Preamble
If you are one of those audiophiles who doesn't take single-ended triode amplifiers seriously, get ready for a paradigm shift. I guess if you need one of those mega-power solid-state monoliths to boost your ego and impress your audio buddies, then a 3.5 Watt amp with a pair of 2A3 direct-heated triodes just won't set your heart aflutter. I can understand that. This is why I want to tell you about the Bel Canto SETi40 integrated amplifier.

The SETi40 has all the credentials that the triode-maniac insists upon: pure class A operation, zero negative feedback, and one direct-heated power triode per channel, run hot and hard. But in this case, the tube that Bel Canto's John Stronczer has chosen to design with for the last fifteen years, is a radio transmitting triode: the redoubtable 845. These tubes are plentiful and cheap. A complete re-tube will cost about $200 after 8000 hours, or so.

The 845 is from the same family of tubes, and is the same size, as the 211 triodes used in the Audio Note Ongaku. This is a big tube and it is a good one. Pick it up. Handle it. An EL-34 pentode is like a peashooter in comparison to this magnificent piece of glass. Pause for a moment while holding the 845 in your hand. It will make you feel like Ming the Merciless.

When the SETi40 is switched on, you will be startled to see that the tube heaters glow bright yellow-white like an incandescent lamp. I think the U.S. Navy used the 845 in the transmitters on PBY Catalina flying boats. If they didn't, they should have. The fiercely glowing filaments would have kept the radiomen warm on those long patrols over the Pacific.

Design
The Bel Canto SETi40 integrated amplifier is a highly refined piece of technology that deserves our admiration for its level of sophistication and ease of use. This isn't a home-brew spam-can with a few holes punched in it for some oddball triodes and junk-store transformers. Of course, you're going to pay for this level of engineering, but you get a lot for your money.

The unit weighs about 30 kilos (65 lbs.) and most of that is devoted to the amplifier's massive transformers. The case is heavy gauge steel finished in black crinkle enamel. The effect is serious and businesslike and more than a bit retro-cool. It reminds me of the finish on those Bell & Howell slide projectors they sold when Kodachrome was introduced in the early 1930s; or the camshaft covers of a Ferrari GTO - take your pick. The message is received loud and clear: we're here to stay. My favourite styling cues, though, are the retro-tech rings-of-gold encircling the massive 845 power triodes like something out of an H. G. Wells novel. They are functional, too, protecting one from the furious heat dissipated by the tubes' filaments, while, at the same time, acting as heat sinks. They also diffuse the glowing illumination of the power tubes in an attractive and chic deco style. Finally, I must mention the way in which the unit's transformers have been molded into part of an organic whole. The transformer cover, with its stolid left and right bastions conjoined by an artfully curved façade, reminds me constantly and consistently of Frank Lloyd Wright's design for Unity Temple in Oak Park, Illinois. Why this should be, I cannot say precisely except that there is something monumental about the design of the whole Bel Canto SET line that touches my collective unconscious. Dare I suggest that there is something here that reminds me of an altar with candles glowing in the darkness?

If the owner cares to look inside, he will find high quality components well spread out on a 1/8^th inch-thick fiberglass printed circuit board. No hard-wiring for Bel Canto, contrary to current fashion among other single-ended amplifier manufacturers. "Why", I asked Bel Canto? "Better sound", they claim. Using circuit boards, there are fewer manufacturing inconsistencies - makes sense to me. I was surprised, however, to see a bank of high-speed solid-state rectifiers inside the SETi40. Some single-ended purists claim that tube rectifiers are the only acceptable way to build a power supply. This may be true when you are running 300Bs at 350 VDC, but when you are dealing with 1200 VDC and selling to the public…don't mess with Mother Nature.

Features
The SETi40 was designed as a remote-controlled integrated version of the Bel Canto SET 40. It produces 40 Watts per channel over a bandwidth of 5Hz to 35kHz, and is said to have exceptionally low distortion, primarily second order harmonic. There are three gold-plated RCA input jacks on the rear panel as well as a robust switch for selecting 4 or 8 Ohm output impedance. The five-way binding posts are excellent quality. The on/off switch on the rear panel sets the amplifier to standby mode. After a very brief wait in standby, the amp can be fully powered up.

The remote-control functions are comprehensive: volume, balance, mute, input selection and standby/on/off. Volume control is accomplished with a very advanced analog Crystal 3310 chip stepped attenuator. Changes in volume settings are displayed via a red LED readout, large enough to be easily seen from the listening position. Relays, closely located to the volume chip, are used for input switching. All controls worked silently, without clicks, pops, or thumps. I found the remote control to be a worthwhile addition to the design and hope that more manufacturers will incorporate one into their future offerings.

The input circuit uses pairs of 12AX7 tubes for each channel in a modified series-regulated push-pull (SRPP) configuration. Some single-ended gurus consider this arrangement to be less than optimal. I won't attempt to argue the point here. Bel Canto has some good reasons for going this route, as outlined in a white paper on the company's web site. The SETi40's output power tubes are self-biasing and, therefore, never need to be adjusted, even after replacement.

