Audio Research Classic 60 power amplifier Page 4
The final set of comparisons was made with the Japanese Air Tight amplifier that had so impressed Dick Olsher in May. This 80Wpc, $5950 stereo design is typical of classic tube amplifier design. It uses a pair of Gold Aero KT88s for each channel, with input and driver stages comprised of a 12AX7, a 12AU7, and a 12BH7. It is also typical of classic tube design in that it has a high output impedance and much higher levels of distortion than the Classic 60: 1% or more when driving 4 ohm loads from the 8 ohm transformer tap. Construction is immaculate, with point-to-point wiring used throughout—no pcbs—and DO enthused over its tonal neutrality, remarkable transparency, and excellent soundstage delineation.
Driving the Avalon speakers from its 4 ohm outputs, with the amp sitting on a Sound Organisation table, the Air Tight was 2dB less sensitive than the American amp, so levels, as before, were equalized at 1kHz.
Using the Lesley test track from the Stereophile Test CD, Dick's wife's soprano voice reproduced as being more robust, less "small," via the Air Tight amplifier. The Audio Research's highs, though not unpleasant, were a little "tinkly" by comparison, though a copy master tape of Stereophile's forthcoming Brahms third piano sonata recording (footnote 4) reproduced with rather too shut-in a high end via the Japanese amplifier. The midrange tonality of the Steinway, however, was perhaps even more true to the original than via the American amplifier. In fact, the Air Tight has perhaps the most musically neutral and natural midrange of any amplifier I have ever used. However, I found it to offer a slightly less transparent view into the soundstage than the Classic 60, this impression confirmed by listening to Stereophile's Poem CD, which has less image depth than the equivalent LP.
Via the Air Tight, both instruments were presented as being even slightly more forward. This lack—and it is a slight lack—of image transparency is, I am sure, due both to the Air Tight's closed-in highs, but more importantly, to the lows, which get congested at highish levels. Powerful left-hand piano chords tended to muddy up the window somewhat.
The Air Tight's highs could be brought up in subjective level by switching to the Cardas cables (the spade lugs on the Audio Research cables are incompatible with the barrier strip on the Avalons), but the lows were unchanged in nature. Though the Avalons boast a 6±1 ohm impedance across the audio band, it was clear that they were not a synergistic match with the Air Tight. In fact, I actually found it harder to catch on to the exact pitch of deep-bass piano notes with the Eclipses driven by the Japanese amp. With the caveat, therefore, concerning the slightly bloated nature of the upper bass with the Audio Research amplifier that I mentioned earlier, I could go on listening to the Avalons through it all night—and sometimes almost did.
It's no use pretending that the Classic 60 isn't an expensive amplifier, given its lowish output power. Yet only rarely during my auditioning did I feel the need for a little more headroom, and then only with master tapes, which tend to preserve their peaks intact. The Classic 60's lows were a little less well-damped than the best solid-state amplifiers, and while possessing more treble content than the Air Tight amplifier, this didn't render its sound unmusical; in fact, with the transparent window it offers into a deep and wide soundstage, it gave me a great deal of pleasure.
Given that its owner will have to be prepared to experiment with cables to get the best balance from his or her preferred loudspeakers, the Classic 60 produces a sound that would make those Norwegian bachelor farmers proud. It's taking the place of my Levinsons as the system workhorse amplifier.
Footnote 4: As I write (mid July 1989), we are in the process of deciding where to have the LP and CD mastered. Release of the LP is scheduled for late October, while the CD will follow presently. I must say that even having heard this recording a bazillion times during the editing, Robert Silverman's performance of the second, slow movement never fails to brings the hairs on my arms to attention.—John Atkinson