Air Tight ATM-211 tube monoblock power amplifier Page 3
Soundstage width is a function of the degree of independence between amplifier channels, and, at least in theory, monoblock amplifiers have an inherent advantage over stereo amplifiers built on a single chassis. In practice, speaker setup, room acoustics, and channel separation in the rest of the system play much greater roles than amplifier channel separation in producing a wide soundstage; in any case, the soundstage with the ATM-211 driving the speakers extended beyond the speakers with some recordings, and images stayed rock-solid within the soundstage. This was excellent performance, but no better than I've heard with some other high-quality amplifiers, including some using a single-chassis stereo design.
However, an area where the ATM-211 proved superior to every other amplifier I've heard in my system was in soundstage depth. I routinely get a very good sense of depth with this system, but with the ATM-211, the soundstage depths of familiar CDs were greater than I've heard at any other time. To explore this effect, I put on the "Depth of Image" tracks from the second Chesky test CD (JD68), and found that, indeed, the signals recorded at 70' and 80' from the microphone seemed to be coming from the space occupied by the house next door.
The ATM-211's rated output is 22W, which would be considered very low for a solid-state or push-pull tube amplifier, but it's much higher (by 5-6dB) than that of a typical SET. The effect of this greater output capability is expected to be greater maximum loudness and perhaps an enhanced sense of dynamics. The sound of the ATM-211 confirmed both of these expectations. Although I didn't have a low-powered SET around for comparison, if memory serves, neither the Wavelength Gemini nor the Cary CAD-2A3 could play as loud or impart as strong a sense of high-level (macro)dynamics as the ATM-211.
The amplifier that I did have on hand for comparison was the Quicksilver Horn Mono, whose output is rated slightly higher (25W) than that of the ATM-211. Like the ATM-211, the Horn Mono could play louder than what I remember of the low-powered SETs; however, at matched levels, the ATM-211's sense of authority and dynamic quickness was superior, the music sounding more vital, more exciting. The ATM-211 also revealed more musical detail, and generally seemed more transparent to the source. These comments are not meant as criticisms of the Horn Mono—which, at $1595, remains my favorite sensibly priced tube amplifier—but to highlight the fact that simple specifications do not tell us all we need to know about what an amplifier sounds like.
And what about the fabled "midrange magic," the "harmonic rightness" of SETs? Was this present with the ATM-211, and to the same degree as with low-powered SETs? Alas, as noted above, I did not have any low-powered SETs on hand for comparison, so any comment I can make is based on my memory of what these amps sound like, and influenced by changes in the rest of the system over time (footnote 1).
Keeping those caveats in mind, I'd say that the ATM-211 approached but did not fully reach that sense of harmonic verisimilitude that characterizes low-powered SETs like the Wavelength Gemini and the Cary CAD-2A3. With the ATM-211 in the system, Sylvia McNair's "All the Things You Are" (Sure Thing: The Jerome Kern Songbook, Philips 442 129-2) was quite lovely; I would have had a hard time identifying anything that was amiss sonically, but I remember her voice with the Wavelength and the Cary amps having greater human warmth, more like a real voice and less like a reproduction—and this despite the fact that the new Series 3 Avantgarde Unos sound better than the Series 2s that I was using with the other amps. Was that a kind of coloration, euphonic distortions added to the signal that replace something lost in the recording/playback process? Perhaps. If so, then it might follow that the ATM-211 adds less of this type of distortion, striking a different balance of "musicality" and "accuracy." I think this is the spot in the argument where I came in.