Phono Preamplifiers

For those not requiring a host of loading and gain options from a phono stage, EAR Yoshino's 'one-size-fits-all' circuit configuration has its advantages. The +48.8dB (MM) and +68.5dB (MC) gain options are sensibly chosen, equivalent to input sensitivities of 3.63mV and 378µV (0.38mV), respectively, which is almost exactly the 'average' output of today's pick-ups (re. 1kHz/5cm/sec). The PhonoBox's single-ended output, meanwhile, will drive any power amp you might care to choose – a full 10.6V is possible here from the variable output option although the ~280ohm source impedance does increase markedly below 50Hz, reaching 6.4kohm/20Hz and peaking at 12.5kohm/11Hz [red trace, Graph 1 below]. This coincides with a roll-off in response through the low bass (–0.4dB/20Hz, corresponding with the IEC pole at 7950μs) that successfully quells the influence of any arm/cartridge resonance.

The active/passive RIAA equalisation is otherwise very flat and extended out to 100kHz, with two broad but mild –0.2dB dips either side of 1kHz [black trace, Graph 1]. The RIAA-eq'd distortion [see Graph 2] is largely determined by the trio of tubes and increases from 0.02% (re. 0dBV) to 0.1%/5.5V at 1kHz, and to 0.06%/20Hz and 0.12%/20kHz (re. 0dBV). Noise is also just below the threshold of most vinyl systems, the 77-79dB A-wtd S/N ratio (MM/MC) an excellent result in this context. The overload margins are well judged too – the MM input supports an 84mV ceiling and the MC offers 8.7mV – a margin of +25dB for standard 5mV MM (re. 1kHz/5cm/sec) and 500μV MC pick-ups. Assuming a maximum practical LP groove modulation of +18dB, EAR's PhonoBox will accommodate all MM/MCs without clipping. PM