Outboard DACs

Version 2 it may be, but the 780D still employs the tried-and-tested Sabre ES9018S DACs from ESS in preference to the newer 9028 and 9038 Pro versions. And for good reason, as its performance is absolutely 'top-drawer', from the vanishingly low distortion that falls to just 0.00005% over the top 30dB of its dynamic range [see Graph 1, below] and the very wide 110.6dB A-wtd S/N from a modest (by balanced XLR standards) 2.4V peak output. There is one minor 'bug' – peak level digital inputs at high frequency (~20kHz) cause the device to clip and THD jumps to 0.5%, but falls right back to 0.0003% at –1dBFs/20kHz. This only occurs at 48kHz sampling, not at 96kHz, 192kHz, etc, and is largely of technical/academic interest.

Of more practical/subjective impact, perhaps, is Simaudio's choice of slow roll-off minimum phase digital filter (one of several options within the ES9018S) that trades zero pre-ringing and limited post-ringing for poor stopband rejection at low sample rates (just 11dB at 48kFs) and roll-offs of –0.5dB/20kHz, –9.7dB/45kHz and –6.1dB/90kHz with 48kHz, 96kHz and 192kHz media, respectively. This choice of filter is a very good compromise for higher sample rate files (88.2kHz+).

Meanwhile the wide S/N ratio assists in delivering the 780D v2's excellent low-level resolution – good to within ±0.1dB over a 100dB dynamic range before deviating slightly to ±1dB between –100dBFs and –110dBFs. Digital jitter is typically well suppressed by the ESS DACs, and so it is here with just 33psec, 19sec and 10psec recorded with 48kHz, 96kHz and 192kHz/24-bit test files [see Graph 2, below]. Finally, while the analogue output stage has a moderate 120ohm source impedance, the careful layout still confers a wide 130dB stereo separation. PM