now be developing an appreciation of why amplifier power supplies are not regulated!
 
Although down regulators are very simple and easy to add to circuits, they are just not practical for use in high power circuits due to their inefficiency.  But there are other types of regulators, which are more efficient.  These are the "up" regulators.
 
An up regulator requires two power supplies.  These have different voltages where one is set for the worst case voltage and the other is set for the best case voltage (say 120 volts and 90 volts for example).  
 
The two power supplies are connected together by a power transistor whose resistance can be varied to allow more or less of the high voltage power supply to be added to the low voltage one.  This allows the high voltage supply to bring the voltage "up" and prevent it from falling based on load or mains voltage.  The rail voltage can therefore be kept constant between the two extremes by electronically controlling the coupling transistor.  
 
The big advantage of an up regulator is that it only has to handle a percentage of the total power supply voltage (in this example, 30%) instead of all of it.  Therefore the losses and waste heat are only a fraction of those produced by a down regulator.  But it requires two power supplies, is more complex, and more expensive than a down regulator.  
 
An up regulator still wastes far too much power and produces too much waste heat.  So it is still impractical for use in all but very low-power amplifiers.
 
The next general type of regulator is not a linear regulator like the types I have been describing.  It is the switching regulator.  
 
A switching regulator is rather complex, but I'll simplify its operation for clarity.  A switcher fundamentally places a transistor in series with the output from the power supply.  This transistor is then switched on and off at a high frequency to feed power to the electronics.  
 
The transistor oscillates at a fixed frequency and its "on" time is varied so that it feeds a percentage of the power supply's current to the electronics based on their need.  By feeding a capacitor bank, a switcher can adjust the current flow to produce a stable voltage.
 
Switching power supplies are very efficient (although not 100%) because their transistors are used in only the on or off state.  They are not partially turned on like the transistors in linear supplies where a significant resistance is presented to the voltage that produces waste heat.  
 
However, a transistor does not change state instantly.  There is still a small percentage of switching time during which the transistors are changing state and resistance is present.  So they still produce some waste heat, although this is relatively small, can be tolerated, and therefore switching power supplies can successfully be used in power amplifiers.
 
But there are big problems when using switching power supplies in high power applications.  The main one is noise -- both electrical and mechanical.  When switching high power and voltages at high frequencies, radio frequencies are produced.  These emissions can adversely affect associated audio electronics and cause instability, oscillation, noise, and general misbehavior.
 
Powerful switchers also make mechanical noise because there is physical vibration of the switching transistors due to the high currents involved.  Switching power supplies are vastly more complex than a simple, 3-part, linear supply and therefore the reliability of switching supplies can be a problem.
 
There are also many technical problems when designing switching power supplies that make them quite difficult to make work satisfactorily.  I won't get into any more detail about this, but rather simply point out that because of all the problems, it is extremely rare to find a linear amplifier with a switching power supply.  They do exist, but are not 100% efficient and are not a practical solution for the voltage regulator problem in power amplifiers.
 
Of course, I have just outlined the basics at this point.  There are many variations on the theme that are beyond the scope of this paper.  But you should now have enough information to appreciate the solutions that follow.  
 
So how can the efficiency problem of high power, regulated power supplies be solved?  Well, the answer came from thinking outside the box.  Specifically, since the heat is produced by applying a voltage to a resistance, the solution had to come from figuring out some way to eliminate doing so.
 
There is a way.  But it could not be done by regulating the continuous DC from the output of a power supply's capacitors because voltage is always present there.  The solution had to be done by figuring out a way of regulating without having voltage present.  That sounds crazy and impossible, but it can be done.  
 
What about the output from the rectifiers?  This is pulsating DC.  While the peak of each pulse is at high voltage and power, the voltage at the end and beginning of each pulse is at -- ZERO!
 
If the regulating power transistor operated only when the voltage was at zero, then there would be no current present, none would be wasted, and no waste heat would be generated.  But how can that regulate the voltage?  Here's how:
 
The Magtech uses two power supplies as you would in an up regulator.  I call the low voltage one the "ride" supply.  It is exactly like the power supply in a conventional, unregulated amplifier.  
 
The second power supply is the "boost" power supply.  It has a higher voltage and current rating than the ride supply and can add massively more power to the ride supply when needed.
 
The ride supply voltage is set for "easy" operation under optimum conditions, i.e., when the mains voltage is at maximum and the amp is at idle.  Under these conditions, only the ride supply drives the amplifier circuitry and the boost supply is just on standby.
 
Note that for the Magtech amp, this is the "easy" condition when the regulator does nothing.  By comparison, this is the toughest condition for a down regulator because it has to drag down the power to the worst case level and dissapate massive amounts of power and heat when doing so.  
 
But in the Magtech, this is the voltage that is desired and that the regulator will maintain.  Under these easy conditions, the boost supply is not needed.
 
When significant power is required, the rail voltages will start to fall.  This is detected by the power supply's monitoring circuitry, which then switches on the coupling transistors to connect the boost supply to the ride supply.  The additional power provided by the boost supply prevents the rail voltage from falling, thereby regulating it.
 
The key to efficient operation lies in the way that the coupling transistors are operated.  First, they are either fully switched on or fully turned off.  This means that they have either infinite resistance or essentially none.  This prevents them from putting any resistance in the circuit that would cause them to dissipate heat.  
 
Secondly, digital control circuitry is used to monitor the rectifiers' wave form and cause the transistors to switch states (either on or off) at the exact point where the DC pulses cross the zero voltage point.  This is important because even though transistors change states very quickly, they do not do so instantaneously.  So there is some resistance during the change of state.  This is the same problem that causes switching power supplies to be less than perfectly efficient.
 
If the transistors changed state while the power supply voltage was applied to them, there would be waste heat generated.  By only allowing state changes at the zero voltage points, there is no waste heat.  
 
Now if you are observant and thoughtful, you might comment that this does not sound like a very good regulation scheme because the two power supplies are either at maximum voltage or minimum voltage because the regulator operates as an all-or-nothing affair.  Your thinking is good, but you are overlooking an important feature in the Magtech's power supply.  
 
The digital control circuitry constantly monitors the pulsating waves from the regulator and the rail voltages.  It will then make a decision to turn the coupling transistors on or off at each zero point to add as many or few pulses as required to hold the voltage constant.  
 
Under heavy load, the coupling transistors would remain on (possibly even continually), letting most or all of the pulses through.  Under light load, they would only be switched on occasionally to let a few pulses through.
 
While it is true that the regulator has a maximum resolution of 120 pulses per second, each pulse has to charge up a very large bank of capacitors (80,000 uF). Doing so takes time and much current.  Therefore, even though each pulse has a lot of current and energy, it can only make a very small change in the capacitor bank's voltage.  
 
The electricity and voltage in the capacitors are analogous to the water in a swimming pool.  You can dump a large, 55 gallon drum of water into the pool (a pulse from the boost power supply), but it won't change the level of the water in the pool (the voltage in the capacitors) very much.
 
By adding more or less pulses as needed, the regulator can maintain a stable voltage to within 0.2 volts.  By comparison, without the regulator, the power supply's voltage would vary by more than 50 volts.  Which would you prefer?
 
You can now see why the Magtech regulator produces no heat and is virtually 100% efficient.  Technically, I can't claim that the regulator is absolutely 100% efficient because nothing is perfect and there is a very tiny amount of resistance in everything, including the coupling transistors when they are "on."  
 
But the resistance of the transistors is less than one Ohm, so they still do not get even warm when operating.  Furthermore, they only operate when the amplifier is working fairly hard, so the regulator isn't even active when the amplifier is at idle or at very low power.  
 
In some ways, the Magtech's power supply is like a switcher in that its transistors are either on or off.  But there is no specific oscillation involved as in a switcher.  Also, it is relatively simple and operates very little and at low frequencies, so its reliability is outstanding (no failures have ever occurred).  And because it never switches under power, there is no noise or radio frequency problems with it.  
 
In short, the Magtech's power supply is unique and solves all the problems of other regulators that have prevented power amplifiers from being regulated -- something they badly need even more than other types of electronics.  The Magtech regulator's circuit, and particularly the digital control technology involved is the subject of a patent, which currently is pending.
 
The Magtech amplifier modules are the same sophisticated ones used in the ESL amp that are capable of very high power, the ability to drive 1/3 Ohm loads, can handle the most difficult loads (as presented by electrostatic speakers), and need no protective circuitry that ruins the sound of many solid state amps.
 
When the ESL amplifier modules are combined with a practical voltage regulator, the result is an amplifier with seemingly unlimited power, virtually unmeasurable distortion, and the ability to drive even the most difficult loudspeakers with ease.  The Magtech offers a truly new level of performance in amplifiers.
ROGER SANDERS - ESL AMP WHITE PAPER
Sanders Sound Systems website
Conventional amplifiers have serious problems when forced to drive (ESL) Electrostatic loudspeakers. Roger Sanders was the first to develop an amplifier specifically designed to drive these unusual speakers:

BACKGROUND 

 
Electrostatic loudspeakers (ESLs) are very different from conventional magnetic speakers and place unusual and difficult demands on the way amplifiers deliver power to them.  A magnetic speaker presents a mostly resistive load to an amplifier, while an ESL appears mostly as a capacitor.
Conventional amplifiers have serious problems when forced to drive electrostatic loudspeakers. Roger Sanders was the first to develop an amplifier specifically designed to drive these unusual speakers:
 
Resistors dissipate power as heat.  So the voice coils of magnetic speakers get hot as they use up the current the amplifier sends to them.  A capacitor stores an amplifier's electrical energy instead of dissipating it as heat.  Therefore an ESL doesn't actually "use" power like magnetic speakers.  ESLs are sometimes called "wattless" speakers because of this.  Their behavior is highly reactive, which means that they send the electrical current back to the amplifier when the musical signal reverses polarity.  Amplifiers tend to be unstable with reactive loads.
 
