Vintage

HCC or 'High Current Capacity' was the watchword of Harman's amplifiers throughout the 1980s, almost all of which were designed to offer very generous dynamic headroom and above-average dynamic current to support very high power into low impedance loads. The PM650 is no exception. Rated at a conservative 50W/8ohm, in practice it delivers 2x75W/8ohm and 2x113W/4ohm with sufficient reserve to maintain 87W and 150W into 8/4ohm loads under dynamic conditions before increasing to 220W/2ohm and a full 255W/1ohm – equivalent to 16.0A at <1% THD for 10msec [see Graph 1, below]. Not only was this impressive 35 years go, it's still got the jump on 'equivalent' amplifiers fresh out of the box in 2020.

Modest levels of feedback mean that distortion is low but not vanishingly so. More importantly, at 0.015-0.020% over the full 50W bandwidth, distortion is impressively consistent, only increasing at high frequencies above 10kHz to 0.025%/20kHz [see Graph 2, below]. With the tone defeat button pressed, the PM650's response is very flat and extended, showing –1dB points at <1Hz–96kHz. With the tone controls in-circuit, but set to 12 o'clock, there's a –0.28dB dip at 200-300Hz and +0.3dB lift at 20Hz. Meanwhile the subsonic filter offers a gentle –2dB/20Hz to –6dB/11Hz roll-off and the 'high cut' a similar roll-off acting at –3dB/5.5kHz, –6dB/8.5kHz to –16dB/20kHz.

Overall line-in gain is higher than necessary at +45dB and the A-wtd S/N ratio slightly below-average at 80dB (re. 0dBW) but stereo separation is good at >70dB through the midrange (down to 50dB/20kHz). In short, the PM650 integrated amplifier could still hold its own today. PM