Thoughts on Wah inductor and Scratchy pot!

[rove]

I have modified my Crybaby by changing a few resistors for more gain, etc., as well as changing the sweep cap to .022 for a bassier wah sound.  I also added an LED and true bypass (GCB95 rev E, no buffer) which required cutting a trace on the pcb.  Well my original pot was scratchy, so I picked up a 200k pot from smallbear and threw it in the mix and great sounds all around. 
Recently, however, the new pot has become scratchy after only about a month or so of moderate use.  I replaced the electrolytic capacitors and no change.
Also, the fun part, I bought a halo style inductor from ebay (dandyjob.com, as recommended by Battle of Midway) and threw it onto a section of vero with the original dunlop inductor with a switch to go between (this is probably a temporary mod to see which inductor i like better).  To my ears the halo style inductor sounded much clearer and more full range than the stock dunlop and will simply replace the original when all is said and done.  It seemed to add a bit of sparkle or extra top at toe down and maintained clarity in the heel down position despite the low sweep range I am using.  nice, a highly recommended mod.
So I thought I would post this experience in hopes of both extolling the virtues of the new inductor, and in hopes of figuring out why, with either inductor, new pot, electros, etc I still am stuck with a scratchy pot!
thanks all.

[jonathan perez]

well, the explaination can be found on geofex as to why the 500mh inductor sounds "clearer" than the 600-ish mh stock inductor.

unless RG pitches in here. 

small bear has recently had problems with the pots, but if you contact steve, he can help you out.

edit: your electro might be leaky. but small bear as indeed had problems.  (last time i post anything when i just wake up)

im glad you like your wah! although all i did was tell you information, it makes me feel a bit toasty. 

[Aharon]

I had the same problem with  an amazing sounding wha i built...........sounded great but i had a scratchy pot no matter how many times i changed it.
Finally i decided it must be DC on the pot causing it to scratch.
Changed the 2 electros in my circuit and voila...........scratch is gone,the electros were leaky.That could be your problem.
Aharon

[petemoore]

sounded great but i had a scratchy pot no matter how many times i changed it.
  tested pots that looked to a DMM to function well?
  that makes it look more like a mid-hump freq overresonance or whatever, the sweep has a hump in the middle of it that causes a 'half oscillating' distortion...sounds kind of like the pots causing it, and it was, but in a second order, tweeking the circuit is what cured the 'problem' for me.

[rove]

Thanks again for the tip on the inductor.
I replaced the electrolytics again and am having the same issue with the scratchy pot.
I am aware of the issues with the small bear pots, but I got the black top 200k which I don't believe was affected, though I suppose a bad pot isn't out of the question regardless of whether it was form the bad batch.  I have a hot potz in another wah shell sitting around so maybe I'll swap that out and see for sure...
thanks again for the ideas.

[Mark Hammer]

I still contend that high-use pots should be pretreated with this stuff: http://www.stabilant.com/

Forms a stable conductive layer that acts a bit like a lubricant.  Like a liquid solder joint for the wiper.

[Shepherd]

sounded great but i had a scratchy pot no matter how many times i changed it.
  tested pots that looked to a DMM to function well?
  that makes it look more like a mid-hump freq overresonance or whatever, the sweep has a hump in the middle of it that causes a 'half oscillating' distortion...sounds kind of like the pots causing it, and it was, but in a second order, tweeking the circuit is what cured the 'problem' for me.

Did it only "scratch" when swept quickly?  Or even in slow rotation?

[petemoore]

Remove PS.
Remove cover
Remove rack stop/rack stop screw, pull the flat gear back
clip the DMM [analog meter might be better] across a side of the pot [wiper to an outside lug], real slow like turn the pot Cw/CCw, it should move along as the DMM counts up or down fairly steady, if it jumps, go back over and watch it jump again, try meter from wiper to other side. a fault on the wafer can cause that point to 'skip' to a different resistance or even open, and can probably be seen [if looked for while turning real slow] with a meter value jump.
  I have a BT200k from SB, works great.

[boyersdad]

I've been having a similar problem with the scratchy pot. It seems to only be in one spot, near the toe.

When you rock the pedal REALLLLY slow you can't hear the scratching, and can't hear a change in level or drop out, which I assume would be there if there was a bad/dirty section on the resistive strip.

I've already replaced the electros (twice), so I'm going to measure with my AMM like Pete suggests.

Hopfully it IS just dirty, and hopfully I can clean it, and save the $16 for a replacement.

[boyersdad]

Okay, so things checked out on the meter, so I decided to take it a bit further. I desoldered the pot, and hooked it up to my audio probe. I used clip leads to the wiper from my guitar, and rocked the pot back and forth listening for the scratch. Nothing. Sounds clean and scratch free.

So it seems now that I'm back to square 1... But at least I know the pot is okay.

[boyersdad]

Update:

Well, as much as I hate to say it, after soldering the pot back in, the scratching disapeared! I tried moving and jiggering wires before, to no avail.
I don't know why it worked, but it worked. Maybe you can try this if you run out of other options!

[rove]

Measuring with a DMM shows a consistent jump/temp short at the same spot every time, thinking this points to the pot...