Sanders Magtech 500w stereo power amp

SD 05 MAGTECH ST
NZ$ 9,500.00 ea (incl. GST)
Sanders Sound Systems

UNIQUE Amps to drive any load down to 1ohm with no distortion and the Electrostatic Specialists -Hand Crafted In Colorado

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TAS THE ABSOLUTE SOUND NAMES MAGTECH AMPLIFIER ONE OF THE BEST FOR THIRD YEAR IN A ROW
TAS GOLDEN EAR AWARD SEPTEMBER 2014 
THE STEREO TIMES MOST WANTED COMPONENTS 2013
TAS - EDITORS' CHOICE AWARD - MARCH 2013 
TAS - EDITOR'S CHOICE AWARD - MARCH 2012
TAS - EDITOR'S CHOICE AWARD - MARCH 2011

This powerful amplifier (500W into 8 ohms, 900W into 4 ohms) is the most consistent amplifier I have ever heard. Regardless of the load it performs equally well at all frequencies and never shows strain. At the same time its transparency and low noise floor allow it to fully reflect the character of upstream components and subtle nuances and harmonics. To accomplish that, Roger Sanders developed (patent pending) a voltage regulated power supply that 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. ......
.Donald Shaulis - STEREO TIMES

The popularity and success of the original Sanders ESL - Electrostatic Amplifiers for driving electrostatic speakers led to many requests for a companion amplifier that was specifically designed for driving more traditional, conventional speakers. Two years in development, the Magtech amplifier is that amplifier, it will drive even the most demanding speakers with ease. 

The Magtech Stereo Power amplifier will deliver over 500 watts/ch into an 8 Ohm load, and over 900 watts/ch into a 4 Ohm load.  Momentary output into a 2 Ohm load exceeds 1200 watts/ch. The amplifier is completely stable and will not be damaged even when driving a 1 ohm load.

DESIGN PHILOSOPHY - Electronics have their lowest distortion and optimum performance at a specific design voltage.  If the voltage varies, the amplifier's performance will suffer.

An additional problem in amplifiers is that they require bias to eliminate crossover notch distortion and determine their class of operation.  The bias will vary as the voltage does, which will further reduce performance.

An amplifier's voltage will fluctuate wildly as dynamic music is played.  This causes the amplifier's distortion and bias to vary constantly and fail to meet its full performance potential.

As if all these problems are not enough, as an amplifier's voltage sags under load, the power it can deliver is greatly reduced.  If the voltage would remain stable, the amplifier could produce much more power.  Since most audiophile speaker systems require several hundred watts of power to avoid clipping and compression of the dynamic range, power is extremely important.

THE SOLUTION

All quality, line-level electronics use voltage regulation in their power supplies to produce a stable voltage, regardless of load or the mains voltage.  Audiophiles would not consider using a source component that did not have regulated power supplies.  So why use amplifiers with unregulated supplies?

The main problem is heat.  Amplifiers operate at much higher voltages and currents than line level source components.  These higher voltages and currents forces conventional regulator designs to waste large amounts of energy, which wastes expensive electricity and causes the amplifier to get very hot.

Also, many regulator designs radiate RF (Radio Frequency) energy when switching high currents and voltages.  This RF gets into the amplifier's electronics and can cause instability, oscillation, and noise.  As a result of these problems, modern power amplifiers do not use regulated power supplies and fail to take advantage of the benefits available from doing so.

Sanders has solved these problems by developing a voltage regulator that is essentially 100% efficient.  There is no heat dissipated by the regulator system.  There is no high-power/high-voltage switching that causes heat generation or RF problems.

The regulator in the Magtech amplifier maintains a stable voltage regardless of load or reasonable changes in the line voltage feeding the amplifier.  It runs stone cold, produces zero RF energy, and is simple and reliable.

Unlike other amplifiers, the distortion in the Magtech amplifier is virtually unchanged regardless of power level.  The bias is stable regardless of load.

The regulator makes it possible to obtain a 50% increase in power over the same amplifier operated unregulated.  In its stereo form, the Magtech will deliver 500 watts/channel into an 8 ohm load and 900 watts/channel into a 4 ohm load.

The Magtech is built into the same chassis as the ESL Amp, so it is compact enough (17" wide, 5-1/2" tall, 14" deep) to place on a shelf or into a cabinet.  It is also light enough (54 pounds) to be picked up.  Like the ESL amp, it runs very cool and may be left on continually without concern for power usage. 

The Magtech amplifier also uses the same advanced technology that makes the ESL amp able to drive the most difficult loads without performance-degrading, protective circuitry.  The Magtech amplifier is the only amplifier on today's market that features a linear voltage regulator.  The result is a compact, yet extremely powerful amplifier that is ideally suited to driving the most difficult magnetic speakers.

Features

Specifications

Reviews

Videos

Features

Magtech - the only amplifier with a linear, voltage regulator (Patent Pending) 
Over 500 watts/channel into an 8 Ohm load, 
Over 900 watts/channel into a 4 Ohm load.  
Over 1200 watts/channel into a 2Ohm load. 
The amplifier is completely stable and will not be damaged even when driving a 1 ohm load.

