Integrated Amplifiers

Comparing this 70W/8ohm-rated CSA70 with the 100W/8ohm CSA100 [HFN Aug '20] is not especially instructive for, despite the similar On Semiconductor-based output stage(s), the latter has a bigger PSU and tube-centric preamp stage that largely sets the 'tone' of the product. So the CSA70 is a distinct, standalone amp in the range, capable of delivering 2x90W/8ohm and 2x140W/4ohm with sufficient headroom to sustain peaks of 110W, 206W, 352W and a full 475W (21.8A) into 8, 4, 2 and 1ohm loads, respectively [see Graph 1, below]. Add to this fine load tolerance a usefully low 0.01-0.07ohm output impedance and response that's flat to –0.3dB from 1Hz-20kHz (and –1.9dB/100kHz). THD is held to within 0.003-0.004% from 20Hz-1kHz over 1-50W/8ohm, increasing to 0.04%/20kHz. Gain is more than typically required at +42dB and the A-wtd S/N ratio only slightly below average (white noise, not hum) at 83dB (re. 0dBW).

Measured via its fixed line output (which has a high 1kohm source impedance) the CSA70's digital stage employs a WM8740 DAC in place of the ESS9018 used in its other amplifiers. A 0dBFs digital input yields a 1.9V output, a respectable 104.8dB A-wtd S/N ratio and bass/midband distortion that falls to a minimum of just 0.0002% over the top 30dB of its dynamic range. This increases to a minimum ~0.001% at 20kHz [see Graph 2]. Jitter is squeezed to ~250psec while the limited 7dB stopband rejection is traded for greatly reduced ringing on transients – all this defined by the slow roll-off linear phase digital filter (the CSA100 uses a fast roll-off linear phase filter). The responses roll away to –2.1dB/20kHz, –4.7dB/45kHz and –6.1dB/90kHz with 48kHz, 96kHz and 192kHz digital files, respectively. PM