Outboard DACs

Although PS Audio is coy about the technical updates to its 'MK2' DirectStream DAC, the fundamental differences in PCB design and layout between the last version we tested [HFN May '18] and this iteration are clear enough from our respective lid-off shots. There are differences in the analogue output/filter stage too, realised here in the higher (3.7V vs. 2.8V) peak output albeit from a slightly higher (200ohm vs. 150ohm) source impedance. Mid/treble distortion, too, is higher in the MK2 although, again, PS Audio's vague '<0.1% THD+N @ 1kHz (full scale)' spec. would satisfy virtually every DAC design currently on the market... In practice, the transformer-coupled balanced output has higher THD at low rather than high frequencies at 'full scale' – 0.04%/20Hz vs. 0.008%/20kHz – although the former is still improved over the 0.1%/20Hz recorded for the MK1 DAC.

Otherwise distortion has increased by up to 20dB (x10) in the MK2 below –30dBFs [see Graph 1] even if figures of 0.009-0.05% (20Hz-20kHz/–30dBFs) are still perfectly low enough. Furthermore, such is the increase in requantisation noise and 6dB shift in 'headroom' that the in-band A-wtd S/N now clocks in at a sub-16-bit 92.5dB (improving to 105.5dB with a full digital mute). It's arguable this smooth white noise might result in a pleasing difference between the MK2, the MK1 and competing DACs or that the high ultrasonic noise is an aggravating factor with some amplifiers. Correlated jitter is also largely buried by this noise just as the response shows an improved (flatter) bass while reaching out to –12dB/90kHz with high rate inputs. Lower Fs files track this same response 'curve' but stop at their respective Nyquist limits [Graph 2, below]. PM