Denon PMA-232 (circa 1976)

The Denon PMA-232 is a pre-main amplifier from the mid-1970s, sold in Japan at ¥47,500. Denon described it as designed "with an emphasis on transmission characteristics," and the engineering bears that out. It is built around wide bandwidth, low distortion, and a carefully done phono stage. It was also styled to match the TU-332 FM tuner, so Denon clearly meant it as the center of a matched system.

The power side is a fully complementary DC amplifier circuit with discrete transistors throughout, all stages directly coupled. The output stage uses a newly developed 60W-class epitaxial planar fully symmetrical power transistor, chosen for low minority carrier accumulation and reduced switching distortion. Denon also added a large heatsink, a high-current power supply, and a DC-balanced differential amplifier to extend the transmission band and cut low- and high-frequency distortion. Rated output is 40W + 40W into 8Ω (35W + 35W at 20Hz-20kHz), with dynamic output of 55W into 8Ω and 90W into 4Ω. THD is rated at 0.03% at 1kHz. Frequency response extends to 200kHz (+0/-1dB), and output impedance is a low 0.16Ω or less.

The preamp section is where the PMA-232 gets interesting. The phono equalizer is a 3-stage, direct-coupled E-E feedback type using low-noise, high-voltage NPN transistors, with a high-collector-loss transistor on the final emitter follower. Denon claimed this flattened the equalizer's maximum output voltage out to 20kHz and greatly improved allowable input above 10kHz, a weak point in many designs of the day. RIAA deviation is held to +0.25/-0.2dB. Phono input sensitivity is 2.3mV/50kΩ, with a maximum allowable input of 200mVrms at 1kHz. The tone controls use an NFB method with an emitter follower at the front stage. They have automatic defeat at the center detent, so the signal path flattens when the controls are centered. A low filter at 30Hz (12dB/octave) is included. Speaker protection is a fast-response circuit, with a separate detection circuit guarding the power transistors.

The PMA-232 is compact: 396mm wide, 147mm high, 281mm deep, and 9kg. It has screw-type speaker terminals for reliable contact, and the power, filter, and monitor switches use a new slide system. Power consumption is rated at 100W. A 10-page English service manual exists and circulates online.

Documentation on the PMA-232 is otherwise thin. There are no period reviews in the major English-language hi-fi magazines, no surviving owner discussions of note, and no reliable market pricing data. The solid technical record comes from the Japanese Audio Database.

Known Specifications

• Type: Pre-main amplifier (integrated)
• Rated output: 40W + 40W (8Ω, 1kHz); 50W + 50W (4Ω, 1kHz); 35W + 35W (8Ω, 20Hz–20kHz)
• Dynamic output (IHF): 55W + 55W (8Ω); 90W + 90W (4Ω)
• THD: 0.03% (1kHz, rated output); 0.08% (2kHz/20kHz)
• Frequency response: 5Hz–200kHz (+0/-1dB); output bandwidth 5Hz–45kHz (IHF)
• Phono input: 2.3mV/50kΩ; max allowable input 200mVrms (1kHz)
• Line inputs: 140mV/80kΩ (Tuner, Aux, Tape)
• RIAA deviation: +0.25/-0.2dB (20Hz–20kHz)
• S/N ratio (IHF-A): 75dB (phono); 85dB (line)
• Channel separation: 70dB (1kHz); 55dB (20Hz–20kHz)
• Tone controls: Bass +7.5/-5dB at 100Hz; Treble +7.5/-5dB at 10kHz (2.5dB steps, auto-defeat at center)
• Low filter: 30Hz, 12dB/octave
• Dimensions: 396 × 147 × 281 mm
• Weight: 9kg
• Price: ¥47,500 (circa 1976)

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