Atma-Sphere • MA-2 Mk 3.1 Mono Amplifiers

by Marc Mickelson | October 13, 2011


An output-transformerless (OTL) amplifier has to vex some audiophiles and engineers alike -- those who cling desperately to the notion that there is a single unerring "proper" way to design an audio amplifier. On the one hand there is the dictum that fewer parts are best for sound, and that must go double when it comes to eliminating a component as dominating as the output transformer. On the other hand is the notion that the output transformer is of absolute primacy -- akin to wheels on a car. Without it, there is nothing smoothing out the amplifier's impedance and making the mating of amp and speaker possible.

So an OTL amplifier is a enigma -- a product whose design philosophy makes fundamental sense but whose execution seems illogical, even wrongheaded. I've long given up fixating on notions of right and wrong as they apply to the interdependencies at work when various electronics, cables and speakers come together to form an audio system. Too often "proper" is trumped by "better," as in "better sound," which in rare instances becomes something greater still.

"Greater" describes the Atma-Sphere MA-2 Mk 3.1 mono amplifier. I've been following the progression of this amp firsthand over the course of the past decade, as Ralph Karsten, its creator, has refined its circuit and improved its performance. Not that there was much room for improvement, as earlier MA-2s vexed me enough to consider them among the very best amps I'd ever heard. They were fixtures on my personal best-amplifier list, along with push-pull and single-ended tube designs, and even a solid-state amp or two. In its latest incarnation, the MA-2 features new power-supply transformers that have 50% greater capacity than the earlier transformers. Among the improvements the new trannies wrought was a dramatic drop in distortion. THD is now less than 1% at full power, which is infinitesimal for a tube amp, no matter its design.

The heart of the amps remains the patented Circlotronic OTL circuit and "Balanced Differential Design" that Ralph Karsten has championed and refined for over 25 years. The amp's sole gain stage comprises two pairs of 6SN7 triodes that form a differential cascode amplifier. The power comes from the 6AS7 triode tubes -- twenty in each amp -- which output a nominal 220 watts. As with all Atma-Sphere products, the MA-2 is fully balanced from input to output, though it does have provision for single-ended connection.

Gone from earlier versions of the amp is the ability to adjust the bias of the output tubes -- it's now done automatically -- but the DC-offset adjustment remains. The MA-2 has always looked, well, different. First, it's huge, all of that space required for the sea of output tubes, while its circular front-mounted meter and Wrinkletex finish are decidedly retro -- "captured Russian sub chic" I've called it in the past. You can now, however, get the amp in a silver anodized finish, and there is a cover that hides the power transformers and big power-supply caps. Atma-Sphere also offers an optional tube cover that extends the appearance to the back of the amp. The MA-2 continues to make an aesthetic statement, and it has grown on me, the abundant heat from all those tubes -- 52 in total -- notwithstanding.

If you own an older pair of MA-2s, Ralph and his electronics artisans (you'll know what I mean by this once you see the methodical point-to-point wiring of any Atma-Sphere product) can update it to latest-and-greatest status. The price depends on the vintage of your amps, but what doesn't vary is the three-year warranty you get when your amps are updated. Contact Ralph for details.

Making the connection

We've reached the point in this review where I carp about the need to use equipment like the MA-2s to their greatest effect -- via their balanced connections. After all, Ralph Karsten designed the amp to be used this way, and you're paying for the parts and wiring required to create a balanced circuit, so why not make use of all that and maximize the amps' sonic potential at the same time? One reason may be that you own a very good single-ended preamp, like the Convergent Audio Technology (CAT) SL1 Legend, which was a wonderful mate with the MA-2 Mk 3.1s, bringing image density and midbass heft to the presentation.

