February 2002Atma-Sphere MA-1 Mk II.2 Mono Amplifiers
by Marc Mickelson
In his February "Audio Hell" installment, Bill Brooks relays a story about an audiophile who doesn't like tubes because he "likes accuracy." This underscores the broad beliefs we audiophiles have about tubes and solid state, even though none of them are universally true anymore. I would love to own separate systems that utilize each, but not because either is more accurate than the other. In general, I enjoy the sound of tubes more than solid state, but for reviewing, having a system that makes best use of solid-state amplification would be a wonderful tool.
But there are factions within each of the larger categories, and I won't be wishing to have systems that conform to each of them. In terms of tube amplifiers, the OTL camp is vocal and seems to be growing, as makers such as Tenor Audio and Naked Truth Audio have emerged to take up ranks along with Joule Electra, Transcendent Audio and Atma-Sphere. With over 25 years of experience designing and building OTL amplifiers under his belt, Ralph Karsten of Atma-Sphere is the dean of current OTL makers, and his designs are both old and new. First, Atma-Sphere OTLs are based on the circlotron output circuit, which is the basis of other OTL designs, but Atma-Sphere amps are also fully class A and differentially balanced. The latter, as Doug Schneider and I found out when we visited Atma-Sphere, is the part of his design that Karsten considers his real achievement. Atma-Sphere OTL amps also use no feedback, which many designers of tube and solid-state equipment feel to be at the heart of the best possible sound.
The MA-1 Mk II.2 is Atma-Sphere's middle child among its monoblocks. At $9800 USD per pair, it costs more per pair than the well-known MA-60 Mk II.2 amp ($4650 per pair), which is a SoundStage! Reviewers' Choice Hall of Fame award winner, but less than the current top of the line, the MA-2 Mk II.2 ($27,200 per pair; a gargantuan two-chassis MA-3 is in the works), which looks like a tube tester from around back given the number of tubes it uses. The look of all three amps is decidedly retro, with the MA-1 Mk II.2 taking the award for the best looks because of its chrome chassis and open-air tube placement. The amp is manufactured in mirror pairs too, which is a nice touch and one that requires that Atma-Sphere stock different chassis assemblies for each channel. The internal workmanship of these amps is gorgeous. No wonder the guys from Atma-Sphere sign their names to it.
After you install the 14 6AS7G output and four 6SN7GT driver tubes per amplifier, you need to adjust tube bias and DC offset, which is a matter of holding down toggle switches on the front edge of the amplifier, making adjustments to the trim pots with a screwdriver, and reading the results on the front-mounted meter. Single-ended RCA and balanced XLR connectors are on the front edge of the amp, so your interconnects may need to be a half meter longer to reach. If you use the RCA connectors, you'll need to insert the included shorting plug between XLR pins 1 and 3 or you'll hear buzzing. The all-copper speaker terminals are around back. The ones on the review sample were not color coded, but they were marked with a small + and - on the plastic skirt beneath, requiring a flashlight to determine which was which. An IEC power-cord receptacle rounds out the connections.
The MA-2 Mk II.2 is a large amp, at least two times longer than it is wide, but at 40 pounds, it isn't as heavy as a non-OTL amp of similar size would be. Atma-Sphere rates its power output as 140 watts into 8 ohms, 135 watts into 4. Its frequency response is rated at a very impressive 1Hz-200kHz within .5dB (-3dB at 1MHz). Each amp uses 500 watts of power, but if you live in the great white north of the Midwest, as Ralph Karsten and I do, you'll be happy about the heat that comes from these amps for all the power they consume -- in the winter, that is. They raised the temperature in my 12' x 24' listening room five degrees.
I had heard that there were upgrades for the stock MA-1 Mk II.2, and I asked Ralph Karsten about these. It's easier to quote him than paraphrase:
As is Atma-Sphere's way, older MA-1 amplifiers can also be brought up to current Mk II.2 status. You'll want to check with the company for pricing. The review amps were current and stock with no upgrades.
