Outboard DACs

With a peak level (0dBFs) digital input the NEO iDSD clips at full volume so, in practice, the maximum variable output via the balanced XLRs is 5.6V with the volume at '–1dB'. This is still substantial and more than sufficient to drive any power amplifier, aided by a moderate 50ohm source impedance and wide 110dB A-wtd S/N ratio. Hand-in-hand with this low noise comes excellent low-level linearity, the single DSD1793 DAC achieving a resolution of ±0.2dB over a full 100dB dynamic range. The fixed (balanced) volume setting is not far behind, yielding a maximum 4.28V output (re. 0dBFs) at 0.0012-0.0045% distortion, falling to a minimum of 0.00014-0.0002% at –20dBFs [see Graph 1, below]. While the latter is impressive, the cloud of low-level sidebands detected on the jitter tests was unexpected [see Graph 2, below]. This complex pattern has sidebands at ±33Hz, ±66Hz, ±99Hz, etc, amounting to some 550psec – not debilitating by any means but atypical of iFi Audio's latest form.

For this stripped-down DAC, iFi Audio makes a feature of its minimalism, eschewing the switchable digital filters that are included in its costlier Pro iDSD model [HFN Sep '18]. By default, the NEO iDSD comes with iFi Audio's GTO (Gibbs Transient Optimised) digital filter, although alternative algorithms can be loaded as firmware updates if preferred. On test this looks like a limited-tap linear phase filter offering a balance between a modest 53dB stopband rejection, symmetrical pre/post ripples in the time domain and an extended response that's flat to –0.14dB/20kHz, –0.8dB/45kHz and –2.6dB/90kHz (48kHz, 96kHz and 192kHz media, respectively). The performance of the headphone amplifier largely follows suit – sharing the same digital front-end. PM