Audio Research Classic 60 power amplifier Page 2

My study of the Classic 60's schematic leaves me with a great deal of respect for its designers. Far from being based on an "obsolete" technology, the Classic 60 appears thoroughly modern in concept. Its Minnesota pedigree shines forth, its circuit being as painstakingly elegant and as thoroughly thought out as if the amplifier had been designed by Lake Wobegon's famous team of conscientious Norwegian bachelor farmers.

Though the SP-10 was my preamplifier of choice for many years—and still resides in my closet awaiting a new complement of tubes—the last Audio Research power amplifier I had spent any serious time with was the all-tube D-250 back in 1984. The massive D-250 was not particularly neutral by 1990 standards, but never failed to elicit music from the speakers it drove. It formed a synergistic combination, for example, with the original Celestion SL600s, though its prodigious turn-on and turn-off thumps led me to fear for the lives of the minimonitors' woofers. In fact, much as I loved the sound of the D-250, I was almost glad when it had to be returned: a tube power amplifier with that much stored energy in its power supply is almost too much of a wild beast to have in the home. Imagine patting the head of a tiger sprawled on your listening room rug instead of the domestic kitty and you'll get a feel for what I'm talking about.

I was less happy with the next generation of Audio Research components, the first to feature hybrid tube/FET circuitry—original SP9 preamplifier, M300 power amplifier—their sound having a little too much of the Minnesota snow blowing through it for my tastes. Since that time, therefore, though many solid-state power amplifiers have passed through my listening room, the only tube amps were a pair of VTL 100W monoblocks. Impressed as I was with the overall musicality of this "traditional" tube design, its rather midrange-forward tonal balance failed to gel with the balance of my preferred SL700 loudspeakers, and I have ended up using a pair of my "old dependables"—Mark Levinson No.20.5s—for the past 18 months or so.

When the Levinsons are cold, they have a rather tizzy character, and only reach their promised neutrality after warming up for a day or so. (This is one environment-unfriendly amplifier when left on continually, a pair typically drawing a kilowatt from the wall socket.) My first impressions of the Classic 60, garnered with Audio Research interconnect and speaker cable, were also that it sounds rather thin in the treble, if not as tizzy as a cold pair of Levinsons. Leaving the amplifier powered up for a couple of days rendered the amplifier much more neutral-sounding in the treble; though the amplifier is not midrange-forward like the VTLs, a residual brightness remains audible in the mid-treble. This was not unmusical, however, and added to the amplifier's excellent impression of transparency. It was also preferable to the Levinson's residual HF grain, which seemed to be somewhat higher in frequency.

That's when I started experimenting with speaker cables. It seems that the sound of the Classic 60 is far more dependent on the cables with which it is used than I had expected. Replacing the Audio Research cables with Cardas Hexlink endowed the sound with even better clarity, but the slight treble accentuation remained. Bonnie Raitt's Nick of Time CD (Capitol CDP 79128 2) was just too bright with both Cardas and the Audio Research speaker cables, even though you could rejoice in the wealth of recorded detail laid open for your inspection.

Replacing the Cardas with AudioQuest Clear made the treble tonally correct, but now the upper bass lost its tight, well-defined nature. With the ARC and Cardas cables, though the Classic 60 doesn't rival the No.20.5 in the weight or definition of its low frequencies, it still has superb definition for a transformer-coupled design. With the AudioQuest Clear, whether the quality of the bass was musically correct or not became much more dependent on the loudspeaker in use and the type of music being played. The Celestion SL700 benefited from the bass quality with the Clear cable on both rock and classical orchestral music; the Eclipses became rather over-ripe with bass guitar and kick drum. The reggae-style, back-beat bass drum at the start of Bonnie Raitt's "Have a Heart" track—"Hey...shut up, don't lie to me"; just love that lyric—became rather too loose with the Avalons. But with orchestral music, this low-frequency signature added a degree of reality to the sound that was quite—no, very seductive.

Ashkenazy's Sibelius 2, with the Philharmonia (London 410 206-2)—a very early digital recording by Kenneth Wilkinson—was recorded in London's Kingsway Hall. It starts with solo basses following a roll on the timps, cellos and violas then joining in, playing a pizzicato theme above which woodwinds intone a slow-paced melodic fragment that never fails to send a shiver down my back: an icy piece of music that for me conjures up the wind over a frozen Finnish—or an appropriately Minnesotan—landscape. With the Classic 60 driving the Eclipses, those basses sounded real, if miniature-sized. The leading edge of the pluck, the roundness of the fundamental and low harmonics of the sound, the nasal tonality imparted by the instruments' bodies, all blended as they do in real life to give the impressions of whole instruments. When the cellos entered, their sound was distinct from that of the basses—fundamentals an octave higher, nasal colorations also pitched higher—yet musically complete.

Audio Research
3900 Annapolis Lane North
Plymouth, MN 55447-5447
(763) 577-9700