Krell

"The ORIGINAL" - World Leading, class-A, iBias Amplifiers & AV Processor - made in the USA
The Leader in Audio Engineering

WELCOME TO THE "KRELL" RELAUNCH - A FAMOUS, OLD. HIGHLY RESPECTED BRAND, BACK IN NZ WITH NEW XD SERIES:
High-end audio is a demanding pursuit; an ongoing quest for excellence in music reproduction that drives equipment manufacturers to strive for the absolute in design and performance. With a keen understanding of this passionate drive, 
Krell Industries was founded in 1980.

As of 2018 Krell Industries has finalised a roadmap for reinforcing and building the brand through an extensive program of new product development, expanded marketing initiatives, and overall strategic direction. To move the effort forward, Krell enlisted the assistance of audio industry veteran Walter Schofield, who joins the company as its new Chief Operating Officer. In this role, Mr. Schofield will drive all sales, marketing, and new product initiatives. and Krell founder Rondi D’Agostino continues to serve the brand as Managing Director. “Walter’s knowledge of the audio market is second to none,” said Dave Goodman, Director of Product Development, Krell Industries. “Throughout the course of his career, he continually proved himself an expert at revitalising time-honoured brands like Krell with successful strategies for significantly growing their market share. We’re thrilled to have him on board.” Mr. Schofield joins Krell Industries after a successful tenure with Emotiva Audio, where, as Vice President of Global Strategy, he helped to dramatically increase the brand’s presence and sales across the globe by opening new channels of distribution and myriad new partner accounts. Before joining Emotiva, Mr. Schofield held senior management positions with some of the most successful brands in high-end audio, including Mark Levinson within Harman International / Harman Specialty Group, and Meridian.

KRELL'S NEW XD SERIES WITH ENHANCED CLASS-A, iBIAS TECHNOLOGY:
Krell's history is rich with breakthrough Class A amplifiers that have helped build the Krell legacy of offering the best sounding amplifiers available. Audiophiles have always considered Class A technology to be the best sounding operating state for amplifiers. However, despite Class A's unrivaled sound quality, it has fallen out of fashion because of recent demands to reduce power consumption and heat in home electronics products. Krell engineering took this challenge and redefined the meaning of high performance power amplifier. Our goal - unmatched performance, elegant design, and a compelling array of features. The breakthrough - a patent pending circuit delivering Class A operation without the excessive heat and wasted energy of conventional designs, housed in a striking new form factor, with network connectivity for advanced access and monitoring. The sound is open and unconstrained, in a manner that rivals live performance and the true sound of voices and instruments. Music and dialogue are reproduced with a richness, detail, and startling dynamics that fill a room.
Plainly stated, Class A designs are the most musically accurate circuit topology available. Class A amplifiers do not suffer from the inherent distortions that all Class AB amplifiers experience. In a traditional Class A design, the output transistors conduct full current at all times regardless of the actual demand from the speakers. Often, only a fraction of this power is needed to reproduce an audio signal at normal listening levels. The rest of the power is dissipated through the amplifier’s heat sinks, producing large amounts of wasted heat. With Krell's iBias™ technology, bias is dynamically adjusted, so the output transistors receive exactly as much power - but only as much power - as they need.
Krell's iBias Class A technology allows our latest amplifiers to run in full Class A mode to full power while minimizing heat generation. Previous efforts at using a "tracking" bias, while effective, only measured the incoming signal and set bias levels from this information. Our new patent pending iBias technology significantly elevates the effectiveness of previous designs by calculating bias from the output stage. This seemingly small change in topology results in a dramatic improvement in sound quality, especially midrange richness and purity.

The core of the technology is an innovative, patent pending design for a dynamic intelligent bias circuit. Our iBias Class A circuit directly measures the output current of the amplifier and adjusts the bias to the optimum level. Because iBias Class A measures the output current, the real time demands of the specific speaker connected to the amp are directly incorporated into the circuit function. In addition, iBias Class A even reduces the bias when the signal is at very low levels, making its operation undetectable by ear and even by standard amplifier measurements. 
In others typical sliding bias schemes, the circuit merely estimates how much bias is needed based on the input signal and an "assumed speaker load." Compared with iBias Class A, these sliding bias technologies are much less effective - and much less accurate.

We are excited to announce a NEW and FULLY REVAMPED range of XD AMPLIFIERS using KRELL'S unique and enhanced class-A iBias technology.

For nearly three decades, Krell has earned a distinguished reputation for engineering innovation and product excellence. The company's history is replete with product introductions that have deeply impacted the high-end audio industry. The most discriminating audiophiles and product reviewers have consistently recognized Krell components for standard-setting performance. The sheer breadth of Krell amplifiers' dynamic range capabilities conveys a startling realism that transcends previous designs. Seemingly unlimited frequency response, combined with unerring accuracy and fortitude, extend a tradition that began with the first Krell amplifier; the KSA-100. The KSA-100 was the first high power, high-current, true Class A biased stereo power amplifier available to audiophiles. It was the first Krell product, and its resounding success established Krell as an important new technological contributor to high-end audio.

From the KSA-100 to the present, Krell continually "pushes the envelope" of performance in our search for greater amplifier power. Exploration of new technologies, driven by a never-ending quest to elevate the standard of excellence, has resulted in breakthrough audio designs. Over the years, the Krell line of power amplifiers, including benchmark products such as the KRS-100, KRS-200, and the Audio Standard models, has established a legacy of unparalleled sonic performance.

The Krell product line has diversified, but Krell's fundamental research into amplifier design and performance remains at the core of the company's achievements. Every Krell component upholds the legacy, incorporating unique technologies that are the direct result of Krell's discoveries in audio amplification. They provide unprecedented linearity with the control and accuracy that only comes from superior current capability. The sound is lively and unconstrained, in a manner that evokes live performance and the true sound of instruments. The Krell legacy will continue to evolve with products that deliver innovative engineering, perfection in build quality, and outstanding audio performance.

Krell amplifiers are best known for their ability to drive any loudspeaker to sound its best, without regard to impedance, efficiency, or driver style. It is linearity, an amplifier's ability to output an exact duplicate of the input signal, which is the ultimate measure of that amplifiers worth. Krell designs toward the common goal of linearity; through the rigorous application of Krell design principles that focus our efforts on four major performance factors: distortion, bandwidth, output impedance and current capability. They excell in each of these areas, delivering supreme accuracy from whisper level to astounding, awe inspiring amounts of power with grace and elegance. -A with unique iBias technology.

