Outboard DACs

We have tested other implementations of the superb two-chip AK4191EQ upsampling/noise-shaper and AK4499EXEQ DAC [HFN May ’24] so a baseline has already been established. In practice, however, there are key aspects of the RD160’s performance that are determined by both the DPC (Digital Processing Core) and its balanced analogue output stage. The latter will deliver a maximum 8.8V from a 110ohm source impedance, rising to 258ohm/20Hz – HiFi Rose claims the RD160 has a particularly extended LF response but, in practice, there are a host of DACs flat to 2Hz. The A-wtd S/N is a spectacularly wide 120dB but distortion is analogue over the top 20-30dB of its range, from 0.0025-0.023% at 0dBFs down to 0.00015-0.0006% at –30dBFs [all 20Hz-20kHz, see Graph 1]. The real bugbear takes the form of a low-rate ±3Hz jitter amounting to ~50,000psec but that might be missed with cursory spectral analysis [see Graph 2 – grey spectrum = black spectrum magnified x35 on the X scale].

Otherwise, response and stopband rejection are determined by the choice of six digital filters, including two linear-phase (Sharp and Slow) and two minimum phase types (Short Sharp and Slow), though these are only enabled in ‘Bypass’ and ‘To PCM’ modes, not in ‘To DSD’ or in ‘Upsampling’ modes. The two sharp filters have the same –0.3dB/20kHz, –1.6dB/45kHz and –4.2dB/90kHz response with 48kHz, 96kHz and 192kHz media, respectively, with a similar 104dB stopband rejection. By contrast, the slow-roll off types trade a limited 8.5dB stopband rejection and –8.5dB/20kHz, –10.7dB/45kHz and –13.4dB/90kHz response for minimal ringing/time domain distortion. The ‘Low Short’ filter is a hybrid type that shows in-band ripples. PM