Phono Preamplifiers

Phono stages with multiple gain and/or loading options often trade versatility for ease-of-use, using fiddly DIP switches to select between the various options. Not so here as the MM/MC inputs, the four gain options, cap (MM) and impedance (MC) loading, and IEC subsonic filter are all logic-controlled with the output relay-muted to prevent 'thumps' when switching on-the-fly. In practice, the M3x Vinyl is best suited for MM and high-to-medium output MCs, offering an especially wide 92.9dB A-wtd S/N ratio with the former and a maximum 10.8V single-ended output from either MM or MC input selections. The +6dB gain option is precise, taking the default +40.1dB MM setting to +46.0dB and the +60.0dB MC option to +65.9dB, the latter with a proportional 20dB drop in A-wtd S/N to 73.0dB.

These settings represent a range of input sensitivities of 9.89mV (MM) to 509µV (MC, +6dB) and are engineered with input overload margins of 111mV-5.7mV, respectively, or +21dB. This is equivalent to +27dB using a 'standard' 5mV 1kHz/5cm/sec MM and is sufficient to accommodate the 'hottest' +18dB groove modulation (re. 11.2µm/300Hz) that I use in our pick-up lab tests. The active RIAA equalisation [see Graph 1]extends out from 20Hz-100kHz (±0.2dB), rolling away to –2.6dB at a subsonic warp frequency of 5Hz [or –5.0dB/20Hz and –38dB/5Hz with the IEC filter – dashed trace]. The M3x Vinyl's source impedance [red trace, Graph 1] also increases from 97ohm (1kHz) to 2.3kohm (20Hz) as a function of the default low bass filter. The RIAA-eq'd distortion [see Graph 2] is several orders of magnitude lower than required at 0.00028–0.025% (re. 0dBV), allowing the 'colour' of any pick-up to shine through! PM