A potentiometer, or pot, is a three-terminal variable resistor used to adjust volume, tone and gain on guitars, basses, amplifiers, preamps and mixing desks. Over time dust, oxidation and old lubricant build up inside, so the knob starts to crackle, the volume jumps and you get dropouts when switching from clean to overdriven sound.
In most cases the problem is a dirty track rather than wear. You can clear it yourself in half an hour if you choose the right product and do not rush to switch back on.
What you will need
Important: Only work on equipment that is fully disconnected: unplug it from the mains and remove all cables. Valve amplifiers contain capacitors that hold dangerous voltage even after switching off, so only open one if you are experienced, otherwise use a technician.
Step 1
Choose the right product
If the pot crackles because of dust, grease, flux residue or oxidation, use WD-40 Specialist Contact Cleaner. It dissolves contamination and evaporates quickly without leaving a film.
If the equipment got caught in the rain, was stored in a cold garage or used on a damp stage and condensation has formed on the board, WD-40 Multi-Use helps: it is non-conductive and drives moisture out of the contacts.
Step 2
Disconnect the power
Switch off the guitar, amp or mixer and disconnect all power and signal cables. Both products are liquids, so any voltage during treatment creates a risk of a short circuit.
Step 3
Get access to the pots
On an electric guitar or bass, removing the rear cavity cover with a screwdriver is usually enough. An amp takes longer: you often need to remove the knobs and pot nuts and slide the chassis out of the cabinet. Take photos at each stage so you can put everything back correctly.
Step 4
Treat the potentiometer
Find the gap in the pot casing near the terminals and give a short, precise burst of cleaner inside through the straw. Wipe off any excess straight away with a dry cloth so it does not run across the board.
Leave it for 5 minutes and keep turning the knob from stop to stop the whole time, so the cleaner spreads along the resistive track and flushes dirt from under the wiper.
Step 5
Let it dry and test
Wait until the product has fully evaporated, reassemble the instrument and connect it. Turn the knob slowly at low volume: the crackle and jumps should be gone.
If there is still noise, clean it once more. If that does not help either, the track is probably worn and the pot should be replaced or checked by a technician.
Tip: For the pot gap on a tightly packed circuit board,
WD-40 Smart Straw is handy: the straw puts a fine jet exactly where it is needed without spraying neighbouring components.
What next
To stop the pot crackling again, store your gear somewhere dry, in a case, and turn the knobs through their full range regularly. Preventive cleaning once a year, more often for touring equipment, saves unpleasant surprises on stage.
These uses come from the experience of WD-40 users in many countries. Always follow the instructions and warnings on the product label.
More guides in «How to use».