Denon PMA-235 (circa 1975)
The Denon PMA-235 is a pre-main (integrated) amplifier from the mid-1970s. It launched at ¥66,500. A wood cabinet (ACA-5) was sold separately for ¥5,000. As far as the record shows, the design was built around wide-range response. Denon said the PMA-235 was engineered not just for audible performance but for careful control of output bandwidth, phase, transient behavior, and crosstalk even beyond the audible range.
The power amplifier section uses a pure complementary OCL circuit with Motorola Darlington output transistors, a triple magnetic-shielded transformer, and large filter capacitors. The equalizer stage is a 3-stage direct-coupled NPN transistor circuit running on a high 53V stabilized supply. That allows deep negative feedback and a maximum allowable phono input of 200mVrms or more at 1kHz. The tone control section uses a newly devised NFB circuit that automatically centers both bass and treble, so there is no need for a separate defeat switch. When centered, the response is flat from 5Hz to 300kHz. A fast-acting protection circuit guards the output transistors against speaker-terminal shorts.
Rated output is 35W + 35W into 8Ω (20Hz - 20kHz, both channels driven), rising to 50W + 50W into 4Ω at 1kHz. Dynamic power (IHF) is rated at 108W into 8Ω and 160W into 4Ω (both figures as 2-channel sums). THD is 0.08% or less at rated output, with an intermodulation figure of 0.1% or less. Frequency response extends to 200kHz (+0/-1dB). The RIAA deviation on phono is held to +0.15/-0.3dB from 20Hz to 20kHz. S/N ratio is 75dB or better on phono and 80dB or better on line inputs. The unit weighs 11kg and measures 396 × 147 × 281mm (W×H×D).
Surviving information on this model is thin. No formal period reviews have surfaced, and most of what's known comes from the spec sheet and a handful of owner mentions. A forum post on diyAudio has an owner listing the PMA-235 alongside a Yamaha AX-1070 and a single-ended tube amp. Another poster on Head-Fi considered it as a purchase option. No detailed listening impressions appear in the record.
Known Specifications
- Rated output: 35W + 35W (8Ω, 20Hz–20kHz); 43W + 43W (4Ω, 20Hz–20kHz); 50W + 50W (4Ω, 1kHz)
- Dynamic power (IHF): 108W (8Ω); 160W (4Ω)
- THD: 0.08% or less at rated output
- Frequency response: 5Hz–200kHz (+0/-1dB)
- Inputs: Phono 1 (2.3mV/60kΩ), Phono 2 (2.3mV/30kΩ), Tuner, Tape, Aux (150mV/70kΩ and 40kΩ)
- S/N ratio (IHF A-weighted): 75dB (phono); 80dB (line)
- Dimensions: 396 × 147 × 281mm; 11kg
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