BETTER SOUND 
Building on the unique Active Cascode Topology foundation of the NEW Rrange of amplifiers feature more precisely balanced current sharing among the seven sets of Active Cascode Quartets that make up the output stage. This greater precision elevates an already impressive performance envelope and provides greater amplifier reliability. Audible at all volume levels, this improvement is independent of load current. Although negative feedback in the Evolution amplifiers was already extremely low, a mere 14 dB---several orders of magnitude lower than other manufacturers' power amplifiers, modifications to the feedback circuitry allow for more ideal operation completely independent of the signal level. The results are greatly enhanced inner detail and micro-dynamics with smoother high frequency response. 

  
LESS HEAT, LOWER ENERGY CONSUMPTION with KRELL'S unique iBias technology

Featured

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Reviews

Awards

Featured

KL 03 IA K300D
NZ$ 16,250.01 (incl. GST)
Renowned American amp brand, Krell Industries, has just unleashed the K-300i Integrated Amplifier .Krell made an impact with their KAV-300i integrated amplifier in 1999. Today, they are hoping...
When it comes to high-end solid-state amps, no manufacturer is more revered or influential than...
KL 05 PA ILL2
NZ$ 12,995.00 (incl. GST)
  The Illusion II is the perfect center piece for a world class digital and analog audio system. Added to the normal selection of balanced and single- ended inputs are five digital inputs. The...
KL 12 AS D300
NZ$ 17,995.00 (incl. GST)
Plainly stated,
Circuitry Highlights Krell iBias Class A technology allows our latest amplifiers to run in...
Krell’s new iBias range is claimed to be more efficient, or less power-hungry, than pure Class A....

All Products

DACs

KL 01 DC VAN
NZ$ 9,250.00 ea (incl. GST)
An ESS Sabre DAC feeds a classic Krell balanced, fully discrete Class A circuit which is also used in the Krell Illusion II Preamplifier. Krell Current Mode technology is employed to assure unequaled...
Coaxial and HDMI inputs support PCM up to 24-bit/192kHz. Optical input supports up to 24-bit/96kHz...
DACs

Integrated amplifiers

KL 03 IA K300C
NZ$ 14,250.00 ea (incl. GST)
Renowned American amp brand, Krell Industries, has just unleashed the K-300i Integrated Amplifier. Krell made an impact with their KAV-300i integrated amplifier in 1999. Today, they are...
When it comes to high-end solid-state amps, no manufacturer is more revered or influential than...
Integrated amplifiers
KL 03 IA K300D
NZ$ 16,250.01 ea (incl. GST)
Renowned American amp brand, Krell Industries, has just unleashed the K-300i Integrated Amplifier .Krell made an impact with their KAV-300i integrated amplifier in 1999. Today, they are hoping...
When it comes to high-end solid-state amps, no manufacturer is more revered or influential than...
Integrated amplifiers

Preamplifiers & Line-stages

KL 05 PA ILL2
NZ$ 12,995.00 ea (incl. GST)
  The Illusion II is the perfect center piece for a world class digital and analog audio system. Added to the normal selection of balanced and single- ended inputs are five digital inputs. The...
KL 06 PA ILL
NZ$ 29,995.00 ea (incl. GST)
Crossover Highlights Owing to Krell’s work in the Modulari Duo Reference loudspeaker, the unique crossover feature is a highly sophisticated option. When the optional board is present, additional...

Power amplifiers (Stereo & Mono)

KL 10 AS D125
NZ$ 11,995.01 ea (incl. GST)
Plainly stated, Class A designs are the most musically accurate circuit topology available. Class A amplifiers do not suffer from the inherent distortions that all Class AB amplifiers experience. In...
KL 11 AS D175
NZ$ 14,500.01 ea (incl. GST)
Plainly stated, Class A designs are the most musically accurate circuit topology available. Class A amplifiers do not suffer from the inherent distortions that all Class AB amplifiers experience. In...
KL 12 AS D300
NZ$ 17,995.00 ea (incl. GST)
Plainly stated,
Circuitry Highlights Krell iBias Class A technology allows our latest amplifiers to run in...
Krell’s new iBias range is claimed to be more efficient, or less power-hungry, than pure Class A....
KL 15 AM S375
NZ$ 31,995.00 pr (incl. GST)
Plainly stated, Class A designs are the most musically accurate circuit topology available. Class A amplifiers do not suffer from the inherent distortions that all Class AB amplifiers experience. In...
EXTENDED REVIEW: The Krell Solo 375 mono block demonstrates how the amplifier business has exploded...
KL 16 AM S575
NZ$ 40,995.00 pr (incl. GST)
Plainly stated, Class A designs are the most musically accurate circuit topology available. Class A amplifiers do not suffer from the inherent distortions that all Class AB amplifiers experience. In...
EXTENDED REVIEW: The Krell Solo 375 mono block demonstrates how the amplifier business has exploded...

Surround Sound Processors

KL 19 PR FOUND
NZ$ 15,500.00 ea (incl. GST)
The 2013 New York Audio Show, held at The New York Palace Hotel, was practically bursting with...

Home Theatre amplifiers & receivers

KL 20 AV THEATRE
NZ$ 15,500.00 ea (incl. GST)
Krell Class A iBias Technology
EXTENDED REVIEW: "Krell has had its share of ups and downs in the past few years, and not just of...
KL 22 AV T300
NZ$ 22,995.00 ea (incl. GST)
Plainly stated,  Class A designs are the most musically accurate circuit topology available. Class A amplifiers do not suffer from the inherent distortions that all Class AB amplifiers...
KL 23 AV C5200
NZ$ 17,995.00 ea (incl. GST)
Plainly stated, Class A designs are the most musically accurate circuit topology available. Class A amplifiers do not suffer from the inherent distortions that all Class AB amplifiers experience. In...
Do you remember what it was like sitting for your high school or college lessons? Well, get ready...
KL 24 AV C7200
NZ$ 21,995.00 ea (incl. GST)
Plainly stated,  Class A designs are the most musically accurate circuit topology available. Class A amplifiers do not suffer from the inherent distortions that all Class AB amplifiers...
Do you remember what it was like sitting for your high school or college lessons? Well, get ready...

