Known Factory wiring fault in SOME McIntosh MC611 monobloc amps
 

I own a pair of McIntosh MC611 monobloc amplifiers that I purchased new over a year ago.
Since that time I have sensed that something was wrong and I have been continually trying to track-down an imbalance in my system. I wasted many hours, labour and equipment-switching to diagnose the problem.
Only recently, with the help of the dealer and a technician did I find out what the problem was. In fact it is two problems:
1)
There was a mistake made at the factory, in which plugs from the input board (J8 & J9) were reversed, resulting in one channel being out-of-phase! (improper imaging/no centre image)
2)
The Single-ended/Balanced switch on the back panel does not function properly. Corrosion from the circuit board coating chemical on that switch causes intermittent problems with the signal and a lack of proper power output of the amp, resulting in a volume imbalance. (which also ruins imaging)

I wasted a lot of time and trouble getting this problem diagnosed, but the McIntosh factory is not interested in making this in a general recall.

So, let's call this a 'Public Service Announcement'. I would not wish for anyone else to go through this trouble, expense and aggravation. I have been told that there is a (secret) Service Advisory regarding this problem, so there must be more of you out there with the same trouble.

However, you will not see any information about it on the McIntosh website! Let it also be known that it will not get detected on a test bench. See test meter readout. Also switching polarity at the speaker will bring out the problem but will also introduce harmonics – due to the nature of the circuitry.

If there are more of you out there, be advised….and I think we should be entitled to some compensation from the manufacturer.

Known Factory wiring fault in SOME McIntosh MC611 monobloc amps
 

Well that would be frustrating to say the least. Good of you to post this!

Thank you; I will make this a Sticky Post for now.

Thank you.

Let also be known that if someone gets BOTH MC611's that are wired wrong, it would be very difficult to tell - except the harmonics in the SQ and poor bass.

Any idea if McIntosh has corrected this on more recent production? My 611's are new and I have had them for about three months. Not sure when they were actually built.

McIntosh should (I assume and you know where that can lead) be able to identify which serial number amps going forward are corrected. One future upgrade I would consider is upgrading my 601 to 611 and knowing that would be helpful.

Great post and root cause problem solving Banter. Thanks.

Looking back when I bought my 611's, the dealer got them new from McIntosh so they were recent production. This was in January of this year. I will reach out and try to find out something from my dealer. I do not seem to hear that there is any issue with my pair.
FWIW

Yikes. That’s disturbing. Thanks for the heads up.

Thank you all for your kind words. I would like to emphasize here that the McIntosh SS amps are some of the finest out there. If you have one - any model, you should have a huge sound stage and pinpoint imaging. You probably have got used to the sound quality, so invite a friend for a listen. The voices should be crystal clear with pinpoint imaging. If not, after eliminating speaker placement investigate the problems I have highlighted. They are not difficult to resolve.

If it helps, remove the preamp from the chain. Hook up a CD player with variable output direct to you amp.

Also to those that think the new production would not have this problem. Here is my understanding. Both cable assemblies for the negative and positive signal is same part number. The plugs are not keyed, color coded or labeled, So very easy to get them mixed up during assembly.

As to the Balance/Unbalance issue, this could be in any model.

I'll bet the input mode switch (S1) is not a sealed switch and the contamination occurred during the soldering process, be it by hand or wave soldering. Flux residue is the most likely cause. Seen this many times.

Too bad you had these problems, hope you have smooth sailing now on.