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Product Review - Krell Theater Amplifier Standard - May, 2002

Chris Montreuil


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Specifications:

Output:  200 Watts RMS per Channel x 5, into 8 Ohms
Inputs: XLR Balanced and RCA Unbalanced on Each Channel, DB-25
MFR:   0.25 Hz - 170 kHz +0, - 3 dB
Dimensions:  10" H x 17" W x 17" D
Weight: 100 Pounds
MSRP:  $7,500 USA

 

Krell; http://www.krellonline.com

Introduction

“So what do you think, mom?”

“It looks chubby,” she says.

Sometimes I really do not know why I bother. I am sure you have gone through this before as well. For some reason I feel the need to justify this obsession of ours. To do so I look towards the inherent weaknesses of those who are missing the boat, hoping to prey upon said deficiencies so as to convince them that this is normal behavior. I do not know what level of success our readers have experienced, but I for one have been nothing short of a failure in this regard. With my mother I often try to appeal to her love of aesthetics. With that I had a litany of cosmetic arguments for Krell’s Theater Amplifier Standard. A clean rounded casing that screams elegance. A minimalist front panel sporting a solitary push button that illuminates a darkened room with an eerie blue halo. All this, not to mention a gorgeous silver finish, was not enough to dissuade her from noting its rather squat appearance. My first mistake was planting it alongside my current multi-channel reference, the Theta Dreadnaught, whose sculpted front panel and elongated casing invoke a more sophisticated look. While the look of the Dreadnaught had been favored over the Krell, their respective levels of sonic performance made for a far closer competition.

Buzzwords Galore

The Theater Amplifier Standard, TAS for short, is the amplification component of Krell’s Standard series triumvirate. Along with its DVD and Home Theater Standard brethren, the series represents Krell’s all out assault on multi-channel music and movie playback. The entire line features a gorgeous silver finish that Krell has dubbed "Krellcoat". Buzzwords are not limited to finish alone, as the smooth rounded casing throughout the line has been given the enigmatic Architech Construction moniker. Whatever odd terms used to describe the TAS, its fit and finish are exemplary, not to mention attractive, despite the claims of certain family members.

The revamped façade is a welcome change to these eyes, but the TAS also boasts internal upgrades that Krell claims has yielded sonic improvements. One look at the interior layout and you can see a good measure of thought and care went into the TAS. Each channel has its own vertical circuit card with heatsink. The layout is appropriately well ordered. The two toroidal transformers that comprise the majority of the unit’s weight are isolated in the base and are separated from the channel cards by an aluminum plate. The transformers rated at 2 kVA each! The Dreadnaught, featuring the same power specs as the Krell, possesses a single 2.2 kVA EI transformer. (The Dreadnaught is also several thousand dollars less in price.) In an e-mail exchange with Bill McKiegan, Krell’s VP of Sales and Marketing, the decision to go with two transformers was made, as having multiple secondary windings allowed them to run pairs of bridge rectifiers in parallel for higher current capability and lower power supply impedance. What this means in the real world is that under the most difficult of loads, the Krell will be less inclined to clip and has the potential to deliver more current than the Theta. The massive transformers feed a bank of storage capacitors that total 108,000 µF for all five channels. Because the capacitors are housed on the amplifier’s backplane and not separated, the TAS is able to deliver high current from the entire supply to any channel at any given time.

While some may argue the benefits of discrete storage for two-channel reproduction in a multi-channel context where effects can focus on a specific channel at any given moment, a shared power supply can be advantageous. Incoming signals go through a balanced instrumentation-style input stage. The output of the input stage drives a fully discrete, current-mode voltage gain stage. Its output in turn drives a quadruple-Darlington output stage, which comprises three Class A driver stages driving a Class AB output stage. So while most of the TAS is biased into Class A operation, its output stage is not. Krell feels this is the best way to achieve near Class A operation without all the necessary heat expenditures a fully Class A topology, as in their higher end models, would require. Each channel has ten (five pairs) of complementary bipolar output devices. Again this allows for high current output and dynamic headroom under the most demanding of musical passages.

The input stage of the TAS is dual differential balanced, although its output stage is single ended. Krell’s reasoning for such a decision was to allow the end user the ability to run in bridged mode for increased power. My experience with the TAS suggests that any additional power is purely overkill. I personally would have preferred fully balanced operation over the ability to bridge channels, but Krell knows its customers a lot better than I do, so I’ll give them a pass on this one.

Negative feedback has become a buzzword as of late with many manufacturers, Theta adopted a zero feedback approach (it's also fully balanced input to output stage). When I inquired about Krell’s take on feedback, I had the good fortune of receiving a response from the engineer charged with heading the TAS project. Since his technical expertise far outweighs my own this is a direct quote:

"We do use negative feedback, but very modest amounts of it. We design the amplifier to work extremely well even without feedback, and then apply a small amount to further lower the distortion, increase the bandwidth, and reduce the output impedance. The negative feedback is "nested," meaning that some feedback is applied to the driver stages and some to the whole amplifier. Our experience has shown that a properly-designed amplifier stage with a small amount of negative feedback sounds best."