Reviews

Krell's Foundation brings the listener closer to that ideal than any 7.1 AV processor I have heard to date."
Mark Henninger - imagic
More than anything else, the new Foundation amazed me with its fidelity, which has always been Krell's mission—to deliver the ultimate in sound quality.  The vast majority of audio equipment is ill equipped to extract the total fidelity found within these high-resolution yet ubiquitous soundtracks. Krell's Foundation brings the listener closer to that ideal than any 7.1 AV processor I have heard to date.
 
The fact it's priced at the same level as moderately expensive projectors and speakers makes Krell's AV processor a relative bargain for the sound it produces. The Foundation is a fantastic 7.1 AV processor from a company with a long record of accomplishment, producing some of the best solid-state electronics in the entire audio industry. The Foundation deserves an audition from anyone who is truly serious about home theater and considers it to be within his or her budget. 
The 2013 New York Audio Show, held at The New York Palace Hotel, was practically bursting with esoteric audio products; many rooms contained systems priced in the 6-figure range. The overwhelming majority of the show was about 2-channel audio, but Krell was there with the new Foundation AV processor, a moderately priced (by Krell standards) 7.1 surround-sound preamp/processor with a number of features that help differentiate it from rather stiff competition.
 
One of the more impressive aspects of the Krell HT demo system was the relatively mainstream components used to highlight the new processor's prowess. This system was not a "price no object" Krell showcase—it was more of a "high price is justified by superior engineering" system—yet engineering without compromise is the precise heritage it comes from. After a long talk with Krell President Bill McKiegan, I came away convinced that the new Foundation completely justifies its price tag.
 
I had the room essentially to myself, and I chose a seat in the second row, perhaps 11-12 feet back from the front stage, just in front of the side surrounds and perhaps 8-10 feet from the rear surrounds. I chose the helicopter attack on the ranch from Skyfall to serve as a reference scene, because I am very familiar with it.
 
What I heard was quite stunning—a rear soundstage that had the same depth and definition I am used to hearing from the front. I know that is the multichannel ideal, but up until that point it had not occurred to me that the soundfield could truly be seamless and three-dimensional around the full circumference of the system.
 
I asked McKiegan about the impressive performance of the Foundation, which resulted in a brief lesson about Krell's priorities—specifically, to treat each pair of adjacent channels as an engineering challenge, optimizing those preamps to match each other so they form a perfect envelope around the listener. When the balance between the channels approaches perfection, the audio illusion is seamless. Each "channel pair" in the system becomes its own discrete, high-end 2-channel system, with the same 2-channel qualities that audiophiles are always looking for—the sonic image from two speakers takes on a three-dimensional character, with each sound discretely rendered in its proper position.
 
Since a 7.1 surround system has seven channel pairs, there are seven stereo soundfields that ideally surround the listener seamlessly. That is exactly what I heard from the Foundation—a rendition of a key scene in Skyfall that was well beyond the capabilities of my Pioneer Elite SC-55 and 7.1 speaker system, which I used to re-watch the same scene later that day. The proof? Krell's Foundation-based system immediately triggered involuntary goosebumps—something that only happens to me when I listen to the very best high-fidelity systems.
 
I asked why someone would choose Krell for a surround preamp/processor in a world where there are many choices at every level of price and quality. The result was a lengthy discussion about the company's history, the state of 4K and HDMI, and why a Vizio E701i was used in the presentation.
 
Then there's the issue of room correction. Instead of using something like Audyssey or Trinnov, Krell designed its own algorithms from scratch for the Foundation. Why? As a rule, the company designs and engineers everything in-house, to its own extremely high standards. In this case, the result is called ARES—Automatic Room Equalization System. Here is what the company has to say about it:
Quote:
"ARES analyzes all the speakers in the system, their location, phase, and distance from each other, to determine the best crossover frequency, delay, and more. In addition, ARES incorporates the acoustics of the room to determine unique EQ curves for each of the 7.1 output channels. Unlike other room EQs, ARES can be programmed to only adjust the troublesome low frequencies, leaving high frequencies unaltered."
 
The Foundation is a decidedly premium product with a price to match: $6500. That is not quite unobtainium to a serious home-theater enthusiast, but at that price point, there is concern about the risk of becoming obsolete, especially since audio and video standards keep evolving. I asked McKiegan how Krell would deal with future changes in video technology, and I liked his answers.
 
I mentioned that the home-theater market is poised on the edge of a revolution in resolution. 4K is on the way, and HDMI standards will need to be updated to accommodate 4K at higher frame rates than 30p. What happens when that day comes? McKiegan assured me that Krell could upgrade the video components, prompting a discussion of the company's long history of updating and upgrading gear as technology progresses. Faced with evolving standards, buyers of the Foundation will likely have the option of upgrading the existing unit or trading it in toward a newer model that includes the updated components.
 
So what else sets the Foundation apart? First and foremost is an all-balanced output stage—7.1 channels of it, with two summed subwoofer outputs. Another very nice feature: All ten HDMI inputs are concurrently active, so switching between them is instantaneous. Two-channel audio aficionados can also take advantage of a stereo preamp mode, featuring a dedicated all-analog signal path. 
 
More than anything else, the new Foundation amazed me with its fidelity, which has always been Krell's mission—to deliver the ultimate in sound quality. In my conversation with McKiegan, he touched on the past and future of high-definition audio. SACD and DVD-Audio are simply not mainstream products, but Blu-ray discs with uncompressed high-resolution audio sell in every Wal-mart, Target and Best Buy across the nation. The vast majority of audio equipment is ill equipped to extract the total fidelity found within these high-resolution yet ubiquitous soundtracks. Krell's Foundation brings the listener closer to that ideal than any 7.1 AV processor I have heard to date.
 
The fact it's priced at the same level as moderately expensive projectors and speakers makes Krell's AV processor a relative bargain for the sound it produces. The Foundation is a fantastic 7.1 AV processor from a company with a long record of accomplishment, producing some of the best solid-state electronics in the entire audio industry. The Foundation deserves an audition from anyone who is truly serious about home theater and considers it to be within his or her budget. 
"Super fine and detailed, the Foundation made the instruments appear on a deeper stage and at the same time experience Al Jarreau's vocal artistry to the fullest."
Heimkino.- leading home theater magazine,
The first Foundation processor review has appeared in the June issue of Germany's leading home theater magazine, Heimkino. They awarded the Foundation their reference level rating of 1+. Below are some of the translated highlights -
 
"Super fine and detailed, the Foundation made the instruments appear on a deeper stage and at the same time experience Al Jarreau's vocal artistry to the fullest."
 