A watt is a measurement of power.  It is the product of volts times amps.  Volts is a measurement of the pressure or "push" behind the electrons flowing along a conductor.  Amps (a short form of "ampere") is a measurement of the flow of electrons along a conductor.
 
Amplifier power is measured in watts, which is fine when working with magnetic speakers.  But an ESL doesn't operate on watts, it operates on voltage.  Therefore, an amplifier's wattage rating can be very deceptive when evaluating its ability to drive an ESL.
 
To take an extreme example, let's look at two amplifiers, both rated at 100 watts.  One has a 1 volt power supply that delivers 100 amps of current.  The other produces 100 volts at 1 amp.  Although both amplifiers generate 100 watts, the one with the higher voltage will drive an ESL to much louder levels than will the low voltage one.
 
Resistance in AC (alternating current) circuits is called impedance, because it often varies with frequency.  A resistor has essentially constant impedance, so the impedance of a magnetic speaker will be nearly constant, although there will some variation due to crossovers and resonances.
 
In a capacitor, the impedance is inversely proportional to frequency.  So an ESL will have a high impedance at low frequencies (perhaps several hundred), and a very low impedance at high frequencies -- typically around 2 Ohms.
 
VOLTAGE LIMITATIONS:
 
ESLs are voltage operated devices.  The higher an amplifier's power supply voltage, the louder it will be able to play an ESL (assuming it can also deliver sufficient current).
 
Because high voltages are not needed for magnetic speakers, and because high voltage parts are expensive, conventional amplifiers often lack sufficient voltage to drive ESLs to truly loud levels.
 
When an amplifier runs out of voltage, it clips (called "voltage clipping").  This results in distortion and compressed dynamic range.  Depending on the amplifier and its behavior when clipping, the music will take on a wide variety of non-musical qualities.
 
If an amplifier is clipping, it really doesn't matter how well-built the amplifier is, or how impressive its design philosophy -- it simply won't sound as good as an amplifier that isn't clipping.  Therefore, the most important amplifier specification is its power rating. When observed on an oscilloscope, most audiophiles are amazed at how often their favorite amplifier is clipping when playing music moderately loudly.  Modern speakers require several hundred watts/channel to loudly reproduce today's highly dynamic music without distortion.
 
ESLs have a legendary reputation of being able to produce effortless and crystal-clear sound, with magnificent resolution of subtle inner-detail.  A clipping amplifier will destroy these qualities.
 
Sanders Sound Systems’ ESL amplifier operates at high voltage (plus/minus 92 volts).  This will drive most ESLs to "ear-bleeding" levels with voltage to spare.  The result is electrostatic sound that retains its totally effortless and clear qualities at any tolerable listening level.
 
PROTECTIVE CIRCUITRY:
 
Most transistor amplifiers require protective circuitry to prevent their output transistors from being damaged when they attempt to drive low impedance loads at high levels.  In high quality amplifiers, this circuitry switches the power on and off to the output transistors very quickly.  This causes voids and voltage spikes to be added to the sound which is one of the major causes of the harsh sound often heard in overloaded solid-state amplifiers.  In fact, it is this and the introduction of large amounts of odd-order harmonic distortion from voltage clipping that is the cause of the dreaded "transistor sound" -- not the use of transistors per se.
 
Sanders Sound Systems's ESL amplifier has such a massive output section that it does not need any protective circuitry.  It can drive loads below 1 Ohm without damaging its output transistors.  Since it has so much voltage and current capability that it virtually never clips, it doesn't exhibit any "transistor sound."
 
PROBLEMS AND SOLUTIONS
 
CURRENT LIMITATIONS:
 
An amplifier must deliver more current as the impedance of the speaker decreases.  This requires a larger power supply and output devices that can pass large amounts of current.  Such parts are costly, so modestly-priced amplifiers are only designed to drive relatively high impedance loads -- like 8 Ohm speakers.  Better amps use superior parts and can handle 4 Ohm loads.
 
But few of even the best amplifiers can handle the very low, 2 Ohm impedance of an ESL well.  Many otherwise fine amplifiers find themselves unable to pass sufficient current through their output stages to drive an ESL at high frequencies.  This is known as "current clipping", and results in poor high frequency performance.  Tube amplifiers are particularly bad in this regard due to their relatively high, 4 Ohm output impedance.
 
The Sanders Sound Systems Electrostatic Amplifier ("ESL amp") solves this problem by using a massive output stage.  Each output transistor is capable of delivering 250 watts -- and there are eighteen of these per channel.  As a result, it can deliver a staggering 135 amps of current with a combined power rating of 4500 watts per channel!
 
The output impedance of an amplifier must be lower than the impedance of the speaker, or current clipping will result.  With so many output devices, the output impedance of the ESL amplifier is virtually zero.  Current clipping simply is no longer an issue.
 
POWER:
 
As previously mentioned, "power" in the usual sense, does not apply to ESLs.  But it is useful to try to make comparisons to get an idea of what can be expected for a purpose-built ESL amplifier.  Also, many of the features that make the ESL amp so effective for ESLs also work splendidly with magnetic speakers.  So it is worth rating an ESL amplifier using conventional power measurements.
 
The term "volt-amps" is used instead of "watts" when evaluating an amplifier's ability to drive the capacitive load presented by an ESL.  Volt-amps is still the product of volts x amps (as is watts) but the difference is that they are not necessarily being delivered simultaneously.  Another way of saying this is that the voltage and current are out-of-phase with each other.
 
When driving a resistor, the voltage and current flow together.  In a capacitor, the current leads the voltage by 90 degrees.  This out-of-phase power delivery drives transistors out of their safe operating area.  In conventional amplifiers, it can cause output transistor failure and/or the premature triggering of protective circuitry.  This can cause the amplifier to deliver only a small fraction of its rated power and cause harsh sound quality.  The ESL amp's output stage is so robust that it can drive out-of-phase loads with ease, and since it needs no protective circuitry, there is nothing to ruin the sound quality.
 
Sanders Sound Systems’ ESL amplifier can deliver more than 2000 volt-amps per channel into an ESL.  That means it will act like a conventional amp rated at more than 1000 watts per channel.
 
When driving magnetic speakers, the ESL Stereo Power amplifier will deliver over 400 watts/channel into an 8 Ohm load, and over 780 watts/channel into a 4 Ohm load.  Momentary output into a 2 Ohm load exceeds 1200 watts. The amplifier is completely stable and will not be damaged even when driving a 1 ohm load.

When driving magnetic speakers, the ESL Monoblock Power amplifier will deliver over 360 watts/channel into an 8 Ohm load, and over 700 watts/channel into a 4 Ohm load.  Momentary output into a 2 Ohm load exceeds 1000 watts. The amplifier is completely stable and will not be damaged even when driving a 1 ohm load.

EFFICIENCY:
 
Many modern amplifiers are extremely inefficient.  Enormous amounts of their power, in fact most of it, is wasted as heat.
 
Audiophiles who prefer to leave their amplifiers on continually have discovered that a large, inefficient power amplifier can add over $100 per month to their electric bill.  In a ten-year period, their amplifier could cost them $12,000 to operate!  To produce so much waste heat, some of these amplifiers even require special mains wiring.
 
At Sanders Sound Systems, we believe that the use of such amplifiers is absurd, unnecessary, and environmentally irresponsible.  Proponents of these amplifiers claim that inefficiency is necessary to keep distortion at very low levels.  Many years ago, this was true.  But with modern technology, it is possible to make amplifiers that are extremely efficient while still maintaining vanishingly low distortion levels.
 
Sanders Sound Systems’ ESL amplifier has un-measurable distortion levels (less than 0.01%) from 20 Hz to 20 kHz up to the onset of clipping.  It does this while dissipating only three watts at idle and actually idles cold to the touch.  It may be left on indefinitely without concern for electricity usage.
 
STABILITY:
 
The weird phase angles and high reactivity of ESLs tends to cause conventional amplifiers to become unstable.  The Sanders Sound Systems ESL amplifier is specifically designed to be unaffected by reactive loads.
 
The result is an amplifier that is completely stable under all conditions -- even at turn-on where no muting circuit is needed or used.  There is no "pop" or "thump" at either turn-on or turn-off and the amplifier switches on instantly.
 
SIZE AND WEIGHT:
 
Many of today's best amplifiers are so large and heavy (over 100 pounds) that one person cannot lift them.  They cannot be placed on a shelf or in an equipment rack.  Some are so big that they are split in two parts a "mono-block" for each channel.  It often is difficult to find a place on the floor to put them.  Many spouses are less-than-pleased about having such large amplifiers cluttering their living space.
 
To produce large amounts of power for driving resistive loads in highly inefficient amplifiers, it is necessary to use outrageously large and heavy power supplies and huge heat sinks.  So it is not surprising that such amplifiers are immense.
 
Despite its vast output potential, Sanders Sound Systems's ESL amplifier weighs 52  pounds and is sized scarcely larger than a full-sized preamp.  Its dimensions are 17" wide x 5.5" tall x 16" deep(43cm x 14cm x 40.6cm).  The Monoblock version of the ESL amp is the same small size as the stereo amp, and even two of them will fit in most racks.
 
Sanders Sound Systems has achieved this remarkable compactness by using a chassis made mostly of lightweight machined aluminium, and using the power supply to drive speakers instead of having its power converted to waste heat.
 
Because the ESL amplifier generates so little heat, the heat-sink requirements are greatly reduced.  Additionally, high-efficiency heat-sinks are used that make it possible to further lessen the weight and size of the amplifier.  Nor is this compactness achieved at the cost of having a noisy cooling fan.  The amplifier is completely silent.
 
BUILD QUALITY 
 
The quality of construction is typical of the finest components made today.
 
Resistors are high reliability, precision metal film, 1% tolerance.
 
