Outboard DACs

Eversolo’s implementation of the AK4191EQ upsampling/noise-shaper with the AK4499EXEQ DAC extracts a superb performance, the DMP-A8’s balanced analogue output realising 4.2V from a (flat) 49ohm source impedance with a peak (0dBFs) digital input. Distortion – very likely ‘analogue’ rather than ‘digital’ – is spectacularly low at just 0.00003-0.00009% (20Hz-20kHz), requiring a shifted 0dB to –140dB Y scale [Graph 1, below] in place of the usual 20dB to –120dB scaling. This result is complemented by a wide 116dB A-wtd S/N ratio and low-level linearity that’s true to within ±0.1dB over a full 110dB dynamic range. Very, very few other DAC products can match this, including those using proprietary DSP-based solutions. Jitter, too, is squeezed down to below 10psec at all sample rates – the DMP-A8 chalking up more state-of-the-art figures.

The AK4191EQ modulator includes six filter coefficients, including two linear-phase (Sharp and Slow) and two minimum phase types (Short Delay Sharp and Slow). The two sharp filters have the same –0.3dB/20kHz, –1.8dB/45kHz and –4.6dB/90kHz response with 48kHz, 96kHz and 192kHz media, respectively, with a similar 104dB stopband rejection. By contrast, the slow-roll off types trade a limited 8.5dB stopband rejection and –8.6dB/20kHz, –10.9dB/45kHz and –13.8dB/90kHz response for minimal ringing/time domain distortion. The ‘Low Dispersion’ filter is a hybrid type but shows in-band ripples [red trace, Graph 2] while the ‘Super Slow’ filter [blue trace, Graph 2] is a NOS type with no stopband suppression, an early roll-off to –3.5dB/20kHz, –4.8dB/45kHz and –7.6dB/90kHz but no time domain distortion. The latter is best used with 96kHz+ sample rate music files. PM