Pre/Power Amplifiers

This, to all intents and purposes, is the power amp stage from NAD's fully-fledged digital/analogue BluOS-equipped M33 integrated [HFN Aug '20], the Purifi ET400A Class D module delivering the raw specification of the more affordable C 298 power amp [HFN Oct '21] but with 'Masters series refinement'. Both the M33 and M23 are rated at 200W/8ohm and while the M23 nudges ahead with 237W/8ohm and 455W/4ohm, it is not any 'beefier' than the 223W/430W, respectively, achieved by the M33. The uplift under dynamic conditions to 268W, 543W, 730W and 420W into 8, 4, 2 and 1ohm loads shows the same progressive increase in THD to 'soften' the blow near clipping into 8/4ohm loads [see Graph 1] but the M23's output into the lowest 2/1ohm is actually slightly lower than we measured for both the M33 and C 298. Incidentally, the three gain settings of +19dB, +23.9dB and +29.2dB (balanced input) do not influence power output or frequency response which holds true to –0.07dB/20kHz and –10.8dB/100kHz into all loads from 1-8ohm.

Distortion is extremely low through bass and midrange frequencies – fractionally lower than achieved by the C 298 – at 0.00025%/1W, 0.0002%/10W and 0.0003%/100W, the inevitable 'Class D' rise at higher treble frequencies delayed here to above 10kHz, if only reaching a mere 0.002%/1W, 0.004%/10W and 0.025%/100W at 20kHz [see Graph 2, below]. Again, these Purifi Eigentakt modules buck the trend of more traditional Class D solutions whose high frequency response and distortion are markedly influenced by speaker load. Residual noise is about 3dB lower than that from the C 298, yielding an above-average 88.4dB A-wtd S/N ratio (re. 0dBW). PM