McIntosh MI502 Class D Power Amp Lab Report

Lab Report

Dial 'McIntosh MI502' into the Interweb and you'll see one cut 'n' paste post after another describing it as a 'Digital Amplifier'. It's not, of course, so while making a mental note to avoid these 'resources' in the future we'll focus instead on comparing the MI502 with other amplifiers using the decidedly 'analogue' Class D NC500 module from Hypex. The Marantz PM-10 [HFN Aug '17] also beat to the tune of a balanced/bridged

pair of these modules and achieved a fulsome ~620W output into 8/4ohm, with 710W, 605W, 325W and 175W into 8, 4, 2 and 1ohm loads under dynamic conditions. McIntosh's MI502 has a more robust switchmode PSU but its 'Sentry Monitor' protection only allows it to maintain 2x550W/8ohm and 2x1000W/4ohm for a limited period before shutting down. Dynamic peaks (10msec duration) slip through the Sentry's guard to reveal a very generous 915W, 1150W, 735W and 450W into 8, 4, 2 and 1ohm loads, respectively [see Graph 1].

Distortion is usefully low through bass and mid frequencies at 0.003%/1W, 0.0075%/10W and 0.008%/100W, the inevitable 'Class D' rise at higher treble frequencies reaching 0.014%/1W, 0.028%/10W and 0.40%/100W at 20kHz [see Graph 2, below]. The output impedance is a very flat 0.025-0.029ohm (20Hz-20kHz) and the response is load-tolerant, offering –1dB limits of 6Hz-25kHz (to –8.4dB/100kHz) into 1-8ohm loads [see Graph, p67]. The overall gain is +29.3dB (balanced XLR inputs) and the A-wtd S/N ratio is 76.2dB (re. 0dBW), the latter only a little poorer than can be achieved with the NC500 modules. The optimised layout of the MI502 does confer an excellent 105dB channel separation through the midrange (82dB/20kHz). PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 21.2A


Distortion versus frequency versus power output (1W/8ohm, black; 10W, pink; 100W, red)

Power output (<1% THD, 8/4ohm) 550W / 1000W
Dynamic power (<1% THD, 8/4/2/1ohm) 915W / 1150W / 735W / 450W
Output imp. (20Hz–20kHz/100kHz) 0.025–0.029ohm / 1.8ohm
Freq. resp. (20Hz–20kHz/100kHz) –0.1dB to –0.70dB/–8.4dB
Input sensitivity (for 0dBW/500W) 97mV / 2220mV
A-wtd S/N ratio (re. 0dBW/500W) 76.2dB / 103.2dB
Distortion (20Hz-20kHz, 10W/8ohm) 0.0048–0.028%
Power consumption (Idle/Rated o/p) 40W / 1.2kW (1W standby)
Dimensions (WHD, with ears) / Weight 483x110x533mm / 10kg
Price £5995

McIntosh Labs
Binghamton, NY, USA
Supplied by: Fine Sounds UK
01592 744710