Stereophile: Plinius SA-Reference power amplifier - Jason Diffusion

Stereophile: Plinius SA-Reference power amplifierhttp://www.printthis.clickability.com/pt/cpt?action=cpt&title=Ste...Fig.2 Plinius SA-Reference, small-signal 1kHz squarewave into 8 ohms.Fig.3 Plinius SA-Reference, balanced channel separation (10dB/vertical div., R–Ldashed).Even in class-A mode, the SA-Reference slightly exceeded its specified outputpower at 1% THD+noise, both channels driven at 1kHz, giving 320W into 8 ohms(25dBW) and 480W into 4 ohms (23.8dBW). With one channel driven, the Pliniusdelivered 740W into 2 ohms (22.7dBW). How the THD+N percentage changed withoutput power into these loads is shown in fig.4; the amplifier is clearly lesscomfortable with the 2 ohm load, though the additional distortion is still well below0.1% up to the clipping point.Fig.4 was taken with balanced drive. Remaining with balanced drive, fig.5 showshow the THD+N percentage changes with frequency into 8, 4, and 2 ohms at alevel of 15V RMS, which is where the distortion starts to rise out of the noisefloor, according to fig.4. Though the overall distortion levels are in the mainrespectably low, the amplifier clearly gets less linear as the output current andfrequency increase. This graph was taken with class-A output-stage bias;switching to class-AB increased the 8 ohm midrange THD+N figure from 0.004% inboth channels to 0.005% left and 0.0085% right. Switching then to unbalanceddrive increased the THD further, to 0.03% left and 0.015% right. None of thesefigures represents anything close to audible, but they do reveal some8 sur 11 21/09/06 14:11