My point is that these amps can fit nicely into an existing system without the need for reshuffling, and this is true even if your preamp doesn't have balanced outputs. Equally good as the CAT preamp -- for different reasons -- were the fully balanced Audio Research Reference 5 and Reference Anniversary, while Karsten's own top preamp, the MP-1 Mk 3.1, may be the best choice of all. With balanced connection, an important consideration is the position of the "high/lo" switch on the rear of the amps. This toggles between 200,000- and 600-ohm input impedance, the latter being the professional standard for balanced signal transmission. If your preamp is fully balanced and adheres to the 600-ohm specification -- the Audio Research and Atma-Sphere preamps mentioned above do -- you'll want to use the "lo" setting. One of the benefits is that the interconnects between the preamp and power amps become non-critical; that is, it's nearly impossible to hear any difference between interconnects used in this location. In addition, the "lo" setting sounded slightly more dynamic and at the same time quieter. For single-ended use, you'll need to short the XLR inputs, inserting the included pins between sockets 1 and 3.

One final in-use consideration is power cords -- plural, because each amp requires a pair of them. I found that the Essential Sound Products MusicCord-Pro ES was not only sonically ideal but also economical, given its $300 price. If you have a pair of cords you like, perhaps used with your previous mono amps, the cord used for the bottom receptacle of the MA-2 Mk 3.1 is more critical to the amp's performance than the one on top, so you could skimp on the top cord if you need to.

To quote. . .

It happened early on with the MA-2 Mk 3.1s, the moment best characterized by that pop-culture philosopher Yogi Berra as "deja vu all over again." Having had earlier versions of the amps in my system, I was prepared for the particulars of their performance, but not for the overall effect on me as a listener -- an instantaneous and enduring sense of hearing each recording in a more elemental way, one that freely transcended the typical limitations of musical reproduction. While this came about because of various things the amps achieved sonically, the cumulative effect was truly profound, which is another way of stating the bromide "the sum is greater than the parts" -- and in this case far greater.

It is impossible to hear these amps and not be impressed with the extreme vividness of the music throughout the entire sonic spectrum. It is literally the case that this is the product of what's not there -- the output transformer. The output of the tubes is mainlined directly to the speakers, resulting in transparency that is truly remarkable. There is tonal neutrality to be sure, and along with it unfettered re-creation of the music's spatial fingerprint and the fine details of each instrumental or vocal performance. These amps provide an utterly lucid and intelligible view of recorded music that is singular in my experience.

Since last having a pair of the MA-2s in my system, a couple of meaningful advancements have occurred in terms of music formats. The first is the ascendancy of the 45rpm LP, so many of which are reissues of music with historical significance. The second is the SHM-SACD, which I was highly skeptical of until I bought a few of them and they made me a believer. When you hear one of the great Music Matters, Analogue Productions or Original Music Group double-LP 45rpm sets, the precision and directness are obvious and represent unequivocal sonic improvement over first-generation 33 1/3rpm pressings. These recordings are made with such care at every point -- from the search for the absolute master tape to the cutting of the lacquer to the pressing -- that they redefine what analog is capable of at this point in time. The same is true of digital when one of the SHM-SACDs is spinning. Their substrate -- a higher-quality polycarbonate material originally developed for LCD panels -- and emerald-green coating are said to allow for greater precision in the reading of the data, but I suspect that, as with the 45rpm LPs, the care that takes place at every step in their creation plays a large role as well.

The MA-2 Mk 3.1s make the superiority of these recordings plain. The amps portrayed the absolutely immense space of the Decca/London classic Espana [London/Original Recordings Group ORG 104] with standard-setting spread in all dimensions, a recording that's a half-century old sounding as resplendent as one made yesterday. With small-ensemble jazz like Jackie McLean's great Destination. . .Out! [Blue Note/Music Matters MMBST-84183], the free and easy purity of the horns and bass made listening a truly relaxing experience. What was more impressive, however, was that the Atma-Sphere amps achieved this all-encompassing transparency to the source material with neither leanness nor brightness, both of which can fool listeners into thinking that the presentation is transparent when exactly the opposite is true. Instead, the MA-2 Mk 3.1s achieved a level of true musical insight; they simply revealed more musical information from each recording.

