Proton D-540

Documentation on the Proton D-540 is thin. The main thing the archive has is one thorough period review: Julian Hirsch's test in HiFi/Stereo Review (November 1985, p.47), which identifies the D-540 as an integrated amplifier and puts it through his standard battery.

The D-540 turned out to be a substantial amplifier. Continuous output settled at 170 watts after one second, and the review measured a 6 dB ratio between peak and continuous maximum power — about four times the continuous rating on short dynamic peaks. Hirsch also found it exceptionally stable into complex reactive simulated speaker loads, with only a single cycle of overshoot on a 10 kHz square wave, and he described the tone controls as good, capable of subtle changes rather than crude boosts.

Beyond that review, the record is mostly blank: no production years, original price, or comprehensive spec sheet are documented in the archive. If you own one, the November 1985 HiFi/Stereo Review report is the best period source known.