Pre/Power Amplifiers

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