I have chosen just one of Stewart Hegeman’s many amplifier designs. There are many worthies. The Two was a 60-watt mono tube amplifier that came out in the days of high-fidelity (as opposed to high-end) sound. It was designed by the man whose 550 pure-pentode design was the breakthrough and the basis for today’s best tubed designs. (The 550 got around the stranglehold McIntosh and Gow had on transformer designs—they patented their breakthroughs and used them to build their own amplifiers exclusively.) What Hegeman did, after studying the transformer issue, was devise an alternate way to eliminate notch distortion and build a different transformer winding, thus allowing higher power output. (It also happens that as a very young man I tried to build one of these from its kit version, to drive my acoustic-suspension speakers. Of course, I had to have help with the project, since then, as now, I was/am a technical klutz. The amplifier was, to me, an astonishment in the form of sound.) Hegeman was a freewheeling rover, who loved music and never made an amp (or anything else) that didn’t pay tribute to the real thing. He later, under the Citation rubric, designed the first serious solid-state design, the Citation B. Pioneering? Yes. A sonic breakthrough? No. But a class act.
Marantz Model 9
You might want to add in the 8B as well, since it and the 60-watt Model 9 are still considered classics, and bring in prices in excess of what they cost during the early days of high fidelity (as opposed to the more recent days of high end), especially in Japan where they go for insanely high prices. These were designed by Sid Smith (of Sea Cliff, no less) under the watchful eye of Saul Marantz, who was always in and ahead of the vanguard of state-of-the-art sound (from his marketing of the first straight-line-tracking arm/turntable—a commercial failure—to his early sponsorship of Jon Dahlquist and the DQ-10 speaker). The amps, to this day, sound amazingly good, powerful, and more than a tad romantic—they live on, though Smith and Marantz do not.
Dynaco Stereo 70
If we want to talk about influence—and a long-lasting one—we’d start with this seventy-watt stereo unit, which, during its 20 year (or so) life span was studied and copied by many young designers. It was a diving board for some, like William Z. Johnson (of Audio Research) whose earliest tubed units were built around the Dynaco chassis and parts (highly modified, of course). The 70, and its descendants the Mk2 and 3 versions—came along just as stereo sound was being born. Fortuitously, its compact size, full-bodied sound (throughout most of the frequency range) put it in direct competition with the much more expensive Marantz and McIntosh units. David Hafler oversaw many amps later on, including the Stereo 120, which I thought the least transistory-sounding solid-state of its day. Then there was the 400 that came down the road later, and did at first sound transistory, thus it was subject to the golden touch of modifiers like Frank Van Alstine and became a formidable contender in the high powered solid-state amp sweepstakes. It wasn’t a Stereo 120 or a Phase Linear 700 though.
Phase Linear 700
One of the first high-powered blockbuster amps of the modern (read: high-end) era. It was designed by Bobby Carver, one of the brightest and most innovative thinkers ever to grace audio. The 700 outpowered the Crown DC 300, the first high-powered transistor design, and was cleaner and less colored than the Crown, to boot. Carver wondered why his home-built big tubed amp of the day sounded much better than solid-state designs. He learned, through his measurements, that tube amps could swing 200 volts, while their solid-state counterparts only 35 or so. And he thought, at the time, that the high-voltage output was the decided advantage tube designs had. So he built into the 700 a very wide voltage swing. He engineered the unit’s power supply in a novel way—one too complex for me to discuss here (even if I did fully understand it). An accidental contribution to the 700’s excellent, low-distortion, and uncolored sound: Its biasing transistor sat very near to the unit’s massive heat sinks, so the longer you played it, the better the 700 sounded. Also, not incidentally in Carver’s mind, the 700 came along during the two-channel era when smaller and much, much less efficient speakers (especially the so-called “air-suspension” designs) were in vogue. These now could be driven to life-like levels, with greater control over the normally bloomy bass of such designs, The 700 also allowed reproduction of troublesome high frequencies with greater cleanness and lower distortion.