• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

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
D

Deleted member 48726

Guest
Should have ignored it. Won't happen in use in a car!
Also, it should not have been allowed to bring SINAD or resolution down.
Otherwise, great, thanx.

It may very well be much much worse in a car. @amirm should really up his game and weld a steel frame, connect the amp with a 5 m. cable to a battery + terminal and a 10 cm. negative to a bolt on the frame and let a gasoline (15 kV ignition transformer) engine pull a 12 V generator. There is so much more electrical noise in a car..
 

voodooless

Grand Contributor
Forum Donor
Joined
Jun 16, 2020
Messages
10,387
Likes
18,325
Location
Netherlands
If my recollection serves me right, according to one of Amir's post, I believe the threshold of hearing is around 110 SINAD? I could be wrong though.
In reality though, if SNR is high enough, the limit is probably much, much lower. I doubt that anyone can reliable double blind this amp vs Topping LA90D or Benchmark amp given that both amps stay within their power limits. SNR isn’t top notch though, so maybe with high efficiency speakers the noise might give it away.
 

Ken Tajalli

Major Contributor
Forum Donor
Joined
Sep 8, 2021
Messages
2,073
Likes
1,866
Location
London UK
It may very well be much much worse in a car. @amirm should really up his game and weld a steel frame, connect the amp with a 5 m. cable to a battery + terminal and a 10 cm. negative to a bolt on the frame and let a gasoline (15 kV ignition transformer) engine pull a 12 V generator. There is so much more electrical noise in a car..
The amp has an SMPS onboard, so it should be immune to all electrical noises through powerlines.
The 60hz blip is different.
 
Last edited:

Hart

Active Member
Joined
Jan 18, 2021
Messages
164
Likes
401
Location
Bay area
Impressive. I always wondered how good McIntosh home amplifiers are. They are certainly iconic and built like tanks. For some reason the magazines did not test them very often, not that they would not have given it a good review like everything else. I am hoping someone sends in a solid circuit McIntosh home amp for a review. Curious about Bryston, Krell as well. Carver, Sunfire and even Aragon disappointing. I had an Aragon 8008BB back in the day, was well received back then.. has (class A A/B) amplifier technology improved and everything back then was not as good?
 
Last edited:

pseudoid

Master Contributor
Forum Donor
Joined
Mar 23, 2021
Messages
5,185
Likes
3,529
Location
33.6 -117.9
I have an old (over 20+ years old I believe Sony 4 channel amp I could send. Believe I have an Alpine as well. I have a crate of amps, head units, speakers, and active crossovers left over from those days...I miss installing those systems. Cars these days are so complex with the audio system integrated w/ the backup camera, security, GPS, etc it's almost impossible to modify one. I may send the Sony in if @amirm wants to measure it. These car amps probably aren't a time drain like an AVR so maybe?
Yes, me too!
Upon reading @amirm's review, I moved both our cars out and I tore up the whole garage looking for that :mad:crate:mad:, but two hours later; I gave up the search.
I know that somewhere in the bowels of our garage, I have a few multi-channel powerAmps but I cannot even remember the brand names. Sony CDX90 is/was the head end.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
44,651
Likes
240,792
Location
Seattle Area
BTW, the owner let me know that there is a panel you remove which then lets you set the gain and filters. This would have allowed me to get good channel match.
 

pseudoid

Master Contributor
Forum Donor
Joined
Mar 23, 2021
Messages
5,185
Likes
3,529
Location
33.6 -117.9
BTW, the owner let me know that there is a panel you remove which then lets you set the gain and filters. This would have allowed me to get good channel match.
202312_MC427AdjustPanel.jpg
 

NDRQ

Active Member
Joined
Nov 24, 2018
Messages
180
Likes
248
Since McIntosh is one of those expensive audiophile brands, i expcted garbage tier performance, but this is quite good.
I always likes the outlook of their amplifiers, maybe i dont have to be afraid of their performance. :D
 

MrZoidberg

New Member
Joined
Sep 10, 2021
Messages
2
Likes
18
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.

