# Tech help: Dunlop GCB80 Volume pedal POT cleaning



## Dorian2 (Jun 9, 2015)

I've taken out my old early 90's Volume pedal lately to try a few things, but the pot is really scritchy. Much more annoying than scratchy... It's a closed Potentiometer as I understand is common in older pedals, maybe new ones too. So I figure I'm going to take the lid off and do a little scrubbing in some bathwater with it.

I've got the pot out already no issue at all obviously. I'm thinking about just using a small electronics or precision screw driver to release the latches. Any suggestions to mitigate unforeseen circumstances such as destroying the pot, etc...lol. Ae there certain little things like wipers that I should be aware of and maybe suggestions on how any of you guys do this? I was going to use possibly some 99% isopropyl and/or some DeOxit....but I haven't opened it up yet to really get a good take. I'll probably have it apart by the time any one responds, so I'll check back in a bit. I included photos just so you know the values, manufacturer etc. Not yet sure if it will require a new one yet.

Thanks in advance

Pete


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## mhammer (Nov 30, 2007)

Having taken many pots apart and reassembled them, I 'll say that you want to pry the tabs up only as much as is required to jiggle the back off. So the tabs will not be bent up straight, and certainly NOT bent back.

A simple dry Q-tip to wipe the resistive strip will be enough for starters. That will let you know how dirty the strip is, and possibly what the dirt is. Although, given that it is sealed, the dirt will be primarily stuff scraped off the resistive strip, rather than anything from outside the pot. This is normally a case where I recommend using Stabilant 22. If it was a much older pedal, I'd say skip it and buy a new pot, but 25 years old may not be a complete writeoff.

If you were nearby, I'd offer to loan you a vial of Stabilant, since it would only take a few sesame-seed-sized dabs to restore it. You can buy the stuff, but it would likely set you back more than the cost of a new pot.

But, as I say, for now just start out with a dry wipe of the strip. And if it seems dirty enough that it needs more, the isopropyl alcohol it is.


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## Dorian2 (Jun 9, 2015)

mhammer said:


> Having taken many pots apart and reassembled them, I 'll say that you want to pry the tabs up only as much as is required to jiggle the back off. So the tabs will not be bent up straight, and certainly NOT bent back.
> 
> A simple dry Q-tip to wipe the resistive strip will be enough for starters. That will let you know how dirty the strip is, and possibly what the dirt is. Although, given that it is sealed, the dirt will be primarily stuff scraped off the resistive strip, rather than anything from outside the pot. This is normally a case where I recommend using Stabilant 22. If it was a much older pedal, I'd say skip it and buy a new pot, but 25 years old may not be a complete writeoff.
> 
> ...


Thanks. Seems that the lid is on pretty tight so I'll see where this goes. I'm thinking I may need to be a bit patient to get it off properly.

Seems someone else on another forum has the same idea as you 



> "Pry the tabs, lift the back off and really clean the crap out of there with a cotton-tipped applicator.
> 
> Keep in mind that all pots, especially if used as much as a wah or volume pedal pot, generate their own dirt. The wiper makes contact with the resistive strip by having pressure applied, which means friction, which means a very gradual micro-erosion of resistive strip particles and micro-deformation of the surface. The analogy I like to use is that of a newly paved road that starts out velvety smooth, but over time develops little pot holes and cracks, with the rubble removed from the asphalt paving sitting atop the pavement. When you drive over it, the "noise" you experience in the ride is a consequence of adapting to both the little dips and the little bumps from the rubble. Keep in mind that the rubble sitting atop the pavement now also serves as a kind of abrasive material that your car rubs against the rest of the pavement, further damaging the surface.
> 
> ...


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## mhammer (Nov 30, 2007)

Ha!

Yeah, that wordy little SOB gets around.

I generally use my X-Acto knife to slip under the tabs and pry them up. Since the blade is thin, that allows me to pry the tabs up at a shallower angle, which isn't as hard on them. Whatever you can use to accomplish a similar action is preferred.

Chances are pretty good that once you remove that back cover, the wiper assembly will be able to lift up completely from the resistive strip, permitting unfettered access to the entire strip at once, making a decent wipe with the Q-tip easy to do. Not all pots allow for this, but in this instance, you may have that luxury.


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## Dorian2 (Jun 9, 2015)

mhammer said:


> Ha!
> 
> Yeah, that wordy little SOB gets around.
> 
> ...


I had a hell of a time trying to get the top off of that thing. Couldn't manage it last night. Tighter than a Witch's cleft ....


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## mhammer (Nov 30, 2007)

But is it as suggested, an assembly where the shaft can be pushed in to lift the whole thing off the resistive strip?


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## jb welder (Sep 14, 2010)

Mark, I think you would have to remove the gear for that, and perhaps a c-clip on the shaft.

