C85 preamp intermittently twice as loud in 1 channel as normal

DWJames

Active Member
Hi all,
My c85 preamp has started playing up a little today. I've had the stereo balance set off to one side as I've been working in the room and don't sit in the proper listening position. When I've centred the balance again, the channel I had turned down was then almost twice as loud as the other and sounded harsh and overdriven. After a minute or so there's a bit of crackle and it returns back down to its regular level. But it's done this twice today. Muting and tone bypass work as expected but don't affect this issue when its happening. Is this likely to be a dirty balance, volume or loudness pot or something more sinister?
I'll give a proper blast with the deoxit if I get a minute. Hopefully that sorts it.
Cheers
James
 
Thanks Pete, I've given those pots a good soaking and plenty of rotating.
I'll find out tomorrow if it's done the trick :)
 
Cheers guys. I gave it a good De-ox and the loud channel issue is gone :)

I do still seem to have a problem with one channel cutting out if it's been balanced over and super quiet for a while, but if I unplug and re-plug the RCAs to the power amp, there's a pop and it clears and is fine again. I'm also getting a slight pop when changing sources sometimes, so I'm guessing a cap or 2 need looking at.

cheers,
James
 
but if I unplug and re-plug the RCAs to the power amp, there's a pop and it clears and is fine again. I'm also getting a slight pop when changing sources sometimes, so I'm guessing a cap or 2 need looking at.
You have some bad solder connections. Usual suspects on these pre's are Regulator pass transistors,RCA jacks, and those copper buss stuffiners on the PC board.
 
You have some bad solder connections. Usual suspects on these pre's are Regulator pass transistors,RCA jacks, and those copper buss stuffiners on the PC board.
Brilliant, thanks. I'll get the Iron out :thmbsp:

What does a regulator pass transistor look like? :scratch2:
 
so I reflowed the solder on the RCA joints to the main board and on the 2 voltage regulators in the middle of the board which have the heatsinks on and got a flawless 6 hours out of it since :)

The glue that holds the voltage regulator heatsinks to the board has gone crispy and fallen out leaving the heatsinks floating a little. Should I find a couple of suitable screws and mount them to the board or should I just reglue them, and if so, with what? Silicone?
 
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