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McIntosh MC 427 Amplifier Review

Rate this car amplifier:

  • 1. Poor (headless panther)

    Votes: 1 0.6%
  • 2. Not terrible (postman panther)

    Votes: 2 1.3%
  • 3. Fine (happy panther)

    Votes: 35 22.7%
  • 4. Great (golfing panther)

    Votes: 116 75.3%

  • Total voters
    154

amirm

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This is a review and detailed measurements of the McIntosh MC 427 (MC427) stereo car audio amplifier. It is on kind loan from a member. It has been discontinued but used ones go for about US $500.
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier review.jpg

Not much to distinguish the amplifier from other car amps other than the bright blue logo. Unlike all the others I have tested though, this one is class AB, not Class D.

There are two small fans which I don't like to see. Fortunately in use the amp ran very cool, barely getting warm and I don't think the fans ever came on.

McIntosh MC427 Amplifier Measurement
As usual we start with our dashboard of 5 watts into 4 ohm load:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier measurement.png

Are you seeing what I am seeing? Distortion product at nearly -120 dB??? And in a car amp? Incredible. SINAD is noise limited and lands the MC427 neck and neck with a state of the art class D car amp:
best car amplifier stereo review.png


Notice the high current usage of 7 amps to produce 5+5 watts of power (nearly 100 watts in!). Noise performance is excellent for a car amplifier:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier SNR measurement.png


Unlike most class D amplifiers, there is no load dependency in frequency response test:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier Frequency Response measurement.png

There is an offset between the two channels though and they roll off differently but this may be due to age.

Crosstalk is not great:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier Crosstalk measurement.png

It is similar to the last car amplifier I tested so there may be a common issue here with terminals they use or something like that.

Multitone performance is yet again excellent:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier Multitone measurement.png

Guess what 19+20 kHz intermodulation performance is:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier 19 20 kHz intermodulation distor...png

Yes, excellent. :)

Let's see if it meets the power spec of 100 watts per channel:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier power 4 ohm measurement.png


McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier Max and Peak power 4 ohm measure...png


Of course it does and then some. But better have good supply of current seeing how almost 40 amps were drawn.

Here is 8 ohm:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier power 8 ohm measurement.png


Sweeping at different frequencies shows the class AB strength in not caring a lot but the amp did go into protection at lower frequencies:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier power 4 ohm vs frequency vs dist...png


I was pushing it into clipping though which often causes that.

Finally, the amp was stable on power up other than a minor glitch:
McIntosh MC 427 MC427 stereo 2ch high-end car audio amplifier warm up measurement.png


Conclusions
The MC427 delivers performance that is eye popping for a car audio amplifier. Distortion near -120 is insanely good, beating many home amplifier! Measured power exceeds specification. The only cost is much less efficiency.

This is really superb execution on behalf of McIntosh engineering. I don't know the merits of buying one used but the MC427 really shows how it is done.
------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

IAtaman

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Thank you for the review Amir.

Why is there a 60Hz bump in the SINAD dashboard for one of the channels?

I did not know McIntosh did car amps. And good ones as well! Without tubes! Who knew :)
I am sure quite a few people would be happy to see a high-end brand perform well for a change.
 

ROOSKIE

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Great measuring car amp.
To bad about the low efficiency (for class d)
I'd be on the fence as in my car I really value efficiency and then the price is more than many current non-McIntosh products... and honestly don't exactly need measurements to be this clean for the car.
Thanks for the recent car gear tests.
 
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amirm

amirm

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Why is there a 60Hz bump in the SINAD dashboard for one of the channels?
It us the mains powered analyzer creating a small ground loop. I couldn't get rid of it.
 

IAtaman

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Great measuring car amp.
To bad about the low efficiency (for class d)
I'd be on the fence as in my car I really value efficiency and then the price is more than many current non-McIntosh products... and honestly don't exactly need measurements to be this clean for the car.
Thanks for the recent car gear tests.
It's class AB I believe, not D. And I guess the difference in energy consumption would be minimal at normal listening levels.
 

IAtaman

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It us the mains powered analyzer creating a small ground loop. I couldn't get rid of it.
Yeah, that's what I thought too. Is it fair to say then the battery powered SINAD would be better than what the dashboard shows?
 
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amirm

amirm

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It's class AB I believe, not D. And I guess the difference in energy consumption would be minimal at normal listening levels.
It was twice as much as last amp I tested at 7 amps.
 
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amirm

amirm

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Yeah, that's what I thought too. Is it fair to say then the battery powered SINAD would be better than what the dashboard shows?
I think the noise floor is higher than that and so made no difference.
 

IAtaman

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It was twice as much as last amp I tested at 7 amps.
Sorry, I am not sure how you test car amps so I am a bit confused (maybe a good idea for a video?). When you say it draw 7 amps, I presume at 12V? So half of that would be 3.5Amps - that's 42W, or 0,056 HP difference. If you leave a window a tiny bit open by accident while you are driving on the highway, you consume more energy. Large mirrors costs more than that I think - I would not worry about it.

Out of curiosity, I asked ChatGPT. She calculated that for a typical car 10 hp is spent on overcoming aerodynamic drag while traveling at 100kmh/ 60mph, and that the side mirrors constitute to 3-6% of the aerodynamic drag of the car. So side mirrors would consume consume about 0.3 - 0.6 hp - 6 to 10 times more than the difference between a Class D and a Class AB amp. As I said, I would not worry about it :)
 
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Newman

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amirm

amirm

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Sorry, I am not sure how you test car amps so I am a bit confused (maybe a good idea for a video?). When you say it draw 7 amps, I presume at 12V? So half of that would be 3.5Amps - that's 42W, or 0,056 HP difference.
The issue is how much spare current your stock alternator has and how many of these you deploy. If listening at lower levels is should be fine.
 

DWPress

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Needs blue meters - even if I can't see them, it's a McIntosh....
 

restorer-john

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It seems the amplifier was made and sold betwen 1995 to 1997. The date codes on the Philips NE5532s pictured above (@JSmith ) are 1996, so I don't doubt the years made.

1701848327494.png


from Roger Russell's site:
1701848435850.png


So ~27 years old and still going strong.

Awesome @amirm.
 
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