Outboard DACs

If ever an outboard DAC was a 'game of two halves', then this is it – based on the ProLogue Eight CD player [HFN Nov '08], the EVO 100 employs a tried-and-tested SRC4192/PCM1792 upsampler/DAC chipset to good effect but it's the transformer-coupled 12AX7/12AU7 triode output stage that dominates its subjective 'colour'. On the digital front, while PrimaLuna is still using this legacy DAC, with 'fast' linear phase digital filter, the suppression of stopband (alias) images is much improved over the Eight – from 29dB to 89dB here. Output is lifted from 1.88V to 2.15V but the A-wtd S/N ratio is boosted more significantly from just 95dB to 105dB even if low-level resolution remains comparable at ±0.5dB over a 100dB dynamic range and –3.5dB at –100dBFs. Jitter is reduced to a very limited 80psec PSU modulation with 96kHz/24-bit data.

Nevertheless, the 'sound' of the EVO 100 is dominated by its tube output. We have tested numerous tube-equipped preamps and DACs that demonstrate vanishingly low levels of distortion, so what follows must surely have been a deliberate engineering choice. Output impedance is excessively high at 2.38kohm through mid and treble, increasing further to 3.5kohm/100Hz and 12.1kohm/20Hz, suggesting the EVO 100 will be fairly cable and preamp-sensitive. As expected, the response falls away at bass frequencies to –0.16dB/100Hz and –1.6dB/20Hz but reaches out to +0.1dB/20kHz, –0.5dB/45kHz and –7.4dB/90kHz with 48kHz, 96kHz and 192kHz media, respectively. Distortion peaks at ~1% and then steadily falls to a minimum of 0.014% between –35dBFs and –40dBFs. By conventional standards these are high figures, but the levels and trend are impressively consistent with frequency [see Graph 1, below]. PM