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Equipment Review
August 2001

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Atma-Sphere M-60 Mk II.2 Mono Amplifiers

by Ken Micallef

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"One of the great bargains in audio."

 

 

 

 

Back when I was a Cary aficionado, having owned both a Cary preamp and SLA-70 stereo power amp before purchasing SLM-100 monoblocks, I thought no one short of Penelope Cruz could persuade me to leave the world of push-pull mega wattage. The Carys were all I thought I wanted in a tube amp. They were smooth, lush, dynamic; they made everything from Guns N' Roses to Dean Martin sound wonderful, warm and inviting. I upgraded the Carys twice -- with ohm-matching switches, paper-in-oil caps, pentode/triode switching, Cardas wiring and lots of NOS tubes.

But after selling a pair of interconnects to a New York-area minister who wouldn't stop talking about his Atma-Sphere/Merlin combo, I dug into Atma-Sphere, whose designs sounded suspect to me. Wha? No output transformer? You had to use only 8-ohm or greater speakers? Puh-lease.

It was Julius Futterman who, back in the barren 1970s -- an era of solid state supremacy and slide-rule-toting, distortion-measuring engineering geeks -- created the first somewhat widely available OTL amplifier designs. OTL, or output transformerless, designs are amps without borders. More precisely and less poetically, they are amps without the big and bulky output transformers necessary for most of the species to step down voltage and match impedance to speakers. The simpler the better, right? Just as with the old "straight wire with gain" adage applied to preamps, OTL amps get you closer to the music. But they do take some tricky engineering to get you there.

Foregoing an explanation of such technical matters that are well beyond my pea-picking brain (see the original SoundStage! review of the M-60 Mk IIs for an in-depth mechanics-of-OTL explanation), let us leave the early '70s and relocate to 1978, when Minnesotan Ralph Karsten founded Atma-Sphere Music Systems and soon introduced the first reliable OTL amps. The Futterman amps had a tendency to blow, you see, and take down not only power tubes, but occasionally precious speakers and your hard-earned audio dough too. Karsten found a way around this not-minor bugaboo, and along with the insurgent Japanese and their never-say-die loyalty to the tube way, he designed and produced his first M-60 OTL amplifiers in 1980, just in time for a hungry audio public slowly returning to beautiful tube sound.

Since then the M-60 has become a very popular piece with critics and, more importantly, the tube-amp-buying public. Follow the links at the Atma-Sphere Music Systems' website and you will find the ASOG, or the Atma-Sphere Owner's Group, where Atma-Sphere loyalists proclaim their love for all of Karsten's products, from the behemoth MA-2 Mk II.2 power amp and its golden array of 20 6AS7 output tubes and six 6SN7 driver tubes, to the MP-3 preamplifier.

Back to Minister Yagerman's Merlin VSM speakers powered by the Atma-Sphere M-60s: I was saved. The detail, transparency and slam factor left my Cary amps sorely wanting. Every instrument, every vocal had a distinct place in the soundfield, with natural weight, placement and presence. Beyond a proverbial veil being lifted, the sound was extremely organic and natural. Kick drums sounded like warm bass drums; I could hear air being moved. Transients were faster and treble was more extended. Everything was highly resolved through the Atma-Spheres, but very naturally, without a hint of harshness or glare in any part of the spectrum. Was it the speakers or the amps or both? I only knew that the sound was so pure as to leave me stunned. Yagerman played vinyl and CD, and the sound remained natural, focused, agile and highly detailed.

I liked the Atma-Spheres, so I bought a pair. Little did I know that when I selected certain options for my M-60 Mk IIs, I was actually ordering the new M-60 Mk II.2s, which have increased from $4200 USD per pair to $4650. Ralph Karsten describes the differences between the pair of amps that were originally reviewed and the ones he would build for me (or you, for that matter) in this way:

"We went with a different power transformer, which is a slightly larger unit in the version II.2. We boosted the power-supply capacity in the output section by 50%. We added the quick-bias feature, where you have the two switches on the front panel for using the bias meter. And finally, we boosted the filter capacitance in the driver supply by 50%. What we did in the driver supply when we boosted the capacity was, basically, we made the power supply a bit more stable. We found that at high power levels we were getting a little bit of noise. The driver circuit was modulating the power supply a bit. So we stabilized the power supply and cut the noise down by an order of magnitude. The result was a measurable drop in distortion in the neighborhood of 40%. We added resistors to the output section to help the tubes work better together, and the effect of that was to reduce distortion by about 90%."

