Bel Canto Design Evo200.2 Stereo/Mono Power Amp

Evo200.2 with all the goodies. Power supply and output stage cap upgrades. Output resistor upgrade (GEN2 output stage).

Bel Canto eVo 200.2 power amplifier
By Kalman Rubinson • Posted: Mar 4, 2001
The word on Bel Canto's upsampling DAC was already out when I visited their room at the 2000 Consumer Electronics Show looking to get one of the first samples. But despite my protestations, all Bel Canto's Mike McCormick wanted to talk about was their company's new digital amp, the eVo 200.2. Sure, there's a future out there in which all sources will be digital and D/A conversion will occur in the speaker (or later?). But today, I see no practical advantage in a digital amplifier with only an analog input. It may be more efficient and it may be new technology, but the amplifier has got to stand on the same footing as any analog design and justify its existence by the way it sounds. The eVo did make a good case for itself at the demo, so I signed up to get one for review.

The eVo 200.2, a two-channel amp of trim dimensions and reasonable heft, is based on the class-T digital circuit developed by Dr. Adya Tripathi and Tripath Technology Inc. But while it uses digital signal processing, the eVo is really an amplifier with a switch-mode (class-D) output stage. Switch-mode amps switch their output transistors fully on and fully off at high speeds so that the speaker is alternately connected directly to the positive and negative supply rails. With no audio modulation, the time the plus transistors are on is equal to the time the minus transistors are on, and no audio signal is passed to the speaker load by the intervening low-pass output filter (footnote 1).
Standard pulse-width modulation (PWM) amps operate with a fixed switching frequency and vary the width of each + or - pulse so that the post-filter output recovers the amplified audio signal. Because no power is wasted as heat dissipated in the output transistors, a class-D amplifier can in theory approach 100% efficiency at converting the power in the wall socket into power used to drive the loudspeaker.
Class-T, not D
As far as I can glean from the available information the Tripath/EVo approach differs somewhat from strict class-D operation. Class-T amplifiers dither the switching frequency, adjust the "dead time" to suit the output devices, and modulate the switching frequency with the signal. In the EVo, the no-signal switching frequency is about 600kHz and the low-pass LC filter is set at 80kHz. The N-channel output devices (only two per channel) are capable of switching on and off in 30 nanoseconds, which means they can operate at rates approaching 33MHz! When an input is provided, the switching frequency is varied from about 200kHz up to 1.5MHz.
Because this variation is in inverse relation to the amplitude of the audio, it's supposed to provide very good linearity at low levels and very good efficiency at high levels. (Dare we infer that there is less linearity at high levels and, inconsequentially, less efficiency at low levels?) I can't find any description of how this modulation relates to a change in pulse width or duty cycle. The application notes do use an example of PWM in their general description of operations, although they insist that "Tripath uses a different technique, having nothing to do with PWM." Because "Tripath does not disclose the exact nature of its technology in order to protect its intellectual property," it will be especially interesting to see what John Atkinson discovers on the test bench.
What is apparent from Tripath's information is that its technology, while seemingly simple, needs to be optimized for the particular implementation, and a slew of application notes are provided their manufacturer customers for this. Bel Canto has built the eVo 200.2 with high-quality audio in mind. They use high-speed, audio-quality, differential input devices, optimize the "dead time" for the specific output devices, configure the two channels in anti-phase, and they provide on the printed circuit boards a dual-zone star grounding scheme with double-sided ground planes. The anti-phase relation between the two channels permits easy bridging without the additional stages, and the use of differential input amps provides for balanced and unbalanced inputs.
Initial Impressions
As the eVo emerged from its shipping carton, it was immediately apparent that its fit and finish are excellent. The front panel bears only a Bel Canto medallion and power LEDs. The rear panel has, from right to left, an EIA power socket and power switch, four plastic-capped heavy-duty binding posts for speaker connection, and four input sockets (two each of balanced XLR and unbalanced RCA). Between the input sockets are two small push-push switches: one selects between the balanced and unbalanced inputs, and the other (marked Stereo/Mono) can bridge the two channels to provide a continuous short-term output of 800W into a bridged 4 ohm load. The rear-panel layout is asymmetrical, but in a way that makes bridged connections more convenient.
Switch the amp on from the rear, wait a few seconds for the relay to click gently, and there's music. The simple and clear manual was hardly needed except to confirm that the amp is intended to remain powered up. With any of the inputs and any of the speakers I tried, the case of the eVo remained cool to the touch.
I inserted the eVo in my main system in place of the resident McCormack DNA-1 (Rev.A mod) and listened. Ho-hum. The eVo sounded kinda flat in perspective, and thin—not bad, but it seemed in great need of run-in before facing judgment (Bel Canto suggests at least 40 hours). Backlogged anyway with other obligations, I relegated the eVo to several weekends of less stringent duty at my weekend home in Connecticut.
As I listened to the eVo through the Paradigm Reference Studio/60s with CDs, digital cable radio, and DVDs during this period, I grew quite comfortable with its relaxed tonal balance and natural soundstaging. (Was the eVo breaking in or were my ears adapting?) My impression was that the eVo was unimpressive in the best possible way: It did not call attention to itself, and did not color the harmonics or dynamics of the music. Little seemed out of place, even in my very live Connecticut listening room.
Notably, the EVo's bass was full and tight on the Studio/60s, especially when compared to the Blue Circle BC22, and it was fully the equal of the Bryston 9B-ST in that regard. Where the eVo offered something distinctive was in its modestly laid-back midrange to treble. This resulted in a less than lively presentation with some program material. This fault, however, is a known feature of the room (and the program material), and the eVo merely made it more apparent.

