As I previously reviewed and recommended the Atma-Sphere MA-1 Silver Edition OTL for induction into the Audio Hall of Fame, it didn’t take long for the hallmark purity and neutrality of the more affordable M-60 MkIII to have me questioning once again why output-transformerless (OTL) amplifiers never seem to get the press they deserve. But more importantly, I’m selfishly wondering why I still don’t have a pair of these tubed beauties permanently parked in my listening room. The M-60’s distinctive retro appearance doesn’t begin to reveal what’s cookin’ inside. The performance of the Atma-Sphere OTL is impressive in ways that are difficult—if not impossible—to describe.
The latest incarnation of the classic M-60 is a chip off the ol’ monoblock so to speak. It shares with its larger, more powerful siblings an all-triode, Class A balanced differential design, as well as a direct-coupled (OTL) output stage. While there’s no output transformer to get in the way of good sound, careful speaker matching—eight ohms or higher—is recommended for best performance. The M-60 now features automatic biasing with only one toggle switch and a screwdriver needed to adjust the DC offset. The third hand I had to grow to set the bias on the older model MA-1 can now be used exclusively for alligator wrestling with Virtual Dynamics cables. Also new are input jacks (XLR and RCA) around back instead of on the front panel. This should allow for a shorter pair of interconnects, which is no small matter at today’s cable prices. Plus, that bright green and pink wire you thought looked so cool in your favorite audio mag can now be hidden discretely behind your system.
Tubes include four 6SN7s per channel on the input side and eight 6AS7s in the output stage—enough to keep my listening room toasty warm year round. While I believe my review sample represents the $6350 base version, there are also a number of internal options available for those with deeper pockets. Upgrades include custom Teflon coupling caps, V-Cap Teflon caps, power supply boost, and a Caddock resistor package. It will also cost an extra $360 if you want polished stainless front panels; otherwise the standard finish is black Wrinkletex. Total price for a fully loaded M-60 MkIII will set you back $8870.
For the purpose of my listening tests, I paired the M-60 with Atma-Sphere’s entry-level MP-3 preamp, a Meridian G08 CD player, and relatively sensitive, 8-ohm Coincident Super Eclipse speakers. I know a few guys who own the larger OTLs and are perfectly happy using them with lower sensitivity, lower impedance (4-ohm) speakers. With a 60W OTL, I’d personally recommend sticking with a higher-sensitivity speaker or you may not fully appreciate the extraordinary bass this amp is capable of. While the bottom end has plenty of impact, it’s not the kind of impact that is going to jump out of the speaker and slam you up against the wall. What’s so extraordinary are the tight focus, definition, and layering in the bottom end. I’ve heard tight focus before, but not so deep into the bottom octaves. It‘s quite spectacular. The bass is also extremely nimble and quick—unfettered speed is the only way to describe it. Matching the M-60 with the right speaker will allow the music to figuratively run wild. I ran out of power a few times, but I really needed to push this amp hard to do so—harder than I would during any normal listening session.
Other than being fascinated by the bass performance, I was impressed by many aspects of the M-60. In my experience, few tube amplifiers have the purity and neutrality of this one. Expansiveness of soundstage and extension on top has to rank with the best, too. The sound is smooth, but not syrupy smooth, with no excess fat needing to be trimmed. The Atma-Sphere is a very different animal than the Joule Electra OTL; in a direct comparison the Atma-Sphere may sound a tad thin to some, though I believe the Joule tends to be too rich or overcooked. To each her own, I suppose. If you like bloat and coloration, you probably won’t like the Atma-Sphere.
Most important is the M-60’s ability to bring you closer to the music. A film or layer of grunge is removed that you didn’t even know existed before. It’s often described as the difference between being a spectator at a musical event and being part of it. When I first sat down to listen to the M-60 I couldn’t help thinking of that guy in the V-8 commercial slapping his forehead and saying, “I coulda had an OTL!”
If you don’t have the coin for Atma-Sphere’s reference all-tube, dual-chassis MP-1 preamplifier, the more economical MP-3 stuffs both chassis into a single box and costs less than half the price. I’ve not yet heard its big brother in my system, which may be a blessing in disguise as it seems my pocketbook is in worse shape than the economy right now. Instead, I’ve put quite a few miles on the MP-3 since it landed and have been surprised and quite happy with its level of performance paired with solid-state and tube gear alike.
The MP-3 comes housed in basic black with few frills other than an optional phonostage and various internal upgrades similar to the M-60. I guess you could call it a sleeper of sorts, at least based on its industrial appearance. Inputs and outputs are balanced only, save for the dual RCA tape monitors. (An XLR-to-RCA adapter is available from Atma-Sphere if needed.) Like the M-60, the MP-3 is a fully differential all-tube design with direct-coupled output. The review sample was a linestage version with a pair of 12AU7s in the line section and a couple of 6SN7GTs on the output side.
While I’ll admit to preferring the unique M-60 amp, the MP-3 preamp is still an excellent complement, as it shares many of the amp’s sonic qualities. The MP-3 also does well mated with other components, as it doesn’t have a strong sonic signature to color the sound of the rest of your system—unless, of course, you consider neutrality a sonic coloration. This preamp is one that may change preconceived notions about tube gear, although the MP-3 doesn’t remind me of solid-state, either. I’ve always felt there should be a third choice—music!
In addition to neutrality, the attributes I enjoyed most about the MP-3 included openness and gobs of air, great retrieval of ambient information, and a breathy quality in the midrange. This preamp is also fairly quick, with good dynamic range, well-defined images, and plenty of space between them. At $3950, the MP-3 is a tough unit to criticize (it might have been nice to have a remote). Actually, even if I had to move from my listening chair occasionally to adjust the volume, I could live with the MP-3 for a very long time, if my wallet were a little healthier these days.
A brief tour of Atma-Sphere a few years back made me realize just how lucky we are to have such diversity in this hobby. A dozen or so years ago I didn’t think an OTL amplifier would ever be for me, until a friend talked me into listening to one. Now I’m hooked. If you’re considering taking the plunge, the M-60 MkIII and MP-3 preamp will keep you smiling until the cows come home. And even if you’re not ready to take the plunge, you should audition the Atma-Sphere OTL anyway. You’ll be richer for the experience.