Can an "exotic" output transformer-less amp survive in the late 20th Century hi-fi marketplace? Even in single-ended circles, word has it that Atma-Sphere is the company "most likly to succed." Art Dudley listens to their M-60 Mk.II monoblocks.
Atma-Sphere M-60 Mk.II monoblock amplifiers: $3300 per stereo pair. Manufactured by Atma-Sphere Music Systems, 160 South Wheeler, St. Paul, MN 55105. (612)690-2246.
I can't remember where or when, but I think I recall a science fiction story in which a trip to the past spells D-O-O-M for inhabitants of the present, owing to the fact that some bonehead time traveler steps where he shouldn't and squishes a prehistoric bug. That bug, it turns out, was the ancestor of a quite spectacular butterfly, which in turn might have inspired some sensitive guy or another, who in turn might have been moved to express himself and in so doing soothed enough savage breasts to keep society out of the doghouse through at least the 20th Century. Or something.
So it's obvious: A thousand years from now, someone else will travel back in time to the late 1940s, when the fledgling hi-fi industry was just emerging from the ashes of a World War in the only two places where enough technological bits On' pieces were left over to make such a thing possible - England and the United States. This clod, however, will bring with him some slow-growing virus, which will cause enough ear infections in enough would-be music enthusiasts that tons of awful sounding hi-fi gear slips into homes unnoticed - and so eventually the hobby gets taken over by the geeks who would approach audio only as a theoretical engineering exercise, and who in fact derive more pleasure from measuring amplifiers than listening to them...
How else can you explain the ascendancy of transistors over vacuum tubes in audio amplifiers?
Somehow, somewhere, somewhy, everything went nuts. And while everybody hoped for the best, the transistor's motto turned out to be Veni, Weenie, Vici: I came, I sucked, I conquered. Then bigger transistor amps that sounded even worse took the same road to success, partly because the loudspeaker industry insisted on fumbling toward inefficiency, and partly because everyone was just too stupid or too timid to speak up and say, "Hey - I don't care how well this stuff measures because it sounds like serrated shit."
Well, not everyone.
Consider poor Julius Futterman, toiling away in the glass vineyards of New York City. Even throughout the 70s, when the world turned all around the transistor, he continued designing and hand-building vacuum tube amplifiers for a very small and very patient clientele. He did so because he was convinced that tubes simply sound better - and that he alone had a way to make tubes work at their best.
What Julius Futterman did was to make the first usable audio amplifier without the need for output transformers - big, expensive, and potentially signal-soiling things needed to match the high-impedance-friendly characteristics of most power tubes with the comparatively low-impedance loads of most loudspeakers. And take my word, for anyone to succeed in getting the anode of a tube to directly drive a loudspeaker is a very big deal. I don't know how Futterman did it, and I quite possibly wouldn't understand even if it were explained to me slowly. What matters is, he did it.
Note, by the way, that I said "usable" and not "practical." The relatively complex Futterman amp had problems of its own - like low output power and a fairly high breakdown rate. So enter fellow New Yorker Harvey "Gizmo" Rosenberg, a man familiar to Listener's readers as a modern day thermionic techno-shaman, gizmological inquisitor, and the Seventh Earl of the clan McTannoy. Rosenberg bought the rights to Futterman's OTL (Output Transformer-Less) technology before the older man's death in 1979, and enlisted the help of circuit designers George Kaye and Ted Hammond to bring more refined, more powerful variations of the Futterman theme to market under the New York Audio Laboratories name.
Others have tried their hand at the OTL game since then, and with varying degrees of success. (New York Audio Labs, in fact, fell from the scene in the late 1980s.) And I don't think it's unfair to regard Atma-Sphere Music Systems of St. Paul, Minnesota as the most noteworthy of these.
Atma-Sphere's Ralph Karsten has been quietly plying the OTL waters for almost twenty years, now - too quietly, in fact, if you ask co-worker Michael Benyo, who considers it his mission to raise their profile at least a little. And that just might happen if you heed the buzz accorded their newly revised M-60 monoblock amplifiers.
Although the first M-60 was built as long ago as 1980, the actual refinement of its OTL circuitry was a long time in coming - and it wasn't until the recent triode revolution and the raising of the musical stakes that Karsten did a serious re-think and kicked the M-60 into Mk.II status.