Dorian2, the back casing is sealed tight. You may have to pry between the casing and phenolic (or whatever material that is) with a sharp knife.
If there is a glue or wax sealant, a bit of heat applied may help.


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## mhammer (Nov 30, 2007)

jb welder said:


> Mark, I think you would have to remove the gear for that, and perhaps a c-clip on the shaft.
> 
> Dorian2, the back casing is sealed tight. You may have to pry between the casing and phenolic (or whatever material that is) with a sharp knife.
> If there is a glue or wax sealant, a bit of heat applied may help.


_Complete_ removal, yes. And obviously, the gear prevents that from happening...thankfully. What I'm talking about is the ability for the wiper structure to be lifted up above the strip, high enough to see the whole strip and easily fit the Q-tip under to clean it.


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## jb welder (Sep 14, 2010)

mhammer said:


> What I'm talking about is the ability for the wiper structure to be lifted up above the strip, high enough to see the whole strip and easily fit the Q-tip under to clean it.


Ok, I see what you mean. But I think he is still trying to get the casing off. Any tips?


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## Dorian2 (Jun 9, 2015)

jb welder said:


> Mark, I think you would have to remove the gear for that, and perhaps a c-clip on the shaft.
> 
> Dorian2, the back casing is sealed tight. You may have to pry between the casing and phenolic (or whatever material that is) with a sharp knife.
> If there is a glue or wax sealant, a bit of heat applied may help.


My issue right now is the unfamiliarity of the pot and how to approach it without busting it. It does appear to have some type of seal around the lip. @mhammer , I may have misunderstood you previously. I didn't try pushing the shaft up, I'll see if that and/or the heat will work. I'm really treading lightly because I really don't feel like spending $30 on a new POT. At least the HotPotz2 anyway. I might have to if something goes awry, but I'll let you guys know what happens a little later tonight. Thanks for the help guys....appreciate it.


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## mhammer (Nov 30, 2007)

I have a similar wah pot in one of my parts bins. If you can wait for a bit, I'll try opening it up and provide more specific advice from that...not unless JB beats me to it. I trust a guy with a snake on his face....especially when he owns a discount sex shop.


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## Dorian2 (Jun 9, 2015)

Thanks @mhammer. I'll wait. No hurry for me. Just let me know when you have a chance.

Thanks

Pete


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## jb welder (Sep 14, 2010)

mhammer said:


> I have a similar wah pot in one of my parts bins. If you can wait for a bit, I'll try opening it up and provide more specific advice from that...not unless JB beats me to it. I trust a guy with a snake on his face....especially when he owns a discount sex shop.


Any luck with that pot Mark? 
And did you get those double discount coupons?


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## mhammer (Nov 30, 2007)

Thanks for reminding me. Plum forgot. Been busy refinishing the stairs and front hallway (with a wee bit of soldering inserted).

I'll check this evening.


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## Dorian2 (Jun 9, 2015)

Thanks for taking the time out of soldering your house together to check that @mhammer! I tried reminding you last night as a matter of fact, but the site was a bit wonky.


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## mhammer (Nov 30, 2007)

Okay. I poked around and peered into the bin-of-weird-pots. If anyone wanted to recreate Active Surplus, from the late 70's, this box could certainly help you do it.








There are two pots similar to the "sealed" Hotpotz, one is Allen Bradley, and the other Ohmite. Here's a nice picture someone posted of the same kind of Allen-Bradley. I know I have a Hotpotz somewhere, and seem to recall it is VERY similar to this one. Different resistance value, of course.








I took the Allen-Bradley apart by prying up the tabs. Here is a pic of what it looks like inside. Unlike what I recalled from another pot, the wafer with the wiper does not simply slip out. However, I found it very easy to wiggle a Q-tip under the wafer to clean the resistive strip. Cleaned some black gunk off it. Replacing the backj cover on the pot was easy and painless.

I hope this is relevant, helpful, and hopeful. Thanks for your patience. My apologies for tardiness.


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## Dorian2 (Jun 9, 2015)

Pretty much the same look as the Dunlop there @mhammer . I did just that but the pothead just would come off with normal jiggling. I'm not quite sure how tight they normally are, or how much excess force I can apply in one way or another to get the top off. I'll try a couple of other things and update when I can.

EDIT: The pot is an Allen Bradley BTW, but that top is on tighter 'n a Nun's .... no offense to any Nuns who might be reading this.

Anyone know where I can order a Dunlop ECB24A (470K) at a reasonable price in Canada? There are a couple of USA outfits that sell them? Or any alternatives to this Potentiometer.


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## Dorian2 (Jun 9, 2015)

Just an update. Recieved the new Hot Potz yesterday so hoping to get at it sometime after this weekend. I've got the entire pedal taken apart, so I was wondering if anyone would suggest picking up a couple of new jacks for IN/OUT? Or should I just desolder and clean?


