Scratchy pot on Crybaby... with a freshly installed Dunlop HotPotz II

[nordine]

How? For the life of me i cant figure out why the wah is still doing this scratching in the middle part of the travel. Any guessings?

[anotherjim]

Scratchy pot can be due to a DC voltage present across any 2 of the lugs. Could it be that what you are plugging it into is leaking DC on its input? One end of the pot is directly wired to the output jack tip, there is no capacitor in series with it to block any DC coming in via the output.

[nordine]

yeah, tried putting an electrolytic at the end of the wah. didnt work. tried putting a whole output buffer to the wah, didnt work either.

[Transmogrifox]

First thing is to completely rule out DC.  Measure across the pot using a DMM set to "mV" range with the pedal plugged in and activated just like when you play.

If there is no DC then maybe you were the lucky individual who got a bad pot.

How hot did you solder the pot and how long did you keep the soldering iron on each lug?  It is possible to damage it from overheating.

The best thing is a good-sized chisel tip so you can get the solder melted quickly, get the wire on, and get the heat off quickly.  In contrast the worst thing is to use a soldering iron that is barely too hot and dwell on the solder lug for a long time before the solder melts.

Is the travel smooth on your wah mechanics?  This is the only other thing I can think -- is maybe a slight catch or mis-alignment could cause just enough force on the pot shaft to push the brush off the wiper.  I'm thinking along the lines of a force that pushes or pulls, or bends the shaft as opposed to jerky rotational motion.  If the travel feels smooth and you don't see anything getting bound up then it's probably ok.

You might try adding some more grease to the gear, but I am doubtful an ungreased gear would cause forces capable of vibrating the pot's internal works enough to make an audible scratching sound.

[anotherjim]

As Transmogrifox said above, measure for DC.

We are assuming the pedal isn't modified in any way and similar to the scheme I posted above.

[nordine]

soldering was proper. will measure the pot for DC. now, if i get DC, then what are the usual suspects there? already changed both .22 caps and the only thing i got was enhanced RF catching, scratchyness was still there.

great call with the mechanical stuff, will check it more closely, thanks guys!

[nordine]

solved it!

it was a busted IC IT SEEMS. changed the output buffer IC and the scratching was gone, still weird.

[anotherjim]

Wot, there's a Feckin' output buffer!?! What version is it?

[DiscoVlad]

The 535Q (and probably everything else using that board eg. Dimebag CFH, 95q, Slash signature, others) has opamp input and output buffers. Maybe it's one of those?

[nordine]

it was an old GCB-100 that i was modding, so i added the opamp output buffer.

now, theres this version too, the GCB 95F (F for Fasel), which has IC buffers for input and output: