Atma-Sphere S-30 MKII

The S-30 is a 30-watt per channel, OTL (output transformerless) tube amplifier that offers deep, well-defined bass, rivaling solid-state designs in speed and clarity. I can’t speak to its performance in the lowest octave, as I haven’t had the opportunity to pair it with speakers capable of reproducing frequencies below 35 Hz. However, for those who appreciate the signature midrange of the 300B tube but are put off by its limitations at the frequency extremes, the S-30 is worth auditioning. The midrange is exceptional, with superb coherence, a wide and deep soundstage, and remarkable tonal fidelity. Human voices, particularly female vocals, are rendered beautifully—assuming the source recording is of good quality, which, unfortunately, is not always the case. The high frequencies are equally impressive—truly some of the best I have heard. Having listened to the S-30 with four different speaker systems, I’m convinced of two things: 1) The amplifier’s strengths are easily noticeable across a variety of speakers, and 2) there is a unique synergy between the S-30 and my Quad ESL-63s. The microdynamics are outstanding, which allows me to enjoy the music at lower volume levels than I previously would have, as the detail remains clear and present even at soft listening levels. The Quads, though not highly efficient, pair very well with the S-30, and it’s rare that the amp reaches clipping. When it does, it happens gracefully—there’s no harshness or brittleness. The soundstage may become a bit “cloudy” or congested, but that’s the extent of it. The S-30 comes with Sovtek 6AS7 power tubes. From the Atma-Sphere user group, I’ve heard that the Svetlana version of this tube has a slightly different sound, but there’s no clear consensus on which is superior. Some domestic manufacturers have made versions of this tube, but they aren’t considered rugged enough for this application, and there doesn’t seem to be any noticeable improvement in sound quality with these alternatives. According to Ralph Karsten at Atma-Sphere, the power tubes are estimated to last around 10,000 hours, which is a significant advantage in terms of longevity and cost-effectiveness when it comes time for retubing. Output power 30 watts per channel into 8 Ω load 45 watts per channel into 16 Ω load Impedance Input Impedance: 100 KΩ single-ended, 200 KΩ balanced Output Impedance: 7 Ω Input 3 V sensitivity RCA and XLR true balanced input Tube complement 10 x 6AS7G output tube 6 x 6SN7 driver tube Gain 23dB ( for 8 Ω ) Power Bandwidth 2Hz-75KHz within ½ dB Frequency response ( 1 watt, open loop ) 20 Hz squarewave Tilt; unmeasureable 1Hz-200KHz within 3 dB Hum and noise Less than -75db below 1 watt, -95db below full power (30 watts) Distortion Total Harmonic Distortion ( THD ) typically 1% at full power Intermodulation ( IM ) distortion typically under .04% at full power Phase shift less than 1° @ 20KHz Output section risetime 600 V/µs Feedback 2 dB Power consumption 400 watts Dimensions 13″ deep x 17″ wide x 8″ tall ( 33 x 43 x 20 cm ) Weight ( without tubes ) 24 lbs ( 10.9 kg )