Outboard DACs

I discuss Musical Fidelity's application of the popular ES9038Q2M DAC, and its additional 'upsampling' mode, in our sidebar A Flourish Of Filters. That 8th filter position is potentially confusing – in this mode the ESS DAC's on-chip 8x oversampling filter is disabled, but a medium-coefficient minimal phase filter remains within the preceding XMOS processor. Muting the ESS filter block should reduce the PSU/ground noise along with any signal-correlated clock modulation on the ESS DAC's silicon die. However, on the lab bench there was no difference in A-wtd S/N, and the correlated jitter – just 10psec or less with any of the default filters – was already suppressed to state-of-the-art levels before invoking 'filter 8' [see Graph 2, below]. Still, the 12dB stopband rejection and simplified ringing of this filter will all feed into a subjective difference. Try it and see...

This, and other updates, contribute to the M6x's evolution over the M6s DAC [HFN Jan '18] and inaugural M6 DAC [HFN Mar '13]. So, while much of the M6x's 'digital' performance is not hugely dissimilar to that we recorded for the ES9028-based M6s, the much-improved power supply, the clocking and the dual-mono balanced output have a real impact on the 'analogue numbers'. For example the M6s DAC had a 4.3V output with a 116.5dB A-wtd S/N ratio and moderate 45ohm source impedance while the M6x has a slightly lower 4.1V/115.5dB output from a superior cable/amp-agnostic ~0.5ohm impedance. Distortion is also much reduced in the M6x, so where the M6s held to ~0.003% over the top 30dB of its dynamic range, the M6x offers a ~20dB improvement at 0.0002-0.0003% over the same range [see Graph 1, below]. The wide 125dB channel separation also speaks of a carefully considered PCB layout. PM