Bel Canto eVo2 two-channel power amplifier By Steven Stone   •   September, 2004 Most power amplifiers are primarily differentiated by their size and color. Eventually, even an amplifier fetishist grows weary of digging for the minute variations that make each amplifier special. Perhaps that's why it's so refreshing to discover an amp that embraces some truly unique new technology. Bel Canto, a small company located in darkest Minnesota, has managed to find a way to manufacture a digital amplifier, dubbed the eVo2, whose performance rivals that of more conventional analog designs.

History and Design
Bel Canto's original products were single-ended tube amplifiers. These large, hot, low-powered behemoths have very simple circuits that, although inefficient, produce wonderfully lush, beautiful sound. That's why founder John Stronczer named his company Bel Canto, which is Italian for "beautiful singing."

After making and refining tube amps for several years, Stronczer began to explore the possibility of making a solid-state model. After examining and discarding conventional solid-state designs, Stronzer learned about a new circuit: the Tripath modulation chip. This chip digitizes an analog signal into a continuous delta/sigma digital bitstream and permits the introduction of proprietary noise-shaping into the signal path. This digital signal-processing (DSP) function not only reduces digital noise, it moves the noise up into a higher, inaudible frequency range. The Tripath chip also allows for a feedback loop path to further reduce any nonlinear distortion.

Unlike previous digital amplifiers, which lack enough bandwidth and a high enough modulation speed for good high-frequency reproduction, the Tripath chip, which operates at 750kHz, can produce clean, low-distortion signals up to 80kHz. The Tripath circuit differs enough from conventional class-D digital amplifiers that it's designated class-T.

Following Bel Canto's philosophy that a simple circuit is better, the eVo2's signal path is short and sweet. Although the eVo2 has both balanced XLR and single-ended RCA inputs, once the analog signal enters the unit, only a single-ended signal goes into the Tripath chip, where it is digitized, and it remains in the digital domain all the way through the amplifier.

After the Tripath chip, the signal goes to a second gain stage, which amplifies its level before it goes into MOSFET power devices. These N (negative) channel devices use +/-45V power rails and are turned on and off by the digital signal itself. This technique, called pulse-density modulation, produces the current that then drives the speakers.

Additional circuitry, in the form of a digital feedback loop incorporating DSP and an 80kHz filter, reduces any remaining distortion and digital artifacts. The feedback loop occurs prior to the output filter, which thus can't slow down the transient response.

The eVo2's circuit design avoids the signal errors and crossover distortion problems typically found in analog class-A/B solid-state amplifiers. All analog signal processing happens at extremely low voltage levels, when the signal initially enters the amplifier. The digital switching design allows the two high-current MOSFET power devices to operate at greater than 90% efficiency, vastly reducing thermally created distortion. Equivalent sig-nal-power performance from a class-A/B solid-state amp would need nearly twice the power transformer, which would add to the weight and cost.

The eVo2's power de-vices are so efficient that they generate very little heat; there's no need for the usual massive heatsinks found in most power amplifiers. This, too, means that the amplifier can be much lighter and smaller than a conventional design. Installers take note: Even when the eVo2 runs at maximum capacity, it generates very little heat, so it can be placed in a confined space without the need for cooling fans.

The eVo2 can be used as a stereo or mono amplifier. From stereo to monaural operation, the amp's rated output goes from 120W to 400W into 8ohms. Because of its massive 1500VA transformer, when harnessed to a 4ohms load in mono, the eVo2's output nearly doubles, from 360W into 8ohms to 700W into 4ohms. The eVo2's combination of light weight, low heat, and pro-digious power make it an ideal choice for custom installations where space limitations rule out more conventional amplifier designs.

A Beautiful New Voice
The first thing I noticed about the Bel Canto eVo2—even before I took it out of its box—was its weight. Or, more correctly, its lack thereof. Given its impressive output capabilities, the eVo2 should weigh more than a measly 36 pounds. If it were a conventional solid-state design, it would probably weigh at least twice that, but its unique circuit design allows the eVo2 to be much lighter and smaller than the competition.

Liberated from its packing, the eVo2 makes a stylish first impression. The understated good looks of its silver anodized front panel contrast nicely with the black oval inset in the center. Only a well-concealed Standby/On button and centrally located blue LED disturb the panel's Zen-like minimalist purity. Unlike those amplifiers whose appearance resembles an early-'70s Detroit muscle car, the eVo2's physical presence feels like a new Audi TT sports model—smooth, understated, and technologically advanced.

The eVo2's rear panel contains input hardware for both balanced (XLR) and single-ended (RCA) inputs. Selector switches for Stereo/Mono and XLR/RCA, two pairs of five-way, EU-certified speaker outputs, and an IEC AC cable receptacle complete the rear panel.

A Soprano or an Alto?
Producing an efficient power amplifier is nice but nothing new—mediocre-sounding class-D digital amps suitable for driving subwoofers have been around for years. The Bel Canto eVo2 earns a special place in this videophile's heart because not only is it efficient and so runs cool, it also sounded remarkably good.

While the Bel Canto amp is a stereo design, it can be bridged for mono operation. And that's how I evaluated it—or rather five of them, to be precise. Given its $3290 price (each), I expected the eVo2 to work flawlessly, and all five review samples did just that, though I did manage to trip the front pair's protection circuits several times. In each case, the amplifiers came back online after the preamp volume control was turned down to less lethal levels. During normal operation, the eVo2s were absolutely silent, in terms of both physical noise from their transformers and background noise from the speakers. Only by practically inserting my ear into the tweeter of one of my Dunlavy SC-VIs could I hear the faintest hiss to signify that that speaker's eVo2 was indeed turned on.

When I combined the eVo2 with Meridian's latest incarnation of their 800-series processor, I was immediately struck by the entire system's lush musicality. I found the eVo2 so harmonically neutral that other components in the system had far greater effects on the harmonic balance.

As I've written in the past, all amplifiers have some sort of sonic personality or variation from absolute neutrality. In recent years, these variations, especially in top-echelon amplifiers, have become increasingly minute and subtle. The eVo2's sonic personality was among the most harmonically neutral I've heard in more than 25 years of reviewing. If I were forced to decide on which side of warm/cool and subtractive/additive the eVo2 fell, I'd say warm and additive—similar to a good tube power amplifier. But the eVo2's warmth was exceedingly subtle—not obvious, as with the Manley Snapper tube amp and Pass X-3 solid-state (which is very tube-like). The eVo2 didn't sound noticeably warm so much as it didn't sound colder than neutral, as Bryston's PowerPac 120 does.

A top-flight amplifier must have the ability to pass sonic information to the speakers without reducing the level of detail. Usually, the first inkling that an amp is subtracting anything from the signal comes when listening to soundstage characteristics—as J. Gordon Holt has told me many times, depth is always the first thing to go. Because movie soundtracks rarely have very much in the way of consistent depth information, 2-channel music—more specifically, classical music—provides the best clues about an amplifier's ability to re-create depth.