Yamaha C-85 Noise in MC phono section

ebk231

Active Member
Hello

My c-85 has been recapped and many other parts replaced. When I started the MC section did not work at all. Now it works but there is a high level of what I will call white noise, think noisy phono amp sound. The sound will go away after about 20 mins or one side of an LP after that just a little noise at full volume, the kind of quiet background you would expect after doing a recap. When the sound is present it is equal on both channels and never happens in the MM section. I have tried different cartridges and turntables with the same result.

Any insight or direction is much appreciated.
 
Does the noise die away the same way as you have described if you dont play anything thru the phono stage?

Could be transistors going noisy the get less noisy as they warm up
 
Toady I let it idle with MC section engaged nothing playing through it and the noise did go away. Maybe I will just go ahead and replace all the transistors in the MC section and see what happens.
 
Well if you had posted in the Yamaha Section, avionic would tell you which transistors to replace. Maybe a shot of freeze spray will work to diagnose what parts heat up and work. Spray one at a time and see if the problem comes back when a transistor you just shot cools off and gets noisy.
 
Hello

My c-85 has been recapped and many other parts replaced. When I started the MC section did not work at all. Now it works but there is a high level of what I will call white noise, think noisy phono amp sound. The sound will go away after about 20 mins or one side of an LP after that just a little noise at full volume, the kind of quiet background you would expect after doing a recap. When the sound is present it is equal on both channels and never happens in the MM section. I have tried different cartridges and turntables with the same result.

Any insight or direction is much appreciated.
Is the noise present without anything connected to the MC phono jacks ?
 
Last edited:
Is the noise present without anything connected to the MC phono jacks ?

I will try that when I get home cant remember off the top of my head.

What all have you replaced in the MC headamp?

All electrolytics, the bigger transistors and the resistors right by them, the big carbon resistors were changed out for some MF's and I swapped a bunch of the other transistors from a donor unit to get the MC amp working.
 
Well if you had posted in the Yamaha Section, avionic would tell you which transistors to replace. Maybe a shot of freeze spray will work to diagnose what parts heat up and work. Spray one at a time and see if the problem comes back when a transistor you just shot cools off and gets noisy.


I knew he would find his way here :D

Just seems odd that its in both channels and goes away from both at the same time.
 
I knew he would find his way here :D

Just seems odd that its in both channels and goes away from both at the same time.
Yes, he gets out to find the other Yamaha threads on AK.

That is a diagnostic point, the both channels...seems something in common to both channels would be more likely than the 3rd transistor in the left channel, for example.
 
ust seems odd that its in both channels and goes away from both at the same time.
That points to the power supply. But its the same power supply as the equalizer(MM) and 14db flat amp.:idea:
 
Maybe one of the heat sink mounted transistors?
You could always try it. Do you own and o'scope ?



edit: I don't think those are the pass transistors for the MC pre-amp. Stand -by....
 
Onsemi's MJE15032G and MJE15033G from Mouser,Digikey or Element 14(Newark) for the pass transistors. ------> TR149 and 150.
 
You could always try it. Do you own and o'scope ?



edit: I don't think those are the pass transistors for the MC pre-amp. Stand -by....
I do own a scope but I dont really know how to use it yet. I also have DCA 55 transistor tester. I tested it without anything plugged into the phono jacks and the noise was pretty much the same. I forgot to mention I also swapped in some 4148 diodes in the MC amp and also replaced the RCA jacks. I had to replace some of those bigger transistors and resistors in the MC amp so I replaced all of them throughout the preamp. I also ran some additional grounds to the front panel, was
having some issues when I would do testing with out the top and bottom on the chassis.

0316181752.jpg 0316181749.jpg 0316181751.jpg 0316181751a.jpg 0316181751b.jpg
 
Thank You for all the help! Really cant say enough about how great that is, part #'s help me a ton! I still have the donor preamp I can try swapping those transistors
Won't hurt anything to give them a try. As long as they are still serviceable.
 
Won't hurt anything to give them a try. As long as they are still serviceable.
I swapped them around from the other preamp and it cured it at least on my initial test. Im going to get the ones you linked these are a mismatched brand anyway. Thanks for all the help!
 
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