Krell

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

THIS FAMOUS BRAND IS BACK IN NZ WITH THIER NEW "XD" SERIES CLASS-A iBIAS AMPS - A TOTALLY REVITALISED BRAND COMMITTED TO BEING LEADERS ONCE AGAIN - MADE IN THE USA

"After a few years spent flying under the radar, Krell is very much back in business. While the company's main focus has always been two-channel audio its also now a serious player in the multichannel game too. 

"It's hard to overstate the importance of Krell Industries in the history of high-end audio. Founded by Dan and Rondi D'Agostino in 1980, Krell was the audio equivalent of Lamborghini—an audacious riposte to more Ferrari-like rivals such as Mark Levinson and Audio Research. For almost three decades, Krell went from strength to strength, introducing a stream of ever more ambitious products that tested the depth of their customers' pockets, along with the strength of their audio equipment shelving. Then, starting around a decade ago, the brand slowly slipped off the radar screens of most audiophiles.

We now know that the D'Agostinos were the target of what Dan has described as a hostile take- over by a group of investors. The new owners were more interested in making a deal to put Krell-branded high-end sound systems in Acura cars than in pursuing the comparatively small home audio market. Before long, some products were being manufactured in China, and Krell's edge slipped away.

While Dan moved on with a new venture, Rondi D'Agostinos stayed on and fought for the company she had co-founded 30 years earlier, eventually succeeding in regaining control. Krell is now working to reestablish its brand as a world leader in a somewhat smaller, yet even more competitive, high-end audio market. 

Krell amplifiers have always been overstated in design and understated in their on-paper specifications. Back in the 1980s, we would talk about “Krell watts,” where the amp's massive power supply and conservative on-paper power rating meant that it could drive speakers in real world systems way beyond what the numbers would suggest.

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.

Krell newly revised 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 unrivalled 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 minimising 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 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.

Power Supply Highlights

Power supply technology has always been an important contributor to the Krell sound. The power supplies of our Krell iBias Class A amplifiers have been optimised for use with the iBias circuit. Depending on the model, up to four toroidal transformers feed amplifier modules that include the audio circuitry, rectifier, and power supply filtering mounted to an individual heat sink. This design shortens the electrical path from the power supply to the output transistors, reducing the overall impedance and allowing the circuit to respond faster and control the speakers even better and more accurately.

Unlike traditional Class A amplifiers, iBias Class A amps have a compact design that allows rack-mounting, making them ideal for custom installation as well as traditional audiophile systems. This convenient form factor is made possible through thermostatically controlled ventilation fans. The fans used are specifically chosen for quiet operation, and operate at the speed required to maintain the ideal internal temperature. They run only during periods of peak energy demand - when the music is at its loudest - so they are inaudible in normal use.

Network Connectivity

The new amplifiers include RJ 45 Ethernet connectivity and an internal web page that is accessible from any smartphone, tablet, or laptop. Network connectivity brings convenience, monitoring, and reporting to end users. Amplifier configuration options include display brightness and timeout. For energy conservation, the amplifiers can be programmed to power off at a preset time of inactivity. Individual channels can be muted and firmware updates can be initiated from the web server.

Once the amplifier is connected to a network router with Internet access, the amplifier's advanced protection systems are now viewable on an Internet-connected device. Excessive current, output DC, fan speeds, short circuit, and overheating are all monitored in real time. If an issue occurs, the fault is displayed on the front panel and reported on the web server interface. Emails will automatically be sent to as many as three email addresses to notify the end user and/or the dealer of the condition.

Circuitry Highlights

The new iBias circuitry is built on a foundation of core Krell circuit technologies. All signal gain is realized in the current domain using proprietary multiple-output current mirrors with extraordinary open loop linearity. Each amplifier channel uses all discrete components. There are no generic integrated circuits or op amps used anywhere. Gain is distributed among several stages, allowing each to have a large linear operating area.

Audio signal voltages are converted to current at the amplifier input, and the audio signal remains in the current domain throughout the entire amplifier.

Current mirrors in the final gain stages use a new output power device that operates at a 73% higher voltage, delivers almost 10% more current, and offers 120 watts of additional power handling capability as compared to other devices.

With this combination, the iBias amplifiers may now deliver substantially more power while using a smaller footprint. Normally used in demanding, high-bandwidth video circuits, these transistors allow the design of gain stages with superb accuracy and very low distortion. The signal path is fully complementary and fully balanced from input to output. Independent complementary pre driver and driver stages for the positive and negative output transistors make the output stages extremely fast and linear. This unique circuit is impervious to low-impedance or reactive loads; it simply drives any loudspeaker with absolute confidence, achieving the very best possible sonic results.

Most amplifiers use coupling capacitors in the signal path to block DC and prevent damaging offset voltages from reaching your speakers. Krell amplifiers are fully direct-coupled, with no capacitors in the audio signal path. This design gives the Krell amplifiers lower internal impedance, which allows firmer, more precise control of your speakers. It also provides flatter, more extended low-frequency response, because coupling capacitors not only block DC but also affect the lowest bass frequencies. Krell employs expensive, non intrusive DC servos that remove DC without impacting the musical signal. Thus, the iBias Class A amplifiers deliver the full breadth of the music with detail, impact, and space intact.

Everything Audiophiles and Home Theatre Fans Could Want in an Amplifier

Krell iBias Class A amplifiers are the first to deliver the rich musicality of Class A amplifiers, the uncompromised dynamics of classic Krell amplifiers, and the efficiency and low power consumption of Class G and H amplifiers.

Because the iBias circuit eliminates crossover distortion, the amplifier is able to resolve more of the detail and micro-dynamics in even the best analog recordings. Simply put, the music breathes. Whether an iBias amplifier is called on to reproduce the extreme dynamic range of high-resolution digital files, the minute intricacies of a 45-rpm, 180-gram vinyl record, or the complexity of today’s latest blockbuster action film, it does so without altering or abating the music in any way.

The iBias amplifiers' unprecedented ability to retrieve the subtlest details gives their sound an incredible dimensionality, with an ambient, broad and extraordinarily deep soundstage. As spacious as the sound is, though, the amplifiers are still able to produce pinpoint stereo imaging if the recording calls for it.

It's all the power and control for which Krell has always been famous, with a level of resolution and musicality in the midrange and treble that has simply never been heard before.

In short, the new patent pending iBias Class A Krell amplifiers give today's audiophiles and home theater fans everything they could possibly want in an amplifier.

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

Testimonials

Featured

KL 03 IA K300D
NZ$ 15,995.01 (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...
I am writing this email to you while listening to our brand new demo KRELL demo K-300i Integradted...
KL 05 PA ILL2
NZ$ 13,995.01 (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...
EXTENDED REVIEW: The Illusion II preamplifier and power amplifier from Krell Duo 175 - The...
KL 12 AS D300
NZ$ 18,500.00 (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....
KL 19 PR FOUND
NZ$ 14,500.01 (incl. GST)
The 2013 New York Audio Show, held at The New York Palace Hotel, was practically bursting with...
KL 20 AV THEATRE
NZ$ 14,500.01 (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...