There is no unanimity among listeners as to whether the SHM approach yields a definitively better digital disc, and the Atma-Sphere amps gave insight into this micro controversy. Certain recordings, especially Steely Dan's Aja [Universal Japan UIGY-9026], have become touchstones for disagreement. Some listeners swear by it, and others swear at it, claiming that various CD versions actually sound better. Heard with the Atma-Sphere amps, Aja on SHM SACD was surprisingly reverberant, especially during the opening bars of "Black Cow," and slightly recessed in perspective compared to the Mobile Fidelity LP [MFSL 1-033], which displayed crisper transients, a more up-front perspective and propulsive midbass drive. Both sounded more dynamic than the standard-issue LP [ABC Records AB-1006]. I would wager that we'll see a 45rpm version of Aja in the not-too-distant future and it will be definitively the best version ever produced. It's an evergreen -- even audiophiles who own multiple analog and digital copies will buy another if it represents true sonic improvement over what already exists.

Where this transparency yields its greatest returns is the midrange, the money region of any audio system. The midrange of the MA-2 Mk 3.1s is so pure and direct that with some recordings it seems impossible that it could be the product of any amplifier. This isn't merely a tonal phenomenon but a dynamic one as well, small vocal inflections and the corresponding shifts in volume adding to the overall sense of reality that the amps achieve. In his early days, Bob Dylan achieved great subtlety with his singing, and while the Sundazed mono reissues of his catalog may not be as impressive as the various 45rpm LPs, they readily display Dylan at his vocal best. His performance of "The Lonesome Death of Hattie Carroll" from The Times They Are A-Changin' [Columbia/Sundazed LP 5108] is an intricacy of finesse and nuance, each vocal twist or turn adding to the song's urgent message, which has great relevancy today, as the gap between economic classes widens.

The mono-ness here -- what Joe Harley of AudioQuest and Music Matters has astutely named "primal purity" -- is all the more compelling via the Atma-Sphere amps, which expose everything within the music's fabric. This isn't mere detail presented for its own sake. It aids in the understanding of the music's mood and message, and it's the ultimate effect of these amps, the point of their seemingly infinite transparency. There is an overwhelming feeling that the music is happening before you, which is a different and more compelling kind of presence and the very premise on which high-fidelity reproduction is built.

Two longstanding issues of OTL amps have been perceived reliability and bass. It's "perceived reliability" because this is frankly a remnant of early OTL designs, not contemporary ones. One of the most unnerving acts an audiophile can witness is Ralph Karsten yanking tubes from one of his amps, which merely continue to play without a flinch. Indeed, a former owner of Atma-Sphere amps recently told me that he discovered some of his tubes had gone bad only after he replaced them -- the amps never complained. The same thing happened with a tube in one of the review amps. I saw, instead of heard, that it was kaput and replaced it.

Bass has never been a strength of OTL designs, including the Atma-Sphere amps, but only if you consider it in the context of solid-state bruisers that provide the same high power output. With the MA-2 Mk 3.1s, there isn't the same kind of sock and slam as you'll get from Luxman B-1000f monoblocks, for instance. However, within the fabric of the music, what the Atma-Sphere amps achieve seems neither subtractive nor even close to deficient. Upright bass, kick drum, even electronic depth charges retain their weight and power in relation to the rest of the musical spectrum and display nimbleness as well. The MA-2 Mk 3.1s, and indeed every Atma-Sphere amp I've heard, are not about sonic fireworks. They are about putting less in between the recording and the listener -- in theory and, as even a casual listen will reveal, in use.

Hybrid vs. OTL

While my long-term reference amps, the Lamm M1.2 Reference monoblocks ($22,290/pair), are thoroughly different from the MA-2 Mk 3.1s in terms of their design -- utilizing both solid-state devices and a single tube, along with that pesky output transformer -- there are some broad similarities in the effect of their performance, even if the specifics of their sound are rather different. The Lamm amps present music with endearing naturalness in terms of its tonality and presentation of musical detail. They never sound mechanical or etched, and they present instruments and vocalists with the sort of three-dimensional presence that tubes do so well, while never being short of the power that brings dynamic life to the music.