eVo Redux
Back in the Big Apple, I teamed up the eVo with the Blue Circle BC21 preamp and, as I reported last month, the combination was remarkably potent. Rest assured that what I described was indeed the BC21's tonal balance; with all combinations of preamp and amp, the BC21's character remained constant. The EVo, however, was neutral, generously lending its muscle to support the BC21's bottom-up world view.
The BC21/EVo combination provided much guilty pleasure for me, as it endowed the music with exceptional power and weight. Not real? When recordings rarely make any reference to a real acoustic anyway, who cares! Besides, with electric bass, synthesizer, or otherwise, how can I know if the musicians intended it turned up to 11 or not? So rather than take the EVo/BC21 combination to task for eschewing chaste accuracy, I preferred to revel in the kick and slam and not fuss about absolute truth. [That's one slippery slope!—Ed.]
When the Blue Circle preamp was replaced by my reference Sonic Frontiers Line-3 and connected via JPS Superconductor-II balanced cables, the details of truth and beauty began to emerge. The eVo had been afforded all the break-in any amp was entitled to, and it showed. Digital, switching, or no, the eVo proved to be an absolutely first-class amp with some remarkable talents.
Without question, the EVo's bass reproduction was, within its generous power rating, as good as anything I have heard. It had the depth and definition of the best monster amps, but without any proclivity for overhang or boom. Glen Moore's string bass on "Man in the Oven" (King on the Road, Cardas) was powerful yet crisp, and as palpable as if I was hearing it from a front table in a small club. And while the eVo could be all bang and boogie with the BC21, it could also, when paired with the Line-3, deliver accurate and shuddering organ-pedal tones while retaining the distinctive character of each pipe.
The EVo's neutrality extended through the midbass and into the midrange. It did not emphasize any tonal band, and, if anything, seemed ever so slightly reticent from the presence range up. The amp was neither cold nor gray but, within the compass of neutrality, shaded away from warm. In the upper treble (above 3kHz), the eVo could sound a bit bright at extremely high levels. This might have been merely the perceptual complement of its presence reserve, but I wonder if it might, as well, have been some residual artifact from the characteristic class-T clipping noise well above the audio range. Surely, there was no grain or harshness anywhere in the EVo's presentation.
Recently, I did some comparisons of various incarnations of Louis Armstrong's "St. James Infirmary." Distinguishing the CD (Blue Moon BMCD 3067) from the LPs was not difficult, but the eVo made the differences between a late (Audio Fidelity AFSD 6132) and an early (AFSD 5930) release apparent. With each step back in time, Armstrong's voice became richer and warmer beneath the characteristic growl, and I got the impression of greater detail and resolution. Instruments were quite natural, with good placement, but the ambient bloom of each part of the mix seemed distinct. In general, the eVo was more successful in dissecting the mix than other amps, but its literal presentation was less sensually engaging.
The EVo's responses to dynamic changes were excellent. Very subtle changes, such as those resulting from the slight variations in volume created as performers move their heads or instruments in relation to the microphone, were easily apparent. Macrodynamic contrasts were delivered with appropriate force and without apparent compression or strain. While Murray Head's voice is highly processed and intentionally disembodied on "One Night in Bangkok" (RCA PD-13959, 12" single), the voices of the full chorus, the smaller ensemble of women, and the forward, breathy flute had jolting impact in this highly synthetic but hugely spacious mix. Beneath it all, the powerful beat was a pachyderm stomp. However, when dealing with recordings that attempt to re-create a live event, I felt that the eVo 200.2 rendered the interaction between dynamics and perspective in a unique way.
The Small Print: Isn't Louder Closer?
When you sit closer to the performers at a concert, the music is louder and the lateral spread of the ensemble seems wider, even though we know that the musicians are not playing any louder. This is true of vision as well: a horse 20' away occupies a larger portion of one's visual field than does a horse 50' away, even if the horses are the same size. We interpret proximity, in part, from image size.

