Pre/Power Amplifiers

Let’s kick off with a look at Audio Research’s latest power meters. Accurate? Yes, up to the 0.2W mark but then the reading drifts upwards with 1W/8ohm registering as 2W on the meter and a 20W/8ohm output shifting the needle halfway between the 20W and 200W positions. Ironically, the S-200 has no need to over-represent its output because power is offered in abundance. In practice, that 200W rating is smashed by a full 355W/8ohm and 550W/4ohm with more on tap under dynamic conditions where 470W, 839W, 1.31kW and 1.68kW is possible into 8, 4, 2 and 1ohm loads, respectively [all re. 1kHz/10msec/<1% THD; see Graph 1]. With a full 41A of clean current in reserve, the S-200 will drive almost any loudspeaker ever likely to cross its path. And it does so with a markedly ‘squeaky clean’ specification...

Frequency response is incredibly flat (within ±0.1dB from 20Hz-100kHz) though there’s an anomalous infra-bass lift of +8dB/3Hz – an issue with the DC servo, perhaps? Output impedance is also usefully low at 0.013-0.019ohm (20Hz-20kHz) while the A-wtd S/N ratio is phenomenally wide for a big power amp at 99.4dB (re. 0dBW). Then again, opening the window to its fullest is never a guarantee of subjective bliss... Hand-in-hand with this specmanship comes very low distortion, slightly lower under steady state [see Graph 2] than dynamic conditions. THD is 0.002%/1W, falling to a minimum of 0.00075%/8W, then rising gently to 0.001%/20W, 0.0028%/100W and 0.0052% at the rated 200W (all re. 1kHz/8ohm). Versus frequency, distortion rises gently at the extremes to 0.0014%/20Hz and 0.008%/20kHz (all re. 10W/8ohm) and just 0.033%/20kHz at a full 100W [red trace, Graph 2]. All in all, the S-200 is a departure for ARC. PM