AGD Gran Vivace Monoblock Amplifier Lab Report

Lab Report

The designer of this amplifier has gone to great lengths to develop a very 'clean' implementation of Infineon Technologies' Merus AUDAMP24 Class D solution. Levels of switching noise and other spuriae are extremely low, typically <–120dB below full output, while the A-wtd S/N ratio is some 15dB wider than achieved by the older, MOSFET-based IRAUDAMP solutions at 95.3dB (re. 0dBW). Overall gain, via the balanced inputs, is a sensibly low +23dB requiring ~2.8V for full output while efficiency (power out versus AC mains drawn) is ~90%. AGD rates the Gran Vivace variously as 350W/4ohm and 200W/8ohm while, on the lab bench, it achieved closer to 380W and 195W, respectively, at 1% THD. The near-doubling of output between 8 and 4ohm loads is illustrative of the 'stiff rail' Class D architecture but it also explains why there's little or no dynamic headroom. Figures of 205W, 400W and 335W under dynamic conditions into 8, 4 and 2ohm reflect this [see Graph 1, below] while the drop to 150W/1ohm is due to over-current protection.

Graph 1 also indicates a marked increase in THD into loads below 4ohm – typically >0.1% from 1-100W/2ohm versus 0.002-0.08% into 8ohm. Under continuous conditions, distortion increases from 0.004%/1W, 0.005%/10W and 0.09%/100W (all at 1kHz). Distortion also increases with frequency [see Graph 2, below] from 0.005%/1kHz to 0.07%/10kHz and 0.3%/20kHz (all at 10W/8ohm) in line with the response of the reactive output filter network. Into an open load the Gran Vivace's frequency response rises to +2.5dB/20kHz (peaking at +27dB/43kHz) and is tempered under load to +1.3dB/20kHz and –0.35dB/20kHz into 8 and 4ohm respectively. PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max current is 12.9A


Distortion versus frequency at 1W/8ohm (black, 5Hz-40kHz) and 10W/8ohm (red, 20Hz-20kHz)

Power output (<3% THD, 8/4ohm) 195W / 380W
Dynamic power (<3% THD, 8/4/2/1ohm) 205W / 400W / 335W / 150W
Output impedance (20Hz–20kHz) 0.004-0.057ohm
Freq. response (20Hz–20kHz/100kHz) –0.27dB to +1.4dB / –2.9dB
Input sensitivity (for 0dBW/190W) 205mV / 2770mV (balanced)
A-wtd S/N ratio (re. 0dBW/190W) 95.3dB / 118.1dB
Distortion (20Hz-20kHz, 10W) 0.0003–0.3%
Power consumption (Idle/Rated o/p) 16W / 220W
Dimensions (WHD, each) / Weight 279x127x279mm / 10kg (each)
Price £18,000 (pair)

AGD Productions Inc.
Los Angeles, USA
Supplied by: Whole Note Distribution, Angus, Scotland
0203 9115 549