Pro-Ject X2 B/Phono Box S3 B Turntable/Phono Preamp Lab Report

Lab Report

Pro-Ject's part-passive/part-active RIAA preamp offers a useful range of input sensitivities, an extended response and good input headroom but is arguably better performing with MMs and high-output MCs than mid/low-output MCs. Here's the detail... The Phono Box S3 B's +40dB, +45dB, +60dB and +65dB gain options are realised as +46.0dB, +50.7dB, +65.9dB and +70.5dB via the balanced XLR outputs (6dB less via the RCAs) with input headroom(s) of 106mV, 63mV, 10.9mV and 6.4mV, respectively. Assuming the +40dB/+45dB settings are for MMs and the +60dB/+65dB options are for MCs, then this infers a headroom of ~26dB for the former and ~22dB for the latter, both of which are very generous and more than able to cope with peaks from 5mV- and 500µV-rated pick-ups navigating the highest amplitude grooves.

High headroom also usually translates into a high output for the phono stage, and the Phono Box S3 B follows suit with a maximum 20.5V balanced output from a 195ohm source impedance. However, noise – a white noise or hiss rather than hum – is somewhat higher via the MC settings than MM, achieving A-wtd S/N ratios of 68.3dB and 84.5dB, respectively. Better to use the lowest gain setting that's practical for your choice of cartridge. Otherwise, distortion [see Graph 2, below] is very low at just 0.0004-0.004% (20Hz-20kHz @ 0dBV output) – several orders of magnitude lower than the THD from a typical pick-up, in fact. The equalised frequency response [see Graph 1] is flat to within ±0.2dB from 12Hz-20kHz (–4.5dB/100kHz) while the optional subsonic filter kicks in below 30Hz to reach –3dB/20Hz and offer >30dB suppression of warp frequencies below 7Hz. If you are partnering the X2 B/S3 B with big, reflex-loaded loudspeakers then the subsonic filter is for you! PM


Frequency response (MM +40dB gain setting) and with subsonic filter (dashed trace)


Distortion versus frequency re. 0dBV from 20Hz-20kHz (MM +40dB gain setting)

Input loading (MM and MC) 10, 50, 100ohm, 1kohm and 47kohm
Input sensitivity (re. 0dBV) 4.73mV / 2.91mV / 509µV / 297µV
Input overload (re. 1% THD) 106mV, 63mV, 10.9mV and 6.4mV
Max. output (re. 1% THD) / Imp. 20.5V / 185-200ohm (balanced)
A-wtd S/N ratio (re. 0dBV) 84.5dB / 68.3dB (MM/MC)
Freq. resp. (20Hz-20kHz/100kHz) +0.05dB to –0.2dB / –4.5dB
Distortion (20Hz-20kHz, re. 0dBV) 0.0004-0.004% (MM, +40dB gain)
Power consumption 5W
Dimensions (WHD) / Weight 206x55x153mm / 0.93kg
Prices £1599 (inc. arm and cartridge)/£399 (phono preamp)

Pro-Ject Audio Systems
Supplied by: Henley Audio Ltd, UK
01235 511166