"The fine pins and needles on the skin where get even more intense, when the Foundation played the first scenes of "Battleship" and "Django Unchained" where it reveals all of its capability repertoire: ranging from extremely delicate to smashing, the processor was able to let the listener enjoy all aspects of home cinema in the finest sound quality."
 
"The Foundation offers Stereo and Multi Channel par excellence and absolute home cinema delicacy. I am convinced, if you listen to the Foundation for the very first time, you will experience that special tingling feeling, and realize, what is possible in your home cinema with the Foundation."
KRELL DUO 300 - Winner of Hi-Fi News Editor’s choice award
Ken Kessler

The Krell showed blissful attack with authentic decay, and just the right amount of dryness with the percussion that opens ‘Up On Cripple Creek’. It picked up the snap of the percussion, the kick-drum air movement, with true ‘feel’. Yeah, this is a Krell, alright.

Salvation came from Lou Rawls’ At Last [Blue Note], a bit of recording perfection. It was suitably silky, Rawls’ vocals were languorous perfection, while Dianne Reeves sang as clear as a wine glass from Zalto.

Krell’s new iBias range is claimed to be more efficient, or less power-hungry, than pure Class A. Paul Miller suggests that iBias is a modern take on the popular sliding bias circuits of the 1980s. So what is the motivation for it?

Statements from the company suggest that Krell is doing its part to modernise the high-end, to increase its appeal to audiophiles who are not comfortable with bulky intrusions into their living spaces in a manner acceptable in the past. And yet nothing differentiates the Duo 300, physically, from hundreds of other ball-buster amps.

It’s a big, metal-cased block, with the usual back panel fittings. Yes, the styling is tasteful – but there’s only so much you can do with an amplifier’s looks. This is a Krell by any name and any measure. Which is as it should be.

What does differentiate the Duo 300 and its siblings from the mainstream – though other companies are fitting web links, too – is the Ethernet connection, so each amplifier can be accessed on its own web page through any device that can run a browser, eg, an iPad.

The user can then view heatsink temperature, fan speed and other information. This will also provide alerts for conditions like overheating, fan failure and shorting of the output terminals.

Blissful attack

Finding something suitable to play through the Krell for the crucial, initial impression, we chose vinyl in the form of The Band’s eponymous second LP on MoFi. In part, it’s because of the astonishing bass and that incredible drum sound, but primarily because we love the album, period!

The Krell showed blissful attack with authentic decay, and just the right amount of dryness with the percussion that opens ‘Up On Cripple Creek’. It picked up the snap of the percussion, the kick-drum air movement, with true ‘feel’. Yeah, this is a Krell, alright.

Lou Rawls’ At Last [Blue Note], a bit of recording perfection. It was suitably silky, Rawls’ vocals were languorous perfection, while Dianne Reeves sang as clear as a wine glass from Zalto.

If we seem to lack just a little in enthusiasm here, it’s only because the last Krell product we reviewed blew us away: the astonishing S550i integrated (so it should at 500w! - model since discontinued) 

The Duo 300 is certainly a good amp, but our exposure to assorted Constellation masterpieces and six months with a D’Agostino Momentum Stereo – all much more expensive than a Duo 300 (at 3 to 5times the price!) – have altered expectations of modern solid-state amplification, regardless of the Class of operation, price, or any other respects.

Consider, though, that the Duo 300 is an easy product to live with in many ways, not least the cool running and easy set-up. Moreover, there is a bonus for those who harbour insecurities about massive high-end power amps, thanks to its on-line nanny.

Verdict

Assuredly solid-state in its demeanour, Krell’s Duo 300 doesn’t, for a moment, suggest the (sonic) warmth of a true Class A amplifier likes its ancestors … which may be music to the ears of those who can’t abide ‘valveness’.  this one is for rockers.

.....Ken kessler

If you’re in the market for a new amp and are a member of the cost-is-little-object crowd, definitely check out the Chorus amps from Krell. You won’t be disappointed.
David Vaughn
AT A GLANCE 
Plus 
A new take on amplifier classes with iBias
Superb dynamics and soundstage
Ethernet capability for system monitoring 
Minus 
LED illumination too bright 
Heavy (thats part of the reason why it works so well)
 
THE VERDICT 
Krell’s iBias technology has allowed them to deliver the benefits of a Class A multichannel amplifier in a way that will have audiophiles grinning from ear to ear.
Do you remember what it was like sitting for your high school or college lessons? Well, get ready for a trip down memory lane, because to give the Krell Chorus 7200 (Chorus 4200 & 5200 are similar) the praise it’s due and explain just how much this “little”-amplifier-that-could is going to change the audio industry, we’ll need to start with a short class in “classes.”

There are many different established amplifier topologies out there, designated by class, as in Class A, B, A/B, D, G, and H. Each has its own set of plusses and minuses, but in the audiophile world, Class A has always been king for a variety of reasons. First and foremost is sound quality, which is virtually unmatched to those with golden ears—those things attached to the sides of your head, not the speaker company that Darryl Wilkinson always raves about. Audio signals are basically alternating current—the sine waves you learned about in grade school—with both a negative and positive voltage. Remember, the goal is to make a loudspeaker diaphragm move out (positive voltage) as well as in (negative voltage). The Class A amplifier has the ability to conduct the full audio signal, both the positive and negative portions of the cycle, on each output device, reducing distortion in the process.

Unfortunately, there’s no such thing as a free lunch. There’s one negative—and it’s huge: Class A’s efficiency is about as green conscious as a Lear jet carrying one passenger across the country. A pure Class A design has the output transistors operating at full power all the time; they’re never idle. This means any energy not required to drive the speaker is released through the amplifier’s heatsinks, turning the amp into a power-wasting space heater. Furthermore, the ability to place multiple channels in the same chassis is all but impossible due to the heat buildup, which has essentially shut out the technology for the majority of home theater installations.

What Exactly Is iBias? 
Krell’s audio legacy is built upon Class A amplification, and it’s no surprise that their engineers have been able to develop a patent-pending circuit delivering traditional Class A–like operation without the excessive heat and wasted energy of conventional Class A. Furthermore, the design can be housed in a form factor fit for home theater applications. It’s called iBias, but a better name may be iReallyLikeIt!