Capacitors are of the highest quality and none are used in the signal path.
 
Connectors are either gold or rhodium plated.
 
Both balanced and single-ended connectors are standard.
 
The finest quality, WBT binding posts are used. These are widely spaced and positioned at a 45 degree angle for ease of use and speaker cable routing.
 
There is no wire in the signal path save for a 2-inch piece connecting the circuit board to the output terminal.
 
The amplifier runs very cool.
 
The amplifier is completely modular for easy servicing or upgrading. The amplifier uses so little power at idle that it can be left on continually for optimum performance and longest life without concern for power usage or taxing your room's air conditioning system.
 
A massive output stage using 18 transistors makes the amplifier extremely rugged and reliable. It will drive the most difficult (low impedance and reactive) loads without strain or damage, which is 
why it is ideal for driving electrostatic loudspeakers.
 
The amplifier is completely stable and will not be damaged even when driving a 1 Ohm load.
Colour - Customer's choice of black or silver anodized machined-aluminum faceplate with black chassis.
 
Although called the "ESL amplifier", the same features that make it ideal for driving difficult electrostatic loads also make it ideal for conventional, magnetic loudspeakers, which are easier to drive. It is not limited only to electrostatic speakers. It is particularly good at driving planar magnetic speakers that have very low impedance and require powerful amplifiers.
 
The mains voltage is user-selectable from the rear panel, so the amplifier can be used anywhere without having to be modified at the factory for different voltages.
ROGER SANDERS - DISPERSION WHITE PAPER
Sanders Sound Systems website
I started doing research and development work on ESLs in 1972.  One of the major issues I had to address was "beaming" in large panels.  Back then, I believed the common perception that a good speaker should have wide dispersion.  So I worked on the problem. 
 
I eventually solved the problem of beaming in 1979 when I invented a way of curving a free-standing, tensioned membrane.  It was my design that Martin Logan called the "Curvilinear" ESL and produced starting in 1981.
 
After a lot of study and experimentation with the curved panel, I came to the clear conclusion that it was actually a poor design.  I abandoned it in favor of a planar ESL.  Why would I fail to use my own invention? 
Here is where the physics get very interesting.  I eventually came to understand that there are three serious problems caused by wide-dispersion in speakers.  These are poor frequency response, poor transient response, and poor imaging. 
 
Let's look at each of these issues in detail.  For examples in this discussion, I will refer to two, imaginary speaker systems.  For simplicity and to eliminate confusion, we will assume that both speaker systems are perfect in every way.  The only difference between them is that one will have wide dispersion and one will have narrow dispersion. 
 
Now let's examine what happens to frequency response in both of these speakers.  We will hear the sound from the narrow dispersion speaker being beamed directly to us at the sweet spot.  Therefore the frequency response from the narrow dispersion speaker will sound perfect (because we defined the speakers as perfect in every way). 
 
But the vast majority of the sound from the wide-dispersion speaker will be sprayed all over the room rather than being beamed directly to our listening location.  We will therefore hear most of the sound from this speaker after it has bounced off various surfaces in the room and is eventually reflected to us at the sweet spot.
 
Because the reflected sounds have to travel a greater distance to reach us than the direct sound from the speaker, the reflected sounds will be delayed by the speed of sound.  Another way to say this is that reflected sound will be out-of-phase with the direct sound.  The phase-angle will be determined by the amount of time delay between the reflected sound and the wave length of the particular frequency of interest.
 
For simplicity, let's examine just one of these reflections and how it interacts with the direct sound from the speaker.  Let's assume that the magnitude of both the direct and reflected sound is the same (in real life, the magnitudes can vary all over the map).
 
If a 1 KHz tone arrives directly from the speaker at 80 dB, it will mix with the reflected sound (at 80 dB) at some phase angle depending on how much the reflected sound was delayed.  Let's assume that this particular wave arrives 180 degrees out-of-phase.  If so, the reflected sound would completely cancel the direct sound and you would hear nothing.
 
If the reflected sound arrived 90 degrees out-of-phase, it would reduce the direct sound by 50%.  If it arrived 360 degrees out-of-phase, it would increase the sound by 100%, etc.
 
As you move up and down the frequency range, this particular delayed reflection would interact with each frequency differently (because the wave lengths are different so the phase angle would be different for each frequency).  The result is that you would hear (and measure) the speaker's frequency response as consisting of severe, alternating peaks and troughs that look like the teeth of a comb -- hence we call such frequency response a "comb filter."
 
Now a comb filter sounds perfectly awful.  Conventional, wide-dispersion speakers would be unlistenable if it weren't for the fact that there are thousands of delayed reflections in a room, and they are all random.  As a result, there are thousands of comb filters formed and to a considerable degree, they can average themselves out so that the frequency response from a wide dispersion speaker is tolerable. 
 
But this problem assures that the frequency response will never be perfect in a wide dispersion speaker.  It is often necessary to move the speaker around to get satisfactory response, which is why speaker placement is so important. 
 
The very short and intense reflected sounds from walls directly beside the speaker are particularly troublesome as they tend to dominate the sound.  Hence, smart audiophiles have discovered the trick of using sound-absorbing "room treatment" near the sides of wide dispersion speakers to help achieve reasonable frequency response.
 
You can now see how the frequency response of a speaker is seriously degraded by room acoustics.  This background information will make it obvious why transient response is degraded by room reflections as well.
 
For simplicity, let's examine a single, sharp transient (like a rimshot from a drum).  The transient coming from the narrow dispersion speaker will be perfect (because we said the speaker was perfect).  But what happens to the transient from the wide-dispersion speaker?
 
Once again, most of the transient sound is blasted all over the room where it bounces off various surfaces and eventually arrives at the sweet spot after being delayed by various amounts depending on the distances each reflection has to travel.  So instead of hearing one, crisp transient, you will hear "popcorn."  Like a pan of popcorn popping, we will hear a whole bunch of identical transient sounds separated by very short intervals.
 
These delayed transient sound are actually echoes.  But the typical listening room is too small for the delayed sounds to be separated by a sufficient period of time for our brains to recognize them as distinct echoes. 
 
It is a fact that the delayed sounds are distinct.  We can see that on an oscilloscope.  But we don't hear them that way -- as a multitude of distinct transients.  We hear them as one sound.
 
Our brains have learned to understand that having a bunch of rimshots close together means that there was only one rimshot with room acoustics following it.  So our brains do one of their psychoacoustic tricks and sweep all the delayed sounds together to form one rimshot. 
 
But there is a "catch."  And that is that the transient time of the rimshot now includes all the delayed sounds following it.  This extends the transient time we perceive with the result that the transients are now "smeared." 
 
If you doubt this, just think of the last time you heard headphones.  I'm sure you will agree that the transients you hear in headphones are crisper and cleaner than what you hear from wide-dispersion speakers.  This isn't because headphone drivers are so good (actually most are pretty bad), it's simply because there are no room acoustics in headphones to mess up the sound.
 
Now let's look at imaging.  A holographic image will be 3-dimensional.  It will not only have left/right information, but it will have depth. 
 
Left/right position in the image is determined by loudness differences between the two channels.  But depth is defined by timing information (phase). 
 
The reason you hear the violins in a symphony orchestra to be in front of the brass is because their sounds reach your ears slightly sooner than the sounds from the trumpets and trombones.  This phase information has to be preserved in the recording and then reproduced accurately by the speakers for you to get depth in the image. 
 
By now, you probably know what I am going to say.  The sound from the narrow dispersion speaker will supply proper phase information to your ears.  The sound from the wide dispersion speakers will be blasted all over the room and the delayed sounds will completely confuse the phase information.  As a result, the sound from wide dispersion speakers (and omni speakers are the worst) will have very diffuse and ill-defined imaging. 
 
In summary, the frequency response, transient response, and imaging of a loudspeaker is ruined by room acoustics.  So to achieve outstanding performance, a loudspeaker must eliminate room acoustics as much as possible.
 
My curved electrostatic panel failed to eliminate room acoustics.  I found that a planar panel was far superior because it beams the sound directly to you and eliminates the room acoustics.  So I abandoned the curved panel.  Once you hear highly directional panels, you will immediately understand.
 
Many audiophiles believe that a good speaker should have a wide sweet spot.  But this is a physical oxymoron. 
 
The laws of physics dictate that all stereo speakers will have an infinitely small sweet spot, regardless of their high frequency dispersion.  That spot is when you are exactly equidistant from both speakers.  Only when you are equidistant from the speakers can the phase information arrive at your ears simultaneously from both speakers.  Obviously, there is no hope of imaging well if the sounds from both speakers do not arrive at the same time as the phasing will be destroyed.
 
For a speaker to have a wide sweet spot simply means that the phase information from the room is confusing the sound so badly that you can't even tell when you are in the sweet spot and when you aren't.  A wide sweet spot is a guarantee that a speaker has poor imaging and transient response.
 
I don't compromise.  I want narrow dispersion in my speakers to minimize room acoustics so that I can get the best possible sound. 
 
"Beaming" is not a fault.  It is a huge advantage.  It is the only way to achieve truly high performance in a loudspeaker.
 
Audiophiles sometimes say that narrow dispersion speakers require you to have your head in a vise.  This is nonsense.  You just sit in your listening chair and listen as you would to any speaker.
 
And what about the off-axis performance of a narrow dispersion speaker?  Well, they sound just like wide dispersion speakers when you are off-axis. 
 
That is to say that when you are off-axis, you hear the room acoustics, not the speaker.  So my speakers sound just fine off-axis for casual listening.  Of course, the image is diffuse and of poor quality, just like a wide dispersion speaker when you are off-axis.  So for serious listening, you need to be at the sweet spot.  This is true for all speakers.
 
As an aside, it is best to NOT absorb the rear wave from my speakers.  Let it help energize the room for off-axis listening.  That way the highs will be preserved off-axis.
 
