Bel Canto Design Goes Full Circle

Gallic sophistication

"Like a turd that won’t flush." This deft one-liner is uttered by a frustrated Dennis Hopper as the bad-to-the-bone one-eyed Deacon of Kevin Costner’s Waterworld. John Stronczer, though he surely would use other imagery, has had his own visitation that just won’t go away either.

It’s sometime during the early ‘80s. Deep in the heart of Gaul, a small but fiercely independent group of audiophiles are the last bastion of resistance against the usurping onslaught of American-sponsored high-wattage solid-state amplification. Not unlike his more martial comic-book brethren Asterix and Obelix, Grandmaster Audiofix, aka Jean Hiraga, of Le Groupe l’Audiophile of Paris possesses his own secret brew. Centuries earlier, the original Gallic saboteurs pounded Roman centurions into oblivion by crushing them under oversized burial rocks. Modern-day Hiraga drives sonic mediocrity into the ground with flea-powered SET amplification and Altec super-high efficiency horn speakers. The visiting foreigner Stronczer, just in from the US, attends a secret partisan gathering of Le Resisténce in a private audio chamber below the Louvre. He has a massive epiphany to the accompaniment of a few measly watts. He leaves Paris thunderstruck. What he has just heard still rings in his brain and defies all rational explanation. Unfortunately, the available SET designs back home borrow heavily from the Western Electric 300B technology of the day. They don’t manage more than 5-7Wpc, not enough to drive his favored Spendor SP-1 loudspeakers.

American ingenuity

John Stronczer’s R&D work at Honeywell at the time revolves around high-performance analog and digital integrated circuits. His engineering talents eventually lead him to co-found a custom IC design house that specializes in high-speed fiber-optic communications for Datacom and Telecom applications. Later still, the AMCC Corporation, a publicly held company in San Diego, will acquire this start-up. For now, Stronczer’s significant design expertise propels him to pursue the elusive aural magic of Hiraga’s system that won’t leave his dreams. He moonlights on the side and crafts a 20Wpc SET amp around the 845 tube that’s widely used in radio broadcast applications. The architecture of this amplifier will eventually form the core circuit of a group of high-powered SET amps that are introduced by Bel Canto Design, a company John Stronczer founds in the late 1980s.

Gone fishin’

Fast forward to early 1999. I’ve lived with the Bel Canto SETi40 integrated 845-based 40Wpc amplifier for four months before its rightful owner reclaims it. An absolutely fabulous piece of cutting-edge design with a superbly implemented remote control, I find it well deserving of the glowing acclaim bestowed upon it by the audiophile press around the world. The latest such recognition is the Diapason d’Or, France’s most prestigious audio award. Some months later, Marc Mickelson’s SoundStage! review and subsequent Reviewers' Choice Award of the Bel Canto DAC1 hit the cyber waves. They cause me to contact Bel Canto’s capable sales manager to request a sample -- the rightful owner this time to be yours truly. Some days later, Chad Baures follows up with an e-mail. The subject line simply states, "This stuff will blow your mind." Never one terribly mindful of getting blown, I hastily open the attachment. I can’t believe my eyes. It’s a temporary white paper on a brand-new solid-state digital-amplifier technology. To add insult to injury, Chad whispers a secret into my ear -- "these amplifiers sound better than single-ended designs." Sacre bleu! What a cruel stab to my sensitive thermionic heart. Delivering a potentially fatal final blow with matador-like poise, Baures now offers me the chance to hear one hot off the first production run.

Hooked -- the appointment with the dentist

Now usually boastful claims of new, obliterating-all-previous-standards discoveries in audio go into one of my ears and quickly out the other before anything truly registers. But having heard for myself what the Bel Canto SETi40 and DAC1 are capable of makes me stop in my cynical tracks now. While digital and vacuum tubes seem unlikely bedfellows, a quick look at the Crystal CS 3310 chip that’s at the heart of every Bel Canto remote volume control corrects such antiquated thinking. Never mind, of course, the proprietary and very ingenious implementation of digital upsampling that powers the affordable DAC1. I also recall that in the early days of the Digital Axiom alliance around Muse’s Kevin Halverson, the membership of contributing designers included Jeff Kalt of Resolution Audio and John Stronczer of Bel Canto Design. Hmmm.

