Disc Players

Unlike Unison’s costlier CD Due [HFN May ’16], the CD Uno’s simpler single-triode and op-amp options both feed the same discrete transistor output, its fabulously low ~1ohm source impedance and matched 2.6V (op-amp)/2.7V (tube) output enabling useful A/B comparisons. That said, the op-amp/tube stages invert absolute phase with respect to each other, while the former bests the latter’s 100.4dB A-wtd S/N ratio by some 10dB. Distortion, too, while very consistent with frequency, is far lower at 0.0009-0.0011% through the op-amp option versus 0.32-0.36% (all re. 0dBFs/20Hz-20kHz) once the triode is switched into circuit. Below –40dBFs, however, the distortion from both op-amp and tube options coalesces [see Graph 1, below]. Jitter, unsurprisingly, is also unchanged between the two analogue modes, settling out at 116psec with CD (this is the limit of a 16-bit data pattern) and increasing slightly to 145psec with 48kHz/24-bit data via USB [see Graph 2, below].

The main advantage of the USB input is not found in lower distortion, improved low-level resolution or a wider S/N ratio – in fact it is slightly lower in the op-amp mode than CD at 108.5dB – but in the extended frequency response offered by higher sample rate inputs. With digital Filter 1 (a fast linear phase type), CD reaches out from –0.85dB/20kHz and then to –3.7dB/45kHz and –8.2dB/90kHz with 96kHz and 192kHz media, respectively. Unison’s Filter 2 and 3 are incorrectly flagged, so 2 is the ‘Slow Linear’ and 3 the ‘Fast Minimum’ filter, not the other way around. The responses with Filter 2 reach out to –3.8dB/20kHz, –5.6dB/45kHz and –8.0dB/90kHz, and with Filter 3 from –0.88dB/20kHz to –6.9dB/45kHz and –11.5dB/90kHz, respectively. PM