McIntosh MCC602TM Car Audio Amplifier

McIntosh is a name synonymous with extrodinary home audio audio products. It was no surprise when they started in the car audio industry years ago that its automotive line would be built to the same exacting standards. Well, McIntosh is back at it and is breaking new ground with amplifiers as such the flagship MCC602TM we tested.

Cosmetics
This amplifier is huge. It weighs nearly 50 pounds, and measures a very sizeable 27" x 12.5" x 2.94". Speaking of weight, this amplifier weighs more than the entire battery pack in my hybrid gas-electric car. Other than being large and overweight, this is a beautiful piece of equipment. It has that distinctive Mac look with its dual blue illuminated VU meters and heavy-duty connectors. Heatsinks are large with material milled out under the fins to allow optimal air flow.

Layout
The overall PCB layout is clean, utilizing high quality components. Low ESR, high-temperature capacitors are used throughout. There are more jumpers and wiring bundles than we like to see, but these are required when using autoformers. Power connections for the McIntosh are made via four gauge ring lugs used as power connectors, just mounted in reverse. Clever. Twelve Toshiba 150-watt bipolar output devices are used per channel. Linearity and reliability are improved by the generous number of output devices used.

The amplifier is balanced input to output. This topology means that there are no high current connections to the internal audio ground. Keeping current off of the ground plane minimizes distortion. Normally this design would mean that the two channels could not be bridged for mono operation. The output autoformers solve this problem by introducing a small impedance between the amplifier output and the speaker connections. Configuring this amplifier for monaural operation is done by connecting the channels in parallel. McIntosh was careful to precisely match the voltage gain of both channels, which is required to parallel two channels. In this configuration the amplifier is rated at 600 watts into 1, 2, or 4 ohms.

As for the audio input connections, these can be made through two means, using either standard RCA or balanced XLR.

Autoformers
What are they, how do they differ from transformers? If McIntosh used output transformers in this design, they would have to be much larger than the autoformers they elected to use. An autoformer simply means that the primary and secondary windings are partially shared. This improves coupling and reduces size. Transformer size is determined by the maximum power and the lowest frequency that it is required to produce without saturation. This is the first car amplifier in the McIntosh line that is not direct-coupled.

Power Supply
The MCC602TM amplifier uses dual power supplies. These supplies are isolated and fully regulated. In our test, the supply was regulated down to 10.2 volts. Each of these power supply includes an RF choke per channel to reduce radio interference.

Protection
The MCC602TM does not know the meaning of thermal protection. It simply never got hot enough to thermally cycle. As for the the short circuit test, it recovered without damage. Low impedance protection simply reduces the amplifiers outputs with loads lower than 1/2 of what the amplifier is rated.

Performance
The amplifier was virtually flat from 10 Hz to 20 k. The McIntosh produced 300 watts x 2 into 4 ohms with an astonishingly low T.H.D+N of .0045%! When we drove this amp via its XLR connectors, the distortion dropped below .003%. Distortion dropped to about .001% at 10 kHz. Most transistor amplifiers have just the opposite trend, with distortion rising at high frequencies. The output autoformers may help lower the distortion at high frequencies because they usually attenuate the upper harmonics above 20 kHz.

Separation was very high, > 102dB. The dual mono design and fully balanced topology facilitate this excellent figure.

"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/uS @ 2 ohms, 23V/uS @ 4 ohms, & 31V/uS @ 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 Test
We 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.

Conclusion
Built 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...