McIntosh MC252

Two hundred fifty watts into anything from two to eight ohms - no tap-switching, no excuses, just iron and glass.

Overview

The MC252 is a stereo power amplifier from McIntosh Laboratory. The factory service documentation gives the headline figure plainly: 250 watts into a 2, 4, or 8 ohm load, minimum sine wave continuous average power per channel, with both channels operating. It is not a "250 watts into 8 ohms, 400 into 4" amplifier with a marketing asterisk. It is 250 watts into all three impedance classes. That is the McIntosh autoformer approach - the output transformer presents a constant load to the output stage regardless of what the speaker does, so the amp never has to be re-tapped when a user swaps speakers.

The distortion figures read more like a measurement instrument than a consumer amplifier. Maximum total harmonic distortion at any power level from 250 milliwatts up to rated output is 0.005%. Intermodulation distortion is the same 0.005%, specified with instantaneous peak output per channel not exceeding twice the rated output, across any combination of frequencies from 20Hz to 20,000Hz, with all channels operating. The IMD spec is the one to watch, because IMD usually exposes a power supply that sags under real program material. McIntosh specified it with both channels running at double rated peak, the condition most likely to show weakness, and the number stayed at 0.005%.

The service manual carries the standard McIntosh disclaimer. The company reserves the right to improve design without notice, and because of constant circuit and component upgrades, the accuracy of the schematic material cannot be warranted. In other words, the company tells technicians in writing that the schematic in hand may not match the unit on the bench. McIntosh evidently revised boards quietly over a production run. For anyone restoring an MC252 today, documentation matched to the serial number beats a single downloaded schematic.

The same chassis will also run as a monoblock: 500 watts into a 1, 2, or 4 ohm load, minimum sine wave continuous average power output. This is the "mono bi-amp" configuration, and it is the reason pairs of MC252s turn up in serious systems. Bridging an amplifier normally doubles voltage swing and halves the load impedance it can tolerate. Here the autoformer lets the mono configuration accept a 1 ohm load, which is unusual. Owners running difficult loudspeakers have historically gone this route rather than hunting for a bigger stereo chassis.

The amp is 17-1/2 inches (44.45cm) wide, 9-7/16 inches (23.97cm) high, and 14-3/4 inches (37.5cm) deep, with that depth figure including clearance for connectors. The width is the familiar McIntosh full-size panel, so it stacks cleanly with the company's preamplifiers of the period. At just under nine and a half inches tall, the chassis has room for real heatsink area and real transformer iron.

Power requirements are specified for six mains voltages: 100V at 8 amps, 110V at 7.2 amps, 120V at 6.6 amps, and 220V, 230V, and 240V each at 3.3 amps, all at 50/60Hz. McIntosh's own note directs the user to the rear panel to confirm the correct voltage for their particular unit. This is a multi-market amplifier on a common platform, so check the rear panel legend before plugging anything in. A 100V Japanese-market unit fed 120V will not end well.

The service documentation includes the usual technician's notes: voltages measured at 120V AC input with a 10 megaohm impedance voltmeter, resistor values in ohms, capacitor values in microfarads, inductor values in microhenries, and square pads on the PC boards marking polarized capacitor positives, diode cathodes, and pin 1 designations. It also warns bluntly that parts marked with a critical-characteristics symbol must be replaced only with manufacturer-recommended equivalents. Output-stage and protection components in a direct-coupled amplifier of this power class are not interchangeable with generic substitutes, and the manual says so plainly.

The documentation does not contain a production date, an original retail price, or any independent bench measurement from the audio press. The period review material for this model is thin. A December 2008 entry in Pro-Audio-Review (December 2008, p.10) touches on mastering-room upgrade philosophy and the ear's role as a normalizer, and offers no measured performance data on the MC252 itself. Anyone quoting a hard review verdict on this amplifier should be asked where it came from, because the documented record is mostly McIntosh's own service literature.

The specifications are complete and strict: 250 watts across three impedances, 0.005% THD and IMD, and a 500-watt mono mode down to 1 ohm. The surrounding context is missing. There is no confirmed production window, no original MSRP, no documented common failure point, and no independent measurement to compare against the factory claims. What exists is a manual that describes a very serious amplifier in very specific terms, and a chassis that shows up in the used market as a known quantity among people who already understand what an autoformer does. Any listing that asserts a production year or a price without documentation should get the same skepticism as a schematic that does not match the board in front of you.