In the home, we turn up the volume to make the audible image of the performance seem larger and, as a direct consequence, the performers nearer. This maneuver should not make the performers sound as if they're playing louder, because the true loudness of the performing instrument is encoded into the recorded harmonic content and dynamic emphasis. At least, this has been my experience.
That's not what I heard from the eVo 200.2. When I turned up the EVo's wick, everything got louder, but not much closer. The eVo forced me to find the one volume level that suited the sound captured on the recording. At that unique and appropriate setting, the eVo offered a breathtaking glimpse of the original event. The best example I found was the Glen Cortese/Manhattan School of Music recording of Mahler's Symphony 3 (Titanic Ti-252). Recorded during a live performance at the Riverside Church, the highly reverberant acoustic usually drives me to increase the volume in order to get sufficient presence and detail. With the EVo, I was quickly swamped in ambient soup, while the music was simultaneously too loud and too distant. I had to find that very specific level where the listening room's walls melted away. As the last movement's opening theme shifted to the lower strings, so clear was the depiction that I felt I could hear the violins not playing.
Good harmonic and dynamic performance is required for an audio component to successfully re-create soundstage width and depth. The eVo performed outstandingly in this area, but its soundstaging depended on finding the appropriate volume level. The aforementioned King on the Road was a great example of this. When I got the level right, the eVo extended the front end of my room right into George Cardas' studio.
The downside was that inappropriate settings, whether too loud or too soft, created cognitive dissonance between the ambient perspective and the music's tonal and dynamic characters—the audio equivalent of an optical illusion. The upside is that few amps, at any volume level or price, sound as defined, powerful, and uncolored as the eVo did when set up right. Of course, I can still move my listening chair...
The Large Print
The eVo challenged my presumptions about what's truly accurate. Its dynamic and perspective behavior, as well as a possibly related midrange dryness, made the eVo sound a bit analytic in my system. And, in an A-B comparison, it lacked some of the airiness of the other amps.
But these faults, if they are faults, are small in significance. I won't condemn this otherwise outstanding amplifier simply because its presentation was, in my system, somewhat different from what I've grown to expect—there were too many instances when the eVo stripped away familiar resonance and bloom and communicated the musical event with elemental transparency.
Try Marc-André Hamelin's brilliant Liszt recital (Hyperion CDA66874), recorded in Wigmore Hall by Tony Faulkner and Andrew Keener. The eVo placed all the gleaming power and detail of Hamelin's grand piano right there between the speakers. The hall's ambience lent reverberant weight and dimension to the direct sound while remaining distinct and unconfusing.
If there really is, as many believe, only a single correct volume setting for the truthful re-creation of any particular acoustic event, the eVo made that choice easier to find than with other amplifiers. It was easy to dial in the precise correct level for Michael Daugherty's wry and witty Red Cape Tango (based on the Dies Irae!), with Eugene Corporon conducting the North Texas Wind Symphony (Klavier K-11109). I got the opening antiphonal exchanges, spaced laterally and in depth, to sound proper, and the eVo presented the rest spectacularly.
Conclusions
Regardless of price or of underlying technology, the Bel Canto eVo 200.2 power amplifier is one of the best on the market. Its bass performance is state-of-the-art. Its high resolution and lack of grain are exceptional. Its mild reserve in the midrange will exactly complement many speakers and systems, and should not be terribly significant with the neutral ones. Its subtle and powerful dynamic performance is, however, distinctive as well as instructive. Is it more dynamically accurate than other amps, or is it just more finicky?
That could depend on your equipment and how you listen. At the price asked, the eVo demands consideration. Even if you're planning to spend a lot more, you can't ignore it. Bel Canto's eVo 200.2 is one serious amp.

Sidebar 1: Specifications
Description: Solid-state, two-channel power amplifier with "class-T" output stage and two pairs of multiway binding posts. Inputs: 1 pair line-level RCA, 1 pair line-level XLR. Continuous power: 120Wpc into 8 ohms (20.8dBW), 200Wpc into 4 ohms (20.dBW), 100. Power requirements: 30-600W.
Dimensions: 17.5" W by 3.5" H by 16" D. Weight: 35 lbs.