Krell’s innovative iBias technology allows the amplifiers to run in full Class A mode as needed, while at the same time minimizing heat generation. Krell isn’t the first to attempt using a “tracking” or “sliding” bias that reacts based on the nature of the audio signal, but their approach is quite different. In the past, the tracking monitored the incoming signal and set the bias based upon this information. The iBias technology takes a different approach by calculating the bias from the output stage; it directly measures the output current of the amplifier and adjusts the bias to the optimum level. Because iBias measures the output current, the real-time demands of the specific speaker connected to the amp are directly incorporated into the circuit function. The amplifier monitors the load, accounting for the variables present at any given moment, rather than blindly reacting to the incoming audio.

The president of Krell Industries, Bill McKiegan, likes to compare this technology to a 12-cylinder automotive engine, which shuts down some of the cylinders when you don’t need a lot of power. But when you slam the accelerator to the floor, the engine can deliver 600 horsepower—or more—almost instantly. iBias works virtually the same way. It can be cruising along in efficiency mode yet in a matter of microseconds give you hundreds of watts of full Class A amplification for musical peaks or when the action kicks up in the latest Hollywood blockbuster.

With this new topology comes other benefits. Krell has been able to fit seven channels of amplification into a relatively small—though extremely heavy—rack-mountable chassis, making iBias practical for use in environments where a traditional Class A amplifier would be too large. That’s not to say the Chorus doesn’t generate heat; it certainly does. Krell cools the amplifier using thermostatically controlled fans, which are generally eschewed by audiophiles and home theater aficionados. Still, in all of my testing, I was never able to detect any audible noise from the four fans on the rear of the amp, and the output temperature measured with an IR thermometer never exceeded 115 degrees F, even under the most strenuous tests.

Oh, My Aching Back 
I was out of town when UPS delivered the amp, and the arduous task of bringing the 100-pound beast (110 including packing materials) fell to my 16-year-old son and one of his friends. It took two strapping teenagers to get this baby into the house, and while it’s not the heaviest amp I’ve reviewed, it certainly is one of the most dense, and getting it into the rack was a serious chore.

Aesthetically, the Chorus 7200 is quite beautiful, as far as black boxes go. The front façade is matte black highlighted by a silver band running vertically through the center of the facing, where a backlit Krell logo protrudes slightly from the box. The left side features a small circular power button, while the right has a rectangular LCD that gives you the amp’s IP address when it powers up.

Yes, I said IP address. You see, the rear of the amp has all the connections you typically see on an amplifier: both balanced and unbalanced inputs for all seven channels, the aforementioned fans, a 12-volt trigger input, a detachable power cord, a master power button, and, unusually, an Ethernet port.

Why put Ethernet in an amplifier? In this case, the amplifier can be accessed through any device that can run a Web browser, such as a smartphone, tablet, or computer. Using the interface, you or your dealer can monitor the heatsink temperature and fan speed, as well as configure the unit to send out e-mail notifications (up to three addresses) if its onboard diagnostics detect any faults. Furthermore, if there’s ever a software upgrade for the amplifier, you can have the amp update its software from the Krell servers with the push of a button.

The Fun Begins 

Once I installed the seven-channel Chorus 7200, I hooked it up to my Marantz AV8801 surround processor and calibrated the sound levels to my speakers: three M&K S150s across the front, four M&K SS150 surround speakers, and two subwoofers—a brand-new HSU VTF-15H MK2 situated at about the midpoint of my right wall and an SVS PC-Ultra sitting in the front left corner of the room.

I lived with the Krell for a few days before really putting it to the test, but I was impressed by its neutral tonal quality out of the gate. Not too bright, not too laid-back. When I finally sat down for some critical listening, I truly started to appreciate how sweet this amp sounded.

I began with an eclectic collection of SACDs, including the Telarc SACD Sampler 1 recording of “Moanin’ ” by Monty Alexander from his Monty Meets Sly and Robbie album. This jazz-meets-Jamaica recording features Alexander gracefully moving his fingers across the keys of a Yamaha grand piano while a smooth rhythm section plays in the background, with Sly Dunbar on drums (and riddim) and Robbie Shakespeare on bass. The song is a lot of fun, with Monty’s piano slightly left of center, Sly’s drums to the right, and Robbie’s tight bass filling the room. Every strike of the piano is clean, and the midrange is full of body. As I pushed the volume higher and higher, the instrumental track never strained the amplifier, and it was able to resolve all of the detail in the music without any obvious coloration.

I could say the same for a number of Red Book CDs ripped to FLAC files on my home server. The Spin Doctors’ “Two Princes” is lyrically challenged for sure, but I’ve always enjoyed the rhythm of the track, especially the percussion beat that opens the song and the guitar solo midway through that instantly transports me back to my early 20s. Wow was the first thought in my mind as the drums kicked to life. Was the band playing live in my room? My reference Parasound Halo A 51 amp is a Class A/B that operates in Class A mode up to a few watts, but I can’t say that I remember this recording sounding quite this crisp and clean, with the voices projecting well into the room and the guitars layered in the background.

Class A amp makers tout their products’ ability to re-create voice, and here the Krell truly shined. Take the start of fun.’s “Some Nights,” where Nate Ruess’ voice kicks off the song with a catchy ballad-like opening that transports you back in rock history to harmonies from groups such as Queen and Styx (those bands also shine on the 7200). With this amp in the chain, Ruess’ melody came alive with seemingly limitless dynamics, a 3D-like soundstage, and amazing detail.

This dynamic performance was readily apparent with every Blu-ray I threw at the Krell. The beach landing in Saving Private Ryan exploded into my room, with each discrete effect placed precisely in the soundstage. And the 7200 brought an uncanny immediacy to softer passages, such as the opening monologue recited by Morgan Freeman in Clint Eastwood’s Million Dollar Baby, where it truly sounded as if Freeman was sitting in the room with me describing Frankie Dunn’s personality and why he wouldn’t train girls to fight. Impressive is an understatement.

A Strong Foundation 

I spent the vast majority of my review time using my reference Marantz surround processor, but Krell really wanted me to pair this fantastic amplifier with their entry-level Foundation surround processor ($6,500, an S&V Top Pick of the Year, reviewed April 2014). Michael Fremer raved about the Foundation’s prowess in his review, and I have to concur 100 percent. As good as the Chorus 7200 sounded with my Marantz, the Foundation took it up a notch, and I now have some serious processor envy and a strong case of upgrade-itis due to this combo’s audio muscle. The Foundation isn’t the most ergonomically friendly processor I’ve ever used—setting it up was about as much fun as a root canal—but it’s by far the best-sounding. The soundstage is incredibly convincing: You can’t really tell where the speakers are in the room, and the subwoofer integration is by far the best I’ve ever experienced. Like Michael, when I put my Marantz back in my rack, I felt like I needed a prescription for Prozac to fight the depression I was facing.