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$ 13,995.01 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...
When it comes to high-end solid-state amps, no manufacturer is more revered or influential than...
I am writing this email to you while listening to our brand new demo KRELL demo K-300i Integradted...
Integrated amplifiers
KL 03 IA K300D
NZ$ 15,995.01 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...
I am writing this email to you while listening to our brand new demo KRELL demo K-300i Integradted...
Integrated amplifiers

Preamplifiers & Line-stages

KL 05 PA ILL2
NZ$ 13,995.01 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...
EXTENDED REVIEW: The Illusion II preamplifier and power amplifier from Krell Duo 175 - The...
KL 06 PA ILL
NZ$ 28,995.00 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$ 11,500.00 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...
KL 11 AS D175
NZ$ 15,500.00 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...
EXTENDED REVIEW: The Illusion II preamplifier and power amplifier from Krell Duo 175 - The...
KL 12 AS D300
NZ$ 18,500.00 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$ 32,995.00 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$ 41,995.00 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$ 14,500.01 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$ 14,500.01 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$ 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...
KL 23 AV C5200
NZ$ 16,995.00 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$ 20,995.00 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.”

Given its power output, the Solo 575 might be a relative bargain.
Michael Fremer 

SUMMARY - REVIEW OF EARLIER VERSION, SINCE REPLACED BY NEW XD VERSION: The Solo 575s' taut bottom end produced always entertaining rhythmic drive and pleasing musical flow. Their punchy but nonaggressive top end was likewise fast, and the surprisingly silky ultratop, which appeared when least expected and was always very welcome, added to the endless excitement and strong listening involvement these amps produced in me

EXTENDED REVIEW: Class-A amplifiers have a well-deserved reputation for being power guzzlers that run hot enough to burn fingers. They're inherently inefficient because their output devices conduct full current at all times, and much of that current is dissipated as heat—requiring, in the case of class-A solid-state amplifiers, massive heatsinks. This is why class-A amps tend to produce relatively low power, and tend to be heavy and expensive to buy and run. And these days, energy inefficiency is out of fashion.

These disadvantages are the results of class-A's advantages: When output devices are biased for class-A operation, the crossover distortion normally generated as the signal swings from positive to negative and back is eliminated. And that, say class-A fans, is the source of the breed's magical sound, which is often described as smooth, rich, and coherent from top to bottom.

iBias

While class-A amplifiers figure prominently in Krell Industries' genome, the company has steered clear of them for a while—presumably for the disadvantages described above, and because those disadvantages make traditional class-A amplifiers impractical for home-theater-friendly, high-powered, multichannel systems. And I would guess that Krell isn't willing or able to invest in a separate line of mono or stereo class-A amps designed only for audiophiles.

A class-A amp that would be sensible for use in a multichannel system would have to produce a prodigious amount of power, be of practical size, consume little power at idle, and run relatively cool, eliminating the need for massive heatsinks; Krell's recently developed iBias technology (patent pending) appears to fulfill those requirements. iBias is conceptually similar to the sliding-bias or tracking-bias amps of the past—Nelson Pass's Threshold 800A of the 1970s might have been the first—in which input signal was monitored, and that information was used to adjust the bias voltage, all based on an assumed speaker load. Krell's iBias circuit is said to monitor the amplifier's output current, which the company claims is a far more precise and efficient arrangement because it measures the real-time demands of the specific speaker to which the amp is connected.

Krell uses iBias in a broad range of models: monoblocks, as well as amplifiers of two, three, five, and seven channels. The subject of this review, the Solo 575 is their most powerful iBias monoblock. In fact, the Solo 575 is unusually powerful for a class-A amp, outputting a claimed 575W RMS into 8 ohms or 900W into 4 ohms, yet weighing only 70 lbs and having no external heatsinks. Instead, heat is dealt with by four small, thermostatically controlled fans on the rear panel that exhaust through the top panel.

If you're skeptical about Krell's claim that a class-A amplifier of that size and weight can output that kind of power without heatsinks, you're not alone: If its bias voltage varies with demand, can it even be called a class-A amp? And does it sound like one? Maybe John Atkinson's measurements will offer an answer to the first question. I'm better qualified to answer the second.

Description

Aesthetically, the new Krell looks more like a conventional class-A/B amplifier. Rather than being housed in a milled-aluminum case with a thick top plate, the Solo 575 is wrapped in a thin, U-shaped cover—the kind usually found on better home-theater receivers and processors: That's a money-saver, as is the absence of heavy heatsinks along the sides. But the amp does have a thick aluminum faceplate, of the same (attractive) curved design used throughout Krell's line—including the superb-sounding Foundation surround-sound processor I reviewed in March 2014 for Sound&Vision. Like the Foundation, the Solo 575 has a somewhat dated-looking LCD screen, which displays the unit's IP address—more about that later—and alerts you to fault conditions. For those of you too young to remember, in the old days, amplifiers communicated problems like shorted speaker terminals with smoke signals and, sometimes, flames.

On the Solo 575's rear panel are single-ended RCA and balanced XLR inputs, excellent and easy-to-use WBT NextGen speaker binding posts, a power switch, a 12V Trigger input, an RJ45 Ethernet connector, and the aforementioned cooling fans, as well as Krell's proprietary CAST (Current Audio Signal Transmission) Lemo connector input, for use with Krell front-end components.

From input to output, the Solo 575's circuitry is fully complementary and fully balanced, and uses all discrete components. At the input stage, the incoming signal is converted to current by proprietary multiple-output current mirrors; from there on, all gain is applied as current gain. Throughput is direct-coupled—there are no capacitors in the signal path—for lower internal impedance and, according to Krell, more precise control of the speaker, as well as flatter and more extended low-frequency response. DC servos are used to remove DC from the output.

When I asked Bill McKiegan, president of Krell Industries, about the Solo 575's price which, despite the money-saving construction, he quickly cited the considerably higher prices of earlier Krell monoblocks; I would add that competing amplifiers that output far fewer watts but are housed in more substantial cases can cost upward of US$50,000/pair I've reviewed quite a few of those in the last few years. Given its power output, the Solo 575 might be a relative bargain.

Easy Setup

After connecting it to a network router—that's where the RJ45 jack comes in—and entering the amplifier's pre-assigned IP address from a Web browser on a computer or tablet, the Solo 575 user can access that amp's individual Web page. From there, the user can monitor the Solo 575's thermal status, as well as put it in mute and download software updates. The page can alert you to fault conditions, such as crossed speaker wires. Any detected fault automatically triggers an e-mail to Krell, who then enter the unit's serial number in their database and notify the dealer who sold it to you (as well as the many audiophiles at the National Security Agency).

I spent time driving the Solo 575s' balanced XLR inputs via the transformer-coupled XLR outputs of my darTZeel NHB-18NS preamplifier, but I did most of my listening with the darTZeel's single-ended outputs driving the Krell's single-ended inputs.

Take 1

I'm not biased for or against class-A amplifiers—or, for that matter, for or against class-A/B amps, though the latter are what I've mostly owned over the years. The solid-state class-A amplifiers of my experience have always sounded velvet-smooth, non-electronic, and often tube-like, though some have sounded softer than I like. It's easy to understand the enthusiasm for class-A among many audiophiles, especially in terms of sonic purity and an absence of electronica.