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## Dorian2 (Jun 9, 2015)

Finally getting back to that Volume pedal guys. I would like to verify if I've got the connections correct for the basic passive volume pedal schematic using the 2 Momo jacks and the 500K HotPotz potentiometer.

- Sleeve (ground) of jack A to CCW (Pin 1) of POT.
- Tip (HOT) of jack A to Input CW (Pin3) of POT
- PIN 1 (CCW) of POT to Sleeve (Ground) of JACK B
- PIN 2 SW (WIPER) of POT to TIP (HOT) of JACK B










I also read that there might be a MOD to make the simple circuit better by adding a resistor from Wiper to ground. I'm not sure if it would work in this application though. They called it "changing the Law of the Pot" here:

Potentiometers (Beginners' Guide to Pots)

Opinions or remarks are all welcome.


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## mhammer (Nov 30, 2007)

The wiring shown looks correct (I'm assuming in is on the left and out is on the right). Depending on what sort of pickups you use, and your tonal preferences, you might want to consider compensating the pot in the way that Fender does with some of their guitars. That would consist of straddling lugs 2 and 3 with a small-value cap, like 470pf. Some folks will use a cap in series with a fixed resistor, like 120k. This retains highs as you turn down the volume. Although somefolks prefer to have the loading effects of the pot and lose the highs as they turn down. I can see the merits of each and, like I say, the merit will depend on what you like and whether you have pickups where you have to fight to retain treble, or pickups where you'd rather lose it for pedal-swell purposes.


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## Dorian2 (Jun 9, 2015)

mhammer said:


> The wiring shown looks correct (I'm assuming in is on the left and out is on the right). Depending on what sort of pickups you use, and your tonal preferences, you might want to consider compensating the pot in the way that Fender does with some of their guitars. That would consist of straddling lugs 2 and 3 with a small-value cap, like 470pf. Some folks will use a cap in series with a fixed resistor, like 120k. This retains highs as you turn down the volume. Although somefolks prefer to have the loading effects of the pot and lose the highs as they turn down. I can see the merits of each and, like I say, the merit will depend on what you like and whether you have pickups where you have to fight to retain treble, or pickups where you'd rather lose it for pedal-swell purposes.


Yup, left to right. I have the Vintage Treble Bleed on my LP bridge PUP, so I can compensate with the guitar at this point. But thanks for the tip. I'll do that upgrade if I'm not getting what I want. Also you threw a wrench in my decision now because I'm well aware of what that circuit does....I'm a big fan of it actually. It'll probably go on there at some point I'm thinking. Simple enough to do. Thanks a lot for the reference.


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## mhammer (Nov 30, 2007)

Remember that, when the guitar volume is up full, the compensation circuit in the *guitar's* volume pot does nothing. So including it with the volume pedal pot is not necessarily pointless redundancy. I'm not pressuring you to include it. I'm just noting that dismissing it with "Well, I've already GOT one of those" may be premature.

When volume pots are bypassed with larger/higher-than-suggested cap values (e.g., 1500pf), an interesting thing happens. Enough mids, as well as highs, are preserved that turning the volume down functions essentially like a bass-cut until you get down to around 5 out of 10, and after that you reduce the amplitude of pretty much everything. In past, I've used that on a bridge HB to "thin it out" and sound a little more like a SC for "chicken-pickin", without losing hum-rejection. So, that's there as a viable option. Again, how pedal and guitar volume pots are optimally wired depends on the instrument and what your tonal needs and objectives are. The thing to keep in mind is that there are lots of useful options.


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## Dorian2 (Jun 9, 2015)

mhammer said:


> Remember that, when the guitar volume is up full, the compensation circuit in the *guitar's* volume pot does nothing. So including it with the volume pedal pot is not necessarily pointless redundancy. I'm not pressuring you to include it. I'm just noting that dismissing it with "Well, I've already GOT one of those" may be premature.
> 
> When volume pots are bypassed with larger/higher-than-suggested cap values (e.g., 1500pf), an interesting thing happens. Enough mids, as well as highs, are preserved that turning the volume down functions essentially like a bass-cut until you get down to around 5 out of 10, and after that you reduce the amplitude of pretty much everything. In past, I've used that on a bridge HB to "thin it out" and sound a little more like a SC for "chicken-pickin", without losing hum-rejection. So, that's there as a viable option. Again, how pedal and guitar volume pots are optimally wired depends on the instrument and what your tonal needs and objectives are. The thing to keep in mind is that there are lots of useful options.


Oh,I haven't dismissed it at all. You bring up a couple of very good points that I neglected to consider there. I know your past with regard to guitar and pedal electronics, so it would be sumpin special stoopid to dismiss any expert advice from yourself @mhammer . After thinking about what I posted, it was negligent of me to use the one guitar I have with a treble bleed as an example, as I have a couple more without the circuit anyway. I think I'm going to order the necessary components or hopefully pick some up here in town if possible. I had actually just ordered parts from NextGen yesterday for something else, so I was in the state of mind to forget about it for now. 