Putting It Into Words 

The hardest part of reviewing audio equipment is putting what you hear into words that can impart upon the reader just how impressive (or uninspired) a particular piece of equipment was to your ears. In the case of the Chorus 7200—and Foundation—it was six weeks of audio bliss for me and my family. My son actually sat on the couch with me to listen to music because it had never sounded so alive, but when I broke the news that the processor/amp combo cost $16,000, he knew instantly our days of audio bliss were numbered.

The only complaint I have about both the amp and processor is the non-dimming backlight that hides behind the Krell logo on each unit. When I was listening to music, they didn’t bother me one bit, but when the room lights were off and I was trying to watch a movie, the blue LEDs were so bright that I thought they might be able to lead a wayward ship into port after a long journey at sea.

The Chorus 7200 isn’t cheap by any means, but its iBias technology delivers bliss for a relatively low cost per channel when compared against the cost of traditional high-end Class A amps. If you’re in the market for a new amp and are a member of the cost-is-little-object crowd, definitely check out the Chorus 7200 from Krell. You won’t be disappointed.

I've never encountered another amp that combines the Solo's 375 warm, wonderful, involving sound with such a practical and versatile design.
Brent Butterworth

REVIEW SUMMARY: Spending this sort of money on a pair of mono-block amps is a lot, but the Solo 375 delivers a lot. It combines a very smooth, un-solid-state, un-hifi sound with loads of power and dynamics, plus a design that works great whether you're plopping the amps on the floor by the speakers or shoving them out of sight into a closet or equipment cabinet. In fact, I'd go so far as to say I've never encountered another amp that combines the Solo's 375 warm, wonderful, involving sound with such a practical and versatile design.

EXTENDED REVIEW: The Krell Solo 375 mono block demonstrates how the amplifier business has exploded with classes, so many classes that even people in the audio industry often get them confused. Twenty years ago, almost everything was Class AB or Class A. Now it's also common to see Classes D, G, and H. We also see "made up" classes--marketing terms rather than official designations--such as Class I, Class T, and Class AAA. We can find most of the above classes executed with compact, efficient switching power supplies or with traditional analog supplies using transformers and big storage capacitors.

What's the best? That depends on how you define "best," but audiophiles generally believe Class A delivers the best sound quality. With Class A, the amp's output transistors or tubes never switch fully off, so there's no crossover distortion--that ugly, high-frequency artifact caused when an amp's positive-polarity transistors or tubes hand off the signal to the negative-polarity transistors or tubes.

Why isn't everything Class A, then? Because Class A wastes a lot of power. It dissipates the entire output of the amp's power supply either as sound through the speakers or as heat through the amp's heat sink...but mostly as heat, which makes it impractical to use Class A amps in places where heat can build up, such as in equipment cabinets or closets.

Krell's Solo 375 and the other amps in the company's new iBias Series adapt Class A to a world in which electronics power consumption is an increasing concern and the desire to hide the electronics is a top priority for many customers. The iBias technology uses a Class A output stage in which the bias--the ever-present voltage that keeps the transistors turned on all the time--is continuously adjusted so there's only as much as needed for the signal the amp is playing at that moment. Thus, there's not that huge amount of excess power that must be dissipated as heat. Power consumption is lower, less heat sinking is needed, and the amp can be made smaller. Assuming the circuit that controls the bias works as intended, the iBias amps should give you all the sound quality of Class A with none of the drawbacks.

If this technology sounds vaguely familiar, it should. It's similar in ways to Classes G and H, which use a "tracking" power supply that reduces voltage at lower signal levels but typically employ a Class AB output stage. A few years ago, Sony introduced a high-end Class A amp with a tracking power supply.

However, Krell's iBias approach is different. Rather than using the input signal to adjust the bias or the power-supply voltage, iBias tracks the output current. The advantage of this approach is that iBias can optimize the amp's performance for your specific speakers, rather than for an assumed speaker load. Even though iBias should result in more accurate optimization of the amp's operation--cutting the bias "closer to the edge," if you will--my assumption is that Krell chose to supply a comfortable margin of bias voltage to the transistors. Why do I guess that? Because despite the Solo 375's large chassis, it has cooling fans: two thermostatically controlled, low-RPM fans that are managed so that their sound should be inaudible. Clearly there's some wasted heat being generated.

Krell-375-mono.jpgNot only is the Solo 375's amplification technology innovative, but its control system is, too. If the amp is wired to an Ethernet network through the RJ-45 jack on the back, you can access a web page for each amp. The web page shows current operating temperature, fan speed, overload conditions, etc.

The Solo 375 is rated at 375 watts into eight ohms and 600 watts into four ohms. The iBias line also includes the 575-watt Solo 575 mono block, as well as two-, three-, five-, and seven-channel models. All use a similar chassis design, and all can be rack-mounted.

All of the amps in the line use fully balanced, fully complementary circuits through the entire audio path. In essence, each circuit comprises two "mirrored" halves, one of which operates on the positive half of the audio signal and the other on the negative half. This is the way most of the bigger, more expensive high-end solid-state amps are made; it reduces noise and improves the slew rate (the speed at which the amp can go from zero volts to full output).

The Hookup

The moment I unpacked the first of the pair of Solo 375s I received for review, it immediately became my favorite Krell ever. Or at least, my back's favorite Krell ever. Despite its bulk, it weighs just 60 pounds.

For some audiophiles, this will be a problem. Krell has built its history on amps with back-breaking weight, and some Krell enthusiasts cherish the fact that their amps require two strong people to lift. When a visiting headphone manufacturer saw the two Solo 375s on my floor, awaiting setup, he picked one of them up, and an immediate look of shock crossed his face. "That's a KRELL?" he blurted. I explained the whole iBias technology and pointed out the fans, but he just rolled his eyes. I've seen at least one other audio reviewer express similar sentiment.