Bringing single-ended triodism into the conversation is appropriate, by the way, because the Atma-Sphere OTL approach has something in common with its micro-powered cousins: simplicity. Don't let the twelve-per-side tube count and all the switches and the knobs and the meters fool you - there's not all that much going on in here, and that's arguably to the benefit of your records.
In fact, those of you who are interested in this sort of thing will be surprised to know that each M-60 amplifier has just a single gain stage: two 6SN7s paired in a cascoded differential amplifier. Thus the M-60's only voltage amp is also its phase-splitter, eliminating the need for yet one more music-mucking stage and declawing at least one argument against the push-pull way of life.
The remaining two 6SN7s per chassis are a constant current source for the gain stage and a (cathode follower) driver stage, respectively; that last one is coupled directly to the output tubes - eight 6AS7 triodes arranged in a "circlotron" output stage, with the potential for up to 60 class-A Watts into an 8-Ohm load, with only 2 dB of feedback. And, at least partly as a consequence of Karsten's original differential voltage amp design, the star-ground M-60 is thoroughly balanced between hot and ground, from input to output - thus Atma-Sphere's trademark, "Balanced Differential Design."
In case any of that passed you by, it's worth repeating: All you have in the way of the signal here is a differential amp/cathode follower which is direct-coupled to the output tubes, which are themselves direct-coupled to the loudspeakers. That's it. Very darn simple. As Ralph Karsten says, "This amp is like a bumblebee: It shouldn't work. But it does - and it does so because there's a driver and bias supply of such wickedly low impedance. The low impedance of the driver circuit is the key."
To open an M-60 is to see more evidence of its beautiful simplicity. The parts count inside is surprisingly low given the Carnival O' Tubes outside, and this beautifully made amp is completely hand-wired, with nary a circuit board in sight. And owing to the absence of an output transformer - itself a (necessarily) expensive thing if it's done halfway right - the Atma-Sphere is a shade lighter than you might expect, although its torroidal power transformer is certainly beefy enough.
Enough, already. Sure, the technology behind the M-60 warrants an article unto itself - an original OTL design that works at all is honestly one heck of an accomplishment - but I'm just not the guy to write it. Besides, the way I see it, the big story here is the sound: For once, the buzz surrounding a new hi-fi product is very much deserved, and the Atma-Sphere M-60 offers a combination of strengths that simply couldn't be had until now.
By which, if you don't mind crass comparisons, I mean to say that this amp nips the heels of even the best single-ended designs with its own unique brand of musical presence and excitement - and in some ways exceeds them.
When I hooked these up to my Spendor SP100s, the first CD I played was the recent Sony Bruno Walter Edition recording of Bruckner's Seventh. And the first thing that caught my ear was neither the bass nor the imaging nor even the bloom (whatever that is), but rather the very generous string vibrato of the Columbia Symphony Orchestra players, especially in the early minutes of the adagio. So already these had me listening not so much for the sound but for the specific way in which the players communicated the feeling of the music. A really good sign.
And Bidu Sayao singing "Toi, le coeur de la rose," the Child's song from L'Enfant et les Sortileges, was magical - and in living mono, no less, courtesy of Sony Masterworks and Thomas Frost (see Pat Meanor's interview on page 46). Lately I'd started to think that a 300B tube is about the nicest thing you can do to the human voice if recording and playing it back are on the agenda - and yet here was something within spitting distance of being just as good.
And the Atma-Spheres are subtly dynamic things - very subtle and in fact very dynamic. Wherever the music calls for a change in the intensity of the singing and/or playing - the human hand banging out staccato organ chords, for example, as Garth Hudson is sometimes wont to do in contrast to his otherwise harmonium-like shadings - the Atma-Sphere amps telegraph that information to you like none other short of, honest to God, the big Audio Notes. (Yes, I've had an Ongaku in my house for a couple of weeks, and, yes, it's that good.)
All kinds of subtle stuff, in fact - different vocal inflections, or changes in intensity of bowing or plunking or drumming - comes through with tremendous feeling with these amps. Consider the drumming that goes on behind the second verse of George Harrison's "Long, Long, Long," and the way Ringo's steady opening/closing of the hi-hat makes for such an eerie beat in that passage. Pardon the audio cliche, but I'd never really heard that before, and hearing it now was more than a case of just noticing some otherwise inconsequential sonic detail: It cranked the emtional whomp of this already very moving song up a notch for me.
