Denon PMA-690 (1992)
The Denon PMA-690 is a pre-main amplifier released in 1992 at ¥66,000 in Japan. It's one of those early-90s Denon integrated amps that doesn't get talked about much today, but the spec sheet shows a carefully considered design.
The headline feature is Denon's proprietary "New Super Optical Class A" circuit in the power amplifier stage. A newly developed bias control circuit runs the amp in pure Class A up to typical listening levels, then switches operation beyond that. The control signals travel via optical elements, so the bias control circuit can't inject interference into the main signal path. That's a clever way around the old Class A heat-versus-headroom tradeoff. The supply uses a toroidal transformer and large electrolytic capacitors for instantaneous response.
The chassis layout shows similar care. The power amp and preamp sections are symmetrically separated left and right to keep power supply magnetic flux out of the other blocks. The signal path from input to speaker terminals is kept short, and the switches and volume control are arranged to shorten that distance. A low-impedance volume control improves the S/N ratio at listening levels. A Source Direct switch bypasses tone controls, balance, loudness, and the subsonic filter entirely. There's also a Rec Out Selector to record one source while listening to another, and a phono selector that accepts both MM and MC cartridges.
Power is rated at 105W + 105W into 8Ω and 130W + 130W into 6Ω (20 Hz-20 kHz). Dynamic power is claimed at 270W into 4Ω and 350W into 2Ω. THD is listed at 0.004% (1 kHz, 52.5W, 8Ω). The phono stage is respectable: MM at 2.5mV/47kΩ with 94dB S/N, MC at 0.2mV/100Ω with 75dB S/N, and RIAA deviation within ±0.3 dB from 20 Hz to 20 kHz. Line inputs run 150mV/47kΩ (or 10kΩ with Source Direct engaged), and line S/N is rated at 110dB with Source Direct on. It draws 180W, weighs 12.4kg, and measures 434 × 160 × 398mm.
Documentation is thin beyond the specs. No period review turns up in the English-language press, and there's no real production history beyond the 1992 release date. What survives are the units themselves. A Russian seller on Avito described one as fully serviced and working great, and a listing on meshok.net called it a "class A, high-end amplifier" with "ultra-high resolution." Recent eBay sales have landed around $500 (April 2026) and £415 (June 2026).
It's a well-built, thoughtfully laid-out Japanese integrated amp with an optical Class A implementation and a proper MM/MC phono stage. The model never got the press some of its siblings did.
Known Specs
- Rated output: 105W + 105W (8Ω), 130W + 130W (6Ω), 20 Hz–20 kHz
- Dynamic power: 270W (4Ω), 350W (2Ω)
- THD: 0.004% (1 kHz, 52.5W, 8Ω)
- Phono: MM 2.5mV/47kΩ, MC 0.2mV/100Ω, RIAA ±0.3 dB
- Line S/N: 110 dB (Source Direct on)
- Dimensions: 434 × 160 × 398 mm, 12.4 kg
- Released 1992, ¥66,000
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