Pre/Power Amplifiers

BHK's swansong is not simply a 'doubled-up' Signature 300 monoblock [HFN Jul '16] for although the latter is (still) rated at 300W/8ohm and 600W/4ohm, and the M600 specified at 600W/8ohm and 1kW/4ohm, the new M600 is more cautiously protected into lower impedance loads. So, while the '300 offers 420W, 790W and 1410W into 8, 4 and 2ohm and a full 2120W into 1ohm under dynamic conditions, the M600 delivers 745W and 1390W into 8 and 4ohm but drops back slightly to 1120W and 625W into 2 and 1ohm loads, respectively [see Graph 1]. Incidentally, there's no difference in power output or the wide 91.3dB A-wtd S/N ratio (re. 0dBW) in either the preferred +26dB or (high) +30.5dB gain settings available via the M600's rear panel. Indeed, given the size of the 1.6kVA internal transformer the M600's low noise (half that of the '300) is very impressive.

As with the Signature 300, the M600's distortion initially creeps up gently with power output from 0.0003%/1W to 0.00095%/10W before holding at 0.006% from 100-300W and increasing more abruptly to 0.016%/400W and 0.16% at the rated 600W/8ohm (all re. 1kHz). Distortion also increases more aggressively at high frequencies from 0.00095% at 1kHz/10W to 0.055%/20kHz and 0.12%/40kHz [see Graph 2, below]. Otherwise, PS Audio has retained an impressively uniform 0.07-0.09ohm output impedance which only begins to increase above 80kHz, reaching 1.3ohm/100kHz. This assists its extended frequency response which is flat to within ±0.5dB from 1Hz-60kHz, falling slightly thereafter to –1.4dB/100kHz. Into lower impedances this amounts to –1.9dB/100kHz/4ohm, –3.3dB/100kHz/2ohm and –4.9dB/100kHz/1ohm. PM