I put on a recent vinyl edition of Eiji Oue conducting the Minnesota Orchestra in Copland's Symphony 3 and Fanfare for the Common Man (200gm LP, Reference RM-1511)—a recording with enormously dynamic, well-extended, texturally supple, room-rattling bass-drum thwacks. I immediately heard a muscular, well-textured bottom end as the Solo 575s exerted a superior grip on the woofers of my Wilson Audio Specialties Alexandria XLF speakers, compared to that of my reference DarTZeel NHB-458 monoblocks. The weight and power of the Krell amps were undeniable: They had a bottom-end whomp that reminded me of Bel Canto Design's $50,000 Black amplification system—and that's a compliment.

I had used the Copland LP to evaluate the Swedish Analog Technologies tonearm through my darTZeel amps, and while that bass was impressive in every way, the Solo 575s' transient slam and grip on the Wilsons' woofers took it to another level of excitement. Put it this way: The SAT arm's contribution to the sound of my system was like adding a subwoofer; with the 575s in the system, it was like adding a second sub—or even a third—so powerfully deep, throbbing, yet well controlled was the bottom end. There wasn't more bass; instead, what bass there was was just better controlled and better damped.

The overall sound was definitely drier than the darTZeels, but this was still at the very beginning of my listening. I decided to stop analyzing and instead just listen for pleasure—the way I used to before this became a job—to find out if my auditory pleasure zones would, over time, connect with the sound of my system as driven by the Krells: something that did not happen with the Bricasti Design M28 monoblocks (US$30,000/pair).

I pulled out some of the many thousands of LPs I have that have never been played. One was a still-sealed copy of Music of Lodovico Giustini, Volume I, Performed on the 1720 Cristofori Pianoforte at the Metropolitan Museum of Art by Mieczyslaw Horszowski (LP, Titanic Ti-78, footnote 1). Obscure? Yes! But here's a "harpsichord with hammers" that has no pedals and thus no pedal-actuated sustain. This perfectly quiet pressing (after an ultrasonic cleaning) of a wonderfully dry yet tactile recording, made in the museum's André Mertens Galleries for Musical Instruments, brought the performance to life in my room—and from Horszowski's perspective.

The Solo 575s and the SAT tonearm were made for that instrument's rich, powerful lower register and its paucity of sustain, which were reproduced with unflinching control and solidity. The sonic integrity seemed well maintained up and down the keyboard, and was free of electronica.

Next up were Mozart's four horn concertos, with Lowell Greer playing a valveless natural horn (made in 1987, after an 1818 original made by Raoux, in Paris), and Nicholas McGegan leading the Philharmonia Baroque Orchestra, recorded in the chapel of San Francisco's Lone Mountain College (LP, Harmonia Mundi USA HMU-7012). The recording engineer was Wilson Audio Specialties' Peter McGrath, who was then still recording in the analog domain. (He now makes digital recordings in high-resolution surround sound.) Mastering was by the late, great Doug Sax at the Mastering Lab. I didn't know either man was involved before I removed the shrink-wrap. That's part of the fun of collecting records.

Through the Krells, Greer's horn had a warm, vivid, pleasingly soft sound, its image suspended between the speakers in a soundstage of moderate depth. The other horns, woodwinds, and strings were also nicely rendered, producing an enveloping and satisfying listening experience.

I then compared an original pressing of Neil Young's On the Beach (LP, Reprise R 2180) with the reissue included in the boxed set of Young's Official Release Series Discs 5–8 (4 LPs, Reprise 535704)—initially not to test the Krells, but as part of a review of the Young set. Chris Bellman had cut the new LPs from the analog master tapes (which I saw, stacked behind the board, during a visit last year to Bernie Grundman Mastering). I focused on one of Young's most elegant melodies: "See the Sky About to Rain." It opens with a tremoloed Wurlitzer electric piano laying out the chords, followed by a pedal steel guitar in the right channel, and a thick-sounding drum kit centered behind Young's voice.

Both versions sounded better than I'd ever heard them. What I learned was that the original pressing's richer sound came at the great expense of image precision, focus, and clarity. The reissue put all of the instruments and voices in far more precise focus, though the warmth of Young's voice in the original was now somewhat harsher. The bottom end had greater punch and precision. Though I found the reissue better focused overall, especially the drums, I could make a case for either pressing and both demonstrated that the Solo 575 didn't produce the velvety transients and textures I expect from class-A. With both pressings, the cymbals sounded neither romantic nor soft. In fact, they were a bit crunchier than I'd expected.

Class-A with an *?

During the time when I stopped analyzing the Solo 575s and simply enjoyed the musical ride, I was always, with familiar recordings, well aware of the augmented bass wallop: The effect was always pleasurable, and produced exhilarating rhythm'n'pace. Otherwise, I was able to let go of the darTZeels' more familiar sound and fully accept that of the Krells—though I was also well aware that the Krells' sound was less refined overall. What I expect from class-A amplification—textural richness, suppleness, delicacy of attack, generous sustain, and far-as-the-ear-can-hear decaysnever materialized. But the far more expensive darTZeels (151,000 Swiss francs/pair, equivalent to US$157,000/pair at the time of writing) produced all of those in greater abundance.

Instead, the Solo 575s' overall attack was speedier, with less generous sustain and somewhat steeper/faster decay than through the darTZeel amps. However, those qualities better matched the Krells' punchier low-frequency personality. The Solo 575s breathed as a tightly sprung whole, producing a coherent sound from top to bottom.

I felt that, at higher SPLs, the Krells were adding a splash of hash and/or brightness, which somewhat offset the strong pluses of their tighter grip and rhythmic tautness. This was most audible with pop and rock recordings and vocals, and less so with recordings of unamplified instruments. But this characteristic wasn't to the point of being distracting or objectionable. It was audible only occasionally, and then gone. At the same time, when a recording contained very high frequencies, or a mix with a high-frequency EQ lift, those frequencies were reproduced with an unexpectedly sweet and silky quality.

The last record I played before returning to the darTZeels was an AAA reissue of Sam Rivers's Contrasts, recorded in December 1979 (LP, ECM 1162). Rivers plays soprano and tenor sax and flute, George Lewis plays a monstrous, sometimes blatty trombone, Dave Holland is on bass, and Thurman Barker plays drums and mellifluous marimba. Mention free jazz to many—even some Frank Zappa fans—and they freak out. They're hung up. Why anyone who enjoys Zappa's good-humored, nonstructured meanderings wouldn't dig Contrasts escapes me. In "Circles," Lewis blats away in the left channel, Rivers blows on soprano and Barker drums in the center, and Holland bows in the left channel. It's closely miked and pleasingly raucous. At high SPLs, the entire record produces delirious chaos.

Contrasts brought forth all of the Solo 575's strengths: punchy, woofer-gripping lows, whether from plucked or bowed bass or growling trombone; pleasingly sizzly but not overly hashy cymbal strokes; and smooth, almost silky upper highs from Rivers's flute. The sound was brash yet involving, the images large and pleasingly confrontational. 

Swapping in the darTZeel NHB-458s and playing the heavily panned drum solo in "Zip," also from Contrasts, put the differences between the two amps in sharp focus. The darTZeels produced less bottom-end grip but more nuance. Cymbals had more sizzle and less crunch, and there was more air around Rivers's flute. The soundstage was wider and deeper, and aural images on it were more compact and better focused, though edge definition was less severe. The overall sound of the far more expensive darTZeels was more refined, in terms of both transient performance and dynamic gradations.

