Pre/Power Amplifiers

Although this latest M1200 monoblock offers exactly the same +30.6dB gain as PS Audio's M700 [HFN Apr '20] its performance differs in several important respects. Power output is necessarily increased courtesy of the 1200-series ICEpower module, from 365W/8ohm and 715W/4ohm for the M700 to 628W/8ohm and 1246W/4ohm here. As expected, the Class D architecture yields no advantage under dynamic conditions, in fact the 'TCCCL' (Temperature-Compensated Cycle-by-Cycle Current Limit) regime actually caps the output at 597W, 1080W and 1985W into 8, 4 and 2ohm, 'falling' to 1311W/1ohm, or 36A [see Graph 1, below]. Either way, the M1200 will not run short of breath...

As we saw with the M700, the M1200 shows a trend of gently rising distortion with increasing output – the triode tube input only adding some slight 'colour' here – from 0.0029%/1W to 0.012%/10W, 0.038%/100W and 0.14% at the rated 600W/8ohm. The 1200AS1 Class D module is optimised for best performance/lowest THD into 4ohm [again, see Graph 1] but distortion is otherwise maintained at an impressively consistent level vs. frequency from 20Hz-4kHz, increasing thereafter to 0.065%/20kHz/10W [see Graph 2]. This new module is quieter than that used in the M700, the 83.9dB A-wtd S/N ratio besting the latter's 76.1dB by some margin. I discuss the M1200's much reduced sensitivity to speaker loading in my boxout, p65, but the practical result is a flat ~0.026ohm output impedance from 5Hz-5kHz, rising only gently thereafter to a maximum 0.83ohm/95kHz (10x lower than with the M700). The frequency response now extends from 2Hz-25kHz (–1dB) and to –0.65dB/20kHz and –7.05dB/100kHz largely independent of loading. PM