Denon PMA-255 / PMA-255UK

Name: Denon PMA-255
Brand: Denon

The Denon PMA-255 is one model number covering two different amplifiers. The Japanese domestic PMA-255 appeared around 1975 at ¥86,500. It was a full-featured integrated amp with two phono inputs, tone controls with rotary switches adjustable in 2 dB steps, filters, and a 55W + 55W (8Ω, 20Hz - 20kHz) rated output. The later UK-market PMA-255UK shared the chassis and fascia of the popular PMA-250SE, but with entirely new internals. It was a line-level-only design with no phono stage, rated at a conservative 30W per channel into 8Ω. Both models are covered here, with specs kept separate where they diverge.

The Japanese PMA-255 (c. 1975)

The original PMA-255 was a serious piece of mid-1970s Denon engineering. The power amp section used a pure complementary OCL circuit with all stages directly connected, built around silicon triple-diffused mesa output transistors. Denon put the power transformer in the center with heatsinks on either side of it, and gave the transformer a six-layer magnetic shield. The preamp ran its equalizer at a high 70V supply. The tone control section used a modified BAX negative feedback circuit with bass and treble as rotary switches, each adjustable in 2 dB steps. The center detent bypasses the feedback capacitor entirely.

The spec sheet is thorough for the era:

- Rated output: 55W + 55W (8Ω, 20Hz - 20kHz); 58W + 58W (4Ω, 20Hz - 20kHz)

- Dynamic power (IHF): 164W (82W + 82W, 8Ω); 260W (130W + 130W, 4Ω)

- THD: 0.08% or less at rated output

- Frequency response: 4Hz–200kHz (+0, –1dB)

- Inputs: Phono 1/2 (2.3mV), Tuner, Aux 1/2, Tape 1/2

- Signal-to-noise: 75dB (phono), 85dB (line)

- Dimensions: 396 × 147 × 281mm; 11.2kg

- Optional ACA-5 wood cabinet (¥5,000)

The PMA-255UK

The UK variant is a different story. Built in Europe, it was introduced alongside the higher-spec PMA-355UK (£230) as a replacement for the long-running PMA-250SE and PMA-350SE. Hi-Fi Review noted that the 255UK used the standard bent steel chassis and plastic fascia borrowed from the 250SE, but the internals were "bigger, beefier and all new." The review praised its short signal paths, ELNA audiophile-grade reservoir capacitors custom-made for Denon, and new bipolar output devices, with relay-based mute and short-circuit protection.

The 255UK had no phono stage, just four or five line inputs (sources conflict) and a tape circuit. It was rated conservatively at 30W per channel into 8Ω (with one listing claiming 50W into 4Ω). Hi-Fi Review described it as "a sharp - perhaps too sharp - and articulate all-rounder, with a surprisingly heavy power output," and gave it a Best Buy nod. The same review said it could sound "a bit etched" on some material and lacked the weight of pricier rivals, but concluded: "You can pay more and get a lot less."

The 255UK's rated distortion was less than 0.03%, frequency response 10Hz - 80kHz, signal-to-noise 98dB, and it measured 115 × 435 × 286mm. One seller's description put it this way: "Rated at a conservative 30 watts the sound is more subtle, better focused and the PMA-255UK kicks hard, sounding like a much bigger amp."

Production years for either version aren't documented in the available record. The Japanese 255 can be dated to around 1975 from its price listing. The UK version's exact launch date is unclear, though Denon's "UK Design" concept dates to 1985 with the PMA-707.