In short, the class-A/B darTZeels simply sounded more like class-A amps than did the Krells. Listening to the Krells, I missed what the darTZeels did best; listening to the darTZeels, I missed what the Krells did best.

Playing a long set of tunes stored in the Meridian Sooloos—all from CDs ripped at full 16-bit/44.1kHz resolution—verified the positives and negatives revealed by this comparison, though they were always complementary in ways that made me want to keep both sets of monoblocks on hand, one pair each for different types of music.

For instance, in "There'll Be Some Changes Made," from Chet Atkins and Mark Knopfler's Neck and Neck (now 25 years old . . . how can that be?), via the Krells the taut bass line more effectively tapped my toes and carried forward the tune. The darTZeels' sound was more supple, expressing greater stage depth and, especially, width, and the guitars were better separated from the reverb. The same was true with the CD-resolution file of Chuck Berry's "Rock & Roll Music": the Krells exacerbated the glare of the reverb, but startlingly clarified the piano and, especially, some of the percussive accents buried by the more-than-six-times-the-price darTZeels.

Equivocating Conclusion

In the past few years, apart from my reports in "Analog Corner," I've reviewed mostly power amplifiers. Every one of them has sounded different from all the rest, and I could happily live with some, but not others. The Bricasti M28 monoblocks, for instance, which measured as well as the Krell Solo 575s, according to JA, didn't tickle my auditory pleasure centers as much, despite the Krells' somewhat coarser overall sound.

The Solo 575 monoblocks were in my system for well over a month, and during that time I enjoyed how they drove the Wilson Alexandria XLFs, especially on the bottom. But more important—because the sound was whole from top to bottom—I found no fault with any single aspect of Krells' sound until I swapped them out for the far more expensive darTZeel NHB-458s.

The Solo 575s' taut bottom end produced always entertaining rhythmic drive and pleasing musical flow. Their punchy but nonaggressive top end was likewise fast, and the surprisingly silky ultratop, which appeared when least expected and was always very welcome, added to the endless excitement and strong listening involvement these amps produced in me.

When I returned to the darTZeels, my system's sound was texturally more subtle overall, and in some ways more polite. but I also happily listened to a great deal of classical music through the Krells.

If you listen to rock, and your speakers have good bottom-end extension, and—especially—if they thrive on lots of power and can deliver wide dynamic swings, you need to hear the Solo 575s. ……. Michael Fremer

I was always very, very happy with the sound of my system when the Illusion II was in it.
Brent Butterworth | April 20, 2015

SUMMARY: Bassist Ray Brown's Soular Energy is one of those CDs that sounds at least pretty good on almost any system, but I thought the Illusion II particularly nailed "Mistreated But Undefeated Blues." The part that the Illusion II got especially right was guitarist Emily Remler's tone, which has plenty of body (like her heroes Herb Ellis and Wes Montgomery) with just a touch of twang. I thought the Illusion II got Remler's badass sound just right. 

Even the (arguably) toughest test track I have, the live stereo version of James Taylor's "Shower the People" from Live at the Beacon Theatre, sounded smooth, natural, and colourless (but in a good way) through the Illusion II. Vocalist Arnold McCuller's solo at the end--a bravura performance that taxes the midrange reproduction of audio components--never broke up or got edgy or bright.

EXTENDED REVIEW: It seems like, every few years, Krell goes through a major cosmetic (and sometimes engineering) revamp. Visually, the song always seems to be the same: variations on the unashamedly macho look that began with the KSA-100 amplifier way back in 1981. The new Illusion II digital preamp embodies the same industrial design ideas as the new iBias amplifiers: a more understated (or less overstated) look, with a form factor conducive to rack-mounting. It's still macho, though.

Engineering-wise, there's nothing particularly "revamped" about the Illusion II. It's a straightforward high-end digital preamp--i.e., an analog preamp with a built-in digital-to-analog converter, a concept that's rapidly becoming the norm in two-channel audio. The Illusion II has five digital inputs feeding its 24-bit/192-kilohertz ESS Sabre DAC: one AES/EBU, two coaxial RCA, and two Toslink optical. If it seems like something's missing, it is: there's no USB input. USB audio inputs have become ubiquitous only over the last couple of years; and, according to company president Bill McKiegan, the Illusion II was too far along in its development cycle to add USB. This isn't a big deal; you just need to add a USB-to-coax converter, which I'll discuss in the Hookup section below.

The Illusion II also has four stereo analog inputs: three RCA and one XLR. There's no built-in phono preamp; so, if you want to use a turntable, you'll have to provide the phono pre. XLR and RCA stereo outputs are provided, as is a quarter-inch front headphone jack.

For the Illusion II, Krell uses much the same control system as in its other recent preamps and integrated amps (including the S-300i integrated I usually use for speaker reviews). You can do all the normal stuff, like volume and input selection, from the front panel or remote. A front-panel alphanumeric display with a menu system lets you access more exotic features, such as balance, home theatre bypass, input trim and naming, and the function of the 12-volt DC trigger jack on the back (which can send out a trigger voltage to turn on your amps when you turn on the preamp).

Krell's website touts four main features of the analog circuitry: current mode design; a fully balanced circuit topology, in which separate circuits amplify the positive and negative halves of the audio signal; dual-mono layout, with separate circuit boards for left and right channels; and a power supply with 40,000 microfarads of storage capacitance, which is a lot for a preamp. Of course, all of this reflects well on the construction quality, but none of it really tells you how the Illusion II is going to sound.

The Hookup

Let's get past that big issue I cited above: the Illusion II's lack of a USB input. It seems to me that almost everyone who buys this stereo preamp would want to use a computer as a source device, so finding a way to connect a computer to the Illusion II is priority number one in any installation. What you need here is a USB-to-coax converter: a "dumb box" that simply converts the USB from your computer to an SPDIF coaxial RCA digital output that the Illusion II can accept. I ended up using a Peachtree Audio T1 converter--which costs $79, worked instantly with my Toshiba laptop running Windows 7, and required no driver installation. The T1 only passes resolutions up to 24/96, though; if you want 24/192, spend $149 for the Peachtree X1. Of course, other manufacturers offer higher-end options you can explore. (Unfortunately, I started with the NuForce U192S converter, which I picked up for $49, but I couldn't get it to work with my PC or a friend's Mac, even after installing the drivers downloaded from the company's site. NuForce's only product support was a phone number with an answering machine that promised a company rep would call back, but no one ever did. So I recommend that you get one of the Peachtree models instead.)

I used the Illusion II with a couple different amps: the Krell Solo 375 mono blocks and a Classé Audio CA-2300 stereo amp. Speakers were either the Revel Performa3 F206 midsized towers or the Krell Resolution 1 large towers. Interconnects were all Canare Star Quad, and speaker cables were AudioQuest CinemaQuest 14/2. Most of my listening was using my Toshiba computer as the source, but I also used my Music Hall Ikura turntable and NAD PP-3 phono preamp to get an idea of how the Illusion II's analog section sounds. I also used it in home theater bypass mode along with my Denon AVR-2809CI receiver (used as a surround processor only), with the Krell amps handling left and right channels and an AudioControl Savoy seven-channel amp handling the center and surrounds.

