Turntables, Arms & Cartridges

DS Audio’s ‘optical’ pick-ups are sensitive only to the amplitude of the movement of the stylus, unlike velocity-sensitive MM/MCs whose output increases with groove excursion and frequency. Their output decreases with frequency [HFN Feb ’21], in contrast with MM/MCs, and requires an entirely bespoke eq to render a flat response. In practice this eq is gentler, or some 12dB overall rather than the 40dB required for full RIAA equalisation. The TB-100 combines this eq with the +5V DC power supply sent via the RCA input R– and L– connections to the pair of fixed, narrow-beam LEDs within each optical pick-up. The pick-up’s photocells’ current output (sent via the R+ and L+ pins) is received by a passive I/V converter and input transformer in the TB-100. The equalised response(s) of the 50Hz, 30Hz and subsonic filtered outputs are compared with that of the solid-state DS-E3 EQ unit [HFN Oct ’24] in Graph 1. All DS Audio cartridges have a very powerful bass output so the TB-100’s LF roll-off is no bad thing in systems with big, reflex-loaded speakers.

The TB-100’s tube stage confers added gain (+25.7dB) vs. the DS-E3’s +22.5dB but it also provides the opportunity for massive headroom, realised in the 24V maximum output (1kHz at 1% THD, or 33V at 2%). So, with the 70mV realised from an optical pick-up (re. 1kHz/5cm/sec), and an input limit of 1150mV, this confers over 24dB of headroom – enough to keep the TB-100 safe with the wildest of grooves. Noise is low, but as HF signals are boosted in the TB-100, the 80.7dB A-wtd S/N ratio is bettered by many standard phono preamps. Moreover, THD is dictated by the low-feedback tube circuit in the TB-100, as low as 0.03% from 100Hz-20kHz but increasing to 0.65% at 20Hz. The DS-E3 EQ, by contrast, achieves 0.0003-0.0015% [see Graph 2]. PM