is there a way to "debounce" a pot?

[pinkjimiphoton]

hey fam
workin on a 70's fender fuzz wah, the big aluminum brick one
its gotta dual pot for the wah/vol, b10k for wah, b1m for volume, 2 watt.
the treadle has a bit of looseness to it which is part of the issue..
scratchy... sorta. but not typical wah scratchy... i opened both sides of the pots, just enough to squirt some caig in a couple times to flush clean lube and deox the connections inside. instant huge improvement..

until ya turn the damn fuzz on.

then it gets kinda scratchy... but here's the thing, right? the volume is silky and silent thru the whole run. the wah, by itself, sounds great for wahing...
BUT
when ya try to sweep the pedal slowly, it gets "scratchy" but not like a wah usually does, it sounds almost more like a switch that needs debouncing, like a "jitter" to the sweep.

its more of a SVF wah than the usual crybaby deal tonally close to the japanese shin ei stuff....

if the fuzz is on, and you're playing, and wahing normally, there's the tiniest bit of scratch in the beginning of the sweep, but again, its more of a warble than a scratch sound. its driving me batshit.

i have replaced the electros, checked the coupling caps for dc leakage, which i'd assumed may be the issue with it, but i think it may be just the way the SVF wah implementation responds to the sweep.... if ya go slow, it warbles and kinda has to "catch up".

or maybe it's an idiosyncracy of this kind of filter?

here's the unit:







this is the purported schematic, tho there's no diode clipper on mine, but the rest seems right





any ideas? or am i being overly anal about it and should just ignore it?

or is it the wiper "bouncing" on the track? maybe i should try literally flushing it with some cheaper contact cleaner sans lube to clean it out better then caig again?

open to ideas!

thanks guys

[Ripthorn]

Fascinating. I'm wondering if how the fuzz is implemented is actually introducing artifacts on the wah or vice versa by way of messing work transistor bias or something else. Sorry I'm not more help.

[puretube]

If mechanical cleaning of the wah-pots carbontrack & wiper (!) won`t help enough, you could try if it evens out a bit, by hooking up 2 resistors (100k-330k) from the outer lugs (1, 3) to the wiper (2) of the wah-pot (R19).

[R.G.]

It's likely that you're getting DC across the pot when the fuzz switched in. Check the output cap for the fuzz, maybe other caps as well. Happens when the wiper contact goes intermittent/high resistance on older pots.

[puretube]

No diode-clippers on yours?
What`s fuzzing, then?
Maybe a previous owner took the diodes out, and now the output from pin7 of the opamp appears unattenuated across the Fuzz-Vol pot, overriding everything?

[pinkjimiphoton]

It's likely that you're getting DC across the pot when the fuzz switched in. Check the output cap for the fuzz, maybe other caps as well. Happens when the wiper contact goes intermittent/high resistance on older pots.

that's what i was thinking, too RG.... but i replaced the output cap for the fuzz with a brand new 10uF yesterday, absolutely zero effect on this weirdness!

i'm beginning to wonder if its the way they implemented the filter, and if that's why they ultimately discontinued this stuff. i mean, back in the 70's when everybody was nose in the....errr... bag... and bonged out of their minds seeking 290% distortion nobody probably noticed.

here's what's bugging me... it would seem if it were the wiper contact going intermittent it should happen on faster sweeps, no? cuz a fast sweep it doesn't seem to happen. the slower ya go, the worse!

could it be dc building up from maybe static inside the pot as its being turned?

it sounds like changing the gain on a SHO boost... the crackle ok sound.

perhaps its an idiosyncracy of that chip, or it's implementation as a filter?

tony pepers is building me a pair of the dual pots and sending them, but i'm beginning to suspect its a weirdness of the circuit, and not a weirdness of the pot...

thanks RG

[pinkjimiphoton]

If mechanical cleaning of the wah-pots carbontrack & wiper (!) won`t help enough, you could try if it evens out a bit, by hooking up 2 resistors (100k-330k) from the outer lugs (1, 3) to the wiper (2) of the wah-pot (R19).

good call bro, thank you. i was thinking of doing that.

i was looking at a dual 1meg replacement pot, thinking i could add parallel tapering resistors to make one side "seem like" 10k but was concerned it may be an unuseable taper for the wah.

its a REALLY weird sounding wah... more akin to say, a korg mr multi filter sound than a traditional wah

[pinkjimiphoton]

Fascinating. I'm wondering if how the fuzz is implemented is actually introducing artifacts on the wah or vice versa by way of messing work transistor bias or something else. Sorry I'm not more help.

no bro, i am thinking the same thing. its a really weird way it works, and it does sound like a bias change,
like i said to rg, almost identical to the sound the "crackle ok" knob makes on a super hard on overdrive

but that's WITH the fuzz... without it, it's more like a warble in the filter sweep
which makes me suspect its just a weirdness with this kind of chip.

the 10u cap on the output of the fuzz should block any dc from ever hitting the pot. maybe the output cap for the wah?