All of this adds up to a sense of musical rightness, a quality that the Atma-Sphere amps also possess, even if they achieve it in different ways -- with their standard-setting transparency. This makes for a kind of realism that the Lamm amps don't quite achieve, one that's about revealing the unique qualities of each recording. The midrange of the Atma-Sphere amps is so light-filled and vivid that it seems improbable to be coming from anything other than live music. In contrast, the mids of the M1.2s are more consistent with those of very good tubes -- full-bodied and rounded, a touch dark in tonal terms. Spatially, the Lamm amps are more about in-the-room presence, although they certainly don't gloss over spatial cues and the small movements of the musicians. In contrast, the Atma-Sphere amps present each recording with a unique spatial aura, the musicians existing within, not apart from, the venue captured on each recording.

Down low the Lamm amps display greater density and heft, giving rock, pop and especially muscular jazz more pronounced bass drive and rhythmic propulsion. Yet, when you play the same music through the Atma-Sphere amps, it's hard to argue that there is anything lacking, as the presentation from top to bottom is driving and propulsive -- as well as uniquely compelling.

Perhaps philosophy as much as sonic acuity will lead buyers to one of these amps over the other: the allure of a mixture of tube and solid-state circuitry versus the esoterica that a non-existent output transformer represents. Both make sense on paper and in musical practice as well.

"Best" is as "best" does

Early on in this review, I discussed my personal list of the very best amplifiers I've heard, underscoring the diversity of amplifier technology in the process. To get specific, I'd choose two solid-state amps (the Ayre MX-R and Luxman B-1000f monoblocks) and three tube amps (the Convergent Audio Technology JL2 Signature Mk 2 stereo amp, the Lamm ML3 monoblocks and the subject of this review). These represent a cross-section of amplifier technology: high-power solid state, high-power tubes, single-ended tubes and output transformerless. I didn't assemble this particular list in order to prove my egalitarianism; I simply collected the five amps I've heard and admired most. I could have expanded it to ten amps, but that would only cloud the issue by sending the message that "best" is a more elusive goal.

Keeping the notion of "best" in mind, let's say that I don't have the luxury of picking five amps. I have to choose just one -- the amp that will be the conduit through which all of my music, digital and analog, passes. Which will it be? Solid-state or tubes? Push-pull or single ended?

Give me OTL in the form of the MA-2 Mk 3.1s and I'll live musically ever after.

Price: $41,600 USD per pair.
Warranty: Three years parts and labor, one year for tubes.

Atma-Sphere Music Systems
1742 Selby Avenue
St. Paul, MN 55104
(651) 690-2246

Associated Equipment

Analog: TW-Acustic Raven AC turntable, Graham B-44 Phantom Series II and Tri-Planar Mk VII UII tonearms, Dynavector XV-1s (stereo and mono) and Allnic Puritas cartridges, AudioQuest LeoPard and Nordost Odin phono cables, Allnic H-3000V and Audio Research Reference Phono 2 phono stages.

Digital: Audio Research Reference CD8 CD player, Ayre Acoustics DX-5 "A/V Engine."

Preamplifiers: Allnic Audio L-3000, Audio Research Reference 5 and Reference Anniversary.

Power amplifiers: Lamm Industries M1.2 Reference monoblocks.

Loudspeakers: ProAc Response K6, Tidal Sunray, Wilson Audio MAXX 3 and Sophia 3.

Interconnects: AudioQuest William E. Low Signature, Shunyata Research PowerSnake Series Anaconda and Python.

Speaker cables: AudioQuest William E. Low Signature, Shunyata Research PowerSnake Series Anaconda and Python.

Power conditioners: Essential Sound Products The Essence Reference, Shunyata Research Hydra Triton.

Power cords: Essential Sound Products The Essence Reference and MusicCord-Pro ES, Shunyata Research CX-series (various).

Equipment rack and platforms: Silent Running Audio Craz² 8 equipment rack and Ohio Class XL Plus2 platforms (under Lamm M1.2 amps), Harmonic Resolution Systems M3 isolation bases.