Nuts and Bolts
For many reasons, the Bel Canto SETi40 is a very impressive amplifier. I have already outlined the technical sophistication and the aesthetic appeal of the design. What impresses me most about the product, however, is simply this: it is single-ended and it will drive my Quad ESL-63s with ease. Finally, we have an SE amp that will drive most real-world audiophile speakers - the speakers that music lovers actually own and enjoy - with credible volume and dynamics.

Now, I present the case for single-ended amplification.

Do you remember Andy Granatelli's STP turbine cars that raced at Indianapolis in the late 1960s? A turbine engine is a cigar-shaped tube with a longitudinal shaft to which a spiral of many small perpendicular fan blades is attached. The blades at the front of the engine draw in air. Fuel is injected directly into the combustion chamber, where it is ignited, and the heat from the inlet air and expanding exhaust gasses cause the blades to spin at speeds over 50,000 R.P.M. At Indianapolis, the turbine car was superior to the rest of the field because the engine was smoother, more powerful, and consistently at the peak of its power band. That's what a class A, single-ended amplifier is like: a turbine at full bore. The volume control on your pre-amp is your rev-limiter, and the music signal your throttle and brakes.

Push-pull designs are cheaper and easier to implement for a given power output but they suffer from a number of lamentable limitations, as did the front-engine Offenhauser engine cars that thrilled the crowds at The Brickyard.

Some degree of negative feedback is used in almost every push-pull amplifier because it reduces measured distortion. It seems, however, that negative feedback introduces some subtle, unmeasurable distortions, which are manifest to the ear as poor timing, dynamic compression, and alteration of instrumental timbres. The harmonic distortions of the single-ended amplifier are primarily second-order, a point on the harmonic spectrum that the ear finds quite acceptable. This is why single-ended amplifiers have no need for negative feedback. Continuing with my automotive analogy, I like to imagine negative feedback as steering that lags behind the driver's inputs so that he is constantly over and under correcting in an attempt to maintain a perfect line while traveling at speed. Perfectly direct steering is the equivalent of zero negative feedback.

The last point I want to make is that a push-pull amp must have a phase-splitting front end. The input signal is divided into positive and negative halves in order to drive the pairs of output tubes that are chugging up and down like a pair of pistons. The necessarily imperfect blending of the positive and negative signal halves causes a blurring and veiling in the output stage that reminds me of a carbureted piston engine with a timing problem.

Listening
The Bel Canto SETi40 sounds so different from the other tube amplifiers I have been listening to that I wasn't sure I could muster the vocabulary to tell you about it. That's why I developed the turbine analogy in the previous section, because that was the overwhelming impression I had, and still have, of this amplifier. The differences are subtle, certainly, but undeniably real.

The grainless purity of the SETi40's treble lets one forget the medium and become absorbed in the music. Thanks to its lack of negative feedback, the SETi40 allows one to listen to the music in a new way. Rather than being a distant spectator, we find ourselves participating in the musical event. The emotive intention of the artist is clarified and illuminated by this amplifier in a unique and extraordinary fashion. This struck me once at a concert by flute virtuoso, Jean-Pierre Rampal. I thought to myself, 'He is the music!'. And that's what it's like listening to the Bel Canto. The most subtle artistic nuances are so delicately rendered that one feels the very presence of the musician. And that extends to the recording environment as well.

Take, for example, one of the finest Beethoven Fifth Symphonies ever recorded, Erich Kleiber conducting the Concertgebouw Orchestra (Decca LXT-2851). Even though this is a mono recording, the sonic signature of the hall is easily discernible. And need I say anything about dynamics, drive, and timing? No, this is what we call musical artistry.

Another record that revealed itself to be stunning was the Elgar Violin Concerto with the RPO under Sir Charles Groves (EMI ASD 2883) featuring Hugh Bean on solo violin. This is, perhaps, Bean's signature recording, and certainly one of the best ever engraved on vinyl. The liquid purity of the sound of the violin made me realize how choppy and mechanical push-pull amplifiers sound. The difference is, as the French say, epouvantable.

This natural smoothness can be ruthlessly revealing, though. Listening to the Vaughan Williams, Academy of St. Martin in the Fields/Marriner collection, Greensleeves (Super Analogue KIJC-9109) gave me the uneasy feeling that some equalization had been applied to the Japanese stamper. Nevertheless, The Lark Ascending, featuring Iona Brown on solo violin, sounded sublimely sensual. On one hand we have the delicate, spiraling solo part, and on the other, the rich, resonant cello and bass choirs showcased by the full-throated lower reaches of the magnificent 845 triodes.

Conclusion
If you want further examples of the musicality of the Bel Canto SETi40, have a look at the first installment of my series on the classic London Blueback LPs published recently in Audiophilia. All of the listening for this article was done with the benefit of the Bel Canto.

The SETi40 is a great amplifier, especially if you are wed to a pair of Quad ESL-63s and want single-ended sound. The 845 is a powerful, masculine tube that is capable of driving the Quads (as well as more conventional loudspeakers) to realistic levels without stress. Needless to say, I recommend the Bel Canto SETi40 without reservation.