Are there any specific makes/brands/types or values of Resistor and Cap you'd recommend to try a couple of options with Mark? I did go to school for this, but I haven't practiced it for so long I'm pretty much total Noobsville here.


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## Dorian2 (Jun 9, 2015)

@Lincoln ...Dave or @vadsy might have a source as well here in town if either of those fine gentlemen would like to throw in a cent or 2 as well.


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## mhammer (Nov 30, 2007)

Dorian2 said:


> Are there any specific makes/brands/types or values of Resistor and Cap you'd recommend to try a couple of options with Mark? I did go to school for this, but I haven't practiced it for so long I'm pretty much total Noobsville here.


1) Don't do it because *I* said to do it. Do it because it would work well for you in your context.

2) In the guitar-into-amp context, any old 1/4W resistor and any old ceramic disc capacitor will be perfectly fine.


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## Lincoln (Jun 2, 2008)

Dorian2 said:


> @Lincoln ...Dave or @vadsy might have a source as well here in town if either of those fine gentlemen would like to throw in a cent or 2 as well.


I think I have a couple new wah pedal pots tucked away. They look just like the picture you posted, only I'm not sure if they are 500K. They could be 1M. When I figure out where I put them for safe keeping, I'll let you know Pete


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## Dorian2 (Jun 9, 2015)

Lincoln said:


> I think I have a couple new wah pedal pots tucked away. They look just like the picture you posted, only I'm not sure if they are 500K. They could be 1M. When I figure out where I put them for safe keeping, I'll let you know Pete


I have the POT Dave. I'm wondering if there is a good place in town for the Resistors and Caps I may need for the circuit. I have some on order, but they're for the guitars. I'll check MRO as I've purchased stuff there before, but just wondering if there are any other places you may know of. I used to go to Electronic Connections but they're a bit further from me than before. I could go to Digikey if there's no good guitar/pedal part sources around.


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## vadsy (Dec 2, 2010)

Active Electronics was ok for resistors and caps but they're not around anymore, Electronic Connection may have some of the items but they are usually odd values or the quantities to purchase may be a little high


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## Dorian2 (Jun 9, 2015)

mhammer said:


> 1) Don't do it because *I* said to do it. Do it because it would work well for you in your context.
> 
> 2) In the guitar-into-amp context, any old 1/4W resistor and any old ceramic disc capacitor will be perfectly fine.


It'll certainly apply in my situation @mhammer. At least I believe it will. I'm pretty much using the volume as a Master volume for an amp that's too loud. I'd want to retain any tone leaving the guitar and pedal board without the tone loss. PArticularly the rolling of the highs. Hmmmm...."The rolling of the Highs" sounds like a good song title. I think I'll have to use it....

Anyway, since I currently do not have the required components, but have a possible good source (@Lincoln ) to get them, my question was more in the direction of what is the best combo of Tone cap and/or resistor value that might be considered better than others. Like the 470pf cap and 120k resistor you brought up. Sounds like the Kinmen Mod from what I've seen. I'm looking for a good starting mod that I can then f*** around with with with other values to get it just right. If the one you mentioned earlier works, I'll stick with that. Here's a good page I dug up on some searching that I might reference:



> *The Treble Bleed Modification List*
> 
> (listed in order of increasing capacitor value, for no other reason than I have to choose something)
> NB: *Resistors are IN PARALLEL with their capacitor unless stated otherwise*
> ...


Treble Bleed Mod Round-up – DrKevGuitar.com


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## mhammer (Nov 30, 2007)

That's a great little list. Thanks for the link!

What it clearly illustrates is that there is no particular "best" volume-pot compensation. Rather, the compensation used is a function of the pickup properties, what you stand to lose by loading them down, and what you want to keep.


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## Lincoln (Jun 2, 2008)

@Dorian2 Pete, I checked and I have all the cap & resistor values listed in the link you posted. Anything else you might need along with that stuff?


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## Dorian2 (Jun 9, 2015)

I'm also curious about the different "types" of material in the caps and resistors


Lincoln said:


> @Dorian2 Pete, I checked and I have all the cap & resistor values listed in the link you posted. Anything else you might need along with that stuff?


You're awesome Dave. You're the best!

See you tomorrow. Should I bring my 12 string?


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## Lincoln (Jun 2, 2008)

Dorian2 said:


> I'm also curious about the different "types" of material in the caps and resistors
> 
> 
> You're awesome Dave. You're the best!
> ...


hold that awesome nonsense........when I started laying them out I realized I don't have them all either. Missing the 180 pF from the PRS setup. Can you use a 200 pF for that?


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