Specifications

Power
500 watts RMS per channel into an 8 ohm load
900 watts RMS per channel into a 4ohm load (note - will drive down to below 1 ohm)
Bandwidth:     DC through 100kHz
Class of Operation:     Class AB
Slew Rate:     500 Volts/microsecond
Input voltage required for full output:     2 Volts
Input Impedance:     50kohm (both balanced and unbalanced)
Gain:     26dB
Noise:     More than 110dB below rated output
Damping Factor:     Greater than 600 into an 8 ohm load
THD:     Less than 0.004%, 20 Hz - 20 KHz
IMD:     Less than 0.003%, 20 Hz - 20 KHz
Voltage:     Voltage is user selectable for use world-wide.
Dimensions:     430W x 140H x 406D mm
Weight:     25 Kgs

Reviews

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 

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 
Spend your money instead on bigger and better speakers. Sit back, listen, and feel very pleased about your newfound Magtech wisdom.
Francis Vale

SUMMARY: before, MBL’s stereo soundstage was tantalizingly close to sounding holographic. But the soundstage was now a sensory VR experience. The room also got virtually bigger. The Magtech amps would mightily heave on the speaker back wall, collapsing it. Newly freed artists could be joyously heard as they emerged from their broken plaster jail. The 101D’s and Magtech’s invited George Winston into the house, sat him down at his piano, and turned him loose on “Montana: A Love Story.”  His was a real piano, in a real performance, set in a soundstage that extended way off into the Western sky.

The 101D’s and Magtech’s invited George Winston into the house, sat him down at his piano, and turned him loose on “Montana: A Love Story.”  His was a real piano, in a real performance, set in a soundstage that extended way off into the Western sky.

The transformed soundstage was accompanied by significantly enhanced transparency and detail. Everything you thought you knew about your recordings was a false memory, implanted by alien electronics.

The Magtech monoblocks reveled in revealing new musical universes.  Sanders is really on to something with its innovative circuit design. Whether it is the Magtech stereo amp I use with the Analysis Omega’s, or the Magtech monoblocks driving the MBL 101D’s these Sanders products never cease to amaze. That they also cost much less than other high-end amplifiers is just a bonus. They will drive anything you got and never lose their cool, figuratively and literally.

The review starts with the security forces at my front door. But I digress. 
Back in time we must, some months ago, when electron dementia came running up unexpectedly from behind and whacked both of my two Sunfire Signature amplifiers. These stereo amps can breakdance 1,250 watts/channel at 4 ohms. But in my setup, each Sunfire was acting like a monoblock amp, one per each OMG, MBL101D speaker. These German-made speakers radiate fully circular sound (MBL calls this omnidirectional loudspeaker a “Radialstrahler”). My Sunfire twins had been belting out the round wattage for more than thirteen years when their mindless humming set in.
Now what? A loser amp would be stiletto heeled by these demanding Deutschland Divas. It made for a short list of electrical dates.

I did a Must Love Germans for dating some replacement watts. MBL was busy touting its new Corona amplifier line… “The ideal fusion of high end sound & and innovative design concept.”  The line’s C15 monoblocks specs were attractive, even their cosmetics were good. They were sans heat sink skirts due to a trendy class-D output stage design and chill to thermal stress. Each fashionista was rated at 500W at 4 ohms.  But word was that it’s only 480W for improved sound. This pair of electrified Germans was also demanding US$25,000 (excl tax) for carrying the 101D loads up and down the musical scales. Even though these were fine amps, it seemed to me that Class D movers shouldn’t be charging that much to haul my sonic freight.

Then I was told about Musical Fidelity’s new M8-500s stereo amplifier, a fully balanced design rated at 500 Watts per channel into 8 Ohms, and almost 1,000 W into 4 Ohms. The MF tag line pulled at me, “The M8-500s can drive just about any loudspeaker you choose.“  So, yes, please, sign me up for a review unit. And so it came.  Its 64 pounds of mighty British wattage were quickly wrestled out of the shipping box, plopped into place, hooked up to the MBL 101D’s, and then, and then, WTF? The MBL’s were squeaking skinny distorted sounds. They were being starved for juice. The two Germans rose up against their new UK/AC master.

Desperate for a musical truce I changed the cables, the preamps, the input sources, and still got this weirdly out of shape sound. I double and triple checked all the amp and speaker connections, made sure all the M8-500s switches were in the correct position for RCA interconnects, but all were OK.

I was done to the arcane. When setting things up I had swapped out the M8-500s OEM power cord with a high-end AC cord. Could it be? Unlikely, as this AC cord has been a consistent star performer. To be certain, I tried other vendors’ high-end power cords, all of which had successfully assisted different amps—same distortion disaster.

I noticed that all these other AC cords had ground plugs, but the MF cord did not. In the event, my floating an amplifier ground with an AC cheater plug could just be punting any serious electrical problems onto the interconnect wires, never the best idea. All hope lost, I despairingly plugged back in the original AC cord. Everything was suddenly peachy keen. Aye! I was trapped in the belly of that indeterminate reality beast, the electron Wave-Particle Duality. All manifold possibilities of these AC electrons were determinedly collapsing into a state solely intended to quantum mess with my reviewer certainty.

What should have taken no more than 30 minutes for system set up had now consumed many backbreaking hours. The M8-500s and its OEM power cord sure sounded nice, though. But, MF abruptly asked for its amp back before I could do a proper audition. Apparently MF can’t handle Herr Heisenberg injecting any uncertainty into reviews of its products.

But I digress.

I sat in scrunched sorrow in the den, pondering my miserable audible lot, listening to my Analysis Omega full range ribbon speakers, hoping for sonic salvation. I noticed the Magtech stereo amp powering them. This amp is a mighty affair, effortlessly driving the Omega’s, and with total musical finesse and control. I sprang up and immediately checked out the website for Sanders Sound System, the Magtech maker, and lo, “The Sanders Sound Systems Magtech amp is now available as a Monoblock power amplifier. Performance is similar to the Magtech amplifier with the exception of dramatically increased power output capability!” Huzzah!

