Denon PMA-501 (c. 1977–1979)

The Denon PMA-501 is a solid-state pre-main (integrated) amplifier from the late 1970s, sold in Japan and certain other regions. It was the cheaper sibling of the PMA-701. According to the specs, it kept "almost the same configuration" as that model while attempting cost reduction. Depending on the source, it was priced at ¥59,800 around 1977, or $350 Canadian in 1977. One source places production between 1978 and 1979. As with many Japanese domestic-market models of this era, documentation outside of Japan is thin.

The phono section is the interesting part. Denon fitted a newly developed PCC (Phono Crosstalk Canceler) system, which adds reverse crosstalk to cancel out the crosstalk inherent in phono pickups. An adjustment record was included. By operating two knobs, the crosstalk in the most audible frequency range could be improved to approximately -40dB. That is an unusual feature for an integrated amp at this price.

The power amplifier section uses a DC-DC pure complementary OCL circuit with all stages of differential amplification, a low-impedance power supply, and output transistors with double epitaxial and triple diffusion structures. A two-transformer system separates the high-current power amp supply from the low-current preamp supply. Channel separation is helped by physically separating the two circuit paths. A fast-response protection relay is built in. The phono input is wired directly to the equalizer amplifier, which cuts down on shielding wire and stray capacitance.

Rated output is 50W + 50W into 8Ω (65W + 65W into 4Ω), with dynamic output (IHF) of 160W (80W + 80W, 8Ω). THD is rated at 0.05% or less at rated output, and 0.02% at 1W. Signal-to-noise is 116dB (IHF, A-network, input short) for the main section. The preamp section offers phono (2.5Vrms/50kΩ) and four line inputs (Tuner, Aux, Tape 1, 2 at 150mV/85kΩ), plus pre-out and two tape loops.

One owner on Audiofanzine called it "an excellent intgr [integrated]," and said they still use it with the matching TU-501 tuner. A buyer on HifiShark commented that $500+ asking prices are outrageous for a 13kg amp, and found one for a reasonable $140 Canadian including shipping. The PMA-501 weighs approximately 13 kg and measures 430 × 147 × 310 mm.

Known specs:

Rated output: 50W + 50W (8Ω) / 65W + 65W (4Ω), 20Hz–20kHz, both channels driven
Dynamic output (IHF): 160W (80W + 80W, 8Ω)
THD: 0.05% or less at rated output / 0.02% at 1W
S/N ratio: 116 dB (IHF, A-network, input short)
Frequency response: 5Hz–100kHz +0/-1dB (tone defeat)
Phono input: 2.5Vrms/50kΩ; Line inputs: 150mV/85kΩ
Dimensions: 430 × 147 × 310 mm; Weight: approx. 13 kg
Power consumption: 125W

The record is thin on production numbers, market positioning, and long-term reliability. What survives suggests a well-engineered, thoughtfully featured integrated amp that Denon built to be more accessible than its top models — with a phono stage that was genuinely ahead of its time.