I put the Solo 375s on thick MDF platforms to elevate them above my carpet. I connected them to two different pairs of speakers: my usual Revel Performa3 F206 towers and my cherished Krell Resolution 1 towers. I don't often use the Resolution 1s because they weigh 200 pounds each and are thus impractical to move in and out of my system often, but I thought the occasion merited the effort.

The Solo 375s got their signals primarily from a Krell Illusion II digital preamp, using either a laptop computer or a Music Hall Ikura turntable (with an NAD PP-3 phono preamp) as the source--mostly the former, using my own ripped WAV files or tunes streamed from Tidal. I used balanced professional Canare Star Quad XLR cables to connect the preamp to the amp and AudioQuest CinemaQuest 14/2 speaker cables.

The whole time I used the Solo 375, including some crank-it-up rock listening sessions and a couple of action movies, I only ever heard the fans when my ears got within a couple feet of the amp.

Performance

I've never been a Diana Krall fan, but it's hard not to be captivated by Wallflower, her new album of covers of classic rock tunes. In just the first 20 or 30 bars of her take on Elton John's "Sorry Seems to Be the Hardest Word," I learned a lot about the Solo 375. I was struck by how intimate and warm Krall's voice sounded. She sounded like she was right in the room with me, about eight feet away, with very little ambience. In fact, based on her voice, I'd almost have thought someone deadened up my listening room with about 30 square feet of Sonex foam. But the instruments sounded huge and spacious, much as in Elton John's original recording. The spaciousness didn't sound like the result of exaggerated treble or phasiness, and it rarely produced a "wow" reaction from me; it merely sounded natural. In terms of sheer involvement, this was a higher level than what I'm used to hearing from my Revels.

You're probably sick of hearing the Mark Ronson/Bruno Mars tune "Uptown Funk," but it happened to come up on the home page of the Tidal app, so I played it just out of curiosity. It'd be easy to dismiss this as insubstantial pop fluff; but, through the Solo 375 and the Resolution 1 speakers, I could hear that it's actually a musical and sophisticated production. The Solo 375's sound suited Bruno Mars' voice, which is smooth but not deep and thus might sound grating through some amps. Through the Solo 375, it sounded positively liquid, yet there was nothing soft about the bottom end; the Solo 375 kept each Resolution 1's dual woofers in perfect control, producing tight, deep, powerful bass tones. Again, the unexaggerated, natural-sounding spaciousness pulled me in. 

Based on these and some cuts I'd heard before, I was starting to wonder if the Solo 375/Resolution 1 combo could conjure a really huge sense of space. I found out fast when, on its own, Tidal went straight into Mars' "Locked Out of Heaven." The tune's background vocals almost literally jumped out of the speakers, actually seeming to come from behind me. This is a pretty easy trick for big panel speakers like MartinLogans and Magnepans, but not many systems using conventional dynamic drivers can so convincingly wrap sound around you.

Having heard enough pop singers for a while, I shifted over to one our greatest anti-pop singers: James "Blood" Ulmer. Ulmer's Odyssey album is an idiosyncratic masterpiece, consisting only of drums, violin (often played through a wah-wah pedal), hollowbody electric guitar (with all the strings tuned to A), and Ulmer's inimitable vocal stylings. The Solo 375 got all the spacing right, the natural reverb of the space in which the drums were recorded contrasting perfectly with the much more intimate sound of the close-miked vocals and the reverb-soaked violin lines. Ulmer's vocals also sounded just right: smooth and soulful, but with that little trace of edge that makes Blood Blood. (BTW, I've seen Ulmer live more than any other artist, in widely varying venues and numerous musical settings, so I'm pretty familiar with his sound by now.)

Not surprisingly, the Solo 375 sounded great with rock, too. R.E.M.'s "Pilgrimage," from Murmur, the group's first full-length album, isn't something anyone would mistake for a Led Zeppelin or Deep Purple tune, but all the elements are there: a dynamic, insistent drum sound with a huge-sounding snare and a powerful vocal performance backed by highly reverberant background vocals. (OK, so it has chimes in unison with the guitar. That doesn't mean it's not rock.) The spaciousness that worked so well for the other recordings came through on "Pilgrimage," too, and I especially loved the power of Bill Berry's kick drum and the way his firm snaps of the snare drum came through with loads of dynamics but not a track of edge.

Basically, the Solo 375 sounded like the world's most powerful tube amp. The tonal and spatial character, combined with the warmth of the mids, reminded me of some of the big push-pull tube amps with quartets or octets of KT88 tubes. By and large, that's a good thing.

The Downside

One of the things that made the Solo 375 remind me of a tube amp is that the top end is smooth and not in any way "hifi sounding." Personally, I like that. But I know some audiophiles don't--they want to hear every last little detail in a recording, even if they need a somewhat elevated or edgy treble to get it. If that's you, that's okay. In audio, you gotta go with what makes you happy. Just know that, if what makes you happy is a lot of treble detail (apparent or actual), the Solo 375 probably isn't your amp.

Comparison and Competition

I had a chance to compare the Solo 375 with a couple of other big solid-state amps: Classé Audio's CA-2300 and Pass Labs' X350.5. The latter, incidentally, runs in Class A for the first 40 watts; so, for all intents and purposes, it's almost always running in Class A and thus makes an interesting comparison for the Solo 375. Using a one-kilohertz test tone, I matched the amps' output levels within ±0.1 dB and connected them all to the Resolution 1 speakers.

A particularly illuminating track for comparing almost any kind of audio gear is Trilok Gurtu's "Once I Wished a Tree Upside Down," a light saxophone melody backed by shakers, tabla, and synthesisers. In the intro, the shakers swirl around your listening room; the degree to which they wrap around my listening chair is one way I judge a system's soundstaging capability. With the CA-2300, the treble sounded wonderfully detailed and delicate, but the action all seemed to be taking place in front of me rather than around me. With the X350.5, I got a greater sense of spaciousness and wraparound, but the treble didn't sound as smooth as with the Classé or the Krell. The Krell got the spaciousness just right, but because its treble was smoother/softer, it didn't have quite that level of excitement that the others did. 

I listened to some more jazz and pop cuts through all three amps, but the comments were the same thing over and over. All three had ample dynamics and bass; it's mostly the character of the treble and the spaciousness of the sound that varied. Which one will you like better? That depends on your personal taste. But if smoothness and spaciousness rank high on your list of priorities, the Krell seems like the best bet to me.