Hi guys,

I sent this amp in to Amir. I've been refurbishing McIntosh car amps for a bit, validating my work on a QA401 analyzer, but these amps were measuring (for me) such low overall THD+N I knew I had to send it in to Amir for a spin on the mighty AP! Anyway, here's some further info about this amp:

- It was a restoration project for me. It had acid-based damage on multiple traces due to leaking electrolytics. I replaced all of the electrolytics with appropriate Nichicon capacitors (FG, ES, and UPW) you can see in the photos.
- From studying the design (and some rogue service manuals I found the web) the pre-amp stages have dedicated, highspeed non-signal path op-amps to detect and cancel noise and harmonics in the pre-amp stages, a McIntosh special I think. (Maybe the reason for the higher cross-talk?)
- The output power stage has 4 stages that I can identify - a differential stage, followed by two voltage stages, and the final current stage. It is class AB with a heavy A-bias (for a car amp). That's why it draws 7A for 5 watts output. There is no global negative feedback - the negative feedback for the output stage of each channel is only reflected back to the first differential stage in the power section.
- It does have a special protection feature called PowerGuard. Which is maybe what Amir saw in his 200Hz sweep. It activates the yellow LED. What happens is, when the onset of clipping is detected on the output of any channel, the signal in the pre-amp stage is proportionally reduced to maintain less that 2% THD and prevent clipping at the output. It looks super weird on a scope - you can increase the input, see the output grow, until the output just stops, holding a steady sine wave just before clipping. With my QA401 analyzer, I had to set my THD+N sweep stop setting to -60dB (0.1%) instead of 1%, as the amp itself would pull back the clipping, causing the analyzer to just keep increasing input level until it reached the top step of the signal to the amp.

Attached are the measurements I was able to take on this amp before sending it to Amir. It looks close but the QA401 is definitely no AP test rig :) Plus I wouldn't necessarily consider myself a professional in the measurement department like Amir :)
 

Attachments

  • PXL_20230213_032655589.jpg
    PXL_20230213_032655589.jpg
    316.1 KB · Views: 76
  • Capture.PNG
    Capture.PNG
    2.1 MB · Views: 70
  • MC427 Freqs.png
    MC427 Freqs.png
    37.6 KB · Views: 66
D

Deleted member 48726

Guest
Yes, me too!
Upon reading @amirm's review, I moved both our cars out and I tore up the whole garage looking for that :mad:crate:mad:, but two hours later; I gave up the search.
I know that somewhere in the bowels of our garage, I have a few multi-channel powerAmps but I cannot even remember the brand names. Sony CDX90 is/was the head end.

Remember these?

1702010599907.png
 
D

Deleted member 48726

Guest
Hi guys,

I sent this amp in to Amir. I've been refurbishing McIntosh car amps for a bit, validating my work on a QA401 analyzer, but these amps were measuring (for me) such low overall THD+N I knew I had to send it in to Amir for a spin on the mighty AP! Anyway, here's some further info about this amp:

- It was a restoration project for me. It had acid-based damage on multiple traces due to leaking electrolytics. I replaced all of the electrolytics with appropriate Nichicon capacitors (FG, ES, and UPW) you can see in the photos.
- From studying the design (and some rogue service manuals I found the web) the pre-amp stages have dedicated, highspeed non-signal path op-amps to detect and cancel noise and harmonics in the pre-amp stages, a McIntosh special I think. (Maybe the reason for the higher cross-talk?)
- The output power stage has 4 stages that I can identify - a differential stage, followed by two voltage stages, and the final current stage. It is class AB with a heavy A-bias (for a car amp). That's why it draws 7A for 5 watts output. There is no global negative feedback - the negative feedback for the output stage of each channel is only reflected back to the first differential stage in the power section.
- It does have a special protection feature called PowerGuard. Which is maybe what Amir saw in his 200Hz sweep. It activates the yellow LED. What happens is, when the onset of clipping is detected on the output of any channel, the signal in the pre-amp stage is proportionally reduced to maintain less that 2% THD and prevent clipping at the output. It looks super weird on a scope - you can increase the input, see the output grow, until the output just stops, holding a steady sine wave just before clipping. With my QA401 analyzer, I had to set my THD+N sweep stop setting to -60dB (0.1%) instead of 1%, as the amp itself would pull back the clipping, causing the analyzer to just keep increasing input level until it reached the top step of the signal to the amp.

