Cleaning a scratchy poti of the older Ernie Ball volume pedal

Posted on Leave a commentPosted in Effects, Mark Knopfler gear

The Ernie Ball volume pedals often become scratchy after a long time of usage. While you can replace the current poti model with a brand new poti, it is almost impossible to get a replacements for the older poti types. However, the older potis can be opened and cleaned which – not always but often – cures the scratching. As I did this successfully a few days ago, I took some pictures to demonstrate the procedure.

The poti was the Canadian type used in the mid 90ies but the previous Allen Bradley / Clearostat poti used before can be treated in the same way.

First, I recommend to remove the two screws that hold the black metal block which holds the poti. The string can be released from the poti easily then (you might take pictures before so that later you know how it was assembled).

With these poti types, the wires are plugged to the poti and can be removed without any soldering (again, take notes where they were, or take a picture).

 

Bend open the two mounting tabs with a screwdriver. Be careful not to bend too much as these might break. Often is is enough to open only two of the four tabs, on the side that exceeds the metal block.
Bend open the two mounting tabs with a screwdriver. Be careful not to bend too much as these might break. Often it is enough to open only two of the four tabs to remove the cover, on the side that exceeds the metal block.
Remove the cover, then put a piece of fine sanding paper between the wiper and the carbon resistor. Turn the poti several times to clean the wiper.
Remove the cover, then put a piece of fine sanding paper between the wiper and the carbon resistor. Turn the poti several times to clean the wiper.
Repeat this a few times. Note the amount of dirt removed by this procedure.
Repeat this a few times. Note the amount of dirt removed by this procedure.
Next use a pipe cleaner soaked with pure alcohol to clean the carbon resistor.
Next use a pipe cleaner soaked with pure alcohol to clean the carbon resistor.

Now the poti should be clean. Note that disassembling the wiper from the carbon resistor is not possible with these poti models so you need to clean it like this. Mount the case again, bend down the tabs to close it. An instruction how to assemble the string again can be found in this video:

Note that you can clean a modded volume pedal in the same way, just make sure to assemple all wires and the string exactly as they were before!!

Another note on this topic: I meanwhile tend to believe that the different taper on Mark Knopfler’s volume poti is not due to a different poti model but to an electronic solution possibly built into his rack. A first prototype circuit works promising, and also avoids the noise of a scratchy poti electronically. Watch out for future updates, I hope to offer something here soon.

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