Turntables, Arms & Cartridges

Up to a point, Soundsmith's Strain Gauge pick-ups have more in common with DS Audio's 'optical' cartridges [HFN Jun '17, Dec '17, Jan '19 & Feb '21] than traditional MM/MCs. But only up to a point... MM/MCs are velocity-sensitive devices that employ electromagnetic induction to convert stylus motion into an output voltage. MMs vary the magnetic field around fixed coils while MCs move coils within a fixed field – in both cases the signal voltage increases with groove excursion and, thus, increasing signal frequency. Soundsmith, by contrast, uses the stylus/cantilever movement to deform two very fine piezoresistive strips – the so-called strain gauges – held within the cartridge body. An outboard preamp/bridge applies a constant current through the strips and derives a voltage from the changes in their electrical resistance. The applied current also powers those six blue LEDs!

Like the DS Audio pick-ups, which recover a voltage output from minute photocells, the Strain Gauge types are sensitive to stylus displacement (amplitude) and require only a relatively subtle HF cut to realise a 'flat' response with RIAA pre-equalised LPs. Soundsmith relies on the mechanical roll-off of the 'motor' to achieve this. The SG-230 can also be used as a preamp for CD/line sources, offering a full +15.9dB gain, low 0.0008-0.002% distortion and wide 94.5dB A-wtd S/N ratio (both re. 0dBV). The response is sufficiently flat and extended (±0.4dB from 5Hz-100kHz) that it adds nothing to the 'ups and downs' of the pick-up itself! PM