Network Audio Players/Servers

While this new flagship player/DAC represents a further evolution of the DPC (Digital Processing Core) seen in the ‘1st gen’ RS150 [HFN Jun ’21] and more recent RD160 USB DAC [HFN Jan ’25], it also marks a departure from the AK4191EQ upsampling/noise-shaper and AK4499EXEQ DAC employed previously. Instead, the RS151 uses a single ES9039SPRO from ESS, maintaining its predecessor’s super low distortion with just 0.00007% at the top of its dynamic range [see Graph 1, below] and widening the A-wtd S/N from 119dB to 121dB here. The maximum 8.84V balanced output is more than sufficient to drive any power amp into clipping without the services of an intermediate preamp, but while HiFi Rose claims a low 3ohm source impedance, this is only the case above 500Hz – below this it rises to 935ohm/20Hz.

Unfortunately, the very low-rate jitter seen in those earlier HiFi Rose player/DACs persists in this new model, amounting to >20nsec and with a base modulation of ±2.65Hz in this implementation [see zoom jitter plot, grey spectrum, Graph 2]. Clearly this is not linked to the choice of AKM or ESS DAC, but is possibly an intermodulation between internal clocks. While numerically very high (via all digital inputs), experience suggests this very low-rate jitter may bring a marginal softening to stereo images and top-end ‘air’. Neither were any of the six digital filters enabled in our sample, every selection bringing the same slow roll-off minimum phase digital filter. This trades limited post-ringing for a poor stopband rejection at low sample rates (just 8.5dB at 48kHz) and roll-offs at –1.7dB/20kHz, –5.0dB/45kHz and –6.4dB/90kHz with 48kHz, 96kHz and 192kHz media. Fortunately, regular OTA firmware updates are offered! PM