Noisy WAH even after pot replacement

[stankyfish]

I bought an old Maestro Boomer2 from a friend of mine after taking it for a test drive.  The pot that was in it was original (and terribly noisy), and it was still configured to use the old discontinued Everready 9V (226?) so I knew there'd be some work, but pretty simple and fun stuff -- especially if the end result is a restored Maestro.

Anyway, I tried reconditioning the pot and it didn't go so well.  When I finally managed to get the pot disassembled, a fine black powder came spilling out all over the place.  I cleaned it as best I could, but after returning it back to it's rightful place -- while the pot was much improved in the scratchy department, it was still too bad to be used -- and now it sounds like a whole chunk of the resistive strip is missing.  I may make a go at it again sometime, but in the meantime, I took a Dunlop Hot Potz II, soldered a 33K resistor from CCW to CW to bring the effect resistance of the pot to 25K like the original pot and installed it.

Again, a huge improvement over the old pot, but there's still noise that I can't figure out.  It sounds almost like a scratchy wah pot when I sweep the pedal, but not quite.  Probably just the WAH effect acting over some noise.  When I'm not sweeping the pedal, though, it's pretty quiet.

Any ideas?  I searched the forums and read about a similar problem that was fixed by replacing a bad transistor, but I don't want to go swapping parts needlessly from this thing unless I can be pretty sure that it's going to help.  Of course a vintage pedal isn't much more than a hunk of someone else's tossed out junk if you can't use it -- no matter how cool having all the original components is.

BTW, much thanks to Paul Marossey for all of the great info on the Boomerang -- your website served as a guide and inspiration!

[Ronsonic]

Check for any DC on the pot. Very common source of noise. In fact, if it's a good pot and it's noisy when moved, that's a pretty sure thing. Look for a voltage on it, then find the bad cap that's letting the DC get through. I don't have a schematic to use to point you at a suspect. But ya gotta figure after all these years any electrolytic is due for replacement.

Ron

[Meanderthal]

 Tap the pedal while plugged in. If you hear an amplified tap, you probably have a microphonic inductor.

Try playing through the wah... if you can't hear the noise while playing, don't worry about it, it's still plenty useful. It's only when the crackle gets noticable while playing through it that a wah becomes unusable.

If it's just a sweepable hiss, consider using it as a wind effect... heh.

Oh, good advice from Ronsonic too! Never trust old aluminum electrolytics! And the DC crackle thing... didn't think of that, but, yeah, what he said...

[Paul Marossy]

My vote is for DC on the pot due to a bad 1uF cap in the circuit. Or maybe both of them.

[stankyfish]

Excellent.  I will check those things out.

Thanks!

[boyersdad]

I have a similar problem with my CB right now, but I do suspect the  pot right off as it seems to only be one spot on the pow (with the pad almost all the way to the toe). If you wah REALLLLLLY slowly, there doesn't seem to be any scratch.

The only  reason I'm even questioning that it may not be the pot, is because I physically rotated the pot a little, to change the sweep, and the crackle still happens at aprx. the same spot!

Could this also be DC on the pot, and if so, why do I only hear it on the one spot of the pot?

[Paul Marossy]

The only  reason I'm even questioning that it may not be the pot, is because I physically rotated the pot a little, to change the sweep, and the crackle still happens at aprx. the same spot!

Could this also be DC on the pot, and if so, why do I only hear it on the one spot of the pot?

What kind of pot is it? It sounds like either there's gunk on the inside, or there is a worn spot.

[boyersdad]

It's the stock Hot Pawz 100k. It's a later 95 (Rev G I think?). Is is possible to safely open and clean those pots? Is there anywhere I can get some WD-40 in there?

[jakenold]

It's the stock Hot Pawz 100k. It's a later 95 (Rev G I think?). Is is possible to safely open and clean those pots? Is there anywhere I can get some WD-40 in there?

WD40 is a lubricant. It finecoats whatever you're spraying it on with a thin layer of this teflon-like lubricant. As you might guess, this is not what we want to have on a device, with the sole purpose of conducting electricity. Get some electrical contact cleaner instead.

[Paul Marossy]

Get some electrical contact cleaner instead.

+1

[zachomega]

I have a Maestro Boomerang 2 that desperately needs a new pot as well. 

The original is a 25k pot or something like that.  I bought an Allen Bradley pot which lasted all of 2 days before freezing up in the thing and set me back around 10$ to do it.  I wasn't too happy. 

I tried cleaning the original pot and had the same experience with black powder coming out.  The pot sounds great minus the scratching...although it measures more like 30k now. 

I'll check for DC on the pot (which would be great since then I could use the original pot and delay having to buy a new one for a little longer...but I'm pretty sure it is the pot since the Allen Bradley one seemed not to exhibit any scratching while it was in there. 

Any sources for good 25-30k wah pots? 

Funny enough, mine looks like it was modified by a professional tech to take the standard 9volt instead of the funky battery. 

-Zach Omega

[boyersdad]

Get some electrical contact cleaner instead.

+1

I know some long time tecs that swear by WD-40, at least for guitar/FX pots, and it does work, but I suppose I could use contact cleaner. S'all the same to me.

But what wasn't answered was my question regarding opening these (Hot Potz) pots. Is it do-able?

[Paul Marossy]

But what wasn't answered was my question regarding opening these (Hot Potz) pots. Is it do-able?

No. Trying to do so would destroy the pot.

Any sources for good 25-30k wah pots?

Unfortunately not. I use a Hot Potz II with a 33K resistor wired in parallel with it. Sounds good to my ears.
EDIT: You can take apart the original ones and recondition them, however. Read more about it here: http://www.diyguitarist.com/DIYStompboxes/CTS-PotRebuild.htm

[zachomega]

Great link!  I've had the pot apart before, but I was not thorough enough.  I'll have that bad boy apart again in the near future! 

-Zach Omega

But what wasn't answered was my question regarding opening these (Hot Potz) pots. Is it do-able?

No. Trying to do so would destroy the pot.

Any sources for good 25-30k wah pots?

Unfortunately not. I use a Hot Potz II with a 33K resistor wired in parallel with it. Sounds good to my ears.
EDIT: You can take apart the original ones and recondition them, however. Read more about it here: http://www.diyguitarist.com/DIYStompboxes/CTS-PotRebuild.htm

[Shepherd]

Again, a huge improvement over the old pot, but there's still noise that I can't figure out.  It sounds almost like a scratchy wah pot when I sweep the pedal, but not quite.  Probably just the WAH effect acting over some noise.  When I'm not sweeping the pedal, though, it's pretty quiet.

I breadboarded a boomerang last night and was experiencing similar issues.  Preventing the pot from going all the way to ground with a 50 ohm resistor helped a bunch.  I'll have a better idea how well it worked once I solder the circuit.

Best of luck.