Each monoblock was awesomely rated at 1600 watts RMS into an 8 ohm load, and an over the top 2000 watts RMS into 4 ohms. Their price was equally incredible, US$11,000 (excl tax) for the pair—way less than those two MBL C15 monoblocks. Oh, do come to papa do. And they did.Like their stereo sibling, the Magtech monoblocks benefit from innovative electrical design. Rather than lousing up the technicalities let’s directly quote Sanders:

“Amplifiers operate at much higher voltages and currents than line level source components.  These higher voltages and currents forces conventional regulator designs to waste large amounts of energy, which wastes expensive electricity and causes the amplifier to get very hot.  Also, many regulator designs radiate RF (Radio Frequency) energy when switching high currents and voltages.  This RF gets into the amplifier's electronics and can cause instability, oscillation, and noise. As a result of these problems, modern power amplifiers do not use regulated power supplies and fail to take advantage of the benefits available from doing so.” 
“Sanders has solved these problems by developing a voltage regulator that is essentially 100% efficient.  There is no heat dissipated by the regulator system.  There is no high-power/high-voltage switching that causes heat generation or RF problems. The regulator in the Magtech amplifier maintains a stable voltage regardless of load or reasonable changes in the line voltage feeding the amplifier.  It runs stone cold, produces zero RF energy, and is simple and reliable. Unlike other amplifiers, the distortion in the Magtech amplifier is virtually unchanged regardless of power level.  The bias is stable regardless of load.

Indeed.

I perversely attempted being whacked again by the mercurial electron fates. Once more I used those Nordost power cords. But the MBL’s just wrapped their limbs around the Magtech monoblocks in musical ecstasy. Despite the heat of the melodious moment the monoblocks stayed cool, even when, as Sanders advises, left continuously powered on.

But what’s this I hear? Located immediately below the 101D’s omni woofer wonder is a 12" cone subwoofer. It’s housed in a dual ported, conventional cabinet. On deep bass notes both speakers’ subwoofers were emitting low-level chuffing noises out their front ports. On the other hand, the rest of the sound was clean and prodigious.

Clueless, I let the Magtech blocks and the MBL’s go about their musical mating dance in undisturbed privacy. Their high wattage tango went on for almost three months, when wham! The two MBL subwoofers suddenly burst forth into full-throated roars of approval.

Conceivably, but hard to fathom, my more than ten year old MBL’s and their subwoofers could just now have been breaking in. The Sunfire amps were good. But maybe they didn’t have the AC sac to grab these subwoofer mothers by their baskets and forcibly drag them down into the Stygian depths. Then again, maybe it was the strapping monoblocks needing extra time for their electrical ligaments to limber up. Then again, who the hell knows?

Whatever, it was time to start reviewing. I live in a high-rise apartment building, which has old school, solid concrete construction. But someone standing outside would have seen its cement sides buckling when I played Tracy Lorde’s “Pure Heroine”. The “Buzz Cut Season” and “Tennis Court” tracks were unleashing bazooka bass volleys. My apartment became an acoustically shelled seaport, towering sonic waves pummeling skulls and vulnerable bric-a-brac.

The 101D’s omni tweeter and its unique carbon-fiber petals also fully blossomed. High octave pollen swarmed the room while Bela Fleck jammed with V.M. Bhatt and Jie-Ben Chen on the “Tabula Rasa” album from Water Lily Acoustics.

The 101D was always an aspiring Houdini. The speaker conjured musical ghosts desperately wanting to flesh and blood materialize, never quite achieving it. But with its three, 360 degree firing drivers—tweeter, midrange, and woofer—producing solidly sculpted sound was not easily found in the MBL rabbit hat. Performers were always a bit fuller, a bit harder to nail down around the edges.  And yet even here the Magtech monoblocks worked some spectral magic.

I often found myself rushing into the MBL occupied room to see who had just B & E’d my crib. Newly unmasked performers would just square me in the eye. They forced me to sit down at sonic gunpoint. They made me pay musical attention to what they had to say. 

Before, MBL’s stereo soundstage was tantalizingly close to sounding holographic. But the soundstage was now a sensory VR experience. The room also got virtually bigger. The Magtech amps would mightily heave on the speaker back wall, collapsing it. Newly freed artists could be joyously heard as they emerged from their broken plaster jail. 

Well-recorded pianos are huge and hungry beasts. Given the chance they will chew up your whole room. The Magtech monoblocks opened the larder. The 101D’s and Magtech’s invited George Winston into the house, sat him down at his piano, and turned him loose on “Montana: A Love Story.”  His was a real piano, in a real performance, set in a soundstage that extended way off into the Western sky.

The transformed soundstage was accompanied by significantly enhanced transparency and detail. Everything you thought you knew about your recordings was a false memory, implanted by alien electronics. The Magtech monoblocks reveled in revealing new musical universes. Check out the score to the 1959 movie, “The 3 Worlds of Gulliver,” composed by Bernard Herrmann. It’s a rollicking foreign landscape and your acoustical passport is the Magtech.

Sometimes it got spooky, like on Andreas Vollenweider’s Book of Roses album. It has a track that opens with chalk scratching down hard on a blackboard. When I next looked up I fully expected to see G clef graffiti scrawled across my living room walls.

