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"The only tubes that I want to see in my household are...the picture tube in my TV and the magnetron in the microwave oven," a Glendale, CA, reader recently wrote, and I guess his feelings reflect those of many when confronted by a supposedly "obsolete" audio technology. Forty years after the invention of the transistor and 20 after the widespread introduction of solid-state amplifiers (footnote 1), it must come as a shock to readers of the mass-market "slicks" that not only do a number of American manufacturers manufacture amplifiers and preamplifiers using tubes, but some of those…
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.
Listening
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…
Adding to this high degree of musical realism was a soundstage that verged on being the most transparent I have ever heard, particularly with the Avalon loudspeakers, which far outdo the Celestions in this respect. Now don't get me wrong: the venerable JGH has several times accused me of giving a system's soundstage and imaging performance a higher priority than even tonal neutrality. "And who hears that kind of precision in real life anyway?" he has often snorted down his nose at me before returning his attention to a Tanqueray Martini, straight up, with two twists.
Well, Gordon, old…
The Classic 60 definitely opened up the soundstage in a more expansive nature than the Levinson, there being a superb presentation of depth. This is one of the areas where I have always found the No.20.5 to lack a little finesse compared to the best tube designs, but in the bass, it was no contest. As musically acceptable as the ARC sounded in this region, the Levinson controlled the SL700s with an iron fist, offering control and definition. "There's no substitute for current," a wise old man once said. (Actually, I think it was Martin Colloms.) He was right.
The final set of comparisons…
Sidebar 1: Specifications
Description: stereo, hybrid tube/FET power amplifier. Tube complement: four matched pairs of low-gas 6550s, four 6FQ7/6CG7s. Maximum power output: at least 60W into 16 ohms (20.8dBW), 15Hz-20kHz, with less than 1% THD; typically 62W at 1kHz with 120V AC line. Power bandwidth (-3dB): 12Hz-40kHz. Input sensitivity: 550mV RMS for rated output. Input impedance: 100k ohms. Output regulation: approximately 0.3dB, 16 ohms to open circuit (equivalent to an output impedance of 0.56 ohms—damping factor quoted as approximately 30). Negative feedback: 20dB. Slew rate: 20V/…
Sidebar 2: Reference System
The Classic 60 was used over a period of four months with a variety of ancillary components. Preamplifier was mainly a Mark Levinson No.26, first used with its outboard No.25 phono preamplifier, then with the latter replaced by the excellent External Power Supply version of the Mod Squad's Phono Drive. I also used both the sample of the Audio Research SP14 reviewed by Guy Lemcoe in June, as well as an SP14 loaned by California dealer Howard Rodgers (RogerSound Labs, Upscale Audio). My reference Mod Squad Line Drive Deluxe (soon to be updated to the latest 1990…
Sidebar 3: Measurements
The Classic 60 measured as having a flat response across the audio band (fig.1), apart from a slight rolloff above 10kHz, reaching -0.32dB at 20kHz. This will be just audible as a very slightly soft top octave, but is otherwise inconsequential. Crosstalk was also inconsequential: fig.2 shows the leakage from Channel 1 into Channel 2 with the Channel 2 input shorted, below -120dB across the band, which is effectively buried in the amplifier's noise floor. Looking at the amplifier's response with an input signal consisting of a 200µs, positive-going, rectangular…
John Atkinson compared the Classic 60 with the Mark Levinson No.23.5 in September 1991 (Vol.14 No.9):
The final set of comparisons was with the Audio Research Classic 60. Now it's true that the significantly lower-powered and less expensive tubed amplifier doesn't necessarily compete with the No.23.5 in the market, a more relevant comparison perhaps being between the solid-state amplifier and a pair of ARC Classic 120 monoblocks. But I'm very familiar with the Classic 60, and felt that as long as I didn't fall into the trap of describing differences that are purely due to the tube…
Robert J. Reina compared the Classic 60 with the Cary SLM-100 in May 1996 (Vol.19 No.5):
I spent a great deal of time comparing the Cary Audio Design SLM-100 Revised monoblock to the Audio Research Classic 60 on both sets of speakers. The results were fascinating: both amplifiers were clearly impressive performers with totally different sonic presentations. They shared a wide and deep soundstage presentation, but it was difficult to determine which was more realistic.
The ARC excelled in image specificity, detail resolution, and transparency, but the images on the stage with the…
Robert J. Reina wrote again about the Classic 60 in May 1997 (Vol.20 No.5):
When compared with my reference, the long-discontinued Audio Research Classic 60, the Sonic Frontiers Power 2 presented an interesting tradeoff of strengths and weaknesses. The Classic 60 had the more neutral midrange and midbass presentation, but the Power 2's high frequencies were much more convincing. The ARC did not, however, approach either the low-level or high-level dynamic capabilities of the Power 2. And, although one of the Classic 60's strengths is its resolution of inner detail, the Power 2 exceeded…