Integrated Amplifiers

'The VU meters', says Supraxox 'indicate the peak power output of each channel'. As ever these are largely decorative with a 1W/8ohm output indicated by the number '20' on the display's lower scale, increasing to the maximum '140' at just 10W/8ohm. The amplifier's real maximum output is higher than the rated 70W/8ohm at 2x85W/8ohm but the 120W/4ohm specification is not met simply because the Vouvray's protection activates above 85W/4ohm. Under dynamic conditions, however, the amplifier's full capability is revealed at 110W, 195W and 300W into 8, 4 and 2ohm loads and 310W/1ohm (or 17.6A at 10msec/1% THD). This is illustrated in Graph 1, below, alongside the steady increase in distortion with output from 0.04%/1W to 0.12%/10W and 0.3% at the rated 70W/8ohm. However, and in marked contrast with almost all other amplifiers, this classic application of Toshiba 2SC5200/2SA1943 output devices sees a reduction in distortion with decreasing load impedance, falling to 0.03%/1W, 0.04%/10W and 0.1%/70W into 1ohm. This atypical THD vs. load behaviour is nonetheless consistent with frequency [see Graph 2, below] which, from a subjective standpoint, is likely to be very positive.

Noise, on the other hand, is a little higher than average – a mix of hum and midband noise rather than HF hiss – and the A-wtd S/N ratio is necessarily compromised at 77dB (re. 0dBW). The response rolls away below 20Hz to a sensible –3dB/3Hz and reaches out above –0.17dB/20kHz to –2.8dB/100kHz – figures that will see only mild modification with low/variable impedance speaker loads courtesy of the amplifier's moderate ~0.09ohm source impedance. Finally, overall gain is quite high at +42.9dB (just 20mV required for 1W/8ohm). PM