Outboard DACs

While the rear panel here looks very similar to that of the legacy 2010S2 [see boxout], with its strip of RCA/BNC/optical/USB digital inputs, the new model features an AK4191EQ processor and AK4499EXEQ DAC plus balanced analogue output. Eversolo’s DMP-A8 [HFN May ’24] uses the same two-chip DAC, but while that unit enables all AKM’s digital filters, Exposure pre-selects the best filters for each sample rate.

For CD/48kHz inputs, the ‘Sharp’ linear phase filter offers an excellent 102dB stopband rejection by way of trade-off for the (acausal) pre-ringing. This default filter offers a very flat response (–0.3dB/ 20kHz) while the ‘Slow’ roll-off option invoked at higher sample rates offers gentler –11dB/96kHz and –14dB/90kHz responses with 96kHz and 192kHz media, respectively. AKM’s ‘Super Slow’ filter is invoked with sample rates ≥352.8kHz. However, it’s Exposure’s custom, dual-mono analogue filter/DC-coupled preamp circuits that truly shape the sound.

The maximum 9.3V preamp output (from a 48ohm balanced source), the excellent ±0.1dB low-level resolution [red trace, Graph 1], and 119dB A-wtd S/N ratio will serve a ‘direct drive’ into any power amp. However, the vanishingly low distortion typically associated with the AK4191EQ/AK4499EXEQ is tempered here to a minimum of ~0.001% (re. 20Hz-20kHz) over the top 30dB of the DAC’s dynamic range [see Graph 1]. We know that 0.00004-0.00015% is possible from this AKM chipset but, again, it’s the analogue circuit that sets the tone. Finally, jitter is a moderate ~350psec but while this looks like 100Hz/PSU switching noise, the sidebands are all linked to a discrete ±94Hz modulation [see markers on Graph 2]. Only Exposure will know the cause! PM