Attached are the measurements I was able to take on this amp before sending it to Amir. It looks close but the QA401 is definitely no AP test rig :) Plus I wouldn't necessarily consider myself a professional in the measurement department like Amir :)
Sounds like a solid design!
 

DonR

Major Contributor
Joined
Jan 25, 2022
Messages
3,012
Likes
5,730
Location
Vancouver(ish)
Hi guys,

I sent this amp in to Amir. I've been refurbishing McIntosh car amps for a bit, validating my work on a QA401 analyzer, but these amps were measuring (for me) such low overall THD+N I knew I had to send it in to Amir for a spin on the mighty AP! Anyway, here's some further info about this amp:

- It was a restoration project for me. It had acid-based damage on multiple traces due to leaking electrolytics. I replaced all of the electrolytics with appropriate Nichicon capacitors (FG, ES, and UPW) you can see in the photos.
- From studying the design (and some rogue service manuals I found the web) the pre-amp stages have dedicated, highspeed non-signal path op-amps to detect and cancel noise and harmonics in the pre-amp stages, a McIntosh special I think. (Maybe the reason for the higher cross-talk?)
- The output power stage has 4 stages that I can identify - a differential stage, followed by two voltage stages, and the final current stage. It is class AB with a heavy A-bias (for a car amp). That's why it draws 7A for 5 watts output. There is no global negative feedback - the negative feedback for the output stage of each channel is only reflected back to the first differential stage in the power section.
- It does have a special protection feature called PowerGuard. Which is maybe what Amir saw in his 200Hz sweep. It activates the yellow LED. What happens is, when the onset of clipping is detected on the output of any channel, the signal in the pre-amp stage is proportionally reduced to maintain less that 2% THD and prevent clipping at the output. It looks super weird on a scope - you can increase the input, see the output grow, until the output just stops, holding a steady sine wave just before clipping. With my QA401 analyzer, I had to set my THD+N sweep stop setting to -60dB (0.1%) instead of 1%, as the amp itself would pull back the clipping, causing the analyzer to just keep increasing input level until it reached the top step of the signal to the amp.

Attached are the measurements I was able to take on this amp before sending it to Amir. It looks close but the QA401 is definitely no AP test rig :) Plus I wouldn't necessarily consider myself a professional in the measurement department like Amir :)
Thanks for sending it in. It's great to see some unique and high-performing audio from the past.
 

ROOSKIE

Major Contributor
Joined
Feb 27, 2020
Messages
1,936
Likes
3,525
Location
Minneapolis
I used to have Xtant and PPI back when the Art Series was still around.
Really wonder how they would measure. Gosh they would be 25 years old now
 

milosz

Addicted to Fun and Learning
Forum Donor
Joined
Mar 27, 2019
Messages
589
Likes
1,658
Location
Chicago
How about that, a McIntosh amplifier without their "Unity Coupled Autotransformer" output stage. :)
 

prerich

Senior Member
Joined
Apr 27, 2016
Messages
323
Likes
244
I for one would love to see more McIntosh stuff tested here. I do understand it is very expensive and a lot of their portfolio is out of the realm for most. However some is within reach especially in the used market and. I have been hoping to catch either a pair of MC830s or one of the Mc462 used after seeing @hardisj review on Erin's Audio Corner. I think it would be perfect for My KEF Reference 5's and a great replacement for my Yamaha M60

Pair of MC830's for sale over at The Music Room for a decent price!
 

Adaboy4z

Active Member
Joined
Jan 6, 2022
Messages
197
Likes
214
I've only seen one of these amps in an install and the guy was very protective of it. They are sought after amps for sure. If I ever run into one I would buy it and use it, at the right price of course. Keep these amp reviews coming!!
 

MrZoidberg

New Member
Joined
Sep 10, 2021
Messages
2
Likes
18
How about that, a McIntosh amplifier without their "Unity Coupled Autotransformer" output stage. :)
They did make one car amp with the autotransformers... the mighty MCC602TM. 300w x2 at 8,4, or 2 ohms
 

Attachments

  • IMG_20180130_WA0000_scaled.jpg
    IMG_20180130_WA0000_scaled.jpg
    41.3 KB · Views: 49
Top Bottom