KRELL CHORUS-7200XD 7ch 200w multi-channel power amp class-A w/ iBias

KL 24 AV C7200
NZ$ 20,995.00 ea (incl. GST)
Krell

The Leader in Audio Engineering

New

A comment on the new Krell sound from our XD upgraded amplifiers…Initially, there’s no comparison between the two models (pre and post XD upgrade) – 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

Krell Class A iBias Technology
Krell's new line of iBias amps promise class A performance without the usual pitfalls—high power consumption and lots of heat. The new amps use a fan-cooled chassis to pull off that trick and the result is a series of highly powerful yet compact amplifiers. The new iBias design allows the amp to actively measure the current flow to the speakers and adjusts the amps bias to meet demand—if full power is called for, then full power is what you get. However, if full power is not needed, the amp adjusts the bias so that energy isn't wasted the way it is in traditional class a designs.

The new amps fit in a standard rack—something that was not possible with old-school Krell amps. This was achieved by using ultra-quiet fans—active ventilation. That makes these new amps a great fit for high-end audio and home theatre installations. The new amps are as transparent and dynamic as we have come to expect from Krell.

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.

When developing the CHORUS7200-XD, David Goodman, our Director of Product Development, whom has been with Krell since 1987 and was largely responsible for design work on all Krell products, discovered that with modifications to the output stage, we could vastly improve sound quality, across the board, to all of our amplifiers.

THE RESULT
A deeper, darker, blacker background that provided significantly better macro and micro dynamics, more silence between the notes. Vocals and midrange took on an organic, yet more vibrant tone, enabling us to hear much more body, and even though our amps were great before, there was a very significant improvement. The speakers disappeared; yet, instruments were more focused with appropriate size and specific soundstage locations. All in all, a much better sounding, much improved experience that was easily, immediately heard by all that listened.

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 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 optimized 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 realised 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 microdynamics 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 theatre fans everything they could possibly want in an amplifier.

Specifications

Reviews

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Specifications

7ch 200watt/ch multi channel power amplifier featuring Krell iBias Technology 
200watts/ch into 8 Ohms
7 ea - Single-ended RCA and Balanced XLR Inputs
1 RJ 45 Ethernet Port
1 12V Trigger Input
WBT Speaker Binding Posts
Optional Rack Mount Kit
17 W, 7 H, 21 D in
43.3 W, 17.7 H, 53.1 D cm
Weight: 70 lbs, 32kg

Reviews

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.

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