Outboard DACs

It's not uncommon for brands to claim their products are compatible with ultra high-resolution LPCM and DSD streams when the internal DAC only operates to 96kHz or 192kHz. In practice this means that, for example, DXD or DSD256 inputs are accepted but subsequently downsampled... So the fact Musical Fidelity is entirely up-front about the 192kHz and DSD128 handling of its DAC – the choice of PCM1795 complemented by an ARC (sample rate converter) and op-amps all from TI, née Burr-Brown – is very refreshing! The MX-DAC's balanced output offers a healthy 3.8V from a 45ohm source impedance and achieves a wide 111dB A-wtd S/N ratio, supporting an excellent low-level resolution of ±0.2dB over a full 110dB dynamic range. These figures are consistent regardless of USB or S/PDIF input, as is the superb jitter rejection down to <10psec across all sample rates [see Graph 2, below].

Distortion, over the top 20dB at least, is largely determined by MF's implementation of the OPA2134 op-amps which yield 0.001% at 0dBFs down to a low 0.0003% at –25dBFs through bass and midrange, increasing at HF only at the highest output levels [0.012% at 0dBFs/20kHz, see Graph 1]. MF also retains the 'Sharp' and 'Slow' digital filters built into the PCM1795 DAC,

although they have no discernable effect with sample rates below 192kHz. Regardless of 'Filter' setting, the response reaches out to +0.08dB/20kHz with 48kHz inputs and peaks at +0.4dB/43kHz with 96kHz files. With 192kHz inputs, however, the response peaks up to +1.0dB/75kHz before dropping away to –1.2dB/90kHz (Steep filter) or peaks at +0.6dB/58kHz and rolls away to –5.1dB/90kHz (Slow filter). So if you think you can hear a difference with CD inputs, think again! PM