Denon PMA-590 (1990)
The Denon PMA-590 is a pre-main (integrated) amplifier released in 1990 at a Japanese retail price of ¥59,800. It doesn't get much airtime in vintage audio circles today. The spec sheet, though, shows a seriously overbuilt amp for its apparent spot in the lineup.
The headline feature is what Denon called an "optical Class A" circuit. The power amp section runs in pure Class A up to the average level of the music. At higher output it switches to a non-switching Class A method, which reduces crossover and switching distortion. A newly developed bias control circuit uses an optical element to send the control signal to the power transistor bias circuit - the idea being that this eliminates interference between the main signal path and the bias control, and allows high-speed bias control without contaminating the audio. Denon applied the same approach to a few models around this era.
The power supply is substantial: a large transformer feeding four 8,200 µF electrolytic capacitors in the block capacitor arrangement. A buffer amplifier sits in front of the volume control to lower the impedance of that circuit and improve the signal-to-noise ratio in real-world use. Denon also improved the decoupling between the left and right channels. The chassis uses a "bi-breath plate" construction - two steel sheets sandwiched between polymer sheets, with another steel sheet stacked on top - to increase rigidity. There's also a damper material on the top cover to absorb vibration.
Rated output is 95W + 95W into 8 Ω and 115W + 115W into 6 Ω (20 Hz - 20 kHz), with total harmonic distortion of 0.05% at 48W into 8 Ω. Dynamic power is rated at 270W into 2 Ω. The phono stage is switchable between MM (2.5mV/47kΩ) and MC (0.25mV/100Ω). There's a CD Direct input that routes the CD player's signal straight to the power amp section via a selector switch, bypassing the preamp circuitry for higher purity. A processor loop is provided for connecting a graphic equalizer or surround processor. The feature set also includes tone controls with defeat, loudness, and a subsonic filter (16 Hz, -12dB/oct).
The PMA-590 weighs 15 kg. That's heavy for what looks like a modest mid-range integrated amplifier, and owners tend to remark on it. As one user put it on a Russian forum, "Despite the 'low' index, the specs state an incredible 15 kg. You wouldn't say so by its appearance." Another owner on a Klipsch forum noted, "I can honestly say that I haven't had sound quality this good coming out of my system since the days of my old Denon PMA-590 integrated amp." A service manual for the PMA-590 is also out there.
Beyond the 1990 release date and the ¥59,800 price, little historical context is documented for this model. It doesn't appear to have been heavily reviewed in the English-language press of the period, and its place in Denon's lineup relative to siblings like the PMA-890D or PMA-880D isn't clearly established. The optical bias control, the beefy power supply and the multi-layer chassis all show real engineering effort on what was a budget model.
Known Specifications
- Rated output: 95W + 95W (8 Ω), 115W + 115W (6 Ω), 20 Hz–20 kHz
- THD: 0.05% (20 Hz–20 kHz, 48W, 8 Ω)
- Dynamic power: 270W (2 Ω)
- Output bandwidth: 5 Hz–50 kHz (48W, 0.5%, 8 Ω)
- Line input frequency response: 4 Hz–100 kHz +0/-3dB (1W, 8 Ω)
- Phono MM: 2.5mV/47kΩ; Phono MC: 0.25mV/100Ω
- Line inputs: 150mV/47kΩ (CD, Tuner, Aux1, 2); 150mV/10kΩ (CD Direct, Tape1, 2)
- S/N ratio: 106 dB (CD Direct, Tape), 103 dB (CD, Tuner, Aux), 82 dB (MM), 62 dB (MC)
- Power consumption: 175W
- Dimensions: 434 × 145 × 363 mm (W×H×D)
- Weight: 15 kg
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