I used the MA-1 Mk II.2 amps along with a glut of other equipment, all of which would be considered logical mates with the amps. Speakers were from Wilson Audio, the mighty WATT/ Puppy 6 and Sophia, as well as the Mirage OM-5, all of which worked well with the amps. Preamps were the Audio Research Reference Two Mk II and Lamm L2 Reference. I used a Mark Levinson No.39 as both a standalone CD player and transport, in which case it fed a Bel Canto DAC1.1. Interconnects and speaker cables were either Nordost SPM Reference and Quattro-Fil, Ensemble Dynaflux and Megaflux, or Acoustic Zen Silver Reference and Hologram. Power cords were a variety of models from Shunyata Research, whose Hydra distributed power to the components that needed it. Amps for comparison were primarily my reference Lamm ML2 monoblocks, which is a SET design -- another tube-amp sub-category -- and to a lesser extent the Audio Research VTM200 monos.
Completely dismissing the myth that OTLs are unstable, Ralph Karsten's amps are so reliable that removing tubes and even shorting the outputs doesn't cause them fits. I don't recommend that you test this, but having seen it done, I can convey my own sense of security.
The Atma-Sphere MA-1 Mk II.2 offers an utterly clear and uncongested view into the music. Transients have snap, percussion moves at breakneck speed, and cymbals have a lifelike, steely sheen. All of this imparts an immediate quality that will have tube nay-sayers who "like accuracy" scratching their heads. Wynton Kelly's Piano [Victor VICJ-60259] and Cannonball Adderley's Know What I Mean? [Victor VICJ-60243] on JVC XRCD rang with vibrancy and life, as did the Jacques Loussier Trio's Satie [Telarc CD-83431] on Telarc. The piano on all three discs (Bill Evans plays on Know What I Mean?) displayed the kind of attack and decay we often attribute to the sound of quick drum shots or plucked strings. The space and ambience on Piano in particular were startling in their physicality. I felt like I was in some room other than my own.
But this clarity and immediacy could be a double-edged sword. While the various XRCD and Telarc discs I played sounded beyond terrific, some CDs took on a slightly hot, shouty quality, lending an overall forwardness that made discs like Fountains of Wayne's Utopia Parkway [Atlantic 83177-2] and Roseanne Cash's 10 Song Demo [Capitol 112364] hard to listen to at my normal levels. My reference system does not lean toward mellowness, so the amps may simply be giving more of the truth than I was accustomed to hearing.
The midrange of the Atma-Sphere MA-1 Mk II.2 is as pure as I've heard from any amp. The detail of the voices was consummate and caused me to pull out vocal CDs I hadn't heard in a long while. Tom Waits, in particular, benefited from the MA-2 Mk II.2's high resolving powers and way with vocals. You may know Waits from his later, more experimental works, but Small Change [Asylum 1078-2] from the mid-'70s is the disc I put on to hear Waits at his most diverse. Texture is something Waits' voice has in abundance, and it was even more evident through the MA-1 Mk II.2 amps, as was the silkiness of Doreen Smith on A Tribute to Julie London [Fidelio FACD006]. This laid-back and spacious disc profited greatly from the MA-1 Mk II.2's clarity. These amps breathed life into vocals that I hadn't noticed previously.
