Denon PMA-750
Denon's own advertising put it at $450 and claimed its performance came closest to the company's $8,000 separates. The service manual tells a more interesting story (Audio, October 1982, p.139).
Overview
Denon's 1982 advertising campaign made a specific promise. The performance that came closest to the company's $8,000 PRA-6000/POA-8000 separates came in the $450 PMA-750, a Direct-A integrated amplifier with what the copy called 0 dB, Real-Drive, Super-EQ, and Real Time Circuitry (Audio, December 1982, p.91). The same campaign paired it with the $399 DRA-400 receiver, a non-switching AM/FM design with an MC head amp and digital FM (Audio, June 1982, p.65). That's marketing, not a measurement. It does show where this amplifier sat in the 1982 lineup: below the separates, above the $399 DRA-400 receiver the same ads paired it with.
The service manual, issued under Nippon Columbia Co., Ltd., is where the PMA-750 really shows itself. It's a direct-coupled design. The power amplifier section is described as an all-stage direct DC servo circuit, which means no coupling capacitors in the signal path and a servo loop handling DC offset instead. That's the "Direct-A" name made literal.
Power output is 80 watts per channel into 8 ohms, both channels driven, from 20 Hz to 20 kHz, rated to DIN, U.K., Europe, and U.S.A. standards. Into 4 ohms at 1 kHz it's rated at 100 watts per channel. That 80-watt figure isn't a peak or a music-power number — it's a full-bandwidth RMS rating, and the distortion spec backs it up: 0.008% THD from 20 Hz to 20 kHz at -3 dB below rated output into 8 ohms, rising to 0.02% at full rated output on the U.S.A. spec. Intermodulation distortion is quoted at 0.002% at an amplitude equivalent to rated output. For a $450 integrated in 1982, those are honest numbers, not inflated ones.
The frequency response is wider than the power bandwidth suggests. Output bandwidth is specified as 5 Hz to 100 kHz at IHF THD of 0.035%, and a separate transmission characteristic is quoted at 1 Hz to 250 kHz +0 dB at 1 watt output. The amplifier isn't rolling off anywhere near the audible band. The bandwidth is there to keep phase behavior clean well past 20 kHz, which is the point of the DC servo topology.
The phono stage handles both moving magnet and moving coil. MM input sensitivity is 2.5 mV into 47 kΩ, and MC is 125 µV into 100 ohms. RIAA deviation is specified at within ±0.2 dB from 20 Hz to 100 kHz for both MM and MC. That's tight equalization. Signal-to-noise on the phono inputs is 88 dB for MM (input short-circuited, referenced to 2.5 mV) and 72 dB for MC (referenced to 250 µV). Line-level inputs (tuner, tape, aux) are quoted at 110 dB SNR with inputs short-circuited, and all sit at 150 mV sensitivity into 47 kΩ. The equalizer section itself is rated for a maximum output of 10 V into a 47 kΩ load with THD below 0.002% at 1 kHz and 8 V output.
The PMA-750 is a 12-kilogram box measuring 434 mm wide, 132 mm tall, and 407 mm deep, including feet, knobs, and terminals. Output impedance is a low 0.08 ohms at 1 kHz. Speaker switching covers A and B at 4-16 ohms, or A+B at 8-16 ohms, with a stereo headphone jack on the front. Bass and treble controls are each ±8 dB at 100 Hz and 10 kHz. There's a subsonic filter at 18 Hz, 6 dB per octave, and a loudness contour that adds +7 dB at 100 Hz and +6 dB at 10 kHz. For U.S.A. and Canada units, AC outlets include two switched (100 W total) and one unswitched (250 W). Power consumption is 230 W for the U.S.A. version, 400 W under IEC, 200 W for Hong Kong, and 680 W at maximum output. Regional variants shipped for Germany and France (AC 220 V, 50 Hz), the U.K. (240 V, 50 Hz), the U.S.A. (120 V, 60 Hz), and Hong Kong (200 V, 50 Hz).
One thing worth flagging for anyone hunting one today: the service manual is shared between the PMA-750 and the PMA-770. The two models use the same chassis dimensions, the same 12 kg weight, and largely the same parts list — the manual explicitly notes that the exploded-view parts list is prepared based on the E2 (Europe) version and that certain part numbers are marked "same as PMA-770E2." The PMA-770 is the more powerful sibling at 100 watts per channel into 8 ohms, with correspondingly higher phono SNR figures (90 dB MM, 73 dB MC) and a higher power consumption rating. If you're buying a used PMA-750, don't let a seller talk it up as a 770 — the power rating on the back panel is the tell.
The DC servo circuit is the headline, but the supporting specs (the ±0.2 dB RIAA accuracy, the 110 dB line-level SNR, the 0.08-ohm output impedance) describe an amplifier built to stay out of the way. No tone-bypass switch is documented, and there are no loading options on the phono stage. The MC phono section is a capable one, which in 1982 was not a given at this price.
Documentation for the PMA-750 is thin compared to Denon's turntables and its bigger integrateds. The service manual survives and is the primary source for everything above, but independent bench measurements from the period press are scarce in the available record. The 1982 advertising copy is the main contemporary reference, and it's advertising, not review. Treat the manual specs as the baseline and expect the usual maintenance items for a 40-plus-year-old direct-coupled amplifier: servo adjustment, aging electrolytics, and dirty switches. The adjustment procedure in the manual calls for setting the DC offset trimmers so each channel reads under 0.5 V DC at the test points.
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