I also played Ry Cooder's and Ali Farka Toure's Talking Timbuktu album, which won a Grammy in 1994. A group of previously lost in the background people suddenly leaped over the electron fence and scrambled into my room: “Mogo do min bε angilekan men be yan, wa?” I called the INS.

Happily, there was no such scratching and scrambling with female vocals and strings. They were rendered astonishingly present and freshly supple. Hello Ms. Fitzgerald, hello Ms. Carter, nice to at last completely make both your acquaintances.

But, on some source material there was still an exaggerated bloom to the deep boom. It was especially noticeable while listening to Sirius XM radio.  (Its curated jazz channel is especially good.) The Sirius XM signal is heavily compressed. So I chalked up the occasional boominess up to a compression quirk. But such subwoofer quirkiness suddenly devolved into the mentally deranged.

For the first time in almost a decade of my living in the building some tenant had complained about loud music. But my music wasn’t. Still, here were the building’s security police knocking at my door. They couldn’t even identify where the sound was coming from on my floor. They had to walk right up to my door to locate the source. My unchastened MBL’s just glared back at them and refused to assume the face down music position.

The security police said OK; the music was not that loud. But maybe the bass was too strong. Sure enough, Sirius XM jazz was playing, and there was that exaggerated bass again. Images of sonic termites nibbling away at my building’s steel foundations had munched into my thoughts.

Their tenant-appeasing suggestion was to raise the speakers a bit off the floor.  That might keep the big bad MBL woof from coursing concrete and steel woods and hunting down this unsettled neighbor. So I did, with Black Diamond Racing cones. As a bonus, the bass was also tighter. I probably should have done this cone hack a long time ago. But I was put off by nervous thoughts of losing a Torikumi with the massively heavy MBL’s.

Next, badly handwritten notes began appearing on tenant mailboxes in the building lobby. They were posted around mailboxes near mine. They were unrequited musical ransom demands. The messages raved, “Despite all my complaints you still don’t have the decency to turn down your music in the morning!”  Apparently, the selfsame tenant who called the heat down on me was also targeting other people living in the vicinity of my apartment for their sin of music. My skin crawled.

A week later, I again turned on Sirius XM jazz in the evening.  Once more I puzzled over the wooly bass. The volume had also been left a bit too high for evening play so I immediately turned it down. Not more than five minutes had passed since my fingers left the volume knob than building security police were again knocking at my door. 

How was such a fast and furious tenant response possible?

About two weeks after this last security visit me and two of my next door neighbors were riding together in the elevator, ascending to our floor. One of them abruptly turned to me and asked, “Was that you who posted a note on my front door complaining about the TV being too loud?” The third tenant then chimed in with his own recent and similarly unsettling experiences. Shit! We were all being stalked.

A one-person tenant terror patrol was roaming our building corridors. And he (or she) was pressing their maddened ear against people’s front doors, silencing orange jump suit perhaps in hand. How far would executing his audio fatwa take him? I spoke to building management. They checked their security call records.  Yes, this was a real problem.

Two months later, I was told this audibly gruesome Grinch, whoever it was, had left, perhaps with strong encouragement by building management.

Nothing exists in isolation, including audio gear. The musical abstractions they produce cause highly tangible effects, good and bad. For some in this world The Absolute Sound can only mean The Absolute Silence; of which there is only one terrible kind, Requiescat in Pace, Harry Pearson.

Another, mercifully uneventful, month went past, when the sloppy bass on Sirius XM finally cleaned itself up. The Magtech makeover was complete.

And now I no longer digress.

I had to wait almost six months for the MBL 101D speakers and the Magtech monoblocks to settle down and happily live together. I had never encountered such a lengthy time for amplifier break-in; usually, I see this with new speakers. Apparently, Magtech electron nanobots had been busily interior remodeling my MBL’s. When their unseen handiwork was finished I was left with an essentially new, and quite wonderful system.

The Magtech monoblocks are enormous electron pumps with bottomless reservoirs of effortless watts. True to form, they had puffed and puffed up the 101D’s skirt until the speaker was also forced to reveal some sonic holes in its German panties. Mostly, this design embarrassment was about trying to seamlessly steady a big stack of omni radiators atop a conventional cone head. The 101D sub never could quite pull off this acoustic balancing act. On several recordings the discontinuity between the 12” cone sub and the omni woofer was clearly discernible. Neither component could apparently make up its mind about who was going to shoulder the heavy bass load.

The new MBL 101E Mk.II model rectifies these 101D design problems. The 101E Mk.II superficially looks like the 101D, but closer inspection shows it is a complete redesign. Yet, it still remains true to its Radialstrahler/omnidirectional design beliefs. In addition to a massive overhaul of the problematic subwoofer bits, the omni parts also came in for renovation, including revisions to the omni woofer, midrange and tweeter, and for good measure, to the crossover network as well. MBL is always on full kamikaze attack for audio perfection.

Does that mean the 101D is flawed crap? No, not at all, for whatever may be the 101D’s shortcomings they are still audio paragons, with few peers even today.

The big takeaway is that Sanders is really on to something with its innovative circuit design. Whether it is the Magtech stereo amp I use with the Analysis Omega’s, or the Magtech monoblocks driving the MBL 101D’s these Sanders products never cease to amaze. That they also cost much less than other high-end amplifiers is just a bonus. They will drive anything you got and never lose their cool, figuratively and literally.

