Pre/Power Amplifiers

When an amplifier is bridged to supply twice the volts across a given load, power output typically increases into 8 and 4ohm but can decrease into lower impedances if there's a shortfall in current from the PSU. Constellation has managed this juggling act well enough – the Centaur II coming close to its 500W/8ohm and 1kW/4ohm rating by delivering 585W/8ohm and 930W/4ohm, boosted under dynamic conditions to 685W and 1.25kW, respectively. A full 1.69kW is achieved into 2ohm but output is 'limited' to 880W (or 29.7A) into 1ohm [see Graph 1, below], so while it will surely drive most likely partnering speakers with ease, the brand's monoblocks still have the edge.

Output impedance is a very uniform 0.035ohm (20Hz-5kHz) increasing gently thereafter to 0.049ohm/20kHz. Distortion follows a similar trend with a 'flat' 0.004-0.009% (again, 20Hz-5kHz) at 10W, rising to 0.03%/20kHz in 'Balanced' mode. Incidentally, overall gain is a 'standard' +25.8dB via the 'Balanced' input but falls to +12dB via 'Direct' – a mode that can only usefully be employed with very high (~20V) output preamps. Distortion is also just a little higher in 'Direct' mode [red trace, Graph 2]. Versus level, this low and steady THD is maintained by Constellation's enriched bias up to around 40W/8ohm after which it increases to 0.01%/100W, 0.03%/200W, 0.07%/300W, 0.11%/400W and 0.16% at the rated 500W (all 1kHz/8ohm). Distortion typically increases by x4 for each halving of load impedance [Graph 1]. Frequency response is flat to within ±0.2dB over a very wide 2Hz-100kHz bandwidth (not all Constellation amps extend into the subsonic) while separation is an excellent 110dB (1kHz) to 90dB (20kHz). PM