Yamaha M-4 Slight distortion on both channels, more on right.

Be great if you had and o'scope. A noisy rectifier would be easy to spot.

Not much to that power supply. Just a bridged rectifier and a couple filter capacitors. D604(1D-4B1) and a couple 100µf@100vdc electrolytic capacitors.
 
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Ok, I can get my hands on an o'scope, but I only know the basics. Is testing the rectifier easy enough that you can direct me or should I do some research on this? Do you think that area with the sony glue could have corroded something and cause this? The glue is around the transistor right next to the big filter capacitors.
 
The glue is around the transistor right next to the big filter capacitors.
It normally is. They used the glue to fasten down the heatsink. Sometimes, very liberal amounts of glue.I don't believe that transistor is the problem. That transistor is the protect relay pass transistor.(driver transistor)
 
Are you sure the tone generator /sound card isn't causing the distortion?
 
Are you sure the tone generator /sound card isn't causing the distortion?
Yes, I used it to narrow down which component in the signal path was causing the distortion. I swapped out pre amps and power amps. With other components the tone generator is clean. Also I have used a tone generator from my phone with the same results.
 
Yes, I used it to narrow down which component in the signal path was causing the distortion. I swapped out pre amps and power amps. With other components the tone generator is clean. Also I have used a tone generator from my phone with the same results.
Great..:thumbsup:
 
Check your DC power rail voltages. Should be in the 30 VDC to 40VDC range( or whatever your Yamaha schematic says they should be.) and somewhat equal for the positive rail and negative rail.
If of by more than 3 vDC I would check the filter caps in the power supply area.
 
Finally back to this. Replaced D604 and D603. Didn't get to the caps yet. It is much better, but I still have noticed just a bit of distortion on the right channel. It's late now, I will check voltages etc. tomorrow.
 
Dave has you on the right path but just a WAG on my part. Have you tried plugging the amp into a different circuit in your house? I had a dimmer switch on a circuit years ago that would play havoc to anything audio related I ever plugged into the same circuit. I pulled the dimmer and all was well. Now back to your regular scheduled program.
 
Dave has you on the right path but just a WAG on my part. Have you tried plugging the amp into a different circuit in your house? I had a dimmer switch on a circuit years ago that would play havoc to anything audio related I ever plugged into the same circuit. I pulled the dimmer and all was well. Now back to your regular scheduled program.

Interesting. I do have several other amps, and this noise happens only to this amp and on different plugs in the house. I am going to go over all my testing equipment again tonight just to make sure it is the amp and not something else.
 
Tested sound generator and speakers on another amp (M-35) and they all work fine. Went back to the M-4 and switched between AC and DC mode (Turning amp off of course...). The distortion is much worse in AC mode, but still can find some in DC mode. That seems to be a clue. Going to check voltages etc. and see about replacing some of the caps.
 
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