Older M-60s can be updated too, but the cost is variable and based on the difference between the original cost of the amps and the cost of new amps, plus $300. For example, some M-60 Mk IIs cost $3800 when purchased new, and those amps would cost $1150 to update. It's much more expensive to update M-60 Mk Is, as so much more work has to be done. Ralph Karsten can give you the scoop when you call him to schedule surgery for your amps. And get this: with the upgrade, the warranty is reactivated for three years.

I was initially a little concerned that the M-60 Mk II.2s would not work entirely well in my rig. My gear included a Blue Circle BC21 preamp with power-supply upgrade, Theta Jade transport, Bel Canto DAC1, Oracle Alexandria Mk II turntable, and all Cardas Golden Reference speaker cables and balanced interconnects. Power came out of a Shunyata Hydra power conditioner. Speakers were the 8-ohm Spendor 2/3s and the 4-ohm Audio Physic Virgos. With the M-60 Mk II.2s rated at 65W into 8 ohms, but only 45 ohms at 4 ohms, I was afraid the Virgos would sound slow and off the mark, with little zip or transient punch.

But what surprised me most was that the updated Atma-Spheres actually produced more prodigious and accurate bass than the 100W Cary monoblocks. The Virgos are naturally rich in the upper bass/lower midrange, but the more accurate and well-controlled M-60 Mk II.2s tightened up the bass and gave it a more punchy, taut delivery. With the Spendors, the Atma-Spheres do sound better matched, aiding in the smaller speakers' more extended and exciting delivery and detailed, in-your-face soundstage. But there were no deficiencies with the Virgos, just the usual tube-bass sound, which is slightly exacerbated in the Virgos, the speakers' only glaring weakness.

That ripeness in the upper bass may be a bit colored for some tastes. But the Atma-Sphere amps also helped the Virgos to do what they do best, which is image incredibly well and cast a layered, three-dimensional soundstage that I have rarely heard bettered. Minister Yagerman's M-60/Merlin combination was faster and perhaps more detailed than my M-60 Mk II.2/Virgo combo, but it lacked the deep, layered soundstage and amazing transparency, as well as a bit of the natural warmth.

This was the same sound I heard at the recent Home Entertainment show in NYC, where Karsten was running the M-60 Mk II.2s with large horn-loaded speakers, his own MP-3 preamp and a Sota Sapphire turntable. The amps' pure, organic, musical quality and great coherency were consistent record to record, whether the music was played loud or soft. You could sit in the sweet spot and recognize the honest representation of the Mk II.2s automatically.

The Atma-Sphere M-60 Mk II.2s are the last power amps I intend on owning. Well, someday, when I marry into a rich family, which will allow me a small fortune for the Atma-Sphere MA-2 Mk II.2s in trade for my wit and charm, I might have a change of heart. The M-60 Mk II.2s' clarity and purity are unparalleled at their price, and the amps compete favorably with much higher priced units. For $4650, you'd have a hard time finding a better pair of amps than the M-60 Mk II.2s, and they are outfitted with a power tube that can be had for about $15 apiece, so retubing won't empty your wallet. The Atma-Sphere M-60 Mk II.2s are one of the great bargains in audio.

...Ken Micallef
ken@soundstage.com

Atma-Sphere M-60 Mk II.2 Mono Amplifiers
Price:
$4650 USD per pair.
Warranty: Three years parts and labor.

Atma-Sphere Music Systems
160 South Wheeler
St. Paul, MN 55105
Phone: (651) 690-2246
Fax: (651) 699-1175

E-mail: ralph@atma-sphere.com
Website: www.atma-sphere.com

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