Philips FA860 amplifier Lab Report

Lab Report

For once 'CD Direct' really does have a measurable impact on performance, not only bypassing the bass/treble controls (which are far from 'flat' in their default '0' position) but also the loudness control and L/R balance slider. There is only a 0.1dB difference in overall gain (+44.2dB) with CD Direct engaged or defeated but a difference of 1dB in A-wtd S/N (90.4dB vs. 89.5dB re. 0dBW). With CD Direct, the response is flat to within ±1dB from 4Hz-77kHz (–1.6dB/100kHz) but, defeated, shows a bass shelf of –1dB from 200Hz down to 10Hz, and a –0.25dB plateau out from 3kHz-60kHz. Distortion is more significantly influenced by output level than 'CD Direct', increasing from a low of 0.0015% at 1W/8ohm to 0.011%/10W and 0.022%/20W before stabilising at this level up to the rated 70W/8ohm power output (all at 1kHz). Implying a drift from low power Class A to Class A/B at a few watts, this trend of THD vs. level is more marked [black trace, Graph 1] than the increase in THD vs. freq. [see Graph 2].

While legacy schematics suggest a similarity in the FA860's output stage with that of stablemate Marantz's PM-50 from the same era, in practice the PM-50 had the edge in output, delivering 2x91W and 2x155W vs. the FA860's 2x85W and 2x130W into 8 and 4ohm loads, respectively. Both amplifiers readily exceeded their 2x70W/8ohm and 2x105W/4ohm rating but only the Philips model used electronic/relay speaker protection to limit output to 275W/16.6A into 1ohm loads [see green trace, Graph 1 below]. Output under dynamic conditions was otherwise well served by Philips' dual-mono PSU arrangement, producing 113W, 189W and 265W into 8, 4 and 2ohm loads (1kHz, 10msec, <1% THD). PM


Dynamic power output vs. distortion up to 1% THD into 8ohm (black trace), 4ohm (red), 2ohm (cyan) and 1ohm (green) speaker loads. Max current is 16.6A


Distortion vs. extended frequency from 5Hz-40kHz (1W/8ohm, black; 10W/8ohm, red)

Power output (<1% THD, 8/4ohm) 85W / 130W
Dynamic power (<1% THD, 8/4/2/1ohm) 113W / 189W / 265W / 275W
Output imp. (20Hz–20kHz/100kHz) 0.075–0.095ohm / 0.35ohm
Freq. resp. (20Hz–20kHz/100kHz, 0dBW) –0.07dB to –0.1dB/–1.6dB
Input sensitivity (for 0dBW/70W) 17mV / 149mV
A-wtd S/N ratio (re. 0dBW/70W) 90.4dB / 108.9dB
Distortion (20Hz-20kHz, 10W/8ohm) 0.009–0.025%
Power consumption (Idle/rated output) 21W / 252W
Dimensions (WHD) / Weight 420x118x334mm / 10kg