Pre/Power Amplifiers

Taken at face value, the '250W' Centaur II Stereo should be half the amplifier that the Centaur II 500 [HFN Dec '19] represents but, in practice, the 'little brother' punches very close to its slightly newer sibling. Let's compare the figures: the '500W' Centaur II 500 delivers 2x585W/8ohm and 2x930W/4ohm, boosted under dynamic conditions to 685W, 1.25kW and 1.69kW into 8, 4 and 2ohm but 'limited' to 880W (or 29.7A) into 1ohm. The original Centaur power amp [HFN Jul '13] offered 2x510W/8ohm and 2x825W/4ohm with 570W, 1.06kW, 1.93kW and a full 3.01kW (54.9A) into 8, 4, 2 and 1ohm under dynamic conditions. The Centaur II Stereo smashes its 250W rating with 2x400W/8ohm and 2x675W/4ohm, increasing to 425W, 780W, 1.26kW and 856W (29.3A) into 8, 4, 2 and 1ohm under dynamic conditions [see Graph 1, below]. So, in practice, the Centaur II loses nothing to the Centaur II 500 in its ability to drive the lowest impedance loads.

The novel N-type power amp circuit is sufficiently stable into any likely speaker load that no Zobel, or other filter network, is fitted to the output. Output impedance is a very uniform 0.032ohm (20Hz-5kHz) increasing gently thereafter to 0.041ohm/20kHz while the response is super-flat and extended (±0.5dB from sub-1ohm to >100kHz). Stereo separation is an excellent 115dB (1kHz) to 88dB (20kHz) and the 0dBW-rated A-wtd S/N is 87.1dB (Balanced) and 99.1dB (Direct) where the gain(s) are +26dB and +12dB, respectively. The enriched bias keeps distortion below ~0.01% up to around 70W/8ohm after which it increases to 0.015%/100W, 0.05%/200W and 0.085% at the rated 250W (all 1kHz/8ohm). PM