Finally, the question arises, "Why doesn't the reflected sound from the dipole beams mess up the phase just like in a wide dispersion speaker?"  The answer is that the reflections from a dipole radiator are only one rather than thousands. 
 
Also this beam has to bounce off many surfaces before it finally reaches the sweet spot.  In so doing, it is greatly delayed and attenuated.  It arrives at the sweet spot so late and attenuated that our brains simply ignore it. 
 
Of course, directionality only applies to midrange and high frequencies.  Bass is omnidirectional in all speakers due to the long wave lengths involved.  So bass room resonances still need to be addressed.
 
There is one perilous pitfall you need to be aware of with regards to delayed reflections in all speakers, even narrow dispersion speakers.  This involves sitting close to a wall directly behind you, which is very bad.
 
Typically this occurs if a couch is used for a listening chair.  Most of the time a couch is pushed up against a wall.  If you sit in it, your ears are only a few inches from a wall that is perpendicular to your head.  As the sound beam from a planar speaker arrives at your ears, some of it passes by your head, bounces off the wall, and returns to your ears after a very short delay. 
 
This one reflection is very powerful.  It is almost as intense as the direct beam and it will seriously mess up the frequency response and transient response of the sound. 
 
To avoid this problem, ideally you should sit in a chair out in the room away from the wall.  Even better would be to have the system on a diagonal so that the wall behind you is angled and reflects the rear reflection away from you instead of back at you.  Diagonal room placement is also best for controlling the bass resonances from a speaker. 
 
If your room decor makes this impractical, then there are several options you have.  First, you can put sound absorbing material on the wall behind your head.  The could be a simple as a very soft pillow that you set on the back of the couch so that it is behind your ears.  This is not as effective as I would like because it will only absorb high frequencies.  The midrange will still have a reflection.
 
Probably the best compromise is to have a movable listening chair.  When not being used, the chair can be placed in the room wherever it pleases your wife.  When you want to listen seriously to music, you move the chair out into the room where you have identified the sweet spot (usually with tiny pieces of tape on the floor).  Then the sound can be spectacular.
ROGER SANDERS - ROOM ACOUSTICS AND TREATMENT WHITE PAPER
Sanders Sound Systems website
Rooms have a major impact on the performance of loudspeakers.  I get many requests for information on what is an ideal room and how best to set up my electrostatic speakers in rooms.  This white paper is designed to provide some insight and suggestions that will help.  Most of this information applies to all speakers, not just my electrostats.
 
My electrostats are very tolerant of poor rooms.  But of course, they will work best in rooms that have reasonable acoustics.  In general this means that "slap-echo" should be suppressed.  In most cases, this means that there should be sufficient damping in each of the three room dimensions that you do not hear slap-echo.  
 
Slap-echo is when you slap your hands together and can hear an echo shortly after doing so.  You should suppress this.
Generally, this means that 15 - 30% of the surface area of each dimension needs to consist of some sort of soft damping material that will absorb sound energy.  For example, in most rooms the floor-ceiling dimension is damped by carpet or rugs.  The horizontal dimensions are usually damped by heavy window drapes and soft furniture.  Sometimes additional damping is required in the form of "Echo Busters" or similar commercial room treatment products.  
 
Note that you do not have to buy expensive "audiophile" products.  Any soft material will work, such as foam rubber, cork tiles, cloth, etc  .
 
My speakers don't spray treble all over the room like conventional, wide-dispersion speakers.  So it is not necessary to specifically damp the side wall reflections as is necessary with other speakers.  You can put the damping materials most anywhere that is convenient to eliminate slap-echo.
 
The wall behind the speaker may be damped or not.  It just depends on your personal preferences and the situation in which you plan to use the speakers.  Here is what to consider:
 
Are you only going to listen to the speakers at the sweet spot -- or do you want to hear them well everywhere in the room?  For most home use, listeners want them to sound excellent everywhere.  So it is best to have the rear radiation from the speaker bounce off a hard surface like a bare wall or windows.  This will assure excellent high frequency response when you are out of the sweet spot and listening casually to music elsewhere in the room.
 
This rear radiation will not have any significant effect on the sound at the sweet spot due to the Precedence Effect.  This is where the rear radiation is so delayed that our ears only pay attention to the direct sound.  This is the key to the superior imaging, transient response, and frequency response of my electrostats.  
 
However, there are exceptions to this.  For example, in very small rooms, the sound from the rear wave may not be delayed enough for the Precedence Effect to be effective.  In that case, putting damping material on the wall directly behind the speakers can really help make the sound more clear.   We do this routinely in recording studios.  I suggest you try it both ways and see what you like best.
 
Note that damping only works for treble frequencies.  It has no significant effect on the bass response because base wave lengths are too long and energetic to be absorbed effectively.  Therefore, rooms will always have a few significant bass resonances, with which you must live.
 
Dealing with the bass is best done by trying to achieve the ideal bass frequency response, which would be provided by having an infinite number of infinitely small bass resonances.  Of course, this cannot be achieved in the real world.  But you can certainly help by designing your listening room to have many small resonances instead of a few large ones.  
 
Consider the acoustical techniques used by the engineers of fine concert halls.  They do three things:
They use room dimensions that are 1/3 octave ratios.  This assures that each dimension will have different resonances.  By comparison, a room that was in the shape of a cube would have the worse bass performance because all three dimensions would be the same, thereby producing only one resonance at triple the magnitude of three different resonances.
 
They make the walls non-parallel.  This breaks up the single large resonance in that dimension into a nearly infinite number of tiny resonances.  Observe any good concert hall and you will see that the walls taper outward from the stage, specifically for this reason.
 
Large diffusers are used to further break up bass resonances.  Look up near the ceiling in a good concert hall and you will see very large, irregular, blockish structures that are designed for this purpose.
 
 
Now I understand that you probably can't make your own listening room using concert hall techniques (although I have and it worked extremely well).  But you can help by picking a room with close to the ideal 1/3 octave ratios, using diffusers (usually large pieces of irregular-shaped furniture), and using suitable speaker placement.  
 
Speaker placement is the biggest issue.  Most audiophiles use symmetrical placement where the speakers are the same distance from walls and corners.  This is the worst placement because both speakers will produce the same few resonances and they will be at double the magnitude than if the speakers were placed randomly in the room.  
 
These audiophiles also usually put the speakers on the short wall, which tends to force the speakers into corners, which also aggravates resonances and their magnitude.   Putting the speakers on the long wall at different distances from corners is better than using the short wall.
 
In extreme conditions, like we have in the hotel rooms we manufacturers must use at shows, I place the speakers on adjacent walls, straddling a corner.  I assure that the speakers are at different distances from the walls and corners.  This produces the most resonances at the smallest magnitudes and gives surprisingly good bass frequency response -- I often win the award for the "Best Sound at the Show."   
 
Of course, setting up the speakers to straddle a corner this means that listeners must face diagonally in the room.  But there is nothing wrong with that -- it just looks unusual.
 
You can see photos of such setups on my website under "show coverage."  Scroll down through the show coverage and you will see several photos.  Here is a direct link: http://www.sanderssoundsystems.com/show-coverage
 
Finally, you should make every effort to avoid placing your sweet spot directly against a wall.  Doing so will produce a short reflection from the wall behind you, which will cause smearing of the transients and a poor image.  It is much better if you are out in the room and well away from the wall.  
 
It is also best if the wall is at an angle to you instead of perpendicular to your sweet spot.  When it is at an angle, the reflections off that wall will bounce away from you rather than directly back to you.  This is another reason that diagonal placement of speakers is better.
 
If you must sit directly against a wall, then you should place some damping material on the wall behind your head.  This could simply be a small pillow.  This will greatly help to reduce the intensity of the reflected sound and produce clearer sound.
Roger Sander's White paper on ESL - Electrostatic Speakers.
Sanders Sound Systems webiste
HOW DO ELECTROSTATIC SPEAKERS WORK?
 
Unlike conventional speakers that use magnetic forces to move a relatively heavy cone, electrostatic speakers use high voltages to move an extremely thin, light diaphragm. High voltages produce an attractive force similar to magnetism. You may have discovered this by combing your hair on a dry day. The comb takes on a high voltage charge and you can feel it pull the hair on your arm or watch it pick up dust or small bits of paper.
Note that this charge is STATIC (it doesn't move). In an electrostatic loudspeaker (ESL), a small, high-voltage power supply puts a static charge on the speaker's diaphragm. Hence the name, electroSTATIC loudspeaker. This is also why the speaker must be plugged into the wall like any other electronic component. On either side of the speaker's diaphragm is a STATOR, an electrically conductive, acoustically-transparent grill. The amplifier is connected to both stators through a high-voltage step-up transformer.
 
The transformer is necessary to raise the voltage of your amplifier from a few tens of volts to the several thousand volts needed to drive the diaphragm. Music causes the amplifier to deliver varying amounts of electricity to the stators.
 
Like north and south magnetic forces, positive and negative electrostatic forces are attracted to each other, while similar polarities are repelled from each other. Music drives the amplifier to produce a positive voltage on one stator and a negative voltage on the other. These voltages alternate back and forth between positive and negative very rapidly to produce a tone. For example, "middle C" on a piano has a frequency of 256 Hz (Hertz). That means the polarity on the stators will alternate 256 times per second. The amplifier also alters the voltage as necessary to make the music a particular loudness.
 
Now, let's look at what is happening inside the speaker to make it produce sound. At a given moment in time, in response to the musical signal, let's say the front stator has a positive voltage. The rear one will be negative. Let's assume that the diaphragm has a negative voltage. Remember that the diaphragm's voltage is static and comes from the little power supply and does not change like the voltages do on the stators.
 
The negatively-charged diaphragm will be attracted to the positively-charged front stator because opposite charges attract. It will be repelled from the negatively-charged rear stator because like-charges repel. A moment later, the amplifier will reverse the voltage polarity on the stators, so the diaphragm will move the other way. As the diaphragm moves, it produces pressure waves in the air that we hear as music.
 
