Scratchy Wah pot or something else?

[Focalized]

The last wah I put together, on veroboard. The pot seems to be very scratchy when moved fast, not so much when moved slow. It's right at the peak of resonance.

I only did slightly in between mods from a stock Vox Wah to the values at http://www.wah-wah.co.uk/diy.html

It's the standard 100k from Smalbear. "The Black Bear". Tried some contact cleaner, no help. The sweep is fine and the underlining wah sound is great. Listen to this clip.

https://soundcloud.com/focalized/dr0000-0033/s-W5Hqb

[GibsonGM]

Nice sounding wah, really!  )

Check that there is no DC on the pot - there should be a cap near either end to block it.  Could be an error there allowing DC to flow?  This is what I hear most in the clip, but it's hard to diagnose just from that. 

If not DC, it sounds like the pot could be faulty, so sub in a different pot and mess with it, see if there is no crackle. Should take all of 3 minutes.

The last thing I think it could be is clipping, that you have a frequency peaking at just the right place to clip, but that is not high on my list, believe me.

Let us know what you find!

[Focalized]

Thanks. Would I just measure for voltage at the pot to ground?

Hope not for a faulty pot. This one from smallbear is about 14$. I bought a couple others from there. The McCon-O-Pot and the Joe Gagan Special. The former looking much more sealed. That one and the Hotpotz give me more confidence in it not being dirty or faulty. They're all quite expensive to be mixing and matching.

I built a wah before with the one that is included with the Whipple inductor. Same circuit, pot is still smooth.

Used this layout on this one I have trouble with.

http://4.bp.blogspot.com/-ms7W3UqIPpY/T_cBKqSrK7I/AAAAAAAABsM/mYf8YYp4M6E/s1600/VoxMcCoyStrip.png

[Focalized]

Measuring voltage at the pot to ground. 0 over it all. Even while I sweep the pot if that would make a difference in test.

With the pot being dirty the thing I'm thinking about is why it's more pronounced when rocking it fast.

[joegagan]

sad to say, in my years of testing, none of the 25mm open back wah pots regardless of brand*,  rubber dust cover  , ' long life', have lasted more than a short time before going scratchy. sometimes within minutes.
try a hotpotz2 or other better quality pot to see if it goes away.

* not mentioning names, i tried them all except one- they all share the same problem. the one brand i did not test has been reported as having same characteristic by 3 reliable sources.

[joegagan]

i don't have a theory about why rocking it fast would make it more pronounced.

[Focalized]

It's such a shame pots are so sensitive in a wah.

Like I said the Hotpotz always seems like a reliable design being sealed.

I bought a bunch of broken wahs to use the cases. Repaired a Vox with bad micro-phonics, selling them off. Built one on perfboard that plays clean. This one just has the one problem.

I do have the other two pots to try plus a BYOC kit that I planned to keep once I decided what mods to externalize.

[R.G.]

i don't have a theory about why rocking it fast would make it more pronounced.

The mechanical motion is a springy wiper moving over the resistive surface. The surface is not perfectly smooth. Moving slowly lets the wiper not be bumped away from the surface. Good pots will have many parallel wiper contacts so that if there is one bad spot, the others miss it... mostly.

Anyway, faster motion makes it easier for any irregularities on the resistive surface to lose contact.

That's my theory and I'm sticking to it.   

[Focalized]

I supose i'll try cleaning it again maybe even try one of the three pots from the old wah guts I have. They're pretty old but might be perfectly fine.

[guitarkill]

sad to say, in my years of testing, none of the 25mm open back wah pots regardless of brand*,  rubber dust cover  , ' long life', have lasted more than a short time before going scratchy. sometimes within minutes.

Yes unfortunately this is true.

[Focalized]

Cleaned again with som Radioshack contact cleaner. Mostly better.

I'll probably just buy sealed ones next time.

[guitarkill]

Cleaned again with som Radioshack contact cleaner. Mostly better.

I'll probably just buy sealed ones next time.

Don't expect that to last long if the problem is indeed the pot. Sealed pots won't last any longer, the issue is the design of the pot and how thick the resistive track is. That "Pro Pot" and the Fulltone pot are both a joke - they're no better than a 1/4 watt Alpha pot in terms of reliability, they will both wear out very fast because they are not heavy duty in design. Apparently all they focused on was having a pot with a certain resistance, no thought was given to longevity. 

[Focalized]

Yeah I get the wear thing. This pot was brand new so more dust than normal must have gotten in. And it's one of the cheaper ones being sold. Still $15 though. At least a good sealed pot should keep dirt out but wears just the same.

[guitarkill]

Yeah I get the wear thing. This pot was brand new so more dust than normal must have gotten in. And it's one of the cheaper ones being sold. Still $15 though. At least a good sealed pot should keep dirt out but wears just the same.

Sealed doesn't mean much if the design isn't made for wah pedal use, it will still wear out very quickly.

Anyway, I took apart a pot in an old Schaller wah today to clean it because it was making a gritchy noise at a certain spot. Whoever had this pedal before me had put a ridiculous amount of grease on the gear and it got sticky over time and some of it worked into the pot's insides too. I found that all that grease actually hurt the pot's proper functioning because it caused the inside to stick in a certain place and that caused "pot bounce", where it messed up the electrical connection a little bit making a gritchy noise. The design of the pot itself is solid, it's made to last unlike the "Pro Pot" for example.