Conclusion

Spending this sort of money on a pair of mono-block amps is a lot, but the Solo 375 delivers a lot. It combines a very smooth, un-solid-state, un-hifi sound with loads of power and dynamics, plus a design that works great whether you're plopping the amps on the floor by the speakers or shoving them out of sight into a closet or equipment cabinet. In fact, I'd go so far as to say I've never encountered another amp that combines the Solo's 375 warm, wonderful, involving sound with such a practical and versatile design.

I've heard in most amplifiers. For those who seek the best quality in amplification for their home theaters, the Krell Theater 7 sets a new standard at this price point.
Myron Ho

CONCLUSION: "While the Krell Theater 7XD is not a traditional Class A amplifier because of its dynamic bias, the Krell Theater 7 sounds more like Class A than I've heard in most amplifiers. For those who seek the best quality in amplification for their home theaters, the Krell Theater 7XDsets a new standard at this price point. We all like a good comeback story, and the Krell Theater 7XD certainly is setting up a nice future for this lauded brand.” - 5 STAR PERFOMANCE RATING

EXTENDED REVIEW: "Krell has had its share of ups and downs in the past few years, and not just of the managerial sort that recently resulted in recent new management and a solid attempt at reinvigorating the brand. Nearly a decade ago, the company made quite the statement amongst its better-heeled, die-hard with its $30,000 Evolution 707 AV preamp and similarly priced associated amplification. It also more recently launched the Foundation line, which represented a new strategy of bringing Krell's inimitable build quality and performance to a larger pool of consumers at more attainable price points.

At its heart, though, Krell has always been a company whose reputation lay not just with its build quality, but also its technology. Technology like Class A iBias topology, for example, which first debuted in Krell's new flagship and Chorus line of amplifiers as a novel way to provide coveted Class A sound quality while dealing with the topology's known issues: excessive power consumption and heat dissipation. The new Krell Theater 7 seven-channel amplifier benefits from a trickling down of that technology to a lower price point. At $7,500 retail, the Theater 7 is Krell's entry level seven channel amplifier. Total output is rated at 120 Watts per channel RMS into 8Ω with two channels driven and 105 Watts per channel RMS into 8Ω with all seven channels driven. With 4Ω loads, those numbers go up to 210 and 140 Watts, respectively.

Setup

As you might expect, given that the Theater 7 is a multichannel amp, setup isn't overly complicated. Analog inputs consist of seven XLR balanced or single-ended RCA connectors, and the outputs comprise seven sets of densely packed binding posts. The amp is reasonably beefy at 70 pounds, so you'll need to be careful not to stack it on top of other gear. And stacking other gear on top of it is an equally bad idea, as it needs some room to breathe.

Perhaps the most surprising thing about the Theater 7 is its Ethernet connection, which can be used to monitor the amp's performance and protection circuits, tweak presets like display brightness and timeout, mute individual channels, and update the firmware. You can also set up email alerts to automatically alert you or your dealer to issues pertaining to excessive current, overheating, short-circuiting, etc.

Performance

Krell is known for big, powerful, bass-forward amps, so my first question when sitting down to evaluate the Theater 7 was whether or not it could live up to that reputation at this lower price point. As such, I gave the Theater 7 a torture test right off the bat by playing some movies without a subwoofer and setting my Salk Signature Soundscape 12 speakers to full range. This effectively meant the 12-inch woofers on my Salks would serve as the de facto dual subs for the system, and the Krell Theater 7 would be driving that along with all the other channels simultaneously.

I pushed volume up to THX reference levels on exceptionally bass heavy soundtracks like The Dark Knight and Tron: Legacy. The bass sounded tight and well controlled with both explosions and percussion-heavy music, physically rumbling my innards. Simultaneously, dialog and music were crystal clear. At no point did I hear the Krell stress or strain, a true indicator of its top-shelf build quality and design integrity.

On multichannel music, the Krell offered a rich and refined sound, very much like a traditional Class A amplifier. Unlike many traditional Class A amplifiers, which can double as a grill for your steaks, the Krell was merely warm to the touch. As you would expect from Krell, there was no audible distortion, even with high-resolution music. The Krell Theater 7 was quite neutral sounding, but maintained a musicality that I found soothing.

High Points

The Krell delivers on the promise of Class A sound with little to no wasted heat.
The Krell Theater 7 has power and current to spare.
The Theater 7 delivers the build quality and fit-and-finish we all expect from Krell. That does make it more expensive than other brands' amps with similar performance, but it's nice to know that no corners were cut.
The inclusion of balanced inputs is very much welcomed. This could come in particularly handy if your amp is installed some distance away from your preamp, for whatever reason, or if you know you have issues with interference in your listening space.

Low Points

The Theater 7 could benefit from some built-in handles, the likes of which you find on other power amps of this heft. Beware lifting this behemoth without using your legs. Better yet, make your dealer install it. (really a bit old hat dont you think?)

Competition and Comparison

The ATI Signature 6007 amplifier costs $500 more at retail and will provide you more power still with all channels driven, should you need it. The ATI is a very nicely designed Class AB amp, so you'll be giving up on the warmth and purity of tone you'd get from the likes of this Krell or (at lower listening levels) Pass Labs, etc. The ATI also weighs 136 pounds, so unless you happen to be the reigning World's Strongest Man, you may find it difficult to install by yourself.

In Krell's own lineup, the Chorus 7200 costs $3,000 more, but offers an extra 100 watts per channel. The Monoprice Monolith 7 is a great value, being priced at a significantly lower $1,600 price point, but you will most likely find it doesn't quite rival the refinement and headroom of the Krell. It's great for the money, it's just not Krell great.

Conclusion

While the Krell Theater 7XD is not a traditional Class A amplifier because of its dynamic bias (iBias), the Krell Theater 7 sounds more like Class A than I've heard in most amplifiers. For those who seek the best quality in amplification for their home theaters, the Krell Theater 7 XD sets a new standard at this price point. We all like a good comeback story, and the Krell Theater 7XD certainly is setting up a nice future for this lauded brand.”

Awards

Hi-Fi Choice Best of the High End award - 2011

Krell is one of the defining high-end brands and the Cipher is a classic example of what it’s capable of when pulling out all the stops. This is a technological showcase that is designed to extract the absolute maximum from both CD and SACD, including multichannel discs. No expense has been spared on the lavishly finished casework, the extensive power supply arrangements and the very sophisticated balanced DAC arrangement. The result is a superlative performer.