Product Review - Krell Theater
Amplifier Standard - May, 2002
Chris Montreuil
|
Specifications: Output: 200
Watts RMS per Channel x 5, into 8 Ohms |
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 -
© Copyright 2002 Secrets of Home Theater & High Fidelity
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