Phono Preamplifiers

Tested via its balanced 'voltage' inputs, and partnering balanced outputs, the MasterPhono's notional +40dB, +50dB, +60dB and +70dB gain settings are, in practice, +44.3dB, +54.2dB, +64.0dB and +73.9dB, respectively. This, and the 15ohm-47kohm input load range (custom values may also be applied) endows this phono stage with the capacity to accommodate a very wide range of pick-ups from high output MMs with a sensitivity of 6.1mV to low output MCs offering just 200µV (all 1kHz/5cm/sec). However, while the passive RIAA eq is very accurate [see below] it does soak up a lot of headroom, limiting the respective input overload margins to 66mV, 22mV, 6.8mV and 2.08mV. So while the +40dB and +60dB gain settings offer a good +22.5dB headroom with 5mV MMs/500µV MCs, respectively, the +50dB/+70dB settings are limited to just 12.5dB which is really only suitable for low output MMs and MCs.

Noise is a little lower than average, so the MasterPhono achieves an A-wtd S/N of 88.5dB with the +40/50dB settings treated as MM, and 78.2dB with the +60/70dB options as MC. Both these figures fall well inside the limit imposed by rumble/vinyl noise from the best turntable solutions as does its low distortion – an impressive 0.001-0.035% [20Hz-20kHz, re. 0dBV; Graph 2] being 500-1000x lower than that measured from the best MM/MCs reviewed in Hi-Fi News. MoFi specifies its balanced XLR output at 10V which is precisely met in practice (re. 1kHz/<1% THD) as is the remarkable amplitude flatness of the RIAA-corrected response – true to ±0.02dB from 20Hz-20kHz, rising imperceptibly to +0.2dB/100kHz [see Graph 1, below]. The built-in bass roll-off amounts to –3dB/3Hz, increasing to –3dB/11Hz with the subsonic filter engaged [dashed trace, Graph 1]. PM