Thorens MM-008 Phono Preamplifier Lab Report

Lab Report

This little box may be based entirely around integrated op-amp gain stages but these little chips are well chosen – an LME49723 featuring very high slew-rate/low noise/low distortion for the MC headamp combined with a tried-and-tested NE5532 dual-channel op-amp for the active portion of Thorens' part-passive/part-active eq stage. The dual-channel NE5532 was especially popular back in the late '80s/early '90s when the Signetics variant of this op-amp was core to the 'sound' of Rotel separates... In this instance it contributes to the generous 79dB A-wtd S/N ratio achieved via the MM input (re 5mV in/1V out), the latter offering a one-size-fits-all +39.8dB gain arguably best suited to higher-output pick-ups. There's often a caveat here though, for while high output MMs will optimise the MM-008's noise performance, too high and the wildest groove excursions may breach the preamp's 68mV input overload margin.

In practice, for a 1mV/cm/sec pick-up (5mV at 5cm/sec) this represents a good +22.7dB headroom at 1kHz – perfectly adequate for the highest output Ortofon MMs, for example. The +59.9dB gain offered for MCs, in combination with its 66dB A-wtd S/N and 6.8mV overload margin renders the MM-008 most suitable for middle-ground (500µV) pick-ups – just as a 'universal' phono preamp should. The RIAA eq shows the very mild upper bass/mid treble 'droop' seen with other low-cost solutions [Graph 1, below] while its capacitor-coupled output causes an increase in source impedance from ~50ohm midband to ~200ohm/20Hz [red trace, Graph 1]. Distortion is impressively low, falling to as little as 0.00025% through midband/presence frequencies and only increasing to 0.004% in the bass [see Graph 2] – all well within Thorens' <0.013% specification! PM


RIAA-corrected freq. resp. from 5Hz-100kHz at 0dBV via MM (black) vs. output impedance (red)


Distortion versus extended frequency (5Hz-40kHz) via MM input re. 0dBV (1Vrms) output

Input loading (MM/MC) 47kohm / 10, 100ohm, 1kohm
Input sensitivity (re. 0dBV, MM/MC) 10.3mV / 1.02mV
Input overload (re. 1% THD, MM/MC) 68mV / 6.8mV
Max. output (re. 1% THD) / Impedance 6.5V / 46-207ohm
A-wtd S/N ratio (re. 0dBV, MM/MC) 79.2dB / 66.5dB
Frequency resp. (20Hz-20kHz/100kHz) +0.1dB to –0.3dB / +1.0dB
Distortion (20Hz-20kHz, re. 0dBV) 0.00025–0.0038% (MM)
Power consumption 4W
Dimensions (WHD) / Weight 150x50x117mm / 0.5kg
Price £220

Thorens GmbH
Bergisch Gladbach, Germany
Supplied by: Signature Audio Systems
07738 007776