Outboard DACs

Although the DAC204 is utilising the ‘tried-and-tested’ ES9018S DAC, rather than the latest ES9038PRO, it has still extracted a state-of-the-art performance, not least courtesy of its own code running on that Spartan-6 DSP. Output is configurable with separate +10dB and +20dB attenuation (or gain, depending on your standpoint) with 0dB/+30dB offered once the toggles are either all off or on, respectively. With a peak level (0dBFs) digital input this amounts to 240mV, 759mV, 2405mV and 7440mV from the 46ohm balanced XLR output. The 2.4V output mode (10dB toggle down/20dB toggle up) gives the best overall balance of a very low 0.00005-0.00025% distortion (20Hz-20kHz re. 0dBFs), a wide 111dB A-wtd S/N ratio, and excellent ±0.2dB linearity over a 110dB dynamic range. In practice this low THD is maintained over the top 10dB of the DAC204’s dynamic range [see Graph 1], rather than falling to a minimum at –10dBFs to –20dBFs as is more common.

Weiss has adopted a fairly standard medium-order linear phase digital filter here, offering an 83dB stopband rejection and responses that reach out to –0.3dB/20kHz, –1.6dB/45kHz and –5.7dB/90kHz with 48kHz, 96kHz and 192kHz files, respectively. Time domain distortion – pre-ringing – is necessarily higher with this type of filter but group delay is benign. Weiss claims ‘several signal reclocking schemes’ are at work in the DAC204 and while bursts of very low-level spuriae were detected on test – cause or effect unknown – there’s no disputing that both correlated jitter (<10psec all sample rates) and low-rate phase noise are very low, particularly the latter [see Graph 2]. Finally, the analogue layout yields a spectacular >135dB/1kHz stereo separation. PM