The only thing I didn't like about using the Illusion II is that its digital inputs are accessed differently from the analog inputs. Each analog input has its own dedicated button on the remote and the front panel, but accessing the digital inputs is much less intuitive. From the front panel, you press the Digital button to switch over to the digital inputs, then hold the button down for a second to scroll to the next input. From the remote, you press the Digital button, then scroll through the inputs using the Select button. I think an extra row of buttons that allows direct access to the digital inputs would be welcome.

All comparisons cited in the review were conducted with levels matched to within 0.1 decibel.

Performance

I listened to the Illusion II on a casual basis for about a month before I sat down for a serious evaluation, and in that month I didn't notice any particular sonic character or idiosyncrasy. In fact, my attention was never drawn to the preamp. It always worked fine and sounded great.

When I sat down to do an in-depth evaluation, I started by using the analog inputs with my turntable so that I could get an idea of the sound quality of the core analog circuitry. As best as I can describe it, the sound quality was, well, mostly nothing. I couldn't pin down any particular coloration or tonality, even though I easily heard differences among different amplifiers, audio codecs, and other audio products I tested while the Illusion II was in my system.

One thing I loved about the Illusion II's sound was that I never found it harsh, edgy, or bright. For example, on "Matte Kudasai" from the LP Levin Brothers, by bassist Tony Levin and keyboardist/arranger Pete Levin, the brushed cymbals can sound a bit edgy and steely through some audio components (as cymbals often do), but through the Illusion II's analog stage, the cymbals sounded smoother and brassier.

When I played guitarist Larry Carlton's Sleepwalk LP, particularly the cut "Last Nite," I dug the solid groove that Carlton and his fellow Los Angeles and New York studio aces laid down. Why did I dig it, maybe a little more than I normally would? Because the sound seemed nicely focused, with a particularly solid center image. The bass sounded appropriately full-bodied, the keyboards suitably spacious, and Carlton's guitar had lots of body and soul...just as it should. 

After several more albums, I felt I had a pretty good handle on the sound of the Illusion II's analog circuitry; so, to check out the DAC, I switched over to one of the coaxial digital inputs, fed by my Toshiba laptop through the Peachtree Audio T1 USB-to-coax converter. I know L.A. saxophonist Terry Landry's Amazonas (http://terrylandry.virb.com/listen ) well because I was there for the recording session, conducted with audiophile engineer/producer Joe Harley using Sony Direct Stream Digital recording equipment, and the mastering session, performed by mastering legend Bernie Grundman at his L.A. studio. Again, the groove was solid, and the cymbals sounded smooth. So did Landry's tenor sax, which I thought sounded just a little smoother than usual. It was a nice sound, but Landry's tone has a trace more edge and breath in it than I heard here.

Bassist Ray Brown's Soular Energy is one of those CDs that sounds at least pretty good on almost any system, but I thought the Illusion II particularly nailed "Mistreated But Undefeated Blues." The part that the Illusion II got especially right was guitarist Emily Remler's tone, which has plenty of body (like her heroes Herb Ellis and Wes Montgomery) with just a touch of twang. I thought the Illusion II got Remler's badass sound just right. 

Even the (arguably) toughest test track I have, the live stereo version of James Taylor's "Shower the People" from Live at the Beacon Theatre, sounded smooth, natural, and colourless (but in a good way) through the Illusion II. Vocalist Arnold McCuller's solo at the end--a bravura performance that taxes the midrange reproduction of audio components--never broke up or got edgy or bright.

Comparison and Competition

I still hadn't checked out the Illusion II's headphone amp, so I connected my Musical Fidelity V-Can headphone amplifier to the preamp's outputs. This let me compare the sound of the Illusion II's headphone amp to the V-Can. The V-Can is (was--it's discontinued) a modestly priced but respected headphone amp with a nicely low output impedance of five ohms; I figured that, if the Illusion II could match the V-Can's sound quality, that'd be an admirable result.

Look, I am not the guy who gets super-excited about headphone amps; to me, I just want one that's conservatively engineered and has a low output impedance (which, in general, assures the flattest possible frequency response from the headphones). But the first thing I scrawled in my notebook was, "The Krell is OBVIOUSLY better." The Illusion II's headphone amp had an obviously greater sense of space, tighter bass, more detail, more space, and a smoother sound overall; in comparison, the V-Can sounded rather grainy and low-res. Often, headphone amps are added to preamps as an afterthought, without much engineering effort, but it seems Krell put some serious effort into the Illusion II's headphone amp.

An obvious competitor for the Illusion II is the Classé Audio CP-800, I did extensive A/B comparisons between the two preamps, and the main difference was in the mid-treble, of which the CP-800 had more.

Sometimes the CP-800's more prominent mid-treble gave it a more spacious, airy sound. Sometimes it gave a thinner sound. For example, in Steely Dan's classic "Aja," Donald Fagen's voice sounded smooth through the Illusion II but a little dry through the CP-800, as if Fagen could have used a drink of water. The CP-800 had more apparent detail, yet it also made the cymbals on "Aja" sound a little more like aluminum and less like brass. The CP-800's center image also seemed rather spread out compared with the Illusion II's more focused center. Which is better? I think that's a matter of opinion.

All of these differences were subtle, though. On many tunes, such as R.E.M.'s "Cuyahoga" (from the Life's Rich Pageant LP), David Chesky's "Bronxville" (from the Body Acoustic CD), and most of the tunes on the Levin Brothers album, the two preamps sounded almost identical. Should this be a surprise? They're comparably priced solid-state preamps from companies that have been around for decades and have similar engineering approaches.

The Downside

If you like tons of treble detail--perhaps even slightly exaggerated treble detail--I don't think the Illusion II is your digital preamp. I loved its sound, but I'm 53, and I've noticed that the older listeners get, the more they like smoother treble. I could speculate as to why, but I'd just be speculating.

Conclusion

Absolutely, it sounds great. Some audiophiles will likely consider its tonal balance ever so slightly warm but deliciously wonderful, while others may want a little more top end. As for me, I was always very, very happy with the sound of my system when the Illusion II was in it.

 
Moreover, the sound of the pairing of the Krell Illusion ll preamp and Krell Duo 175 stereo amp I liked much more than quite hard and cold sound of some older models of the mid-1990s — beginning of 2000-ies.
Webblack.net

SUMMARY: Krell amplifiers have long earned the reputation of "kings of bass", and I don’t deny myself the pleasure to start the program listening several albums with excellent written bass parties. Well, the reputation has been brilliantly confirmed. For example, the title track of the album Pat Travers «Crash and Burn» sounded so powerful and even frightening that after graduation I had to take a short break to reconfigure the perception of less aggressive genresIn the transition to the classical repertoire Krell is the ability to control the acoustics resulted in an extraordinary transparency, which were presented to the most complex fortissimo. Needless to say, «the Firebird» by Stravinsky, I was again stunned and plunged into the thrill, however small violin compositions of Haydn sounded appropriately heartfelt and beautiful. Despite his heroic strength, set can sound soft and gentle, when needed, with very believable voices. Three-dimensional scene, so appreciated by audiophile, Krell manages to pair perfectly with the amendment, of course, on your speaker system and room. In General, the performance of the admittedly gorgeous.

EXTENDED REVIEW: The Illusion II preamplifier and power amplifier from Krell Duo 175 - The name of the American company Krell has long been synonymous with sound of the highest level. The next generation of music lovers discovering branded equipment, and all as affected the outstanding quality of sound and workmanship. However, recently the company went through a rather difficult stage.

