Outboard DACs

This high-value product employs the same TI (née Burr-Brown) DSD1793 DAC as iFi Audio's EISA Award-winning xDSD [HFN Jul '18], albeit with a lower-powered headphone amp in tow here. The DAC's default linear-phase digital filter offers a 53dB alias image rejection and excellent jitter suppression to <15psec (all sample rates). With a 0dBFs input, the RCA line outs are just clipped at 3.3V. The S/N is a wide 108.3dB and distortion falls to a minimum of 0.0011% over the top 30dB of its range [Graph 1].

There's much common ground between the DAC/line out and DAC/headphone out, including a response that's ruler flat to 20kHz ±0.02dB with CD/48kHz inputs, just –0.6dB down at 45kHz (96kHz files) and downsampled to a –6dB/48kHz bandwidth with higher rate files. Tested with the ZEN Blue's PSU, there's almost no change in response with loading (10mW/32ohm), partly due to the ZEN's impressively low 400mohm output impedance (the RCA outs are a higher 94ohm), but THD does increase with both loading and frequency [Graph 2, below]. Here, loaded or unloaded, the low 0.002% bass/midrange THD increases to 0.013%/10kHz and 0.075%/20kHz (10mW/32ohm).

Maximum output depends on iFi's 'Power Match' facility: switched on, this is 3.32V (18mW/600ohm) and achieving a single-ended 200mW/32ohm at 1% THD. Switched off there's a 10.1dB drop to 1.03V, or 1.8mW/600ohm, which is sensible for high impedance ear buds. Also from the standpoint of sensitive 'phones, levels of residual noise are very low at –98dBV (13µV), while the A-wtd S/N ratio is a wide 94dB (re. 10mW/32ohm). Take care with the 'TrueBass' feature, however, because this progressively boosts the ZEN's LF response from +1dB/235Hz, +3dB/120Hz, +6dB/60Hz and a whopping +10.6dB/20Hz. PM