WHY USE ELECTROSTATIC LOUDSPEAKERS?
 
ESLs have several advantages over conventional magnetic speakers. These include better transient response, lower distortion, and absence of resonances. Here's why:
 
TRANSIENT RESPONSE
 
The moving part of a magnetic speaker is relatively massive. Its voice coil, suspension system, and cone or dome, add up to a lot of mass. The total weight of all of these parts is much more than the air that the speaker drives. Music consists mostly of transients (rapidly starting and stopping sounds). Because mass has inertia, the mass of magnetic speakers prevents them from responding quickly enough to follow the rapidly-changing musical wave-form with perfect precision.
 
The diaphragm of an ESL is much thinner than a human hair. Its mass is so small, that at audio frequencies, an ESL can be considered to be a massless speaker. As a result, it responds instantaneously to the music and can accurately and effortlessly reproduce perfect transients.
 
DISTORTION
 
The voice coil of a magnetic speaker only drives one point (the apex of the cone or the edge of a dome tweeter). Because cones and domes are not perfectly rigid, the driven surface flexes and distorts the sound. By contrast, an ESL's diaphragm is driven uniformly over its entire surface. There is no distortion of the surface to alter the character of the music.
 
RESONANCES
 
A massive magnetic speaker resonates at many frequencies. It behaves somewhat like a bell. Because these resonances are not present in the music, magnetic drivers "color" the sound. Also, because the "ringing" continues long after the original note has stopped, transient response is poor.
 
An ESL's diaphragm is swamped by the mass of the air in which it is immersed. Much like trying to ring a bell under water, the ESL simply cannot "ring." The result is the legendary purity and clarity of sound for which electrostatic speakers are justly famous.
Considering the price and performance, I doubt you’ll find anything better without spending significantly more. Considering you can leave it on all the time, and it comes with a lifetime warranty, it’s an easy recommendation.
Phillip Holmes

REVIEW SUMMARY: So, does the Sanders technology serve the music? In my opinion, it does, because listening was thoroughly enjoyable, and I frequently was surprised by a new insight or detail, which is a good sign. This preamp might reveal faults in the rest of the system that need addressing, but that is a good thing if the result is better playback.

EXTENDED REVIEW: Slide rules and pocket protectors:
In the subjective audio universe, where gross amounts of 2nd harmonic distortion, horrendous phase shift, and totally inadequate frequency response gets euphemistically labeled “bloom” and “harmonic richness,” the purveyors of audio accuracy must hide their devotion to truthfulness like it’s a cardinal sin. “Zero phase shift?! Grab the matches and gasoline, we have a scientist in our midst.” There are negative connotations to marketing with specifications. Anyone old enough to have heard the first transistor amps will agree they sucked, regardless of what the specs said. Engineers in the ‘60s, ‘70s, and ‘80s, with their use of feedback as a blunt-force-instrument, forever tainted integrated circuits, feedback, and solid state. Though the equipment measured good, it sounded bad. Real bad. In a way, we should be thankful the big corporations made bad sounding equipment. Had they not, we wouldn’t have the audio underground and cottage industries that sprung up to satiate the appetite for good sound.

So, what’s wrong with electronics that have no audible distortion, no audible phase or frequency response issues, no oscillations, no noise and no problem driving any set of cables or amps or speakers? Nothing. Nothing is wrong with that. Are you so hung up on tube rolling and tweaking that you reject the hypothetical existence of an integrated circuit that would do a better job, and keep doing it the same way for 20 or 30 years? Are you that afraid of your music collection?

Though I admit to enjoying tubes, analog, open reel tape, and single driver loudspeakers, I will be the first to admit that there are significant limitations with all the above. If the primary job of an audio system is to be truthful, then does the current crop of high performance digital, and high performance integrated circuits deliver the goods? Increasingly, the answer is yes. We are advancing the state of the art in baby steps. Some of the advancements come from improved manufacturing techniques, giving us higher performance through better matched transistors and purer materials. Some of it has been new ways to accurately measure distortion, or the discovery that the ear can hear things that are hard to measure with simple harmonic distortion analysers. Some of it is trickling down from medical, aerospace and military technology. The same circuits used to hunt down submarines or find tiny tumours have applications in audio. Billions of dollars have been spent to beat the competition, whether it is another chip manufacturer, stage IV cancer, or enemy combatants.

For all audio, I ask a few simple questions. Is the frequency response wide enough, and flat enough, to allow us to hear all the fundamentals and overtones, and in the correct relationship? Is there audible distortion? Does it have enough power to avoid clipping? After those criteria are met, can it recreate an acoustic space (imaging)? Finally, is it reliable? Those criteria are hard to satisfy, and when a piece meets the criteria, it usually satisfies musically. Sure, there are very subtle nuances, almost impossible to measure, that are the difference between the good and the great, but I have a hard time hearing those nuances over audible harmonic distortion and hum. Almost all the equipment I’ve reviewed had issues, usually minor ones, in one or more categories. Some people don’t mind scads of harmonic distortion, limited power or limited bandwidth, and you know who you are. I do mind, but there is a niche product for everyone.

The Goal

So, what has that to do with the latest preamplifier from Sanders Sound Systems? Everything. Roger is an actual engineer, in an industry with many “gurus” and copycats. Let me offer a few interesting excerpts from the Sanders website in the following:

Roger Sanders quote:
“Our previous preamps (line stage and phono) were US$4,000 (excl sales tax), for a total cost of US$8,000 (excl sales tax) for our customers who needed a phono preamp. Since both preamps are now combined, customers who need a full-function preamp can now save several thousand dollars as the new preamp sells for half the price of the previous two.

The goal of a true audiophile grade preamplifier is to offer gain, switching, and other conveniences, while at the same time passing the original signal downstream without adding distortion, noise, or a sonic signature of its own. The Sanders Preamp does exactly that but includes many ergonomic features for convenience and ease of use that are not available on even far more expensive preamps.

The levels of each individual input can be adjusted to get them all matched so that you don’t get “blasted” or have to turn up the main level each time you switch sources. A stereo/mono switch remains standard equipment. The overall gain, individual gain between devices, and channel balance can be adjusted in precise, 1 dB increments. Muting by remote control is standard. A video readout makes it easy to monitor the levels.

… Front panel controls are done through micro-touch electronic switches. Internal switching is done by miniature, sealed, gold relays. Conventional rotary volume controls have channel matching error of around 20%, which causes the left/right balance to shift as you change the level. To solve this problem, some preamp manufacturers use discrete, precision resistors on a multi-step switch.

While this solves the channel tracking problem, they introduce new ones. Specifically, they have very limited resolution due to too few steps (typically 31 steps of 2 dB each). These “stepped attenuators” produce very annoying switching transients at each step.

The Sanders Preamp solves these problems by using the “volume control” knob to drive an optical comparator circuit. The optical circuit operates a microprocessor that controls an electronic gain system. This controls the level using one hundred, one dB steps, with precision of greater than 0.1% between channels.

The microprocessor monitors the signal voltage and waits for it to cross the zero voltage point between waves before switching to the next level. This prevents any switching transients. The volume control knob has detents at each 1 dB point and it rotates continually. So it as an infinite number of detents and you can feel each 1 dB change in level.

There is a digital display with beautiful, blue, light emitting diodes (LEDs). The display continually shows the output level of the unit and switches automatically to show level differences between channels, when you adjust the balance, or when you adjust the input levels. You no longer have to guess at the levels or try to see fine gradations on a knob to know the levels, since you can see them from several feet away…….”

The heart of the new preamp is an extremely sophisticated chip that matches the gain to within .1dB and can remember the various level adjustments for each input. I asked Roger to elaborate:

Roger Sandrs quote:
“The volume control in my preamp is an electronic level control designed and manufactured by Burr-Brown (now owned by Texas Instruments). This chip has many excellent features. It is actually built like a stepped attenuator (using 400 microscopic resistors to obtain 200, 1/2 dB steps, in stereo).

The accuracy of the channel balance is determined by the precision of the resistors. Modern chip-manufacturing technology can now produce resistors with tolerances of better then 0.1% — which is far better than discrete resistors, which are limited to about 1%. Therefore, these Burr-Brown chips offer essentially perfect channel balance.

Conventional stepped attenuators often make “pop” sounds as the circuit changes to different resistors. This is due to the short delay as the switch moves to the next set of resistors, and during this delay, the voltage from the music changes. If the voltage change is significant, you will hear a “pop” when the next contact is made.

The Burr Brown chip solves this problem by constantly monitoring the voltage of the signal. When a change in volume is requested, the electronic resistor switching circuit waits until the voltage monitor shows that the voltage crosses the zero point. It then switches. Since there is no voltage present when the next step in the chain occurs, there is no “pop.”

Of course, music is changing voltage very rapidly, so any delay only lasts a few microseconds at worst. As a result, no human can detect any delay in the process, even when switching through the resistors very rapidly.

The chip has a video driver circuit so that I can have it show its levels on an LED digital display. It also has a microprocessor so that it can be programmed to operate in many different ways. It includes an opamp so that the gain can be controlled.

In my preamp, I control the microprocessor using an optical comparator “pot.” Therefore there are no conventional analog potentiometers to wear out and fail. This also makes it possible to operate the unit by remote control.”

The rest of the preamp includes input and output buffers (discreet) along with regulators. The parts quality is excellent including silver mica caps for the RIAA, Mills wire wound resistors and Mundorf caps. The thickness and quality of metal work are first rate: The top cover of the preamp is very heavy, good for damping vibrations and blocking EMI/RFI. Everything is of very high quality, whether a passive device, cutting edge integrated circuitry, potted toroidal transformer, faceplate, controls with good tactile “feel”, etc. All the components are mounted on one board, with a minimum of connectors and wires that would add noise.

