Phono Preamplifiers

A total of seven gain values are available from the VXN across MM and MC inputs, notionally labelled +40dB, +46dB, +54dB and +55dB (MM) and +54dB, +60dB, +63dB and +66dB (MC). In practice these gain settings are accurately specified, amounting to +40.2dB, +46.0dB, +54.9dB and +55.5dB (MM), and +54.5dB, +60.75dB, +63.4dB and +66.2dB (MC). In terms of sensitivity, this amounts to inputs of 9.83mV, 5.0mV, 2.0mV and 1.68mV (MM), and 1.89mV, 916µV, 676µV and 492µV (MC) for a 0dBV output. I discuss the input headroom for each of these settings, and cartridge matching, in my boxout.

Distortion is very low at 0.0015% midband via the +40dB MM input (re. 0dBV output), with 10.1V possible before clipping, and increasing only slightly to ~0.0046% at very high frequencies [see Graph 2, below]. Distortion from the best pick-ups will be at least two orders of magnitude higher than this! The VXN's source impedance is a 'flat' and usefully low 50ohm despite the high pass filter engineered into its RIAA correction. The latter cuts into the bass by –1.5dB/20Hz and –6dB/9Hz to afford a deal of protection from warped LPs and undamped arm/cartridge resonance(s), a useful feature for audiophiles with large, ported loudspeaker systems. The remainder of the RIAA response is flat to within ±0.15dB right out to 100kHz [see Graph 1].

Finally, the VXN's outboard PSU assists in achieving a low –82dBV residual noise and a reasonably consistent 71.2-72.8dB A-wtd S/N ratio across its four MC gain options (re. 500µV in/0dBV out). There is greater variation across the MM settings, from 82.5dB (+40dB, re. 5mV in/0dBV out) to 87.8dB (+55dB, re. 5mV in/0dBV out) but these are all above the 'vinyl threshold' and better than Exposure's own 82dB specification. PM