Spend your money instead on bigger and better speakers. Sit back, listen, and feel very pleased about your newfound Magtech wisdom.
..........
Francis Vale

The Magtech sounds solid, powerful and extremely dynamic. Bass is tight and firmly controlled, yet full bodied and rich, while the treble is airy but focused and clean.
Ralph Ede

SUMMARY: Designed then for musical appreciation rather than to impress your friends the fait accompli is this – it is like you haven’t got an amplifier in the system at all – it’s so neutral and ‘invisible’ sonically. Designed to maintain the integrity of recordings, the acoustic energy propagates so naturally that the mechanics of the reproduction cease to intrude. Moreover the lack of dynamic constraint and superb localisation of instruments and / or actors makes the whole reproduction of the experience much, much more convincing and in this regard the Magtech will tell you more about the music on your records and how it got there than any number of highly touted and priced alternatives. Those of us that work for a living have reason to rejoice, for the unflappable and unobtrusive Magtech stereo power amplifier serves to prove that simply spending more money on something (much) more expensive is even less of a satisfaction guarantee than it ever was.

EXTENDE REVIEW: PREFACE– THE INELUCTABLE MYSTERY OF HIGH POWERED AMPLIFICATION
After more than two decades as an audiophile, I have a confession to make: There is a lot I don’t know about audio. Indeed, the area where I have devoted most of my energy and attention – high powered amplification – is where I find myself most often confronting important questions without obvious answers. So, let me come clean and highlight through this review some of the questions that perplex me, for the answers to them may well shape my buying decisions in years to come. First question, how much amplifier power do you need? One possible qualitative answer is sufficient power to ensure that your amplifier never clips. To be sure few audiophiles would feel good about sending clipped audio waveforms from their amplifiers to their speakers irrespective of whether you could discern the resulting distortion or not.

But while the qualitative answer has an inbuilt psychologically good ‘feel good’ factor about it – the quantitative answer required to underpin the ‘never clips’ proposition will flat out shock you. Assuming you own a pair of average sensitivity (circa 87dB) dynamic loudspeakers and assuming your choice of music is orchestral or heavy rock (which can peak for very short periods at 109dB or more) and assuming you sit about 3 meters from your loudspeakers the quantitative answer suggests you would want an amplifier rated at 500 Watts per channel.

Second question, assuming one places little stock in the quantitative answers that physics serves up – and surprisingly few audiophiles do – what benefits can be had by employing the use of high powered amplifiers for average sensitivity loudspeakers?

Based on my own subjective experience with high powered integrated and power amplifiers such as the Abbingdon Music Research (AMR) AM-77; the Plinius Hiato; the GamuT DI-150; the Gryphon Diablo; the Bel Canto Ref 1000 MkII monoblocs; the Sanders Sound Systems ESL Stereo and the Jeff Rowland Design Group Continuum 500 (see references for reviews) the effortless and unobtrusiveness power delivery of big amps brings a sense of relaxed and uncongested grace to all sorts of recordings. There is no hardening as the amplitude increases, no collapse of soundstage or roll off of frequency extremes as the amplifier is presented with awkward loads or gasps for breath as it flat out lacks the extra oomph to reproduce the scale and attack of a bass drum. Well-designed big amps also have momentum, an unstoppable metronomic progression which underpins continuity to the music whilst still be able to respond quickly to transient changes. Done right the rise times on big grunts can be blindingly fast aiding transparency and moreover, one often observes very deep, extended, and powerful bass and a retained grace even during massive 109dB orchestral and rock peaks.

Conversely, I’ve found that if an amplifier is under-powered for your needs, you’ll never hear the system at its full potential. The sound will be constricted, dull, muddy and often fatiguing and you will notice a hardening of timbre and a dilution of dynamics as the amplifier strains and gives up as it runs out of power. Furthermore one frequently witnesses a tendency to homogenize individual instruments and their specific locations within the soundstage as an amplifier is being unduly taxed.

Please don’t get me wrong, I am not suggesting for one minute that “power outputs” are any reliable guide to the quality of an amplifier – but one observation I will boldly make up front is this; well-designed high power amplifiers typically possess one consistent ace up their sleeve and that ace comes in the form of large and heavy power supplies with high current capability which is demonstrated by their ability to increase output power into low impedances. Since it is current that ultimately drives the cones in your loudspeakers back in forth it is actually the amplifiers power supply design, not some lofty and frequently misrepresented wattage moniker, which underpins perceptions of sound quality. Since high current capability comes from massive power supplies and lots of output transistors, all of which are expensive items, well designed high powered amplifiers don’t come cheaply.

DESCRIPTION

The relevance of the preface finds its feet in the subject of this review the Sanders Sound Systems (USA) Magtech Stereo Power Amplifier (hereafter ‘Magtech’).On first glance there is nothing on the outside of the Magtech to suggest that anything special lurks within. Indeed cosmetically the Magtech is quite unremarkable (even if pleasingly simple) and entirely lacks the butch machismo expected of muscle bound amplification. Many audiophiles like to have their equipment look as they expect it to sound and in this respect listeners really are in for a ‘Little Red Riding Hood’ experience.

Cosmetically the product is stylistically indistinguishable from the Sanders ESL amplifier and that visual continuity is actually reassuring given the performance that product exhibited a couple of years back when I borrowed a unit to review some large KingSound ESL speakers (see references) I had in residence at that time.