I’ve been researching the dreaded op-amp lately, and it’s kind of a blanket term that should be avoided. You should rather think “integrated circuit”. When I asked Roger about using ICs he responded this way:

“Of course, audiophiles generally believe that ICs sound horrible. Like most audiophile beliefs, this is a myth. The truth is that modern ICs easily outperform any discrete circuit.

If you doubt that, just look at the IC’s measurements and specifications. Don’t believe the specifications? Then listen to ICs using valid listening tests. You will quickly discover that they sound absolutely transparent and that you cannot hear any difference between a modern IC and the perfect reference (a short, straight piece of wire)… I have abandoned discrete circuits like I used in my dedicated phono preamp because they simply could not match the performance of a modern IC.

This should not be surprising. After all, there is no magic. A transistor is a transistor regardless of where it is housed.

A transistor is really just a triode in a solid state. Specifically, its emitter is like a tube’s cathode (heater) in that it is the source of electrons that produce the current through the device. The collector is like a tube’s anode (plate) in that the electrons are gathered there and the current flows out of the transistor from that point. The base is like a triode tube’s grid in that it controls the number of electrons that flow through the transistor.

In a discrete transistor, the junction where all the activity occurs is microscopic. The vast majority of what comprises the visual transistor is just the package that holds the junction. The junction is built on a silicon wafer.

In an IC, transistor junctions are laid down on a silicon wafer, just like in a discrete transistor. The only difference between an IC and a discrete transistor is that an IC usually has many transistor junctions, it has circuit traces that connect those transistors. Additionally the resistors and capacitors that are required for the circuit are also produced on the same chip. As a result, you can have a miniature version of a PCB that contains many components.

There is inherently no difference between a PCB circuit and an IC, as all the same parts and circuit is used. However, the IC will be vastly smaller, usually better designed, and it will be absolutely consistent. As a result, it will generally out-perform discrete circuit designs. And an IC is a whole lot cheaper than building a discrete circuit — especially if that circuit uses tubes.”

One thing to remember is this: All ICs are not created equal. Every manufacturer makes chips for specific applications, though many use the similar circuits and architecture, like differential inputs, cascodes, even folded cascodes, long-tailed-pairs, etc.. Most circuits are direct coupled, so no lossy coupling capacitors. The difference from one chip to another is how they are “tuned” for a specific application.

Some applications like “down hole” applications, which are for the oil and gas industry, require “bullet proof” chipsets. You don’t want to pull one mile of pipe out of the ground because a $1.50 chip burned out. So, the manufacturer compromises some aspects of performance to give much higher reliability. Think of it like this: Ford makes trucks and they make cars. Trucks don’t handle like cars and cars can’t carry as much cargo as a truck. It’s the same thing with chips.

Once you look at premium chip sets from manufacturers like Texas Instruments, you realize that some are not cheap. The truly high performance chips are manufactured to very tight tolerances in clean-room environments. To get very low levels of noise, high gain, and bandwidth up to the gigahertz region, the complimentary transistors on an IC must be as closely matched as possible. This kind of quality costs significant money (ten to twenty times the cost of most “so-so” op-amps). Some of these chipsets cost over US$15 each, in orders of 1,000. That means the cost for a few dozen will be significantly higher. Manufacturers have spent billions creating the technology, processes, and manufacturing facilities to make nearly perfect chips. So, chips aren’t created equal. Even the exact same circuit, built by different manufacturers, will give different results. It pays to buy quality parts, even if they are integrated circuits.

One thing Roger didn’t mention is this: If you take ten transistors and pack them on an IC, you are avoiding the inductance of the individual legs, the noise and distortion added when you solder a leg to a circuit board (because solder is a poor conductor compared to copper), just for the signal to be forced down a PCB trace, through another glob of solder, up the leg of another transistor, and into the transistor body. Just imagine you are an electron, trying to jump through all those different materials. It adds up to audible noise and distortion. Miniaturization eliminates losses by directly connecting one transistor to another, all in the same package. The result is lower distortion, higher bandwidth, higher slew rate, and inaudible noise. I’ve seen noise figures of 0.85nV/√(Hz), which is below the noise floor of all but the most extreme test setups, using equipment that costs as much as a modest house.

Find me a discreet circuit with 0.85nV noise figures, large signal bandwidth of 1.2 Gigahertz, and 3rd-order Intermodulation Distortion at -102dB; I don’t think you can. If you go back forty years and look at early op-amps, they don’t compare at all. It’s like comparing a Model T to a Ferrari 458 Italia.

Am I sold on the efficacy of modern integrated circuits? Yes. Just remember that it’s up to the designer to pick the correct chip for the job, and that a great chip can’t make up for other problems in the product. I might add that some of the chips and resistors are made in the US, if I am correct (I might be wrong).

The break-in period of the preamp lasted about a week. Roger and I disagreed about this. He feels that break-in is mostly in my imagination, but electrolytic capacitors do change some during the first few hours. To me, it sounded like the ESR of the capacitors gradually improved during the first three or four days, then stopped changing within the week. After that first week, I heard no further changes in sound. The improvements were a lower noise floor and better micro-dynamics. In other words, details were more obvious after the break-in period. It wasn’t a dramatic change, though.”

The sound of what?

The Sanders Preamplifier is a piece that many reviewers will hate, because it doesn’t have much sound of its own. Cartridges and speakers are easy to review. All mechanical transducers have ridiculous failings, though we are accustomed to those artifacts. Electronics, though, can be difficult to describe, and the Sanders Preamp (and the rest of Sanders electronics) is near the top of the list. It’s hard to describe any peculiar sounds or character produced by the Sanders Preamplifier.

So, what does it sound like? As a preamp, it has zero noise, and zero audible distortion. Whatever distortion is there, is so low that it’s impossible to point to it and say “A-Ha”! Take, for example, the fine tube preamp from Melody that I just finished reviewing. While I loved the looks and sunny disposition, it wasn’t as quick as the Sanders, plus it had audible 2nd harmonic distortion, audible noise and phase shift. Many listeners might not notice these but if you switch between the Sanders and Melody preamps, and if your speakers have good frequency extension, you can hear the difference. Plus, the Melody doesn’t have the perfect channel-to-channel match and volume tracking of the Sanders.

When I say perfect channel match and volume tracking, I mean it. This isn’t reviewer hyperbole. The volume tracking offered by the precision chipset gives .1dB accuracy, something a traditional volume control or unconventional transformer volume control can’t match. The frequency response of the two channels sounded indistinguishable: a nearly impossible feat by a tube preamp. Regardless of volume setting, the two channels were exactly the same. What that gives you is a world class center image “lock” and stereo spread better than anything I’ve used. In that regard, there might be products that are as good as the Sanders Preamplifier, but I doubt you’ll find anything audibly better. There might be other preamps with better imaging outside the speakers due to an even lower level of distortion or better transparency, but I don’t know of one; and it wouldn’t be because they had better volume tracking. It would be interesting to hear the Sanders compared to other transistor preamps using a similar volume control setup. I’ve always heard similar strengths when comparing transistor with tube pieces, but this preamp takes it to a new level.

Wax on…

The phono stage is as accurate, tonally, as any I’ve heard. There are hundreds of phono stages that have enough RIAA accuracy that I expect all phono stages to be similar. If they aren’t, it’s because the designer goofed. I’ll argue that perfect RIAA deemphasis is a waste of time, for a number of reasons that will make up a separate article of the subject. But, it’s not a bad thing to be accurate to less than a dB. What is more audible and more important is matching the EQ of the two channels. It’s the Achilles heel of tube phono stages. The Sanders LP playback channel-balance is as good as other transistor units.

When compared to tube phono stages, mono records don’t sound as smeared, left-to-right. Playing back mono records with tubes can give you a misshapen centre image, with the highs stretched to one channel, the mids to the other channel, and the bass back to the other channel, making them sound like they were recorded in a house of mirrors. With the Sanders, mono records were locked in the centre. I recommend using the mono switch if you are using a stereo cartridge to play mono recordings. Stereo cartridges will smear mono images for a number of reasons: skating forces, unequal coil windings, cartridge misalignment, warps and off-centre pressings. Also, if it’s a mono recording cut with a stereo cutter head driven by stereo electronics, the two channels will be slightly different because cutting heads aren’t perfect; the cutting electronics and tape machines aren’t perfect either. Roger should be thanked for including the mono button. Thanks Roger.

There is enough flexibility in cartridge loading and gain to make a good match for the majority of cartridges. Is it my favourite? Not quite, but it is more linear, with less noise, than my favourite phono stages. This comes down to personal preference because LP playback will never be as “perfect” as playing back a CD. There are too many variables with vinyl play that can affect the sound. The added noise and distortion of my favourite tube LCR phono stages might be covering up mastering deficiencies, cartridge mistracking and/or misadjustment, along with the possibility of complex interactions of cartridge, tonearm, tonearm cable and phono loading which serves to “enhance” the music.

Compared to my favourite LCR phono stages, the Sanders didn’t have as much image depth (see my caveat below), and large scale dynamics seemed to be slightly suppressed. There are records that sound better on the Sanders. There are records that sound better on a tube LCR. The odd thing is that there are records that sound better on the budget Rek-O-Kut Professional Moving Magnet Preamp and, on a few rare occasions, there are records that sound better on a Dynaco PAS, although the PAS is not accurate). What does it mean? Vinyl mastering and playback is as much art as science, so it cannot be “perfected.” I suppose a company could master and press the vinyl, then put together a package of cartridge, tonearm, tonearm cable, and phono preamp, comparing and tweaking things to sound as close to the master tape as possible, but I don’t know of any such setup.

Surprise! Better than no preamp at all?

