Outboard DACs

This well-implemented 6922 triode-based analogue output incurs a mere 0.0075% distortion across the full 20Hz-20kHz audio range at the max. 3.9V balanced output. Distortion falls to just 0.0005% over the top 30dB of its dynamic range [see Graph 1], the A-wtd S/N ratio remains a wide 110dB and low-level resolution is good to within ±0.1dB from 0dBFs to –100dBFs. 'Reclocking', incidentally, has very little impact on jitter which remains exceptionally low at 6-10psec but the triode output does raise its head in the increased (bass) source impedance (205ohm/1kHz to 1.65kohm/20Hz). However, it's your choice of filter (digital or analogue) that'll have greatest subjective impact.

In order, the filters are Linear Phase Fast [black traces, Graph 2], Linear Phase Slow, Minimum Phase Fast, Minimum Phase Slow [blue], Apodising Fast, Corrected Phase Fast [or Hybrid, green], Brickwall and 'Oversample Bypass' [red]. The Linear/Minimum/Apodising Fast and Brickwall all have sharp roll-offs [the Hybrid filter has a steep but early roll-off], with Linear/Minimum Slow and 'oversample bypass' offering gentler treble roll-offs, reduced 'ringing' but poorer stopband rejection. Specifically, the five 'Fast' filters offer a 75-99dB rejection of digital aliasing images with 48kHz media, falling to 12-18dB with the Slow and 'Oversample Bypass' filters – these are best suited to higher sample rate files. With 48kHz media the responses reach out to –0.0dB, –3.5dB, –0.04dB, –5.0dB, –0.8dB, –12dB and –4.0dB/20kHz, respectively (and –0.3dB/20kHz with 'Oversample Bypass'). With filter 1 (Linear Phase Fast), enabling the analogue filter limits the response to –0.4dB/20kHz, –15dB/45kHz [dashed trace, Graph 2] and –30dB/60kHz. PM