If this engineer and crew are said to have come across a new and better wrinkle to elevate my aural perceptions into suspension of disbelief, I’m inclined to take serious the claims of his sales-and-marketing guy. And yes, I would squirm and cringe if digital solid state turns out to be indeed better than my beloved feedback-less triodes. The last digital challenger I’ve heard, the TacT Millenium Mk II, came mighty close. It actually outperformed every amp I’d ever heard in the resolution department. But it rather trailed my beloved and triode-powered Art Audio Jota in sheer musicality. Its appearance in my system suggested, though, that digital-amp topologies might well be the future -- and if emotionalism were missing in the first example of this new breed, who better to remedy that aspect than the designer of the all-tube Bel Canto single-ended, zero-feedback triode amps? Do you see now why this article is headlined Full Circle? Let’s take a look into our new horse’s mouth, count its teeth, check its breath and learn what makes it tick.

Counting teeth

With their EVo -- for Evolution -- 200.2 amplifier architecture, Bel Canto has licensed a technology called Digital Power Processing[TM] that was developed by the Santa Clara-based Tripath Corporation. Unlike small high-end-audio firms embedded in what, let’s face it, is really a cottage industry, Tripath’s Silicon Valley location and connections helped it raise $21 million of corporate venture capital since 1995. The company currently employs a staff of over 50. Named after its founder, Dr. Adya Tripathi, it has applied for more than a dozen US and international patents to support and protect what fundamentally is a novel and proprietary high-speed DSP IC that controls high-voltage circuits instead of low-level signal or data. Proprietary algorithms provide the computing power, incorporate protection schemes and feature a unique adaptive mechanism whereby the DSP engine learns the non-linearities of the individual output transistors and compensates automatically for perfect behavior. This self-corrective function addresses imperfect switching, ground bounce, output-transistor mismatches, crossover distortion between output device on-off cycles and residual energy from the oscillator in the audio band. It forces the output stage to operate at peak performance at all times.

The mechanism triggering the output transistors of the Bel Canto EVo topology is not pulse-width modulation and fundamentally very different from the digital architectures used by TacT, CAL, Linn, Spectron and Wadia. Class-D pulse-width-modulated amplifiers feature a fixed, 100-200kHz clock frequency that requires steep filtering to extract the massive switching noise from the audio signal and pass low electromagnetic emission inspections. As always, there are exceptions. Spectron's Digital One features a higher sample rate of 500kHz and uses a single inductor and capacitor as output filter. However, Class T -- as the Tripath method has been coined -- uses a waveform that's far more complex.  It’s distributed widely using varying sampling rates from 200kHz to 1.5mHz. Similar to spread-spectrum technology, this doesn’t concentrate energy at any given frequency. Bel Canto implements a simple second order LC filter at 80kHz to demodulate this waveform and thus drive the speakers. Stronczer refers to the technique as essentially a Delta-Sigma power DAC that follows a low-level analog signal-processing stage.

If high-level amplification is like climbing a mountain, conventional linear topologies are approaching the peak on the most difficult and hazardous route while the DSP approach is the easiest and most effective. Both arrive at the top, but with disproportionate levels of expended effort and hence associated cost. If this simile is appropriate, you should expect that the view from the peak and the enjoyment thereof be affected by the condition of the climber. One climber arrives disheveled, out of breath and seriously overheated. The other remains serenely unruffled and fresh as mountain dew. Do you imagine for a moment that their experience is the same?

While Bel Canto is the first high-end manufacture to incorporate DDP, John Stronczer is convinced and candid that before long, all amplifiers will be built along similar lines. But as always, implementation leaves room for varying degrees of performance. Bel Canto’s past design expertise is fully exploited to integrate the modified OEM chip into a proprietary circuit that precedes and follows the DSP engine and includes DC-offset fault detection, one function that isn’t incorporated into the chip. Stronczer estimates that he has about a six months’ head start on the competition. He isn’t about to just sit there now and wait for others to catch up. At the moment, this puts him squarely at the very edge of the state of the art. Remembering that his company is primarily known for manufacturing highly acclaimed single-ended triode amplifiers and preamps, this is a strong statement indeed. It makes him his own most formidable adversary.

