Atma-sphere S-30 Amplifiers

Atma-sphere S-30 Amplifiers 


30 watts/ch into 8-ohm load/45 watts into 16-ohm load tube complement: (5) 6AS7G output tube per channel (3) 6SN7 driver tube per channel


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[Aug 04, 2001]
Mike Currie


Harmonic integrity, soundstaging, image specificity, top to bottom coherence


Power output will be too low for some; will not match well with impedances of some speakers

There has been essentially nothing written about the Atma-Sphere S-30 since its introduction in 1999. I find this surprising, as it is very similar in circuitry (apart from power and the fact that it is on a stereo chassis) to its older monoblock brother, the M-60. The latter has been the subject of considerable praise. It would seem to be a natural match for speakers of reasonably high efficiency and in which impedance does not drop below 8 ohms in the bass and lower mids, since power decreases with lower impedance in an OTL design. There are some who suggest that 8 ohms be considered the minimum throughout the spectrum. I have not found this to be the case.

The S-30 is a 30 wpc, OTL tube amplifier. Bass is deep, extremely well defined, and gives up little to solid state designs in speed and clarity. I cannot comment on the lowest octave, as I haven’t heard the unit drive a speaker capable of reproducing deeper than 35 Hz or so. Those of you who love that 300B midrange, but are put off by that tube’s characteristics at the frequency extremes, would be well advised to audition the S-30. The mids are truly spectacular, displaying a wonderful coherence, very wide and deep soundstage, and outstanding tonal fidelity. Human voice, especially female, is rendered beautifully, obviously assuming a proper recording to begin with - something that happens less often than most of us would like. Highs are as good as I have heard anywhere - period.

After hearing the S-30 drive four different speaker systems, I am convinced that 1) the strengths of this amp are very, very easily discerned on all four, and 2) there is a real synergy between the amp and my Quad ESL-63s. Microdynamics are nothing short of amazing. I find myself listening at significantly lower levels that previously, simply because the detail is there in all of its glory. The Quads are not terribly efficient, but it is the very rare occasion that I can drive the amp to clipping. When it does so, it is very graceful about it. The soundstage goes a little ‘cloudy’ and congested. That’s it – no harshness or brittleness whatsoever.

The stock power output tubes on these amps are Sovtek 6AS7s. I have heard through the outstanding Atma-Sphere user group that the Svetlana version of this tube sounds a bit different, but there seems little consensus on which is better. Various domestic manufacturers made the tube, but apparently are not rugged enough for use in this application, nor have I heard anyone say that any of them improved the sound. Ralph Karsten at Atma-Sphere estimates power tube life at 10,000 hours. Big, big upsides when it comes to retubing time – these are in current production and can
be obtained for $15-18 each.

Front end tubes are a different matter. The amp uses six 6SN7s, with pairs for each of gain, driver, and constant current. After considerable experimentation, I have settled on the following:

- stock Sovteks for the constant current position. I can hear no sonic benefit with tube rolling here

- a nice pair of NOS Raytheon WGTs as drivers

- a great pair of Sylvania VT-231s in the gain circuit. This is the one that really makes the difference

A couple of extremely knowledgeable folks in the user group advocate using 12SX7s instead of 6SN7s (after the appropriate voltage changes, obviously). I have not yet tried it.

In summary, within its power limitations, I find the Atma-Sphere S-30 to be as good overall as any amplifier I have ever used, bar none. I could easily come up with examples that better the S-30 in specific areas, but none have the top to bottom excellence so evident in this amp.

Associated gear:

J A Michell Gyrodec SE
Rega RB-300, Origin Live mod
Grado Reference Master
Cary CD-303
Art Audio VP1 Mk II
Quad ESL-63

Similar Products Used:

conrad-johnson CAV-50; Rogue M-120; Atma-Sphere M-60; Transcendent OTL; several 300B and 845 based amps

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