Compact at just 43cm wide, 40cm deep and 14cm tall the Magtech refreshingly presents no real estate challenge. The plain 3/8 inch aluminium front plate houses a blue backlit “Sanders” logo to indicate operation and the rear panel is adorned with RCA and XLR inputs, speaker outputs, fuse holders (one for each channel and one for the AC line) and an on/off switch. The XLR input connectors (pin 2 ‘hot’) are genuine Neutrik and they use professional metal sockets with locking devices. The RCA connectors are Cardas with Rhodium plating. The WBT speaker binding posts are thoughtfully placed at 45 degrees for ease of routing stiff speaker cables. The inch deep heat sinks along both sides of the chassis, which look oddly insufficient for the amplifiers power rating, mercifully lack sharp edges and are child safe. Closer inspection of the heat sinks however reveals there are no less than 53 fins, each with a surface area of 10 square inches. When you add up all this area, plus the area of the aluminium chassis, which also dissipates heat, the total heat sink area in the Magtech amplifier is nearly 10 square feet! As a result, the heat sinks are adequately designed to keep the amp cool. I dwell on this simply because I see lots of high-quality amplifiers out there with large heat sinks but using just a few big fins. While such heat sinks may look impressive, they are not very efficient and waste a lot of space.

While the Sanders ESL amplifier was designed from the ground up to drive electrostatic speakers, the Magtech, as the ‘Mag’ before the ‘tech’ clues, has been specifically designed to drive conventional magnetic speakers. Recalling the importance of a robust power supply, the Magtech is uniquely equipped with what Sanders refers to – rather un-uniquely – as a ‘regulated power supply’. Readers interested in details on this should read the white paper entitled “The Magtech Regulated Power Supply White Paper” hosted on the Sanders Sound Site. The crux of this reads that the Magtech is equipped with an extremely robust (stiff) power supply, which is capable of maintaining voltage even when the output transistors are demanding large amounts of current whereas unregulated power supplies (more typically found in amplifiers) simply can NOT maintain their voltage, even under only moderate load, and certainly not under high current conditions, leading to degraded sonics.

The power supply then underpins an impressive spec sheet. The Magtech will deliver 63.4 volts RMS to the speakers, which translates into 502 watts into an 8 ohm load. Further down the impedance scale the Magtech delivers 900 watts into a 4 ohm load and about 1600 watts into a 2 ohm load. What makes these spec’s all the more impressive is that the power ratings are for both channels driven at any audio frequency (20 Hz to 20 KHz) and with a THD level cited in the manual of just 0.01% at any power level below clipping. At 1 watt ("small signal"), the specification less honest manufacturers use to rate distortion, the THD is no more than 0.004% and typically 0.0024%. As the reader might imagine the output stage needed to drive these sorts of power levels is nothing short of colossal, comprising of OM NJL4281 and NJL4302 transistors in complementary pairs. Note that these are the new "Thermal Trak" type of transistor that has a temperature sensor built into the transistor junction. This makes it possible to instantaneously correct for the huge swings in bias current due to the problem of instantaneous junction heating caused by sudden, large, current flows. As a result, the amplifier is able to maintain a constant bias current at all times -- something that is not possible in conventional transistor output stages.

In sum the output stage is capable of handling about 7,000 watts of power, so the transistors are never being taxed and protective circuitry can be eliminated from the design. Since protective circuitry sounds harsh and generally awful when in operation, eliminating it is the key – in the designer’s opinion – to making amps sound superb. To deliver its power the Magtech employs of the use of a single 2200 VA transformer and medium sized capacitor bank. In an age when many amplifier manufacturers for reasons of cost savings are reducing transformer sizes and relying more on capacitance to supply the brief bursts of power required – the use of ‘heavy metal’ in the Magtech is both refreshing and commendable.

Megalomaniacs who feel that 900 watts (into 4 ohm loads) really isn’t enough juice to get their Magnapan or Apogee panels vibrating have the option of ordering the Magtech as a mono-bloc and in this guise 2000 watts is available. With these sorts of power levels the reader may be wondering whether the Magtech is Class D in operation. The answer is no. The Magtech is Class AB from the get-go since the designer believes nearly all Class A amps are under-powered and he sees no point in wasting power driving the amp into Class A or even high bias, Class AB operation as he prefers to bias as low as possible to conserve electricity and keep the amp cool.

Mentioning energy conservation and high powered conventionally biased amplification in the same sentence may seem ‘a bit rich’ to some so let me expand on this for a moment. The Magtech runs cool because its transistors have an extremely linear transconductance function and therefore do not require much bias to eliminate crossover distortion. Understand that most of the heat produced in a Class AB amp is produced by the bias current. The sole purpose of the bias current is to eliminate distortion. Through the use of the most modern and linear “Thermal Trak” transistors very little bias current is needed to eliminate all distortion and the amplifier as a result runs very cool. 

Impressively, the Magtech idles with each channel drawing only about 16 watts of power, so the total idle power used by the amp will be about 32 watts which is identical to my Bel Canto Class D 1000 Watt monoblocs. This means the Magtech amplifier can economically be continuously left on and indeed the designer recommends this.

SET UP

In setting up the Magtech there are a few things to observe and consider not all of which is covered in the operating manual.

The first is that the Magtech is a differential/complementary design which means that its frequency response is flat right down to DC. Typically in such designs there are no capacitors in the signal path that would block DC, so if you feed it a DC signal – and many preamps "leak" DC – it will amplify that signal and can easily burn up your woofers due to its high power. So, it is important to avoid DC offsets in your pre-amp when using the Magtech or indeed any other directly coupled amplifier. As a compromise Sanders employs the use of DC blocking capacitors in the unbalanced inputs of the Magtech since tube preamps are the worst offenders and most are unbalanced. The designer leaves the balanced inputs free of capacitors since those who use balanced equipment tend to be the most concerned about capacitors in the signal path. For the record Sanders Sound can easily omit the capacitors in both circuits, or add them to both circuits if a customer wishes. The customer simply needs to specify his desire at the time of his order and there is no additional charge either way.

