Constellation Centaur II 500 Power Amplifier Lab Report

Lab Report

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


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 29.7A


Distortion vs. frequency from 5Hz-40kHz re. 10W/8ohm (black, 'Balanced'; red, 'Direct' mode)

Power output (<1% THD, 8/4ohm) 585W / 930W
Dynamic power (<1% THD, 8/4/2/1ohm) 685W / 1.25kW / 1.69kW / 880W
Output imp. (20Hz–20kHz/100kHz) 0.032–0.049ohm / 0.21ohm
Freq. resp. (20Hz–20kHz/100kHz) +0.00dB to –0.01dB/–0.18dB
Input sensitivity (for 0dBW/500W) 144mV / 3265mV (Balanced)
A-wtd S/N ratio (re. 0dBW/500W) 90.6dB / 117.6dB (Balanced)
Distortion (20Hz-20kHz, 10W/8ohm) 0.003–0.028% (Balanced)
Power consumption (Idle/Rated o/p) 229W / 1.73kW (5W standby)
Dimensions (WHD) / Weight 476x292x616mm / 68kg
Price £64,998

Constellation Audio
Newbury Park, CA, USA
Supplied by: Absolute Sounds Ltd
0208 971 3909