"A"-weighed separation was 116 dB below clipping. While 116 dB is a good figure, this amplifier does not include crossovers that usually reduce SNR measurements.
Normally you'll see a single slew rate measurement for an amplifier. Because this amplifier uses autoformers for load-matching, we got three different slew rates: 15V/S @ 2 ohms, 23V/S @ 4 ohms, & 31V/S @ 8 ohms.
Damping was relatively low, about 56, caused by the impedance of the output autoformers. Remember that the best possible figure for damping for a typical 4-ohm speaker is about 1.25. Damping factors of 50 are fine and do not affect sound quality.
The amplifier passed our reactive load test with flying colors. No aberration of the output waveform was detected. Reactive load isolation is another benefit of using an autoformer design.
The power limiting circuit reduces the gain of the amplifier when the amplifier begins to clip, keeping the amplifier at the 300 watt level. Limiting is always on by default but can be defeated by grounding the "PG" terminal.
Efficiency at full power into 2 ohms was 53%. This number is lower than most class A/B designs. At 1/3 power the efficiency fell to 27%, which is typical for class A/B amplifiers.
Input sensitivity was one to eight volts. Some will have trouble driving this amp to clipping with the one volt setting when using it as a subwoofer amp. I prefer not to use settings lower than one volt as noise and distortion can be introduced.
Listening TestWe tested the McIntosh with Morel Duets and Altec Lansing Voice of the Theater speakers. These old Voice of the Theater speakers are extremely efficient and help to reveal noise and distortion at low power. The amplifier was completely neutral; we could not detect any coloration of the music. There was a slightly audible turn-on thump and turn-off tick.
ConclusionBuilt to the same exacting specifications as their renowned home audio line, this amplifier has exacting performance as well. This amplifier does not have bass boost circuits (bravo, McIntosh!) filters, or crossovers.
Large and heavy for some tastes, but does the job flawlessly.
Cost? You know that VU meters, machined extrusions, output autoformers, copious output devices, and XLR connectors are costly. So, if you have to ask...
FeaturesBalanced design, input to outputAutoformer outputsMassive heatsink with fan coolingPower Guard power-limiting circuitDual mono-block design