Harman Kardon Citation 12
I will never forget the first time I laid eyes on the 12—it was the coolest and one of the most serious looking amplifiers I’d ever seen. I also remember that it was one of the rare electronic components that even “measurements tell everything” reviewers admitted sounded better than others measuring equally well. A real classic from 1972 (how I wish I had bought one!).
I’ve never been a hot enthusiast of this company’s products, but a William Johnson design must be represented. I leave to others choice of model (the D150, maybe?).
Phase Linear 400
Bob Carver’s 700 was higher powered and came first, but the 400, released in 1972, was the real beauty of the early super powered amplifiers with high output voltage swing. I used my 400 with great satisfaction for nearly five years on Dahlquist DQ‑10s.
Since the criterion is “significant,” the highest‑selling integrated amplifier ever made—introducing NAD’s famous “soft‑clipping” circuit—must surely qualify. It was an ambassador to high-end audio for literally hundreds of thousands of impecunious audiophiles all over the world.
I have no experience with Levinson products, but surely a list like this must include one—the 25 watt Class A ML2 perhaps?
Dan d’Agostino’s pioneering work in Class A amplification must be recognized, though I’m uncertain which model—the KSA 100, perhaps? Whatever, contemporary amplifier design is inconceivable without him.
Marantz Model 9 monoblocks
Along with its less-expensive, lower-power, stereo brother, the Model 8B, Saul Marantz’s legendary Model 9 was the best tube amp money could buy back in the 1960s. A 70W (40W in switchable triode mode) monoblock, it set the standard for liquidity and gorgeousness of timbre in its day—and to some diehards still does. Its many latterday descendants include the marvelous and still-very-much-with-us Air Tight ATM-3. Though dark and euphonious in tonal balance (the 8B was arguably more neutral), the Model 9 was and is so beautiful that many listeners forgive it its colorations.
Sold as diy kits or factory-assembled, this very affordable, highly-tweakable, 35Wpc, EL34-based stereo tube amp from David Hafler is the best-selling audio component of all time with over 300,000 manufactured. The reasons for its popularity are obvious: This was (and still is) a simply lovely-sounding amp—sweet, bloomy, forgiving, and relatively neutral and transparent for its day (though it didn’t do the frequency extremes like today’s tube designs do). The ST-70 has too many descendants to list, including the early ARC amps and the late, great Luxman MB-3045. Perhaps the most prominent at the moment is the highly praised Van Alstine Ultrawave recently reviewed by Dick Olsher. (Dynaco also made several worthy solid-state amps, including the very popular 60Wpc Stereo 120 and the 200Wpc Stereo 400.)
Phase Linear 400
Introduced in 1972, this 200Wpc stereo amplifier from the redoubtable Bob Carver was perhaps the first big solid-state amps to offer high power without the usual price tag in grainness and odd-order harmonic roughness. Detailed, neutral, and transparent, the Phase 400 may not have generated all the wattage/voltage of its elder and bigger brother, the highly regarded Phase 700, but to some of us it sounded more lifelike in timbre and texture than the bigger PL. It was certainly a great buy at $500, setting a standard for affordable excellence in the 70s and 80s.
Audio Research Corporation D150
Preceded by the superior D75, D76, and D76A stereo amplifiers, this 150Wpc, 6550-based behemoth was the culmination of William Zane Johnson’s “first-generation” tube designs. An acknowledged classic from its debut in 1975, the D150 set the standard for high-power tube amplification in the 1970s and long after. The very model of neutrality, low distortion, substantial power delivery, and “high definition” (in the midband, not in the lowest bass or topmost treble), it is still highly prized by aficionados and led to the development of ever higher-powered, lower-distortion, higher-resolution, fuller-range designs from ARC, such as the Reference 600 and the current Reference 610T.