I was taken aback by what the Sanders Preamplifier did for my CD and open-reel listening. My reel-to-reel player is a semi-professional unit, the TEAC 35-2B Tascam Series. It has the ability to play two track and four track tapes (7.5 and 15 IPS), and uses separate volume controls for left and right. I can, and often have, connected the tape player directly to the amp, using the tape deck’s volume controls in lieu of a preamp.

With every other preamp or integrated amp, I heard a definite improvement when running the tape deck directly into the power amp inputs. Well, not anymore. Somehow, the Sanders preamp was able to breathe life into the signal, with better dynamics, better imaging and better frequency response. If there was a loss of detail, it was totally swamped by other improvements. Is the Sanders preamp “a straight wire with gain”? No, it’s not quite that good, but it’s closer than other preamps I’ve heard.

The same improvements happened when listening to digital. I’ve never had better digital sound from my sources, regardless of setup. I think the explanation is this: The high input impedance of the preamp makes it a breeze for your source components to drive; the high current, low impedance outputs can “drive the shit” out of any amp you choose. Apparently, my CD player and tape deck couldn’t drive a tricycle down the driveway.

The problem is that most sources don’t have robust output stages. A few sources have what amounts to a preamp output stage built in, but most sources are inadequate. Exceptions include professional studio sources that use output transformers. Those suckers can drive tube amps to max output, and have headroom to spare. But, couple a tube professional open-reel tape deck with a transistor amp, and things might be different. The reason is simple: Tube electronics have higher output impedance, while transistor electronics have lower input impedance, sometimes leading to audible problems.

Closer!

The Sanders preamp is edging closer to the ideal “wire with gain”. In several ways it’s as good as I have heard in my system, and better than the majority of what I have heard in other systems. It does have a little sound of its own, but it’s very difficult to pin down what that sound is. It had fewer artefacts than all the passive preamps I’ve used, including a simple stepped attenuator and transformer volume control. The stepped attenuator caused losses in dynamics and soundstage depth. The transformer volume control had audible phase shift and limited bass.

The touchy-feely audiophile in me says that it has less colour saturation than great tube preamps, but none of those units have the image width or the unmatched channel-to-channel tracking of the Sanders. And tube preamps have noticeably more noise and distortion, whether it’s “benign” distortion or not. Plus, the great tube preamps eat tubes like tic-tacs, so that you have to turn them off, so then you have to warm them back up to listen, and eventually the performance suffers when the tubes start to age significantly. With the Sanders, you can plug it in, turn it on, and leave it on forever.

Compared to my aural memory of other products, which is fickle (and fecal), it seems like the image depth isn’t as good as the image width. (Editing Phillip’s article does make me feel like a road-kill at times – the shock then I’m in pieces. -Pub.) On the other hand, could it be that the centre image “lock” and image width are so good that it makes it seem like it isn’t as deep? I can’t say with confidence. It’s like saying a single driver speaker has great midrange. Well, it better have awesome midrange, because a 5” speaker is going to be challenged to do anything audible at 20Hz or 20 KHz. So when you listen to a world-class full-range system, you think “man those full range drivers had great midrange”, when in reality the full-range system didn’t have anything except for midrange. I wasn’t able to quickly swap in other preamps for comparison. Maybe it’s nothing; all in my imagination; my zeal to nitpick. Maybe there is a limitation. Do you follow? If not, don’t worry. Where else are you going to get expert reporting like this? (Again. -Pub.)

The Sanders’ large scale dynamics were fast and powerful, being the equal to anything I can think of. In fact, the dynamics overwhelmed the undersized power amps I used with the Sanders preamp. The little amps couldn’t handle the dynamic swings from my 45rpm jazz reissues, or dance records, or big orchestral scores. I doubt this preamp will find its way into systems with 3-watt triode amps, but if it does, you better have very efficient speakers or this preamp will wag the dog!

I have heard better micro-dynamics, in plucked strings, for example, from simple tube preamps and transformer volume controls, but at a cost. They couldn’t do the other things the Sanders can do.

The Sanders’ frequency response is adequate for music. I didn’t hear any problems with frequency response, whether steady state tones or dynamic ones. If someone ran into a microphone, it went “booooom”, if the cartridge mistracked on cymbals, I heard it clear as a bell (which might also mistrack). There is no excuse for limited bandwidth in a modern preamp or amp. After switching to really large speakers, bandwidth limitations are immediately evident with many recordings. This preamp was more capable than my speakers, which are plenty capable. The specs say 5Hz to 200KHz, and I can’t argue.

There are/were preamps that have more deep bass grunt, but generally coupled with a darkness that robs the music of life. I’m speaking of preamps from Krell, Spectral, Levinson, Boulder, etc, which might have changed significantly since I last heard them. But those older products were too dark and heavy, the main reason tubes became my reference. It would be interesting, though a pain in the ass, to have a preamp shoot-out: comparing the tonal balance, distortion, imaging and volume tracking of multiple high end transistor preamps. I’ll leave that up to someone with more time than sense.

I didn’t have balanced sources or amps to try with the preamp. I did use the balanced options when auditioning the Sanders 10b speaker system a while back. I didn’t hear a big difference between single ended and balanced options with the 10B system, and I doubt you’d hear a big difference with this preamp. There are some sources that sound worse when using the balanced outputs. The same can be said for amps with balanced inputs. It’s worth experimenting if you have the option to use both. Keep an open mind and use whatever sounds better.

So, does the Sanders technology serve the music? In my opinion, it does, because listening was thoroughly enjoyable, and I frequently was surprised by a new insight or detail, which is a good sign. This preamp might reveal faults in the rest of the system that need addressing, but that is a good thing if the result is better playback.

The Sanders Preamplifier is rather unassuming. It doesn’t have a separate power supply chassis or fancy knobs. The finish is good, but not flashy. The price is downright “cheap” compared to many competing products. When sitting next to one of Sanders’ big amps, it may look like an afterthought, but you would be wrong. Roger, the engineer, made the unit big enough to get the job done, but no bigger. Fancy enough to match the other electronics, but no fancier. This is a genuine preamp, its not about being a fancy status symbol.

Considering the price and performance, I doubt you’ll find anything better without spending significantly more. Considering you can leave it on all the time, and it comes with a lifetime warranty, it’s an easy recommendation.

…….: Phillip Holmes

ROGER SANDERS- ULTRASTAT PANEL WHITE PAPER
Sanders Sound Systems website

Electrostatic Loudspeakers (ESLs) have had a reputation for poor reliability, particularly in high-humidity environments.  The basic cause of failure is the fact that ESLs operate at several thousand volts.  This voltage is confined to very small spaces (typically less than two millimeters), which must be controlled by high-value electrical insulation if sufficient voltage to produce high output is to be used.

This insulation must be perfect as even the slightest flaw will allow a flow of electrons between the speaker's stator and diaphragm.  This can cause the high-voltage static charge on the diaphragm to "leak" off, reducing the speaker's output and/or causing hissing or frying noises.  Worse yet, it can release a sudden burst of electricity from the stator that will melt a hole in the speaker's diaphragm, leading to outright speaker failure.
 
Air is also an insulator, which helps control the high voltages present in an ESL.  Some ESL manufacturers rely on the insulation of the air for good ESL performance.  However, when moisture is present in the air (high humidity), the insulation qualities of the air is greatly reduced.  Therefore, high humidity conditions increase the likelihood of leakage and arcing in ESLs.
 
The problem is compounded if there are any foreign objects between the speaker's diaphragm and stator.  These objects (usually insects or dirt) eliminate the beneficial insulating effect of the air completely, often leading to shorting out of the speaker and damage to the diaphragm and stator insulation.  An ESL's stator insulation must be able to confine the high voltage charge even with a foreign object present.  This is a daunting challenge.
 
Additionally, the stator insulation must be so good that it will not allow any electricity to leak when the humidity is high.  If it does, the output from the speaker will be reduced.  This reduces sensitivity in full-range ESLs.  In hybrid ESLs, leakage changes the frequency response of the speaker by reducing the output of the ESL compared to the woofer.  The result is a thick, muffled sound quality when the speaker is played in high humidity conditions.
 
An ESL's diaphragm has a special coating that conducts electricity from a high voltage power supply within the speaker to form a static charge within the electrostatic panel.   This coating is very specialized and among other things, must not be adversely affected by humidity, it must not corrode, it must not absorb water, it must be extremely smooth, it must be durable, and it must withstand constant flexing and acceleration as the diaphragm vibrates.  If it cannot meet these requirements, it eventually fails to conduct electricity and the speaker fails.
 
These problems are all solved with the use of the Ultrastat panel. This panel does not use perforated metal as the basis for its stators.  This is because perforated metal must be coated with insulation that is impossible to apply perfectly.
 
To achieve perfect insulation, Ultrastat stators are made of a high-value insulating material instead of metal.  The necessary conductors are encapsulated within the insulation matrix to achieve flawless insulation. An added advantage is that the panel can be made to extremely precise tolerances for higher efficiency and improved cosmetics.  This material is unaffected by humidity.
 
The diaphragm coating is the result of over thirty years of testing hundreds of materials for durability. The Ultrastat coating will not corrode and is embedded into the diaphragm material itself so that it cannot come off.  It does not absorb water, so humidity has no effect on it.  If an arc should form, this coating disperses it so that the arc does not cause a hole in the diaphragm.
 
The result of these technological advances is an electrostatic panel that is more durable than conventional moving-coil drivers.  Extensive tests in extremely humid environments like Costa Rica and Asia have shown 100% reliability without any output loss over many years of use.  There has never been a failure of an Ultrastat ESL.  Sanders Sound Systems is proud to be the only ESL manufacturer to have a 100% reliable electrostatic speaker.
ROGER SANDERS - TRANSMISSION LINE WHITE PAPER
Sanders Sound Systems

What is a Transmission Line (T/L) enclosure?  Why use them? To answer   these  questions, it  will be  helpful  to  understand the  problems  caused  by conventional closed   box  or  vented enclosures  as  are  used  in  most  other  speaker  systems.  Closed  box   enclosures (also  known as sealed,  infinite baffle, or  acoustic suspension  enclosures)  ruin the  transient  response  of the  woofer, fail  to support the deep bass, and add extraneous vibrations  that "color" the sound.

