Musical Fidelity M6x 250.7 Multichannel Power Amp Lab Report

Lab Report

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


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 25.6A


Distortion versus frequency versus power output (1W/8ohm, black; 10W, pink; 100W, red)

Power output (<1% THD, 8/4ohm) 180W / 305W (one channel)
Dynamic power (<1% THD, 8/4/2/1ohm) 220W / 385W / 600W / 655W
Output imp. (20Hz–20kHz/100kHz) 0.025–0.039ohm / 0.21ohm
Freq. resp. (20Hz–20kHz/100kHz) –0.16dB to –0.75dB/–10.3dB
Input sensitivity (for 0dBW/150W) 73mV / 898mV
A-wtd S/N ratio (re. 0dBW/150W) 82.3dB / 104.1dB
Distortion (20Hz-20kHz, 10W/8ohm) 0.0005–0.025%
Power consumption (Idle/Rated o/p) 40W / 265W (1W standby)
Dimensions (WHD) / Weight 450x195x435mm / 32.5kg
Price £3099

Audio Tuning Vertriebs GmbH
Supplied by: Henley Audio Ltd, UK
01235 511166