The advantages claimed for this new technology are numerous and impressive. They’re also uniquely communist in the most visionary sense of the word. Consistently high performance is made possible by much simplified, downscaled associated hardware. This should keep manufacturing costs low and allow for uncommonly affordable, lightweight, cool-running and high-powered amplifiers. Better yet, associated sound quality is claimed to be superior to the current state of the art when implemented accordingly. Great sound for the masses -- did I just call it wear-the-same-uniform communism? If this were to happen, how are you supposed to differentiate and distinguish yourself from your mid-fi neighbor? With character instead of possessions, making it visionary communism? While you ponder this philosophical challenge, let’s return to more mundane matters.

Conventional class A and A/B amplifiers referred to as linear amplifiers are notoriously inefficient and waste up to 80% of produced power as heat. This mandates hefty power supplies, huge transformers and massive heatsinks. All this combines to manly but expensive and ultimately redundant hardware if a more efficient, elegant approach were found. Class D switch-mode amps seem to answer the matter of redundancy and do successfully overcome the inefficiency of linear topologies. However, in direct comparison, they tend to lose the battle on the fidelity field very early. Their primary use concentrates on subwoofer amplifiers or battery-powered applications where flat response and very low distortion aren’t paramount. Class-T amplifiers, in theory at least, promise a combination of high fidelity and high power efficiency. Hence the strange moniker Combinant Digital was branded in the hope to associate these qualities in OEM products employing this licensed technology.

A block diagram of the basic Class-T architecture shows a traditional analog input signal buffer from which the DSP engine performs adaptive signal conditioning, digital conversion, mute control, overload protection from output shorts, predictive processing and qualification logic functions. The algorithms are derived from telecommunications processors. The output of the DPP block controls a power output stage that drives the speakers through a basic output filter.

In Bel Canto’s EVo amplifier, the implementation of the class-T topology results in efficiency of greater than 90%. This means that if the amplifier uses the equivalent of 100 watts from the wall, it produces 90+ watts at the loudspeaker. This allows the use of a power transformer half the size of what the equivalent application would require in a conventional linear design. High efficiency also significantly improves reliability of internal componentry. It avoids thermal distortion artifacts and bias drift that result from heat-related non-linearities introduced in the output devices. YBA’s Yves-Bernard André has repeatedly gone on record about thermal distortion being one of the most overlooked and misunderstood aspects of amplifier design. British speaker designer Phil Jones has come to similar conclusions in the loudspeaker field. The absence of bias drift in an amplifier relates directly to rock-solid stability of soundstaging and bass control. The high efficiency of the output stage further eliminates the need for multiple paralleled output devices and the concomitant challenge of matching and biasing. Only two rugged N-channel devices are used for Bel Canto’s new EVo 200.2 amplifier that produces 240Wpc into 4ohms. Retail is set at a very reasonable $2150 USD. Contrast this with the $10,000+ cost for the similarly powerful TacT Millenium Mk II and the word reasonable hits the nail on the head.

The inherent simplicity of class-T operation requires no overall analog feedback to arrive at stunningly low distortion figures. In high-end audio, low distortion is usually considered less than 0.1% of THD+N (total harmonic distortion plus noise) and IMD (high-frequency inter-modulation distortion). The Bel Canto amplifier handily goes beyond, with THD+N and IMD figures of less than 0.05% over the entire audio bandwidth. The ultra high-speed operation of the output stage moves between the power supply rails in less than 30 billionths of a second. It’s thus devoid of small-signal crossover distortion said to result in remarkable low-level resolution.

Popping the hood on Mr. EVo, theory and reality converge. There’s very little inside. The motherboard is 8.5" x 5.5", mounted on stand-offs and populated by two coils, two output devices per channels that are mounted to small chimney-style finned heatsinks, two main capacitors and a few assorted small caps and resistors. A small input board for the XLR and RCA terminals with a flying lead to the motherboard plus a massive potted 500VA toroid complete the parts count. The mysterious headline act, the Combinant Digital computer chip module, 3" x 2" in size, is placed centrally on the motherboard. And that’s it. No heatsinks, no megafarad capacitor banks, no massive shielding as in the TacT, no packed-to-the-gills complexity. Remembering the less-is-more battle cry of most things ingenious, I’m nodding my head in agreement and surprise. This is massively minimalist indeed -- elegant, in fact. Were it not for standardized sizing of components, this amp could fit into a half chassis and have plenty of room left to breathe. I understand that the final production version will have a slightly different internal layout, with one single board for both input connectors and main circuitry. Also, four more storage capacitors will be added.

