Pre/Power Amplifiers

Treated as a balanced line preamplifier, the Unico Pre v2 offers a maximum 17V output at <1% THD from a 260ohm source impedance – overall gain is +15.9dB, bringing the pre/power total to +36.4dB, while the maximum (balanced XLR) analogue input level is 7.7V. Distortion falls to a minimum of 0.0025-0.0045% at 0dBV (1V) out (re. 20Hz-20kHz) which, unsurprisingly, is in line with that achieved by the DAC stage – see below. The 87.1dB A-wtd S/N ratio (re. 0dBV) is modest (again, see below) but the frequency response is very extended at +0.0dB to –0.03dB (20Hz-20kHz), reaching out to –0.6dB/100kHz.

Unison’s ES9018 DAC-based digital section offers a maximum 14V balanced (XLR) output with peak 0dBFs inputs (re. 1kHz to 1% THD) – the volume is at ‘67’ here but the Pre v2 was otherwise tested at a ‘standard’ 6V (or ‘48’). Its output is phase inverting and Unison’s digital filter of choice is the standard linear phase type offering an 83dB stopband rejection and responses that reach out to –0.3dB/20kHz, –1.7dB/45kHz and –5.0dB/90kHz with 48kHz, 96kHz and 192kHz media, respectively. The ECC83 input tubes largely define the ‘colour’ of the Pre v2, though a 3rd harmonic takes charge here instead of the DM v2’s 2nd harmonic [see boxout]. At 6V/0dBFs, THD lies between 0.05-0.075% (20Hz-20kHz) falling to a minimum of 0.0007-0.0022% over the top 30dB of its dynamic range [see Graph 1]. The A-wtd S/N ratio is a modest 102.4dB and low-level linearity good to ±0.2dB over a 100dB range [red trace, Graph 1] while jitter is a mere 30psec of rectifier-induced sidebands [see Graph 2]. Dual-mono construction, meanwhile, yields a superb >110dB stereo separation (re. 20Hz-20kHz). PM