Vintage

Reflecting the pre-CD era in which the TA-F70 was engineered (1979) the overall line-in gain is very high at +49.2dB, so this leaves little room to manoeuvre the volume control should the amp be used with a 2V+ output CD player or DAC, for example. High gain typically impacts on the S/N ratio that might be achieved although Sony has managed a very fine 84.5dB here (A-wtd, re. 0dBW) with low hum and noise thanks to its innovative, early 'Pulse' power supply.

In practice the PSU sustains more than the rated 2x90W/8ohm as the TA-F70 delivers 2x108W/8ohm and 115W/4ohm, but is evidently current-limited to about 5A. Under dynamic, music-like conditions, this is revealed by the near-zero headroom offered into 8 and 4ohm at 121W and 118W, respectively – a consequence of a highly regulated switching supply – and by the mere 24W/2ohm and 7W/1ohm possible into lower impedances [see Graph 1]. Incidentally, the 1W 'peak power' LED might light at 1.7W/8ohm, the 10W LED at 12.7W/8ohm, and the 50W LED at exactly 50W/8ohm, but the TA-F70 is most definitely not suited to insensitive loudspeakers or those with a sub-4ohm nominal impedance!

Sony's output stage has a low 0.014ohm source impedance and, in source direct mode, a very flat and extended response with ±1dB limits at <1Hz to 75kHz. Distortion is very low too, holding to ~0.005-0.007% from 1-10W and then to <0.018% from 10W to the rated 90W through the bass and midrange. The increase in distortion through treble frequencies is modest at 0.02%/20kHz and 0.03%/40kHz [see Graph 2]. This is a very sophisticated design, with more than a hint of 2018... PM

Power output (<1% THD, 8/4ohm): 108W / 115W
Dynamic power (<1% THD, 8/4/2/1ohm): 121W / 118W / 24W / 7W
Output imped. (20Hz–20kHz/100kHz): 0.009 to 0.014ohm / 0.57ohm
Freq. resp. (20Hz–20kHz/100kHz, 0dBW): +0.0dB to –0.25dB / –3.4dB
Input sensitivity (for 0dBW/90W): 9.8mV / 93mV
A-wtd S/N ratio (re. 0dBW/90W): 84.5dB / 104.0dB
Distortion (20Hz-20kHz, 10W/8ohm): 0.009–0.023%
Power consumption (Idle/rated output): 33W / 325W
Dimensions (WHD) / Weight: 430x160x410mm / 8.7kg