When talking about guitar potentiometers in guitar wiring it is important to understand the various classifications of potentiometers in order to choose the right one for your guitar wiring project. If you are rewiring a Stratocasters volume pot then you are going to use a different pot than if you were to rewire a tone pot for a Les Paul. In this instance, it would be likely that you would want to use a logarithmic 250k pot for your Strats volume control and a linear 500k pot for your Les Pauls tone control. You can break down the catagories of pots into two basic destinctions: 1) the pots value 2) the pots resistance curve. Those two destinctions are the most important to understand. Beyond that, there are several kinds of pots but they are all subject to those two classifications.
Understanding A Potentiometers Resistance Curve
The vast majority of potentiometers are either logarithmic or linear. There are other types of curves but they are so rare and speciallized that they have almost no purpose in guitar electronics so I will not talk about them in this article.
The Linear Pot
A pot with a linear resistance curve is going to have a steady, linear resistance as the potentiometers axle is turned. This means that if you have a 500k pot, turning the pot from 0 to 5 will have the same value increase as when you turn the pot from 5 to 10 (250k).
The Logarithmic Pot
The logarimthic pot, often also called and "audio pot" is design specifically for use as a volume control. The reason for this is because of the way the human ear works. If you are familiar with the decibel system then you may have noticed that the difference between 90 to 100 decibles is around ten times smaller than the difference between 100 to 110 decibels. This means that when we use choose a pot for use as an volume control, it must function like the human ear hears in order to sound smooth. In other words, if you turn the volume pot up from 0 to 5, in order for that to sound like the same amount of change as turning the pot from 5 to 10 on the volume control then it must have a much higher change in resistance as the knob is turned higher.
Understanding A Potentiometers Value
The next classification of a potentiometer is its value. Its value is its resistance (measured in Ohms) when turned all the way up. With guitars the value is almost always 250k ohms or 500k ohms. These values are used because they are appropriate in terms of the guitar circuits impedance. Generally when you have a guitar that is using single coils, the right pot to use is a 250k ohms pot because the pot when used in combination with the single coil pickups creates a good impedance match. When using a humbucker based guitar the value used for the pots should be 500k ohms to better match the higher resistance humbucker pickups. Using a 500k pot on a strat would make the pickups sound even brighter and using a 250k pot on a humbucker would make it sound muddier.