The transient response is ruined because the woofer compresses the air in  the box as it is driven into the   enclosure.  The compressed  air  acts  like  a spring and  it forcibly  pushes the woofer  back out of  the enclosure when  the  musical signal reverses phase or the music stops.  The woofer cone needs to  stop when  it gets  to its  neutral position  to accurately  follow the  music and  have  good transient  response. The relatively high mass of the woofer   cone has a lot of inertia and it tends to sail   far past ("overshoot") the desired stop point. As if the woofer’s mass wasn't trouble enough, the compressed air in the box also pushes the woofer past the stop point. The result is a great deal of “overshoot and ringing." This ringing causes the bass to sound muddy, slow, and ponderous.
 
Woofers   have essentially   no bass   output below    their fundamental   resonance frequency.  A closed box has a relatively high resonant frequency so fails to support the deep bass.   To try  to  improve   the  deep  bass,  designers   tend  to  use  very   massive   cones  with  soft suspensions to  try  to lower  the fundamental resonance. Although this does make it possible for the system to have deeper bass, the increased mass degrades the transient response even more.
 
Vented enclosures are    deliberately designed to    have strong resonances    to help support   the deep bass.  Although this  does  give more  output  to a  very limited range  of bass  frequencies, the  response is  highly non-linear  and  unnatural sounding.  Also, resonance is the opposite of transient   response. For good transient response, you want ZERO resonance.
 
The radiation from the back of the woofer is just as intense as that from the front. This   rear energy is directed into the enclosure - but what happens to it? Most of this energy is dissipated forcing the walls of the enclosure to flex and vibrate. This causes unwanted sound to come from the enclosure sides, "coloring” the sound.  Energy that   is not dissipated in   the enclosure is radiated back through the woofer cone, again causing sounds to be heard that are not part of the music.
 
A Transmission   Line solves   all these   problems. A   T/L is    essentially a long, tapered tube with the woofer mounted in one end. The tube is filled with a soft, absorbent “damping material" much like pillow   stuffing.   Obviously a long straight   tube would be impractical   in your living room, so   T/Ls are best rectangular in shape and "folded" into a more or less conventional box.
A T/L causes the woofer to have good transient response because it “damps" the woofer’s motion. Unlike a closed box, the woofer cannot compress the air   in a T/L because the air can “leak" out the end of the line. When the woofer moves back toward its neutral spot, instead of compressed air pushing it beyond that point, the woofer has to "suck" air back into the line. This causes the woofer to stop instead of flying past its neutral point.
 
Most of the rear energy of the woofer (BLUE arrows) is absorbed in the   damping material by being converted to heat as it pushes its way through the millions of fibers in the line. Therefore there are virtually no unwanted sounds coming from the enclosure sides or back through the woofer cone.
 
The T/L    cannot stop    the very    long wave-lengths    of low    frequency sound   (RED arrows). These very low frequencies escape from the end of the line. However,  the damping  material will have slowed  these waves  considerably, and  between that  and the  long length  of the  line, these frequencies will  be significantly delayed before being released  from the enclosure. The result is that the low frequencies come out in-phase with the front radiation of the woofer.  When they are in -phase, they support the deep bass - and they do so over a very broad frequency   range. This is why T/Ls are noted    for having such excellent deep bass.      Finally, all enclosures have resonances that color the sound.  Properly  tapering  transmission  lines   will ensure  that instead of  having  two  or   three  large resonances  like  conventional enclosures, the  T/L  will have an  infinite  number  of very  tiny  resonance's  that are  completely absorbed  by the damping material.  The result is an enclosure that is resonance-free.
 
The bass  from  a  properly built   T/L  is  utterly  clean,  has excellent   deep bass   extension, no   overshoot  or   ringing,  no   resonances,  and  superb transient response. It is no surprise that the transmission line woofer system blends perfectly with an electrostatic element.
 
T/Ls normally are large, complex, and expensive to build. They are still difficult and expensive to build, but there is no other way to build a flawless hybrid electrostatic system.
ROGER SANDERS - ESL AMP BIAS WHITE PAPER
Sanders Sound System website
Many customers ask about how we can run our amplifiers so cool. The answer is that we can use very low bias current because we use modern, highly linear transistors that do not require high bias current in order to have vanishingly low distortion. Many audiophiles have assumed that hot, high-bias operation results in "warm" sound, and so they are surprised that our amplifiers sound so good with low bias. They wonder how bias affects sound.
 
The purpose of bias is to reduce amplifier distortion. Bias has no effect on frequency response, and it is frequency response that defines "warmth", "richness", and "fullness" in sound. In short, changing the bias will not add any "warmth" to the sound; it will only add warmth to the amplifier chassis. 
Different amplifying devices have different transconductance curves, whether they be tubes or transistors. Transconductance is where a certain amount of input voltage results in a certain amount of output current. There is a ratio between the input voltage and output current. This should be a constant at all power levels. Of course, no amplifying device is perfect, so the ratio is NOT constant. Distortion will develop to the degree that a device deviates from a constant transconductance ratio.
 
Typically, very small input voltages will not produce the same transconductance ratio as input voltages that put the device in the middle of its transconductance curve. In fact, the ratio will be zero at very small voltages, because the device won't conduct at all until a certain threshold is reached -- this can be seen as "crossover notch distortion" on an oscilloscope. Likewise, when a device nears its maximum power, the ratio changes as it can no longer deliver more current as the input voltage increases ("clipping").
 
The purpose of the bias current is to put the amplifying device into its linear operating range, and this will vary greatly depending on the type of device and its particular operating parameters. Typically, tubes are very non-linear and require quite a lot of bias to reach reasonably low distortion levels. Power MOSFETS are only slightly more linear than tubes, and the best bi-polar transistors are far better than either tubes or MOSFETS.
 
Before the discovery of negative feedback, some engineers even biased the tubes to the center of their transconductance curve (Class A operation). This was the only way to get distortion down to reasonable (around 3%) levels, but had the penalty of extreme heat generation and rapid tube deterioration.
 
Transistors vary widely, with power MOSFETs being the less linear than bi-polar types. So generally, MOSFET amps will need more bias to reach low distortion than bipolar types. And there are very different transconductance behavior with different transistor designs in the same class, so bias may vary widely.
 
Keep in mind that all modern, well-engineered amplifiers use negative feedback (NFB) to reduce distortion to levels far lower than can be achieved with bias alone. An amplifier's distortion is a combination of both bias and negative feedback. Keep in mind that for most humans, the threshold of distortion detection is around 3%. If very special test tones are used, some people can hear about 1% distortion. No test has ever shown that a human can hear distortion levels below 1% under any circumstances.
 
Sanders Sound Systems amplifiers use a very modern, sophisticated, and expensive type of bi-polar transistor made by Motorola that combines very high power capability with an amazingly linear transconductance transfer function. As a result, we are able to reach virtually un-measurable distortion levels with only a trace of bias.
 
Without bias or NFB, a typical amplifier will have high distortion levels (perhaps 10% or so, depending on the amplifying device). With enough bias applied to move the device into the linear area of its transconductance curve, the distortion will drop to around 3%, or even lower with very linear devices. The bipolar transistors Sanders Sound Systems uses can reach distortion levels of 0.08% without the use of NFB. Then very little NFB is required to reduce the distortion to non-detectible levels (less than 0.01%).
 
Some audiophiles remember the days when huge amounts of global NFB was used in amplifiers and this caused problems with TIM (transient intermodulation distortion). A few audiophiles still believe that NFB is undesirable because of TIM. But this is no longer true. Engineers now use NFB around the local circuits, use only a small amount of global feedback, and compensate it properly. The result is that NFB is now free of problems and has no adverse affects on an amplifier's performance. This is a good thing because it is impossible to make a low-distortion amplifier without the use of NFB.
 
Now let's look at the Sanders Sound Systems ESL amplifier without any NFB and see what effect bias alone has. With no bias at all, crossover notch distortion is present and the distortion is unacceptably high. With just enough bias to turn on the transistors, the distortion suddenly drops to around 0.2%. If we keep turning up the bias, we can reach a minimum distortion level of .06%. This is remarkably low distortion for an amplifier without any NFB. But this much bias requires a continuous power dissipation of more than 70 watts of power.
 
But why should we waste all that power? If we turn the bias down to just 3 watts, the distortion only climbs to about 0.2% -- still well under the 1% human distortion detection threshold. But we prefer lower distortion levels. So by adding just a little NFB, we can cause the distortion level to become un-measurable (less than 0.01%), and there is only 3 watts being wasted as heat.
 
In summary, there is no magic. Sanders Sound Systems amplifiers sound completely clean because they have very low distortion and lots of power. How this is achieved has nothing to do with its frequency response. We use a combination of very good transistors, low bias, and low NFB to achieve this performance, while keeping the amplifier running cool. Adding more bias will not change the sound of the amplifier in any way. 

Testimonials

Wonderful customer service Terry and a game-changer result for me.

Terry,
Letting you know that the Sanders ESL system is set-up and it’s sounding amazing down here in the deep south.

Thanks for meeting me when I flew up to Auckland to audition the system and for hosting me at your studio - such a relaxing setting to listen your way through ‘test’ discs.

Your knowledge and experience of the Sanders system, especially referencing it to other contenders, was spot-on!   That you had visited Roger Sanders in the USA exemplifies your commitment to ensuring that the quality and attributes of the system were revealed in full audio glory. As I said to an audio mate ‘I wished I’d explored electrostatics way earlier.’

Wonderful customer service Terry and a game-changer result for me.

Best Wishes, 
Ian