8. Help, my pot is scratchy

Nothing in this world is made to last forever. This is also true for pots, unfortunately, and thus there will come the day when your pot will no longer do its job to your full satisfaction. There are two fundamental causes for such faults:

Due to the movement of the wiper against the resistive element, the problem may be wear on one or both of the components. This causes contact problems mostly. The consequences may vary and depend mostly on how the pot is applied.

When stationary, i.e. not being turned, the problem will most likely not be noticeable. When changing the volume or fading, there can be "dead spots" when the shaft is turned. Scratchy or crackling sounds my occur. For such potentiometers, there is no hope - they have reached the end of their useful lives, and the only thing you can do is get a replacement.

The second source of faults is dirt. Most pots on an e-guitar are not completely enclosed. Usually, the casing has a lid where the contacts are, so that dirt can enter and then settle on the resistive element. This also leads to problems with the electric contact.

This problem can be recognised from the slight scratching noise that arises when the shaft is turned. Turning the pot knob to and fro a couple of times should suffice to alleviate the problem. In doing so, you basically move the dirt aside. If this doesn't help, you can resort to a chemical cleaning spray designed for electric contacts. They dissolve the dirt on the surface and then wash it away (a proven cleaner is CaiLube MCL Spray, for example). But most cleaners leave their own traces, so that this solution normally is only a short-term fix!

To do it right, the pot is opened and all contacts and the resistive element are cleaned with isopropyl alcohol. After this procedure a potentiometer can definitely awake to renewed life. It is definitely worth giving a try on expensive special potentiometers.

As a rule, however, interference caused by dirt goes hand in hand with increasing wear and tear. So it is safe to say that a scratchy or crackling pot will need replacing fairly soon.

I need a new pot, but which one?

Before embarking on buying a new potentiometer to replace a faulty one, make sure you know a couple of things:

• What is the ID resistance value? If there is no indication on the pot itself, there's no choice but to measure. If that is impossible, a few facts may be helpful: in e-guitars, pots with an ID resistance value of 250kOhm are used in guitars with single coils. Instruments with humbuckers (and mixed designs such as HSS and HSH) take 500kOhm. Low-Ohm pots with an ID resistance of 25kOhmare only used in combination with low-Ohm or active pickups, for example EMG products. They are therefore unsuitable for use with the standard passive electric guitars!
• Logarithmic or linear? Considering the logarithmic sensitivity of our sense of hearing, you should generally go for logarithmic potentiometers, which are standard. But there are musicians who prefer a linear pot for volume control. Basically, you can do as you please as far as this is concerned!
• What's the thread diameter? This is an important point! If you buy a Fender pot and then try to put it into a Japanese guitar, you'll sadly notice too late that the bore is often too small. Better measure it beforehand. Plastic calliper gauges area available for little money from any DIY shop, and they are definitely good enough for this purpose.
• The type of shaft: if you buy a smooth-shaft pot, you cannot, of course, stick a knob for a grooved shaft onto it. Better not find out you did that on Saturday afternoon right before the sound check.