Philips AF 877 Turntable Lab Report

Lab Report

While this deck is a belt-drive design, its execution – dubbed 'Direct Control' by Philips at the time – combines a DC motor, belt, sub-platter and tachometer assembly to accurately govern its speed. Philips claimed 'the advantages of belt and direct-drive design' and, in practice, the AF 877 was not far short of this goal. Speed stability, at least as far as low-rate fluctuations are concerned, proved as secure as a good direct-drive, its low 0.02% peak wow reflected in the sharpness of the W&F spectrum [see Graph 1, below]. Our 40-year-old sample was running –0.35% slow (pitch control set to 0%) but there is none of the dynamic drift we still see with some contemporary DC motor/belt-drive turntables. Higher-rate speed fluctuations – flutter – amount to a peak 0.07%, the sidebands at ±20Hz, ±25Hz and ±40Hz also appearing as discrete signals in the AF 877's rumble spectrum. Bearing noise is par for the course at –67dB (DIN-B wtd, re. 1kHz/5cm/sec) but the through-groove rumble is significantly improved at –70.4dB thanks to the rubber platter mat.

The partnering straight alloy tonearm is some 8.5in in length and while the 'effective moving mass' was specifified at a rather high 16.5g, in practice this turned out closer to 8g – all the better to suit the high compliance MMs of the day. Friction was very low at ~10mg in both planes but while the vertical needle bearing betrayed some slight play only, the horizontal semi-auto mech was rather too 'loose'. The main bending mode of the lightweight tube is a very low 30Hz with a series of harmonic and/or torsional modes reaching out across 100-400Hz [see Graph 2, below]. The higher-Q mode at 590Hz (and 1050Hz) seems related to the large but lightweight headshell. 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 33.22rpm (–0.35%)
Time to audible stabilisation 2sec
Peak Wow/Flutter 0.02% / 0.07%
Rumble (silent groove, DIN B wtd) –70.4dB
Rumble (through bearing, DIN B wtd) –67.1dB
Hum & Noise (unwtd, rel. to 5cm/sec) –58.4dB
Power Consumption 2-4W
Dimensions (WHD) / Weight 419x140x349mm / 5.8kg