Tomorrow's News Today

Master Guide to the Best of 1998

and the Worst (over 110 reviews!) What to Buy . . . What to Avoid
Single Ended Tube Power Amps
Class 1b

Atma-Sphere M-60 Mk II

At $3795, this is an IAR Best Buy. Previously we would have included Atma-Sphere's OTL power amps under the push-pull category. But, as designer Ralph Karsten's literature correctly points out, these are actually single ended power amps, operated in twin pairs in balanced mode. This differs from the usual push-pull category because each half of the Atma-Sphere amp is fully class A, handling the full signal swing in its linear region (just like a single ended amp), whereas virtually all push-pull tube amps operate in class AB mode.

Atma-Sphere's balancing of two single ended halves provides dramatic reduction in even order distortion, the predominant distortion type in all single ended circuits. So the Atma-Sphere amps have much lower intrinsic distortion than unbalanced single ended amps. This in turn allows the Atma-Sphere amps to employ little or no loop feedback, which probably contributes to their superb sense of relaxed ease in reproducing music.

The Atma-Sphere power amps are output transformerless (OTL), which improves transparency and bandwidth (but also raises source impedance and thus makes the amp more susceptible to tonal colorations from interaction with a speaker system's fluctuating impedance curve). They are hard wired, point to point, which eliminates the colorations and transparency losses from PC board wiring and dielectrics.

The M-60 Mk II is an excellent amplifier, with very well balanced performance capabilities in every sonic aspect. In all its sonic achievements it runs an honorably close second to the far more expensive Venture amp (www Note: reviewed elsewhere in the same publication). And, because the Atma-Sphere's excellent performance is so well balanced among all aspects, there's no single weakness or sonic problem that calls attention to itself or detracts from your musical enjoyment. Any music lover or audiophile perfectionist would be very happy with the M-60 Mk II.

The first thing you notice about the M-60's sound is its liquidity and ease. Then you notice that its trebles and transients are very fast, indeed so fast that they are delicate, rather than hard as in other amps that try to impress with artificial phony 'hi-fi'. And its transparency is excellent, revealing a lot of musical information, but without sounding analytical as some other amps do. Soon it becomes obvious that the Atma-Sphere is one of those rare electronic components that gives you the best of both worlds: transparency and natural musicality.

As with Fred Astaire in our analogy above, music emerges from the Atma-Sphere with such relaxed ease that the amplifier seems to be enjoying itself rather than straining, as if it were capable of easily handling tasks even far more demanding than this complex music signal that so befuddles other amps. This sense of relaxed ease helps this amplifier to sound even greater than it is, and puts you more directly in touch with the music (without the sense that any electronics are intervening as intermediaries) - and all this in turn helps you to relax and enjoy the music itself.

With the Atma-Sphere giving you best of both worlds, you relax and enjoy the music more, and there's also more music to hear. On the other hand, some clear amps that sound analytical might give you as much musical information, but in a less relaxing, less enjoyable, more fatiguing context. Also on the other hand, some other amps trying for musicality are too veiled, defocussed, fuzzy, and soft; they might be relaxing to listen to, but they simply don't reveal enough information about the music to sound real (it's like trying to listen to live music playing behind a curtain).

The tonal balance of the M-60 Mk II sounds very close to neutral, with a slight personality tinge toward the warm and mellow (with the warmth region being rich and the hardness regions, the upper midrange and lower treble, being slightly recessed). This tonal balance perfectly complements the ampÕs tonal quality, which is liquid and smooth. The combined effect is a musically consistent portrayal, rather like hearing live music from a distant balcony in a plush concert hall.

Atma-Sphere makes some larger OTL amps, including the MA-1 ($7995) and the MA-2 ($18,795). They have similar sonic virtues, but it's been some time since we heard the MA-1 (and under different circumstances), so we can't say whether they are worth the extra cost over the M-60 Mk II that was playing at CES.

Atma-Sphere also introduced at CES their new 300B OTL amplifier ($5600), which uses 300B output tubes in place of the 6AS7G tubes used in the M-60 Mk II. The 6AS7G tube is from the same family as the 300B, so the two power amps are basically the same, the circuit merely being optimized for each tube. The 6AS7G tube should actually have the advantage over the more famous 300B, because it has lower impedance (that's important in any power output tube, and especially so in an OTL application).

We requested an A-B of the new 300B amp against the M-60 Mk II, and heard surprising differences. The 300B had a very slight edge in midrange transparency, but sounded significantly worse in the trebles, having a less open, less liquid sound in the upper frequencies, where the M-60 Mk II is so outstanding. Most surprising was the change heard in midrange tonal balance. The 300B had a much more forward midrange, and with a peculiar added coloration that we can only describe as looking at music through an orange colored filter.

Note that, if the 300B tube characteristically overemphasizes the midrange in other circuits as well, this could explain why some people think that the 300B is a musically superior tube (these may be the same people who mistakenly think the overemphasized midrange of most horn sound represents greater musical clarity and thus is desirable). If the 300B also characteristically shortchanges the trebles and imparts this weird orange tonal coloration in other circuits, then the 300B is doomed to never be the tube of choice for accurate, honest reproduction, instead being relegated to those amps seeking a particular, peculiar type of midrange emphasis and coloration.

Anyway, getting back to the Atma-Sphere amps, we think that their standard M-60 Mk II, with the standard 6AS7G output tubes, is superior to their new 300B version. We have a hunch that designer Ralph Karsten might agree, and that he created the new 300B amp because of demand from the niche market of 300B tube groupies, just to show that his amp design is amenable to the 300B tube (which is from the same family as his standard 6AS7G output tube).

Atma-Sphere was also playing their new MP-3, a full preamp (including phono front end with MC input) which, at $3795, is intended as a more affordable, single chassis alternative to Atma-SphereÕs flagship MP-1 preamp ($7695). The new MP-3 is an excellent preamp, a fitting mate to the M-60 Mk II. We know this because most of the exhibit sound we heard and reported on from the M-60 Mk II came from vinyl, and came through the whole MP-3. If the MP-3 (or the M-60 Mk II) had had any sonic flaws, they would have been the weak link in the system chain and we would have heard those flaws. Instead, the whole system was musically magnificent, so that means both the M-60 Mk II and the MP-3 are excellent.