Outboard DACs

We’ve tested numerous iterations of iFi Audio’s portable DAC/headphone amps, including the nano iDSD [HFN Dec ’14] and ‘Black Label’ variant [HFN Apr ’18], but this new xDSD model is clearly a cut above. I’ll come to its superior digital performance in a moment for the xDSD is not only significantly ‘cleaner’ but it’s also the most powerful battery-powered amp the brand has offered – rated at 270mW/50ohm and 500mW/16ohm, it delivered a comparable 330mW/25ohm on the test bench with 3.35V or 18.7mW/600ohm for high impedance headphones. Distortion increases with loading only at high frequencies, so at just –1dB below maximum output (262mW/25ohm) there is a lift from just 0.0036% to 0.0044% at 1kHz between 600ohm and 25ohm loads [black versus red traces, Graph 1]. At 20kHz the effect is slightly more pronounced with the biggest ‘difference’ occurring at –25dB (~1mW/25ohm) with 0.0038%/unloaded vs. 0.063%/loaded [cyan vs. blue traces, Graph 1].

Importantly, these figures are an order of magnitude better than we’ve seen from earlier iFi Audio portables as is the spectacular 107-108dB A-wtd S/N ratio, recorded via its fixed 2.1V line output and re. 10mW when configured in ‘headphone mode’. The low 500mohm output impedance is very impressive too, ensuring the xDSD/headphone system response is largely unaffected by swings in load impedance. I discuss the response and digital filters in my Sidebar]. Meanwhile the underlying digital/line performance is superb, the DSD1793 DAC delivering a low 0.0003% distortion at –30dBFs/1kHz, increasing to just 0.0015%/20kHz. Jitter is as low as in any high-end DAC solution – less than 20psec at all sample rates [Graph 2]. PM

Maximum output (re. 0dBFs into 47kohm): 2.12V (unbalanced line out)
Max. power output (re. 0dBFs into 25ohm): 330mW (headphone out)
Output Impedance (20Hz-20kHz): 0.45-0.81ohm
A-wtd S/N ratio (0dBFs; re. line/10mW): 107.2dB / 107.8dB
Distortion (20Hz-20kHz, line/ re. 10mW): 0.0024-0.04%/0.004–0.043%
Freq. resp. (20Hz-20kHz/45kHz/90kHz): +0.0 to –0.3dB/–1.5dB/–9.1dB
Digital jitter (48kHz/24-bit data): <20psec
Power consumption: Battery-powered device
Dimensions (WHD) / Weight: 67x19x95mm / 127g
Price: £399