Pre/Power Amplifiers

While Quiescent’s UK patent offers some insight into the vibration and RFI/EMI mitigation cloaking the T100SPA’s power supply, the brand also offers a basic (audio) specification. Elements of this are met in practice, while others are a little shy of the mark. Fortunately, claims for power and low noise are on the money with the rated 130W/8ohm and 200W/4ohm being met if the THD tolerance is slackened to 2%. With the usual 1% ceiling, power is 2x125W/8ohm and 2x185W/4ohm at 1kHz with sufficient in reserve to support 140W, 230W and 355W into 8, 4 and 2ohm loads under dynamic conditions before being limited to 185W (or 13.6A) into 1ohm [see Graph 1, below]. Overall gain is a little lower than Quiescent suggests at +25.1dB but the 92dB A-wtd S/N ratio (re. 0dBW) is on a par with the better ‘low noise’ amplifiers previously tested in these pages.

Response, and particularly distortion, differ from Quiescent’s ratings but are still meaningful in their own right. So while the wide bandwidth ‘–3dB at 0.5Hz to 600kHz’ might reflect the amplifier’s open-loop performance, in reality the –3dB points are 2Hz-90kHz with a +1.3dB peak at 54kHz prior to the steep ultrasonic roll-off. Moreover the high-ish, but flat, ~0.23ohm source impedance will cause some modification of the amp/speaker system response depending on the latter’s impedance trend. Distortion is higher than rated but, again, is impressively uniform with frequency [Graph 2] from a minimum of ~0.085% at 1W/8ohm to ~0.25% at 10W before falling again to 0.17-0.35% at 100W (all 20Hz-20kHz into 8ohm). Subjectively, a flat THD vs. frequency trend, even with the extended harmonics seen here, can be preferred over a lower but rising distortion profile. PM