The second is an injunction on the use of power conditioners. Sanders distaste of such products is consistent to that of other high powered amp manufacturers such as Krell, Bryston and Gryphon with the central concern being that power conditioners can seriously degrade performance. Most conditioners add series resistance in the power line and this will tend to limit the amount of current fed to the amp and when dealing with amplifiers that are as powerful as the Magtech, they need all the current they can get. So please plug the Magtech directly into the mains receptacle in the wall.

Finally, the manual notes “The Magtech Amplifier is designed to be left on continually”. One reason cited is stabilisation of internal temperature which produces lowest distortion. Understand here that amplifiers are relatively massive devices and it therefore takes several hours for the heat produced by the bias current in the output transistors to completely soak through the entire unit and eventually stabilise an amplifier's chassis, heat-sink and internal temperatures. However, Sanders primary concern here is not temperature stabilisation (important as that may be) but long-term reliability. Remember that Sanders amps come with a lifetime transferable warranty, so it is extremely important that they never fail. Turning a component on and off stresses it. Switches are damaged slightly each time you throw them. Doing so causes a small electric arc between their contacts, and this gradually destroys the contacts. The arcing is worse at turn-off, but an arc will also be present at turn-on. An even bigger problem is the big power supply capacitors. When the amp is off, these caps will discharge to zero volts. At turn on, they are then hit with high voltage (100 volts in the case of the Magtech). Since a large cap at zero volts is a dead short, a massive surge of electrons will flow into the cap when the amp is turned on. This high current flow causes a tiny amount of damage to the cap's plates and will lead to eventual failure if they are cycled enough times.

Remembering that a power amplifier is only going to sound as good as the equipment surrounding it the audition included the use of Lightspeed Attenuator (used at times in place of the Cary pre-amp) and three different loudspeakers; an average sensitivity reference bookshelf speaker (Raidho Acoustics C-1.0, 87dB), a medium sensitivity near full range floor-standing speaker (Nola Contender, 90dB) and a low Sensitivity electrostatic speaker (Kingsound ESL, approx. 80dB).

Furthermore, over the audition period the performance of the Magtech was subjectively referenced against two other high powered amplifiers, a Gryphon Diablo (Power Amp Mode) (Denmark, solid state, Class AB, 250 watt per channel, US$ 16,000) and a pair of Bel Canto Ref 1000 MkII mono blocs (USA, solid state, Class D, 500 watt per channel, US$ 5990 per pair). The scene now set, let’s discuss the sound!

THE SOUND

From the first disc the attributes of the Magtech are clear. The Magtech sounds solid, powerful and extremely dynamic. Bass is tight and firmly controlled, yet full bodied and rich, while the treble is airy but focused and clean. There is nothing sweet, mellifluous or euphonic about the way which the Magtech reproduces music, rather the Magtech appears to be a model of neutrality wearing clarity and dynamics very much on its sleeve.

Feed with demanding opening soundtrack to “The Pacific” (The Pacific, Music from the HBO Miniseries, Rhino Entertainment – 8122-79810-9) and compared to both the power amplifier section of the Gryphon Diablo and the high powered Bel Canto monoblocs the Magtech possessed a noticeably greater ability to follow the dynamic contours of the music. When compared to my 120 Watt Unison Research amplifier I was surprised more than once when climaxes in orchestral recordings I thought I knew well continued to grow and expand beyond the point where (on the Unico) they would have stopped. Further, this is an amplifier that loves pace picking up transient cues instantly, as if it is anticipating the music even before the DAC decodes it.

Continuing with last scale orchestral music, in The Snow Maiden (from Exotic Dances from the Opera, Reference Recordings, RR-71) it was possible to indulge in near concert hall volume levels without feeling that the amplifier was straining. The Magtech possessed purpose coupled with majestic grace as it relentlessly tracked the towering opening tuttis with a broad and deep soundstage adding to the sense of power and the orchestral sweep of the music. The timpani seemed bolder than I’ve earlier recalled the skins with more texture and air with other percussive instruments being sharper and more solid then reproduced by the comparator amplification.

And as good as the Magtech was with dynamic orchestral tracks nothing could have prepared me for the next act which was the reproduction of Olivia’s Ong’s live 2010 concert in Taipei. The anticipation of the crowd was palpable as was the cascade of drums that open the concert above the background noise of the restless crowd. Big, solid, real drums with visceral whacks you feel as the stick strikes the skin, with the resistance of the skin itself and incredible presence and transient impact which ordinarily places enormous strain on lower powered amplifiers here being treated and presented as no stress at all. The leading edge clarity on the drums combined with seemingly perfect decay is the best I’ve heard in my system to date. As the crashing cannonade gives way to the vocals the communication of the immediacy and pulse of the live performance added considerably to the belief that the event is happening a few meters from my listening chair! Another interesting observation during this recording was that the Magtech shone more light on the backing singers which appeared (comparatively) as dull and less defined with both the Bel Canto and Gryphon amplifiers.

