Sony PS-Q7 Turntable Lab Report

Lab Report

Judging by the results of my lab tests, the convenience achieved by Sony's small form-factor 78mm 'platter' and offset, semi-auto arm mechanism comes at a cost. Rumble, for example, is high at –63dB (DIN-B wtd, re 1kHz/5cm/sec) directly from the servo-controlled 'linear torque' BSL motor/bearing and is higher still at –62dB (DIN-B wtd, silent groove) via an unsupported, spinning LP disc. Absolute speed was some –0.4% slow in our 30-year-old sample but it's the levels of wow and flutter that would be more debilitating, subjectively [see Graph 1, below]. The combined, peak-wtd figure of 0.45% is about 10x higher than anticipated from an 'audiophile' deck of today.

The fitted tonearm is more complex than it looks as the pivot point is offset by an L-shaped linkage to the main, square-section alloy tube. The resonant behaviour of this structure is necessarily complex with a main mode at 110Hz followed by twisting and possible harmonics at 170Hz and 270Hz [see Graph 2, below]. The sequence of higher frequency modes will be related to the cartridge mounting, arm 'bearing' and auto-lift/lower mechanism, but despite their number these are relatively low in amplitude. Also, while the tube is a mere 150mm in length, the effective length is closer to 165mm and the effective mass very low at ~6g. As described by Tim the downforce is preset at 2g although, with Sony erring on the side of caution, in practice this was about 10% higher at 2.17g. This, the high MM compliance and 0.6mm spherical stylus profile combine to yield an adequate tracking limit of ~70µm via the left/right channels and just letting go at the penultimate +15dB groove modulation (re. 315Hz/5cm/sec) at ~1% THD. PM


Wow and flutter re. 3150Hz tone at 5cm/sec (plotted ±150Hz, 5Hz per minor division)


Cumulative tonearm resonant decay spectrum, illustrating various bearing, pillar and 'tube' vibration modes spanning 100Hz-10kHz over 40msec

Turntable speed error at 33.33rpm 33.21rpm (–0.38%)
Time to audible stabilisation 7sec
Peak Wow/Flutter 0.20% / 0.25%
Rumble (silent groove, DIN B wtd) –61.8dB
Rumble (through bearing, DIN B wtd) –62.9dB
Hum & Noise (unwtd, rel. to 5cm/sec) –42.5dB
Power Consumption 5W
Dimensions (WHD) / Weight 215x58x235mm / 2.5kg