Pre/Power Amplifiers

As I discuss in our boxout, the M6x 250.7 is a three- and four-channel amplifier combined, and one that delivers 1x180W, 2x170W and 4x160W (and 7x160W) into 8ohm before raising its game to 1x305W, 2x280W and 4x255W (7x255W) into 4ohm. Power consumption increases from 265W at 1x150W/8ohm output to 975W at 4x150W/8ohm and 1.6kW at the full 7x150W/8ohm output. Unlike its Class D rival from Primare [HFN May '22] whose architecture 'fixes' its output under both continuous and dynamic conditions, the M6x 250.7's more traditional linear PSU/Class AB design enjoys additional transient headroom, supporting 220W, 385W, 600W and 655W into 8, 4, 2 and 1ohm loads [see Graph 1, below]. Gain is set at a sensible +32dB (x40) via the XLRs and the A-wtd S/N ratio is only slightly below average at 82.3dB (re. 0dBW), but this is a white noise rather than audible hum from the proximity of the transformers.

The output impedance is a fairly steady 0.025-0.04ohm (20Hz-20kHz) and the frequency response has a slight treble roll-off, amounting to –0.8dB/20kHz and –10.3dB/100kHz, just as its bass extension reaches down to 7Hz (–1dB). Harmonic distortion is impressively stable with increasing output, trending from 0.0015%/1W to a minimum of 0.0009%/20W and then drifting gently upwards to 0.002% at the rated 150W (all 1kHz/8ohm). Versus frequency there's a general trend of increasing distortion [see Graph 2, below] where the M6x 250.7 falls to a minimum of 0.0005% in the low bass before climbing through the midrange (0.001%/1kHz) to 0.025%/20kHz and 0.085%/40kHz. By the standards of a vinyl-playing front-end or, indeed, a typical loudspeaker these are still very low figures, of course! PM