McIntosh MC2255 (1981–1986)

Two hundred fifty watts per channel, rated down to one ohm, and a protection circuit that refuses to let the amplifier hurt your speakers.

Overview

The MC2255 is a solid-state stereo power amplifier. McIntosh built it around the phrase "better sound longer," and the spec sheet reads like that slogan was a requirement, not a tagline. Stereo output is rated at 250W + 250W into loads from 1 Ω to 8 Ω. That is a wide enough load range that the amp barely notices what you connect to it. Bridged to mono, it delivers 500W into loads from 0.5 Ω to 16 Ω.

The distortion numbers show the design philosophy best. Total harmonic distortion and cross-modulation distortion are both specified at 0.02% from 0.25W up to full effective output, measured across 20 Hz to 20 kHz. That is not a single-number-at-1-kHz figure. It holds across the band and across nearly the entire power range, which is a much harder claim to make. Frequency response is quoted at 20 Hz to 20 kHz, +0/−0.25 dB. The amplifier was rated to deliver its output into 1, 2, 4, or 8 ohm loads across that same band with no more than 0.02 per cent harmonic or intermodulation distortion. The signal-to-noise ratio is 95dB, and the damping factor is 30 or more.

Inside, the count is 14 ICs, 85 transistors, and 47 diodes. The back panel carries output barrier strips, audio inputs, and an AC outlet. Power draw at effective output is 1.4 kW, and the amplifier itself is specified for 100 VAC, 50/60 Hz. External dimensions are 411 mm wide, 181 mm high, and 368 mm deep. Weight is where the sources disagree: 37.2 kg in one listing, 82 pounds in others. Those two figures are close enough that they're likely the same number rounded differently, but the Archive has not resolved which is exact.

Production dates are muddled too. The most commonly cited span is 1981 to 1986, though at least one database lists it as released in 1982 and another as 1981-82. The Japanese-market price at introduction is not in dispute: ¥1,098,000.

Key Features

Power Guard: Waveform Comparison, Not Just a Relay

The MC2255's headline protection circuit is McIntosh's Power Guard. It works differently from the thermal cutouts and fuses most amplifiers of the era relied on. A waveform comparison circuit sits in the signal path and continuously compares the input waveform against the output waveform. When harmonic distortion reaches 0.5% or higher, the circuit restricts the input signal rather than clamping the output. The goal is to prevent clipping before it reaches the speaker. The spec sheet rates Power Guard at 2% or less at 1 kHz, 20 dB. It is a real-time correction, not a shutdown.

Seven-Section Self-Diagnosis

Less common for the period is the self-diagnosis system. The amplifier's circuitry is divided into seven sections that are automatically checked. If a fault is detected in any of them, output to the speakers stops until the unit is repaired. The amp fails safe rather than pushing a damaged channel into a driver.

Output Transformer and Thermal Headroom

McIntosh used an output transformer of its own design in the MC2255. The company's stated benefit was twofold: improved impedance matching, and power transistors that run roughly 20°C cooler than in a conventional design. That kind of margin shows up as longer component life over decades of use.

Input Level Switching and Independent Gain

Input sensitivity is switchable between 750 mV and 2.5 V, with an input impedance of 50 kΩ. The manual advises that when the amplifier is paired with McIntosh source equipment, the best signal-to-noise ratio comes from setting the INPUT LEVEL switch to the 2.5 V position and running the front-panel LEFT and RIGHT/MONO GAIN controls fully clockwise. Those gain controls are independent and continuously variable, left and right. The manual also notes that to minimize hum, shielded cables should be run parallel to each other or loosely twisted, kept away from speaker leads and AC power cords. All connections are made on the back panel.

Historical Context

The MC2255 was developed to support McIntosh's "better sound longer" policy, the company's argument that a high-power amplifier should not be a consumable. The design brief was durability and fidelity in equal measure: 250 watts per channel into loads from 1 to 8 ohms across the full audio spectrum, with protection systems intended to keep both the amplifier and the connected speakers out of the repair shop.

At least one account from someone who installed these professionally describes putting well over a hundred MC2255s into service, the vast majority in discos and churches in old Mexico. Those are places where an amplifier runs hard, runs long, and doesn't get coddled. As Audio (March 1990, p.121) noted in its classified pages, the MC2255 and its McIntosh stablemates remained actively bought, sold, and traded on the used market well into the following decade.

Collectibility & Value

Recent listings have shown the MC2255 selling for between $3,295 and $3,850 USD. The Archive's own eBay observations run lower: a unit described as "Autoformer Very Good" at $2,900, and a serviced example at $2,017. Those listing prices are undated, so treat them as rough bearings rather than a market index. The wood case is a separate purchase. A piano-black example listed at $369, and replacement lamps run around $12.69 for a set of ten. Dealers occasionally move units complete with the walnut cabinet, original manual, and original schematic, and that package is worth more than the amplifier alone.

Common faults owners report include intermittent audio dropouts from poor connections at the input jacks, weak output in one channel, and uneven meter brightness from aging bulbs. One Reverb listing described exactly this pattern: backlights out and a crackling, intermittent right mono gain control, still passing audio but sold as-is. Service manuals and schematics are available, and there are specialists who service these. A dealer listing for a fully tested example described the operational condition as excellent with no issues found.

Before buying, check the input jacks for the dropout issue, verify both channels at equal output, and look at the meter lamps. They're the cheapest fix, but the most visible tell of how the unit has been kept.