EAR PhonoBox Phono MM/MC Preamplifier Lab Report

Lab Report

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


RIAA-corrected frequency response over an extended 5Hz-100kHz at 0dBV via MM (black trace) vs. output impedance (red trace) from 10Hz-20kHz


Distortion extended frequency (20Hz-20kHz) via MM input re. 0dBV (1Vrms) output

Input loading (MM/MC) 50kohm / 6.5ohm
Input sensitivity (re. 0dBV) 3.63mV / 378µV
Input overload (re. 1% THD) 84mV / 8.7mV
Max. output (re. 1% THD) / Impedance 10.6V / 50ohm–12.3kohm
A-wtd S/N ratio (re. 0dBV) 78.5dB / 76.6dB
Frequency resp. (20Hz-20kHz/100kHz) –0.4dB to +0.0dB / –0.18dB
Distortion (20Hz-20kHz, re. 0dBV) 0.014–0.118%
Power consumption 14W (2W standby)
Dimensions (WHD) / Weight 180x77x310mm / 5kg
Prices £1000 (MM) to £1499 (MM/MC with volume)

EAR Yoshino
Supplied by: EAR Yoshino
01480 210004