Denon PMA-850II (1978)
The PMA-850II is the improved version of Denon's PMA-850, a reference-class integrated amplifier from the late 1970s. It was released in 1978 at ¥129,000. The series has been described as "way too serious looking" for its era.
The difference between the II and the original 850 is simple: the II has everything. The original lacked a rec-out selector and a Class A mode. The PMA-850II has both, and trades away the muting switch for a Class A/B function. Per thevintageknob.org, that makes it "the rare beast" of the series. The PMA-830, the other sibling in the line, kept Class A but dropped the high filter. The 850II keeps that too.
Inside, Denon went with symmetrical complementary push-pull circuitry throughout, using PNP/NPN bipolar pairs rather than leaning on negative feedback. The power stage runs Pc100W EBT (Emitter Ballast Transistor) devices in parallel. The supply is a large toroidal transformer with 10,000 µF × 2 block capacitors. There's a dedicated MC head amplifier with a gold-plated input terminal, and a high-gain equalizer stage rated at 42 dB with RIAA deviation within ±0.2 dB. The control section can be fully disconnected from the main circuit. That lets you drive the power amp directly from the equalizer output if you want the shortest possible path.
In Class A, it's rated at 22W + 22W into 8 Ω. In Class B, it's 100W + 100W. Some sources list the Class A figure lower, at 2×10W, so treat that number with a little caution. Output bandwidth is 5 Hz to 100 kHz in both modes, with 0.02% THD in Class A and 0.05% in Class B. The tone controls are ±8 dB at 100 Hz and 10 kHz. There's a subsonic filter at 20 Hz (12 dB/oct) and a high cut at 7 kHz (6 dB/oct). The loudness contour adds +7 dB at 100 Hz and +6 dB at 10 kHz. It draws 250W and weighs 18 kg.
The vintageknob's verdict on the series: "All are very healthy units and built to make music for a nice set of decades - pretty rare nowadays!" Hook one to a decent turntable and, as they put it, you'd wonder what hi-fi has done in the thirty years since to improve on it.
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