Despite the fact that the first Krell amplifier under the brand saw the light in 1980-m to year, in recent years, the company had to work hard to maintain a high level of confidence in their products, which has already become habitual for her. Suffice it to say that pre-owned Krell amplifiers still enjoy huge success with buyers willing to pay for them a sum in excess of the original price! What happened? This is due, firstly, with the departure of the Krell, the founder and chief developer of the company Dan D’agostino behind the creation of all classical models of the firm. (PLEASE NOTE- the 2 original engineers who were really responsible for the vast majorty of their designs are still with Krell). Secondly, with ever-increasing user requirements to functional equipment equipment class High End. Component construction principle of the stereo is still not questioned, however, to meet today, for example, pre-amplifier no DAC, and even the wireless module and the streamer becomes more difficult. How successfully managed a team of Krell with upgrading and maintaining the quality of the sound at the proper level? We will check this with the example of the set consisting of the preamplifier Krell Illusion II stereo power amplifier Krell Duo 175.

For each generation of its technology Krell designers continue to invent new forms. The next iteration of stereo equipment, the company also got his very recognisable, though not too original looking. Silver paste with the lights on the center of the front panel came in mind not all inveterate audiophile, however, one must admit that now equipment company looks much more modern, and not as brutal as the classical model. However, the main changes are connected not with the design of the front panel, and hidden inside.

Krell Duo 175

The main stars of the model range of the American firm has always been the power amps, so with them we will start with the introduction kit. Presented to test the stereo amplifier takes an intermediate position in the hierarchy between the entry-level devices and top-end Solo 375 monoblocks.

Power output is claimed at 175 Watts per channel into 8 Ω, actually, hence the number in the title. As we would expect from a Krell amps, when operating at 4 ohms output power is doubled to 350 Watts. That is, as in the previous models of the firm, output stages work in pure class A? Not really. And here we come to the main innovation introduced in the design in recent years. The company’s engineers came up with a cunning move, allowing you to keep all the advantages of operation of the amplifier in class A, but significantly reduce power consumption and heat. This is achieved through the intelligent circuitry iBias, analysing in real time the level of the current given to the load, and adjusts accordingly the current of rest. As a result, the transistors continue to always remain open, however, the flowing current varies depending on actual load. I must say that trying to do something similar has already been attempted by other manufacturers, but the implementation suggested changing the quiescent current depending on the input signal, which did not give the desired result, primarily, from the point of view of sound quality. Looking ahead, we can say that the Krell engineers had achieved the seemingly impossible.

Another innovative feature is the presence on the back of the RJ45 port. It allows you to manage and control the many parameters of the amplifier via a network interface. Of course, this requires you to connect the device to your home network, where he will be assigned its own iP address. In addition, if you encounter any problems the company will be able to remotely read the code errors and make recommendations for its elimination. Frankly, this feature is unlikely to be commonly used by normal users, however, the mere fact of its existence says about the company’s commitment to meet the requirements of the digital era.

On the rear panel are one pair of speaker terminals and the RCA and XLR connectors for balanced and conventional connections. What is less familiar is the presence of four fans for forced cooling of the output transistors. Previously, the company relied solely on the massive passive radiators. However, thanks to the innovative control scheme, the current peace, to intervene in the case, the fans have rarely. In the rest of the Duo 175 is a classic two-channel amplifier Krell, powerful and imposing.

Krell Illusion ll Preamp / DAC:

The second component of the kit — Krell Illusion II, the younger of the two available in the product line of the company pre-amplifiers. Often when first turned on modern audio equipment with a digital filling the user has to spend some time to understand all the settings and assigning inputs. In the case of Krell Illusion ll I listen to ten seconds after activation.

The front panel contains the activation keys for each of the inputs, adjust the volume level and channel balance, as well as navigate through a short menu. The included remote control is traditionally enclosed in a housing of machined aluminium and is covered with small buttons. The digital part of the pre-amplifier is built on the ESS Sabre chip and is able to work with LPCM signal with parameters 24 bit/ 192 kHz. In General, the apparatus is easy to handle and intuitive.

Sound

Audition set it was decided to hold in a pair of Studio monitors, the legendary JBL 4345. Despite the fact that they have high sensitivity, their 18-inch bass still needs good control. And horn mid-range section will allow you to easily identify any flaws in the amplifier part proper transmission of voices and live instruments. As the source was the CD player Bryston BCD-1 and the turntable in the VPI Classic. Switching between pre-amplifier and power amplifier were carried out in symmetric and asymmetric Protocol. In the end, there was a preference for the balanced option.

Krell amplifiers have long earned the reputation of "kings of bass", and I don’t deny myself the pleasure to start the program listening several albums with excellent written bass parties. Well, the reputation has been brilliantly confirmed. For example, the title track of the album Pat Travers «Crash and Burn» sounded so powerful and even frightening that after graduation I had to take a short break to reconfigure the perception of less aggressive genres. If we go back to work a couple of amps on the bass, it is quite obviously the following to improve the sound quality in this range is possible only by acquiring top-end kit from Krell, and that — not the fact that the result will definitely justify the difference in price. All proposed system of records, including Metallica, classic albums Rush, cut by the legendary Bob Ludwig, and challenging enough to play Them Crooked Vultures, was played out almost perfectly. Amplifiers effortlessly disassembled into components and re-assembled in a single unit loud drums and bass guitars and hi-hat don’t forget to sparkle with silver.

In the transition to the classical repertoire Krell is the ability to control the acoustics resulted in an extraordinary transparency, which were presented to the most complex fortissimo. Needless to say, «the Firebird» by Stravinsky, I was again stunned and plunged into the thrill, however small violin compositions of Haydn sounded appropriately heartfelt and beautiful. Despite his heroic strength, set can sound soft and gentle, when needed, with very believable voices. Three-dimensional scene, so appreciated by audiophile, Krell manages to pair perfectly with the amendment, of course, on your speaker system and room. In General, the performance of the admittedly gorgeous.

Since I have had a chance to listen to the work of JBL 4345 monitors paired with earlier generations of Krell amps, it was difficult to refrain from carrying out direct Parallels. 
In my opinion, the difference in sound with the new model number appears no more than between all of the previous generations, designed by Dan d’agostino. That is to say that the use of iBias has led to the loss of signature handwriting is impossible. Moreover, the sound of the pairing of the Krell Illusion ll preamp and Krell Duo 175 stereo amp, I liked much more than quite hard and cold sound of some older models of the mid-1990s — beginning of 2000-ies.
Well, about the bass has been said enough above.....

I submit that they’ve just returned to what made them great in the first place, bringing it up to date with the best advances in audio technology that have come our way in the last few decades.
Jeff Dorgay

SUMMARY: The raw emotion that generated so much excitement over this brand in the 80s is back in spades, yet without losing that magic, there is more low level detail, and more refinement. This is a tough combination to master, yet Krell has. It’s like taking a car with a great paint job, wet sanding it with 2500 grit sandpaper and then buffing to a higher luster than you thought possible – yet there you are.

EXTENDEDE REVIEW: My journey with Krell goes back. Way back. All the way back to the original KSA-50 and PAM-5. I’ve always liked the brand, and thought the name was super cool.

