What is a Guitar Pot and how does it work?
Guitar pots to many beginning guitar builders and modifiers can be somewhat confusing. What type of pot do you need for a volume knob? What is the difference between a 500K and a 250K pot? There are countless questions that beginners have. In this article, I hope to give you a basic understanding of how guitar pots work and information to help you decide what pot to use on your next guitar project.
First we should take a look at what potentiometers are before we talk about guitar pots specifically. Pots are technically electro-magnetic transducers. What is that supposed to mean? Well, basically a pot is something that controls the resistance or flow of electricity. Potentiometers are designed to change or stop the flow of electricity when the dial or knob is turned. Pots, in and of themselves, are pretty simple.
The inside of a guitar pot looks a lot like a record player. Only instead of having a needle and a record, a pot has a wiper and a resistor plate. The wiper slides back and forth across the resistor plate as you turn the knob. The wiper is also wired to one end of the plate. As the wiper moves farther away from the wired end of the plate, the resistance increases because of the increased distance that the electricity has to travel. When the knob is turn the other way, the wiper gets closer to the end plate and decreases the resistance. That is essentially how you control the volume and tone or your guitar.
I get asked all the time what is the difference between a 250K pot and a 500K pot. How do these pots affect guitar tone? Well, either of these pots can be used with all passive pickups. So if you are worried about compatibility with your guitar, there isn't a problem. The real difference between these guitar pots is the resistance levels. That is what K represents. Normally higher value pots create a brighter tone with your guitar. The reason for this is that the higher value pots don't allow treble or higher frequencies to be diverted to the ground wires as easily as lower value pots do. Thus, the higher frequencies come through in the pickups. Lower value pots, on the other hand, tend to bleed higher frequencies to the ground only allowing the lower frequencies to pass through the pickups. That is why 250K pots tend to make guitars sound warmer with an emphasized mid-range.
Keep in mind that the pots work with the pickups to create the sound of the guitar. Humbucker pickups usually produce warmer sounds than single coil pickups. That is why Les Paul guitars are usually wired with 500K pots. These pots help retain some of the high frequencies lost by the double pickups. The opposite is true about Stratocasters. Usually the Strats single pickups are wired with 250K pots to try to keep some of the warmer tones. Capacitors can also be wired into the pot configuration to modify the standard sound. For instance, with the right capacitor a 500K pot could be "turned into" a 250K pot. Now obviously there are exceptions to the rules. You will find Les Pauls with 250K pots and Fenders with 500K pots, but the principles are the same.
Guitar pots also come in even lower values like 25K and 50K. These pots are usually used for active pickups.
Values can also be affected by the total pot configuration. For instance all else being equal, a 500K/500K volume and tone set up in a Les Paul is equal to a 250K-volume set up in a Fender. The two connected 500K pots effectively turn into one 250K pot as far as resistance goes.
Linear vs. Audio Pots
You may have hear the terms audio and linear pots before, but what are they and how do they affect your tone. In all reality if both pots are of equal value, your tone will not be affected. The terms audio and linear refer to the taper of the pot not its resistance. Taper is basically how far you have to turn the knob before it changes the sound. Linear pots are exactly what you would expect. When the knob is turned to 0 the pot is at 0%, at 5 it's 50%, and at 10 the pot is 100%. It is a linear pattern. Each notch on the dial gives you an equal interval of change. This concept sounds great except for the fact that the human ear does not actually hear this way. The human ear hears in exponential changes. Think about the volume on your car stereo. For some reason 1 to 20 is not quite as big of a jump as 20 to 40. That's because we hear in an exponential logarithmic pattern. That is where audio pots come into play. Audio pots take this same exponential idea and incorporate it into a tone or volume control. Meaning, when an audio pot is turn to 0 it will be at 0%, at 5 it's maybe 25-30%, and at 10 its 100%. Notice that both linear and audio pots are the same at the 0 and 10 positions. It's just the middle that differentiates the two. Audio pots are usually marked with an A or Aud where as linear pots are usually marked with a B or Lin.
Some manufacturers use different combinations of audio and linear pots to get their desired sound and control. Gibson mainly uses linear pots for both volume and tones controls. Fender, on the other hand, mainly uses audio pots for both. Some guitar companies even mix the two kinds of pots for tone and volume controls. If you are building a guitar, I would suggest using an audio pot for your volumes and linear pots for your tone.
If you are really interested in wiring, pots, and custom setups, I suggest you check out my guitar wiring books page. There are a bunch of great books that will help you get started in your wiring projects.