Why do new caps make my eq pots scratchy?

[honkyjonk]

I replaced the eq caps on several channels on my Yamaha PM1000,
to change the mid range values a bit (a recommended mod according to an old thread around here)
The eq is way more usable and sounds good when the knobs are still but it's now scratchy when I turn the eq knobs. And it wasn't when the old caps were in there.

I'm not sure what the originals are, but I replaced them w/ panasonic films.
The physical size of the caps is actually way smaller than the originals.
What ever the originals were, they weren't polarized, so I don't know what the deal here is. Seems like these films should work fine. Course, it could be something else that's suddenly making the pots scratchy, but . . . .

Any ideas?

 

[soundguy]

Is it dirty pot kind of scratchy or DC on the pot kind of scratchy?

Did you quickly clip in a new pot to test that it isnt the pot?

stranger things have happened...

dave

 

[jhaible]

Did you desolder / solder directly on the potentiometer pins?

Some potentiometers are very sensitive to overheating. (I think
the RadiOhm carbon pots that you can find in shops in Germany everywhere are of that ilk)

I normally better solder twice than risk a bad solder joint, *except* on pots, where I do it as fast as possible.

JH.

 

[Scodiddly]

DC from cap leakage does make pots scratchy - I'd measure for any DC offset at the pot connections. Maybe you changed from film to electrolytic?

 

[Steffen]

did you swap coupling or filtercaps?

if you changed the filtercaps to lythics you should put back some filmcaps asap ;-)

 

[clintrubber]

That's a remarkable avatar, Steffen ! :wink:
And I see it's just two pixels wide...

 

[Gus]

The cap replacement might not be the problem.

Did you clean the pots when you replaced the caps?

Sometimes cleaning pots can make them worse.

 

[DrFrankencopter]

I've made pots scratchy by the following means:
1. Cleaning....some cleaners remove the lubrication, and the pot goes scratchy:
2. Soldering...excess heat into the wiper can damage it.
3. Testing...shorting a pot with voltage on. I've had a pot glow red on me...

Best bet is to buy a new pot, sub it in and see if the scratcyness disapears. Also, check for solder bridges....

Cheers,

Kris

 

[honkyjonk]

Shiza. I might have heated those suckers up to hot.

The points are actually in very close proximity to one end of a bunch of resistors, close enough to share the same solder. So, could it be that I didn't heat up the solder on the resistor points enough. I.E. the old solder isn't blending right w/ the new?

Here's what it looks like

. . . . . > resistor legs
. . . . . >eq cap legs


. . . . . >other leg for the eq caps


The top two rows share the same solder.