Plus, Krell was always a serious engineering company, and their products were robustly built – you could drive the hell out of their power amps into the most difficult loads without issue. Back when I had a pair of Apogees, Krell amps were the only amplifiers that would power these legendary ribbons without self destructing.

Fast forward to 2018. Krell had been languishing somewhat for the last decade, but now with Walter Schofield in charge of things, and some new product updates from the engineering department, they are again highly competitive. Best of all, that Krell magic is back. For some time, Krell amplification had taken on a bit of a forward, hyperdetailed sound. The new XD amplifiers have returned to more of that slight bit of warmth and tonal saturation, combined with a level of bass slam that made Krell famous. I’ll stick my neck out here and guess that this is a sound that more true music lovers might enjoy, and I’d put the tonality of the current XD amplifier more in the same ballpark as the other solid-state, Class-A amplifiers I truly love: vintage Krell, vintage Levinson, Pass, and Luxman. More of that kind of sound.

Which brings it all full circle, because Schofield used to work for Levinson, so he brings a lot of expertise to bear on carving out today’s Krell, and their place in the market. Krell was serving up great sound at the recent Rocky Mountain Audio Fest, showing off the new XD amplifiers, but even more exciting is that they are offering an upgrade for their past Duo amplifiers to bring them all up to XD spec at a very reasonable cost. In the case of the Duo 175, only $1,000. My inner tree hugging personality loves this, because you don’t have to abandon your old gear to step up to the latest/greatest. Audio Research has had tremendous luck with this and after hearing the new XD side by side with the older version, I expect Krell to do the same. Just so everyone is clear, this upgrade can be done to the amplifiers currently in the i-Bias lineup: 125/175/300 Duos, the Trio and the 375 and 575 Solo. The new K-300i already includes the XD upgrade in their DNA. The “Chorus” line of amplifiers can also be upgraded.

Fortunately, Schofield made my job easy. He sent me an old version along with the new amp. While it’s great to rely on “sonic memory,” nothing gets the job done like having them both side by side to compare. So using the new D-01 DAC/streamer from Esoteric ($20,000) in for review that I’ve become very familiar with, Nagra’ s Classic preamplifier ($17,000) and a pair of GamuT Zodiac speakers ($149,000/pair), all cabled up with Cardas Clear cable, the comparison was a relatively easy task.

Taking this a bit further, I borrowed a good friend’s first gen KSA-50 for a true comparison. Ken Kessler wrote enthusiastically about the KSA-50 for TONE here (http://www.tonepublications.com/old-school/krell-ksa-50-amplifier/) so of course, I had to purchase one to take that trip down memory lane. But like Pokemon, you can’t catch them all, so when the review was done, it went to someone close. Which means loan privileges, of course! So now we had the last version, the new version and a great original to compare.

Initially, there’s no comparison between the two current models – the jump in resolution and musicality is massive. It’s like they are channeling the sound that made Krell famous, while incorporating the changes in technology that have come to be over the last 35 years.

The raw emotion that generated so much excitement over this brand in the 80s is back in spades, yet without losing that magic, there is more low level detail, and more refinement. This is a tough combination to master, yet Krell has. It’s like taking a car with a great paint job, wet sanding it with 2500 grit sandpaper and then buffing to a higher luster than you thought possible – yet there you are.

We’ll have a full review of the Duo 175XD before the end of this year, but for now, consider this more of a comparison between new and old versions to let you know what’s new. Anyone thinking about doing the upgrade, the answer is an unqualified yes – this is the best thousand bucks you will ever spend in high end audio, and this upgrade applies to all their stereo and multichannel power amplifiers. The three channel amp, the five channel, seven channel and the monoblocks. As with past Krell upgrades, the owner is responsible for shipping in both directions. Schofield says that current upgrades are “dependent on production volume,” so it’s best to call service/support and find out what the backlog is.

The folks at Krell are calling this “The New Sound of Krell,” but I submit that they’ve just returned to what made them great in the first place, bringing it up to date with the best advances in audio technology that have come our way in the last few decades. I’d say they’ve found their way back home.

Everything about this amp is absolutely superb
Bob Furstenberg

Krell returns to form with an exceptionally capable amplifier for well-heeled home theaters where quality takes precedence over quantity.
Michael Trei - Feb 13, 2019

"After a few years spent flying under the radar, Krell is very much back in business. While the company's main focus has always been two-channel audio, the Theater 7 shows that it's also a serious player in the multichannel game. For a home theater where the main focus is quality rather than trying to blow out everyone's ears, it's hard to beat Krell's Theater 7 amplifier.

AT A GLANCE
PLUS
5 STAR Perfomance
Class-A sound with improved efficiency
Exceptional transparency and control
MINUS
Not the most powerful amp on the block
Display may be unnecessary for most users
THE VERDICT
Krell returns to form with an exceptionally capable amplifier for well-heeled home theaters where quality takes precedence over quantity.

"It's hard to overstate the importance of Krell Industries in the history of high-end audio. Founded by Dan and Rondi D'Agostino in 1980, Krell was the audio equivalent of Lamborghini—an audacious riposte to more Ferrari-like rivals such as Mark Levinson and Audio Research. For almost three decades, Krell went from strength to strength, introducing a stream of ever more ambitious products that tested the depth of their customers' pockets, along with the strength of their audio equipment shelving. Then, starting around a decade ago, the brand slowly slipped off the radar screens of most audiophiles.
 
We now know that the D'Agostinos were the target of what Dan has described as a hostile take- over by a group of investors. The new owners were more interested in making a deal to put Krell-branded high-end sound systems in Acura cars than in pursuing the comparatively small home audio market. Before long, some products were being manufactured in China, and Krell's edge slipped away.
 
While Dan moved on with a new venture, Rondi stayed and fought for the company she had co-founded 30 years earlier, eventually succeeding in regaining control. Krell is now working to reestablish its brand as a world leader in a somewhat smaller, yet even more competitive, high-end audio market. The Theater 7 amplifier is part of that process.
 
Krell amplifiers have always been overstated in design and understated in their on-paper specifications. Back in the 1980s, we would talk about “Krell watts,” where the amp's massive power supply and conservative on-paper power rating meant that it could drive speakers in real world systems way beyond what the numbers would suggest. With 7 x 105 watts, all channels driven into 8 ohms, the Theater 7 may not sound like a powerhouse, but with most speakers it can really deliver the goods.
 
Krell built its reputation on amps that deliver pure class-A power, free from the switching distortion common to more typical class-A/B designs. The problem is that pure class-A amps are notoriously inefficient and pump out huge quantities of heat. Instead of having to make a choice between ultimate sound quality and efficiency, Krell developed what they call iBias Class A to give you both at the same time. While sliding bias amps are nothing new, the difference with iBias is that the bias level is determined by what's happening at the amp's output where the speaker load is connected, rather than at the input.
 
Setup
Despite being the smallest and most affordable multichannel amplifier in Krell's lineup, the Theater 7 ($7,500) is still a beast by any normal standards. Weighing in at 70 pounds and measuring over 20 inches deep, you're going to need a pretty stout shelf to support it. A bottom-mounted cooling fan ensures that things never get too hot, but Krell still advises that you give the amp plenty of breathing room.
 