The Atma-Spheres are rhythmically quite good, as well, if not to the ultra-tight pacing standards of a Naim 250 or a Fi 2A3. And timbrally? I heard them as unusually wide in bandwidth for a tube amp, with lots of pleasant clarity and detail in the bass, though perhaps a bit of thickness up toward the midrange which colored the low registers of (mostly male) voices.
Perfect amps? The best of all possible worlds (which for me would mean some improbable combination of the Ongaku, the Fi 2A3, and the Naim 250)?
No, we're not there yet - but what's fun for me right now is listening to something like this that's so thoroughly, effectively exciting on its own terms. Really: What's the sense of acclimating yourself to one amplifier - one product - and then judging everything else according to its own, sole continuum of strengths? That question falls easily to mind in the face of something like the Atma-Sphere M-60s, which here in 1997 have come out of audio's left field with their own unique and still unimpeachably musical view.
And so, no - don't expect the shockingly black, silent spaces between the notes that characterize the Ongaku experience (there's a little more haze between and behind the bits of music with the M-60s). And don't be bummed to find that the tiny Fi 2A3s still give you more of that magical single-ended presence - what Joe Roberts of Sound Practices describes as that "pleasant, almost psychedelic illusion that never wears away."
But the Atma-Spheres breathe in and out like the music breathes in and out - and they grab your attention for reasons other than the merely sonic.
In fact, right before I started to write all this, I visited our man Gizmo at the Triode Guild's secret headquarters, where a quartet of modified M-60s are powering two of the only Tannoy Westminister Royal loudspeakers on the continent. And it was just like I heard at home - except MORE. And BIGGER. Studio rock was live-in-the-studio rock. Horns had the power to knock me over and the presence and realism to make the trip seem worthwhile. Piano jazz moved from the salon to the barroom.
Everything breathed "music." And there was no need for audiophool effects to create this level of excitement (hell, a lot of the discs I threw at them were in mono, anyway). So dig it: If every music junkie had the chance to hear a system like this do their ten favorite records - whether mono, stereo, or whatever - and then hear the best five-speaker system money can buy play those same records, surround-sound would be laughed off the planet as the adult toy/marketing wheeze that it is. What we have here is the difference between music and sound, pleasantly distracting though that sound may sometimes be.
Speaking of hammered, the grey-brown finish of the decidedly retro-looking M-60s also appeals to the anachrophile in me. And one of the coolest things about these amps: On the back of each, next to the speaker connectors and such, is a rugged looking metal plate on which are inscribed the instructions for setting bias current and DC offset, albeit in very abbreviated form. It's almost as if Karsten knows these amps'll be around for a long time, so he can picture, maybe, a pair winding up in some garage sale a hundred years from now - still working, but the instruction sheet rotted away long ago and their next buyer needs to get them up and running. Again, the back to the future thing.
Which reminds me: These amps are not for the technologically infirm. Sure, you can listen to them without wearing a pocket protector, but then you can't just sit back and ignore their few idiosyncracies, either: You must check and adjust the M-60s' DC balance upon installation, and maybe once or twice thereafter; you must likewise check and adjust their bias current; and you must bear in mind that these amps run hotter than the devil's armpit. For someone with bad circulation, M-60s - which though certainly not dangerous will noticeably raise the temperature in a small room - might be just what the doctor ordered; for everyone else, these are best appreciated in a big enough room that you don't have to sit right next to them. So, hey - you got all that power, why not move to a bigger room and do something with it?
Some morning, Ralph Karsten is going to wake up, rub the sleep out of his eyes, and say, "Oh, yeah - capitalism. I forgot." Then he's going to drive like hell to the office and double the price of the M-60 monoblocks. And you know what? Atma-Sphere will still sell every M-60 they can make, except now poor slobs like you and me won't be able to afford them.
Do you appreciate the magic of a really good tube amp? Do you listen in a big (and dare I say air-conditioned) room? Do you make an honest living for crappy pay? Then you, my friend, should drive like hell to the nearest Atma-Sphere dealer you can find and clap your ears on a pair of these.
- Art Dudley