[pinkjimiphoton]

No diode-clippers on yours?
What`s fuzzing, then?
Maybe a previous owner took the diodes out, and now the output from pin7 of the opamp appears unattenuated across the Fuzz-Vol pot, overriding everything?

i will take a peek again, but if ya look at the gut shot i posted, nope, not a diode in sight.

it was likely that this was earlier than the schematic, which is from 73, this style i think started a year or two earlier than that, maybe even more.

i think its just plain opamp fuzz. i personally LIKE the sound of an overdriven opamp without any diode clipping.

[anotherjim]

I'd try Puretubes' resistors. I think the idea is that if there's a dead spot in the pot track, it will jump to the fixed resistor midway setting rather than extremes or go open circuit. Those pots look like some I got from an old o'scope. Code 311 Clarostat? You're unlikely to find that resistance combo and most doubles are dual concentric.

I assume you've chop-sticked the board? Especially the film and ceramic caps.

It wouldn't surprise me if that opamp chip was an RCA branded MC1458 in a tin can.

[puretube]

There`s very probable no DC reaching the wah-pot, since it`s hooked up between 2 (3) unsuspectable non-electrolytic filtercaps (C11, C12, C13), with the wiper going to ground (very probable intermittent? - therefore my proposed resistors).
Jimi: simply disconnect the 3 wires to the wahpot, and hook up an unused/new 10k pot or trimpot to those 3 wires for testing the sweep manually, while a buddy of yours plays the guitar ...
Then you`ll hear if the warble`s still there.
If it`s still there, it`s not the pot`s fault - and we`ll keep searching!
(And: yes - the filter-topology is a little strange for "wah" - looks not too vowelly ...).

[pinkjimiphoton]

it does sound more like a filter in an analog synth than vowelly,  for sure... will try to sub in a pot and report back

[pinkjimiphoton]

subbed in a brand new b10k

took me 10 minutes to figure out why the wah part of the treadle wasn't working

no change. gotta be a weirdness of the circuit i guess.

caig deoxit may have worked, significantly les noise today than two days ago when i asked about this.
weird!!!!

[puretube]

Well, in this case it could in deed be a leaky C11 or C13? (letting some DC through)

[amptramp]

You could always try your luck with a wirewound pot.  They don't have some of the failure modes of a carbon pot.  There used to be a series of pots where you could mix and match one pot to another so you could have a wirewound pot ganged to a carbon pot with any taper, shaft length or style you wanted.

[Rob Strand]

Well, in this case it could in deed be a leaky C11 or C13? (letting some DC through)

It wouldn't hurt to try adding a 1uF poly cap  between pot pin 2 and ground, instead of just connecting pin 2 to ground.

If mechanical cleaning of the wah-pots carbontrack & wiper (!) won`t help enough, you could try if it evens out a bit, by hooking up 2 resistors (100k-330k) from the outer lugs (1, 3) to the wiper (2) of the wah-pot (R19).

Another trick is to add a 1M resistor between pin 2 and 3, and/or pin 2 and pin 1.
[Sorry, I read over the thread puretube already mentioned this one.]

Yet another idea would be to wire the pot back to the join of C4 and C5 instead of ground (via added 1uF cap on pot pin to 2).

These are all last gasp attempts to fend off crackly pots.

Edited

[puretube]

Coming back to the "missing diodes". According to the schemo (WITH diodes), the output of the Fuzz would be ~ 0.7V max across the Fuzz-Vol pot. If these diodes are omitted (still assuming we`re talking about the provided schemo), the full output-swing of the lower opamp`s pin7 (probably close to 9V!) will be across the Fuzz-Vol pot. - While this might give a "nice" overdriven opamp-fuzz sound in itself, this is much too much input-voltage for the wah-section, which, when the Fuzz is switched OFF, normally gets it (low-level) input directly from the guitar.
In such an overdriven situation, that filter operates beyond all specifications and acts strange, with the signal causing spikes bouncing against the supply-rails. (And sounding "flatter").
So it would be interesting to observe the overall-volume differences of the pedal (in the "now" state), with Fuzz on/off, Fuzz-Vol up/down, Signal-Mix up/down (all while the overall-Vol and the Wah-Vol pots rest in a middle-position. (Without sweeping the Wah, which otherwise also would change the overall-Vol).
If there`s a crazy level-difference between Fuzz On/Off, that`s not typical Fender-style ...
Ya see: I`m still in search of the lost diodes ...
(you could alligatorclip or solder 2 diodes across the Fuzz-Vol pot`s outer lugs and test the situation).

[antonis]

you could alligatorclip or solder 2 diodes across the Fuzz-Vol pot`s outer lugs and test the situation.

Which is the first thing supposed to do..

[puretube]

you could alligatorclip or solder 2 diodes across the Fuzz-Vol pot`s outer lugs and test the situation.

Which is the first thing supposed to do..

Problem is: we`re not sure if the schemo is truly the right one for Jimi`s pedal.
We don`t know for sure if there had been diodes in his pedal before.
(The PCB-pic doesn`t show if something is missing).

[pinkjimiphoton]

Well, in this case it could in deed be a leaky C11 or C13? (letting some DC through)

on my analog meter at the lowest range, i'm showing no leakage at all, and its a brand new output cap i just put in.