As with any power amp, hookup is straightforward. Each of the seven channels has both balanced XLR and single-ended RCA inputs, but rather than putting a switch in the signal path to select between them, Krell includes seven little copper loops that short the inverted phase of the XLR input to ground when it's not being used. Krell describes the speaker terminals as five-way binding posts, but I found they weren't particularly well-suited to larger spade terminals, working best with either bare wire or banana plugs. The power inlet uses a hefty 20-amp capable C20 IEC plug rather than the more common 15-amp C14 variety, although the supplied power cable has a standard 15-amp plug at the wall outlet end for compatibility. Rounding out the connections are a 12-volt trigger input and a LAN port.
 
While the Theater 7 doesn't have its own control app, it can be addressed remotely via the hardwired LAN connection. When you switch on the amp, the front panel display shows an IP address, and when you enter that IP address on a portable device or computer that's on the same network, a control screen pops up. From there you can update the firmware, switch the amp on or off, adjust the no-signal switch-off timer, monitor the operating temperature and fan status, and carry out other operations. However, this functionality is meant more for a custom installation professional or Krell technical support to diagnose problems remotely than it is for user operation.
 
I primarily used the Theater 7 to drive my PSB Synchrony seven-channel surround speaker rig, but rather than using them with my subwoofer as I would normally do, I simply ran the Synchrony One towers full-range and switched off the sub. This allowed me to evaluate the amp's full-range performance without siphoning off the deep bass frequencies to a separately powered unit.
 
Performance
Starting with two-channel music streamed from Qobuz, I fired up some of my favorite evaluation tracks. It immediately became clear that despite its name, the Theater 7 isn't just for movies. Drumming legend Steve Jordan is famous for the crisp snap that he gets from his snare, and on the reggae track “Words of Wonder” from Keith Richards' Main Offender album the impact and dynamics of his stick work was certainly ear-opening. Charley Drayton's bass on this track is a great test of an amp's ability to control a speaker. With the Theater 7, his bass lines were full-bodied and powerful, yet also tuneful and easy to follow.
 
Any home theater amp should be expected to deliver sledgehammer dynamics and an ability to maintain an iron grip on the speaker drivers, but it can be a taller order to combine that with subtlety and transparency. The track “Ramblin' Boy” from The Weavers' Reunion At Carnegie Hall is a tough test of those properties. When I listened to it with the Theater 7, the purity of Pete Seeger's voice, and the huge sense of natural spaciousness when the crowd joined him in singing, provided an impressive demonstration of the benefits of the Krell's iBias Class A circuitry.
 
While Incredibles 2 didn't have quite the spark that made the original movie so great, there's no denying that the opening nine-minute sequence when The Underminer robs a bank in Metroville is a fantastic home theater demonstration. With the combined sounds of the Underminer's tunneling machine and money vacuum, the Incredibles' attempts to stop him, and a jazzy music background all going at once, this sequence can give any audio system a real workout. The Theater 7 maintained its composure throughout the clip, with dialogue remaining clear and fully resolved. Even without benefit of a subwoofer, the combination of the Krell amp and the Synchrony One tower speakers managed to get the walls shaking in my 14 x 16-foot theater room.
 
After taking into consideration “Krell watts” versus what you get with more typical power amps, 105 watts-per-channel can still be a limiting factor in some larger rooms, especially when inefficient speakers are used. Personally, I'm more of a quality over quantity kind of guy, and I'd always go for an amp like the Theater 7 over a lesser alternative with a higher power output specification. In my setup, I never felt like I was running short of juice. (Of course, if you want to have it all, Krell also offers the 7 x 200-watt Chorus 7200XD amplifier.)
 
Conclusion
After a few years spent flying under the radar, Krell is very much back in business. While the company's main focus has always been two-channel audio, the Theater 7 shows that it's also a serious player in the multichannel game. For a home theater where the main focus is quality rather than trying to blow out everyone's ears, it's hard to beat Krell's Theater 7 amplifier."
 
All I can say is WOW! I have never, and I repeat never, in over 30 years of professional audio sales and system design, heard a solid state product like this before.
Dave Lalin, - Audio Doctor

SUMMARY: All I can say is WOW! I have never, and I repeat never, in over 30 years of professional audio sales and system design, heard a solid state product like this before. 
The phrase "tube like" has been bandied about for years when you have a solid state product that strives to recreate some of the magic of modern tube electronics, however, with the new K-300i, which I understand was the inspiration for the XD upgraded Duo, Chorus and Solo amplifiers series, you have actually done it!
There is an organic wholeness and lack of grain to the sound which once you experience it, you know in an instant, this is not your typical solid state Hifi gear.

I am writing this email to you while listening to our brand new demo KRELL demo K-300i Integradted amp playing Miles Davis, Herbie Hancock and Lee Morgan tracks.

All I can say is WOW! I have never, and I repeat never, in over 30 years of professional audio sales and system design, heard a solid state product like this before.

The phrase "tube like" has been bandied about for years when you have a solid state product that strives to recreate some of the magic of modern tube electronics, however, with the new K-300i, which I understand was the inspiration for the XD upgraded Duo, Chorus and Solo amplifiers series, you have actually done it!

There is an organic wholeness and lack of grain to the sound which once you experience it, you know in an instant, this is not your typical solid state Hifi gear.

The sound of the K-300i just draws you in to the experience of music. Even listening from the next room, the piano and organ have the flowing roundness of a real instrument.

Another extraordinary trait of this little amplifier, pun intended, it weighs 52lbs and feels like it was cut from a solid block of metal. There was a rim shot on the drums which made me lift my head from reading emails while sitting in my listening room. It was so life like and startling, and this is with only a short period of break in.

Combine this magical liquidity and sense of presence with a deep, well controlled bass response, a large soundstage, good top end extension, and thrilling dynamics, and add in a modern feature set with Roon and MQA capability, built in ethernet streaming, Apt X Bluetooth, HDMI in and outputs, and a ton of both analog and digital inputs, with enough power to drive real world loudspeakers, and it makes this one very special integrated amplifier. I will find it hard to recommend anything else but Krell to my clients, and we sell many of the top performing brands of electronics in all of audio.

We have not yet fired up the big guns, our new Demo Duo-300XD & Illusion-2 [reamp/DAC. I expect we will find this gear is even better than the little integrated with the XD upgrades as I’ve read in many publications over the past few months, and again we will likely find it hard to recommend our more expensive reference gear which is well over $50k. This level of sound quality is more akin to radically more expensive brands. Please get the word out that Krell is back! We are so pleased with these new products, you are going to have a bright future.

Krell is one of the foremost gems in the vein of classic American high end manufacturing, and like Harley Davidson, you are well on your way to restoring Krell back to its glory days.

I have owned many classic Krell products like the KSA 250s, a KRC HR, and 450 Mcx Mono blocks, as well as some of the finest tube gear from Conrad Johnson and VAC, so I know what good sound sounds like. The new K-300i is a quantum leap over the older classic Krell gear, and anyone who doubts that just needs to listen for 30 seconds to confirm that.  

Dave Goodman should be congratulated. Whatever he figured out with the XD series circuit advances the art of music reproduction.

Thank you for your recommendation of the K-300i and Krell in general, I can't remember the last time a product in this price point sounded so remarkable and was such a joy to use.

Please feel free to quote me on this, I stand by absolutely every word.

Sincerely,
Dave Lalin - Audio Doctor

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.

Testimonials

Everything about this amp is absolutely superb