Denon PMA-740 (1983)
The Denon PMA-740 is a stereo pre-main amplifier released in 1983 at a Japanese retail price of ¥59,800. Denon was pushing hard on digital-ready power delivery at the time, and this is a technically ambitious integrated amp. The fact sheet says the large multi-shielded transformer, 20,000 µF capacitor, and fast-recovery diode were adopted specifically to cope with the high dynamic range of digital sources.
The headline technology is the non-feedback 0 dB power amplifier, an application of the approach Denon first developed in the POA-8000. The amp isn't wrapped in a global negative feedback loop. Instead, the PMA-740 uses a direct distortion servo circuit. It compares the input signal against the output (main signal plus distortion), extracts only the distortion component, and feeds its inverse back to the input. This drives static distortion toward zero without signal feedback or time delay. Because there's no NFB loop, the amp is said to be immune to back-EMF from speaker loads. A PC150W output transistor handles the power stage.
The specs are solid. Output is 105W + 105W into 8 Ω and 120W + 120W into 6 Ω (both channels driven, 20 Hz - 20 kHz), with THD rated at 0.005% or less at rated output −3 dB. Slew rate is spec'd at ±200 V/µs or more. Output bandwidth (IHF, both channels driven) runs 5 Hz - 80 kHz at 0.03% THD, and frequency response at 1W extends from 4 Hz to 150 kHz (+0/−3 dB). The phono stage handles both MM (2.5 mV/47 kΩ) and MC (0.2 mV/100 Ω), with RIAA deviation of ±0.3 dB from 20 Hz to 100 kHz on MC. S/N ratios are 86 dB (MM), 70 dB (MC), and 106 dB on line inputs. Tone controls give ±8 dB at 100 Hz and 10 kHz, with a −20 dB muting and a loudness contour adding +7 dB at 100 Hz and +6 dB at 10 kHz. The unit draws 195W, measures 434 × 112 × 398 mm, and weighs 10.2 kg.
Documentation outside the Japanese spec sheet is thin. A single used-market listing from April 2024 shows a junk-condition PMA-740 selling at auction for ¥10,800. One Vietnamese listing pairs it with JBL XE6 speakers as a complete set "for singing." No service manual appears to exist in the usual online repositories. The closest match in a typical search is the DRM-740, which is a cassette deck, not this amplifier. No owner reviews, common-failure notes, or market context have surfaced.
Known specs at a glance:
- Rated output: 105W + 105W (8 Ω), 120W + 120W (6 Ω), 20 Hz–20 kHz
- THD: 0.005% or less (at rated output −3 dB)
- Slew rate: ±200 V/µs or more
- Phono: MM 2.5 mV/47 kΩ; MC 0.2 mV/100 Ω
- Dimensions: 434 × 112 × 398 mm; 10.2 kg
- Price (1983, Japan): ¥59,800
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