Functionality

Never unpack a 100+lb. amplifier, especially one without handles, on your own. With apologies to the folks at Krell, I foolishly attempted this and quickly discovered how easy it is to tear the shipping carton. Either enlist the help of a friend, two if possible, or have your dealer install the TAS for you. Once the debacle of package removal had been accomplished, the process of connection to my system was a breeze. Speaker connections are made via a row of five way binding posts, one pair per channel. While it’s a minor nit, I would have preferred the posts to be spaced further apart to facilitate wiring and maintain a more orderly back panel. Line level connections are available in either balanced XLR, single ended RCA, or a multi-channel DB-25. Connection via the balanced input is recommended, as the TAS’s input stage is balanced. When running in single ended mode, shorting pins are provided for the balanced inputs.

To the dismay of after market power cord lovers, the TAS has a heavy gauge captive power cord. For those who enjoy the automated experience, a 12v input trigger is provided for startup from another device as well as a 12v output for linking to other 12v capable components. Although the faceplate features that beautiful power-on push button, the actual on/off switch is located on the rear in all its Spartan glory. Because of its heavy Class A bias, the TAS runs quite hot to the touch. As such, I would recommend placing it on an amp stand for maximum heat dissipation. If it must be placed in a rack, it would be advised to provide significant ventilation/forced air cooling.

As mentioned above, four channels (two pairs) of the TAS can be bridged to create a three-channel amp, consisting of two bridged channels capable of 800 watts into an 8 ohm load and a remaining non-bridged channel putting out the specified 200 watts into 8 ohms. An even more useful feature is the Multi Amp Throughput (MAT). MAT is an internal connection option that passes the same signal to all amplifier channels while only employing a single interconnect. In a multi-zone system, this feature allows an additional level of flexibility and economy of cable management. A second option of MAT is the ability to split the same signal twice with a single line level connection. This is a particularly useful feature if one wishes to run a bi-amplified L/R channel. In this scenario, four channels, fed from the left/right outputs of the pre/pro, would be dedicated to the mains, with a spare channel left to power the center or passive subwoofer. I must say I appreciated this level of flexibility in a component category that is generally bereft of options.

Performance

All of the aesthetic appeal and functionality in the world would not amount for much if the TAS did not deliver the goods sonically. Well, it delivered. The quality that came to mind time after time listening to material, whether it was of the multi-channel or stereo variety, was of complete and utter control. No matter what it was being fed, the TAS never lost its composure. The Omaha Beach sequence in "Saving Private Ryan" proved to be a favorite for the Krell. Thirty minutes of unmitigated action sailed along quickly as I was entranced with the sonic bubble the TAS produced. The clang of spent ammunition had just the right amount of metallic sheen, bullets flew through the soundstage with an uncanny realism, and the bass from exploding mortar shells was rendered with such clarity it could not help but suck you into the action. The most frightening aspect of the Krell’s presentation was that it even at its loudest, there was still headroom to spare. If you have a passive 5.1 preamp system or low sensitivity/impedance speakers, this is the amp for you.

Later in my evaluation I was able to swap out my powered front speakers and replace them with a pair of AAD Q30s to test the low end of the TAS. The Q30s feature a passive bass section so the Krell was now being asked to power the entire frequency range (my Definitive’s cross over at about 100 Hz). As of late I have been on a Beatles kick, and I was shocked to hear the bass line on “Come Together” as played through the Krell. Pitch, weight, extension, you name the quality, the Krell delivered it with perfect poise. On every cut I played, the Krell simply delineated bass like no amplifier I have had in house, Theta Dreadnaught and Sunfire Cinema Grand Signature included.

This is not to say the Krell did not acquit itself well through the midrange and treble. In fact its performance in those areas was superb. On my favorite tracks from Bjork and Portishead vocal reproduction was spot on, if a bit unforgiving of lesser recordings. This is to be expected of an amplifier with such transparency and a low noise floor, though I must say that in that regard, the Theta proved the better of the two. This came through clear on “How To Disappear Completely” off of Radiohead’s "Kid A". Towards the end of the track, Yorke’s vocals reach a crescendo that slowly drift off and float back deep into the soundstage. While the TAS came through in excellent fashion, the Theta seemed to float the notes with a little more air and delicacy that became intoxicating. These are subtle differences that reflect the design goals of the respective companies rather than one sounding "better" than the other. However, I would say that the Krell sounds a bit more neutral than the Theta.

Conclusion

The Krell TAS exudes complete control of the presentation with an unabashed neutrality and complete disregard for difficult loads. The Theta possesses a looser approach and a slightly softer, airier midrange and top end. As its namesake implies, the TAS was at its best in the home theater environment while the Theta shined in a two-channel one. For the multi-channel fanatic who occasionally enjoys listening to music, I would lean towards the Krell. If you are in the reverse situation, the Theta might be right for you. Even in this scenario I would still recommend you audition the Krell. No matter what your predilection may be, its performance merits experiencing first hand.


Referee's Equipment

Definitive Technology BP-2000tl, CLR3000, BP VX/P speakers
AAD Q30 speakers
Theta Digital Dreadnaught amplifier
Lexicon MC-12b surround processor
Camelot Uther v3 mk.4 DAC
Toshiba SD-9000 DVD Player/Transport
Better Cables interconnects/speaker cables
Nordost SPM Reference speaker cables

 

- Chris Montreuil -
 

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