While the bass of the MA-1 Mk II.2 amps has punch, perhaps due to a small perceived bump in the midbass with the speakers I had here for use, it certainly lacks solid-state weight and slam. Test discs for bass like Harry Connick, Jr.'s She [Columbia CK 64376] and Suzanne Vega's Nine Objects of Desire [A&M 31454 0583 2] didn't have the low-end growl they've had with other amps, including the Lamm ML2s, but there was still plenty of impact and pace. A disc that I've been playing for months and from which I included cuts on my CES demo disc, is the remastered version of Dire Straits' self-titled first album [Warner Bros. 9 47769-2]. I used to own this on vinyl, and I then replaced it with the CD, which was one of the first CDs I purchased. The recording is darned good even by today's standards, and the remastered CD shows just how good. When I played "Water of Love" with the MA-1 Mk II.2 in use, the initial wood-block strikes had decay that went on forever, and even the low frequencies were nothing to sneeze at. Then I heard the same track with the 200W Audio Research VTM200 monoblocks, and the bass took on greater substance, as though a subwoofer were integrated more optimally. I know from listening to the less-powerful M-60 Mk II.2 amps driving big Classic Audio Reproductions speakers that OTLs can do bass. The two Wilson speakers I had for use are almost certainly tougher loads, so I'll admit here that your mileage may vary depending on your speakers.
In terms of system matching, I had the best luck using the Atma-Sphere amps with the Audio Research Reference Two Mk II preamp, whose slight warmth filled out the presentation to a welcome degree. Like the MA-1 Mk II.2 amps, the Reference Two is also fully balanced. And while I prefer the WATT/Puppy 6es over any speaker I've heard in my listening room, the Sophias made beautifully detailed music with the MA-1 Mk II.2 amps, and the price of the combination comes in at about what the WATT/Puppy 6es cost. But the most intriguing combination was the MA-1 Mk II.2 and the Mirage OM-5. The Atma-Sphere amps brought these speakers to life like no other amps I tried them with, and the OM-5's powered bass section proved its full worth. Audiophiles may scoff at spending almost $10,000 on amplifiers for $3500 speakers, but this combination proved that there is more than one way to build a terrific-sounding system.
SET vs. OTL
For audio consumers, the main difference between OTL and SET designs may be power. While a good number of OTL amps are rated to deliver enough watts to fill a room with just about any speaker, SET designs need help from a speaker in the form of higher sensitivity. Both require attention to the load a speaker presents, preferably one that's 8 ohms nominal or above and with no steep angles in its impedance plot. I have achieved very satisfying results pairing my Lamm ML2 SET amps with a good number of speakers, including the Wilson WATT/Puppy 6 and, to a lesser degree, Sophia. The same can be said for these speakers and the Atma-Sphere MA-1 Mk II.2.
But the similarities end there, as the overall presentations of these two amplifiers depart rather dramatically. The Atma-Sphere MA-1 Mk II.2 amps put forward their clarity and ability to unravel the elements of the music, while nuance, gesture and, for me at least, that illusive sense of involvement constitute the Lamm ML2s' strengths. It's safe to say that both amps have special qualities, and which combination of these makes more musical sense is up to the listener. However, the difference in price here is immense, so a more appropriate comparison would be between the ML2 and Atma-Sphere's MA-2 Mk II.2, about which I've heard nothing but great things.
I like to play the speculative "Who is this product for?" game in reviews to aid in discerning a product's niche in the marketplace. An Atma-Sphere MA-1 Mk II.2 owner has refined, even esoteric, tastes, which he can afford to fulfill with an expensive amplifier. He will have a speaker that doesn't require solid-state amplification to sound its best. Merlin, Silverline, even Wilson Audio are reasonable choices; Revel and Thiel are almost certainly not (although I now brace for e-mail proving me wrong). Most of all, the owner of the MA-1 Mk II.2s will be someone taken with directness of expression, midrange purity, high resolution, and the characteristic uncongested quality of the MA-1 Mk II.2. He will also need some power for his speakers to fill his listening space, but perhaps not the 220 watts that the larger Atma-Sphere MA-2 Mk II.2 amps provide. He will enjoy the look and reliability of these amps and not be too bothered by the heat they create. He may even be wary of OTLs in general but be drawn to the reliability the Atma-Sphere models have.
Have I described you? If so, give an Atma-Sphere OTL amp a listen, preferably with your chosen speakers. What the MA-1 Mk II.2 does, no other amp I've heard so far duplicates.
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