The Magtech proved no slouch on complex studio albums either. Taking “The Power of Good-Bye” and “Frozen” both Orbit inspired masterpieces from Madonna’s GHV2 (Madonna, Greatest Hits Volume 2, Warner Music Group – 9362480002) as examples, the layered soundscapes are effortlessly reconstructed, sucking the listener into their complex texture and minutiae detail even whilst the underlying beat propels the tracks momentum with solid energy. These tracks play up a particular strength of the Magtech which is not just dredging awesome amounts of bass out of low efficiency speakers but demystifying complexity and thus allowing the listener to see into the recording as a representation of the event. These tracks also show the resolution of the Magtech to be quite simply ‘top draw’ and whilst I have frequently heard people scoff minutiae of detail as musically irrelevant – listening to the Magtech gives me cause to once again ponder whether these same people are simply making excuses for equipment that is incapable of reproducing them?

Staying with vocals for a while longer, a good test of vocal articulation can be found in Warnes “Some-where, somebody” (Jennifer Warnes, The Hunter, 24K Gold Special Edition, Sony BMG Music – GDC 8012-2) where a discrete blend of lead female singer, male accompaniment and instruments meld and can on many systems become confused. With this piece the Magtech did an outstanding job in ensuring that first, the lead voice maintains it position relative to the musical parts with the appropriate weighting and second, that the accompanying male vocal maintained clear articulation and his lines were not lost in the melee.

Music though is more than just sorting out priorities and rendering tracks intelligible, it is also about rhythmic organisation and making that out of the morass that comes from the surface of all too many discs these days. That’s not to suggest that the Magtech can transform a run of the mill recording into a masterpiece, but proving it is not just another ‘dumb metal jacket’ the Magtech can and indeed does manage to extract the musically important core from the mire. Case in point is ABC’s digitally re-mastered but still poorly recorded 1999 album, entitled Classic ABC (ABC, Classic ABC, Mercury Records – 546 804-2). This album serves as my bad recording reference, noisy and grainy 1980’s synth-pop at its worst, but it nonetheless sits on the top shelf of my CD rack because hits like “Look of Love”, “Poison Arrow” and “All of My Heart” are all defining musical moments of 80s nostalgia for me. It takes a well sorted audio system to extract the music from the compressed mayhem and the Magtech rose to the occasion by cutting straight to the heart of the recording and never letting go. Mercifully, the sort of insight the Magtech delivers is what’s there in the recording rather than pulling the recording apart and where the Magtech excels is in the area of momentum, it succeeds even in poor recordings in keeping things rhythmically taunt without becoming forward or bright.

Perhaps though the greatest challenge for any high powered amplifier is reproduction of the human voice at low volumes. In my experience low level listening is traditionally an Achilles’ heel to some behemoths with the sound all too often collapsing into the speakers. Not so with the Magtech. With Katie Melua’s “Haunted House” (Kate Melua, The House, Universal Records – B0014568-02) the Magtech excelled even at low listening levels by successfully creating the tracks suspense and brooding menace whilst not ignoring the litany of low amplitude micro-dynamics, tonal shifts and dynamic contrasts which create the contextual atmosphere.

CONCLUSION

To summarise, during the period of my evaluation there was nothing that caught the Magtech out. Even with different speaker designs and loads it seemed more than equal to every-thing. Tonally colourless, the Magtech performance is self-assured and immensely stable, driven by the kind of contained power that I’d normally associate with a steam roller. If a ‘but’ has to be inserted somewhere it is that readers bought up on the rounded warmth and intimacy of a classic valve power amp may find the Magtech somewhat academic and stark. The injunction here – as always – is that ‘know thyself’ is an essential pre-requisite for all audiophiles and whilst many philosophically claim to desire absolute neutrality in audio reproduction – it is a claim for some that lasts only as long as actually hearing it...

Perhaps the easiest question to answer was what the Magtech sounded like? The answer is “whatever it is connected to” and this observation rather underpins the synthesis that is how you assemble a system around the component in question that really determines the results. Careful selection of upstream components will be important and for what is worth I vastly preferred the Magtech when paired with a high quality valve

Minimalist in the flesh the Magtech is not a trophy product and this will sit uncomfortably in a world of affluent hi-fi aficionados who can (and frequently do) proudly list a string of ever changing and ever more expensive ‘branded’ products that they have owned. Such owners seemingly treat hi-fi like a thoroughbred bloodline in the mistaken belief that brand and high price always translate to high performance. In a very sad sense, ‘high end’ has all too often become a price point rather than a performance benchmark and Sanders Sound Systems Magtech serves as a much needed reminder that audio priced at unconscionably high levels is not only unfair to consumers and damaging to the industry – but also completely unnecessary.

LISTENING ROOM VIEW

Designed then for musical appreciation rather than to impress your friends the fait accompli is this – it is like you haven’t got an amplifier in the system at all – it’s so neutral and ‘invisible’ sonically. Designed to maintain the integrity of recordings, the acoustic energy propagates so naturally that the mechanics of the reproduction cease to intrude. Moreover the lack of dynamic constraint and superb localisation of instruments and / or actors makes the whole reproduction of the experience much, much more convincing and in this regard the Magtech will tell you more about the music on your records and how it got there than any number of highly touted and priced alternatives. Those of us that work for a living have reason to rejoice, for the unflappable and unobtrusive Magtech stereo power amplifier serves to prove that simply spending more money on something (much) more expensive is even less of a satisfaction guarantee than it ever was. Recommended.

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.
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. 
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 :)
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. 

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A complete Sanders system comprising Sanders 10 ESL speakers, 2x Magtech 500w amps & Magetch Preamp