In order to verify the amp’s efficiency, a PS Audio PowerPlant 300 lends itself as the perfect arbiter of truth over fiction. Despite PS Audio’s recommendation to only plug source components such as preamps, CD players and DACs into their least powerful AC regenerator, I side with the "innocent-until-proven-guilty" crowd. In goes the power cord feeding my EVo 200.2 amp. In my sizable room, with volumes pleading for long-term hearing damage, the mode switch that displays the actual power draw through the PowerPlant reads out a puny 30 watts. If the Bel Canto amp is 90%+ efficient, that equals 27 watts of input power at the speakers. Based on my experience with the 20Wpc single-ended Art Audio Jota, this sounds spot-on. The EVo amplifier behaves exactly as predicted by its engineer. It is supremely efficient and runs cool all day long.

Pulling teeth

Now that you have an idea of the technology behind this new amplifier architecture, I imagine you want to know what it sounds like. Stay tuned to our SoundStage! Cyber pages -- a feature review is already in the works. I will pen a brief side bar to add a second opinion to go with it. This will give me some time to become familiar with this Bel Canto piece while the review honors go to someone who will evaluate the amplifier purely on sonic merits and without the possible preconceptions that can occur when you spend time with the people behind the product. However, from what I’ve heard so far, I’m very comfortable telling you that this amplifier is very good indeed. The musicality and ability to communicate emotionally that I felt were lacking in the TacT Millenium Mk II are here in spades. I haven’t determined yet whether my single-ended triode Art Audio Jota is being bettered or not, and if so in what areas, but it seems apparent that the Bel Canto amplifier performs on a similarly elevated playing field. Let’s see what our reviewer has to report.

Toothless wisdom

In closing this exposé, let me leave you with these thoughts: No company raises $21 million of venture capital to sell a few high-end amplifiers to folks like you and me. I frankly marvel at the sheer scale of commitment the Tripath Corporation has made to its investors. I’d say it’s patently obvious that hundreds of thousands of whatevers need to be sold on a continuous basis to amortize the start-up R&D cost and generate income revenues for the stockholders. These whatevers certainly will be powered by Tripath’s exclusive DPP technology, but it won’t have to happen just in audio. The requisite sales volume in the audio industry is possible if a giant like Sony were to embrace the technology or Bel Canto becomes the next unqualified home run. But applications for Digital Power Processing aren’t limited to the audio industry, whether in car, home or pro. Wireless communication is a giant market just waiting to be tapped and dominated by adapted DPP technology. The extension of talk- and stand-by times for cell phones through improved radio-frequency amps is just one of the many challenges this technology is poised to address eventually. Then there’s high-speed networking, motor controllers such as those used in disk drives, energy-conserving power supplies….

While the future is anyone’s wild guess, it’s fairly certain that DPP is a force to be reckoned with in one guise or the other. In the company’s own words, "Digital Power Processing does for power what the microprocessor did for data. It has the potential to become nothing less than a ubiquitous technology. Tripath’s mission is to see that it achieves that potential."

If that’s so -- and I’m ill equipped to argue the point -- isn’t it remarkable that such an invention is introduced to audiophiles and music lovers like you and me by a company that has made its name and mark with vacuum-tube technology? By introducing their EVo 200.2 amplifier, Bel Canto has gone from antediluvian oxcart technology -- single-ended triode circuitry -- to space shuttle magic -- digital power processing -- in one huge quantum leap, omitting everything in between. This is one of the more unusual stories I’ve come across in high-end audio.

Closing credits

Having gotten the low-down on this technology, I’m about to hang up with John Stronczer when I learn in parting that he is off to France. While he doesn’t disclose his destination, I’m hazarding a guess. He’s on an undercover assignment, returning to the scene of his original epiphany, EVo 200.2 under his duster like a sawed-off shotgun. He is going to demonstrate to those Gallic tube maniacs a digital amplifier that boldly goes where even their flea-powered triodes maybe haven’t quite gone before. Or something like that. In any case, he's come full circle indeed.

...Srajan Ebaen
srajan@soundstage.com

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