Usually when we don’t like the way a guitar sounds, the first place we look is the pickups.
After all, there are so many aftermarket pickups to choose from. They promise to make our guitars sound brighter, warmer, louder, or replicate the sound of a particular decade. The pickups translate the string vibration into electrical signals. So that must be where the tone lives.
The pickups are the first link in the chain. For most electric guitars, the next link is the pots (or a switch that connects the pickups to the pots).
A pot (short for potentiometer) can be wired as a voltage regulator or a variable resister. Basically, it allows you to control how much of a certain type of signal stays in a circuit.
Lower pot values like 250k, allow high frequencies to more easily leak off to the ground (the inaudible part of the circuit). This can make a bright pickup sound pleasant, or it can make a dark pickup sound muddy. Higher values, like 500k, produce less high-frequency signal loss.
If your guitar doesn’t already have the ideal pots for your pickups, a new set of pots can tame a shrill guitar or bring a dull guitar to life.
Do Better Pots Improve Tone?
“Better” pots will not make your guitar sound better. However, they can make your guitar sound different. That could be an improvement if you are unhappy with your current sound.
You have probably heard someone say that 250K pots are for single coils, and 500K pots are for humbuckers. It’s actually more complicated than that.
A rule of thumb for guitar electronics is that the guitar’s signal always finds the path of least resistance to the ground (the inaudible part of the circuit).
Figure 1 shows the layout of a typical pot. There are three lugs. The middle lug (blue) connects to a the “wiper,” which is attached to the shaft. When you turn the shaft, the wiper travels along a semi-conductive material (a resistor).
Pots can be wired in several different ways. For a guitar’s volume control, the typical wiring is:
- Lug 1 – Input – The signal from the pickup goes here.
- Lug 2 – Output – The signal exits here.
- Lug 3 – Ground – This lug is soldered to the metal casing of the pot. When the volume is on zero, the full signal goes to ground and shorts the circuit. Even when the volume is on 10, some of the higher frequencies of the signal push through to ground.
The farther you turn the knob to the right, the more resistance the signal has to endure to get to the wiper and escape the pot. This gradually reduces the signal strength until the wiper reaches the ground lug and disconnects the pickup from the circuit.
Since the signal is always looking for the simplest path to ground, some of the high frequencies (i.e. treble) will try to push by the wiper, through the resistor, and exit through the ground lug.
As you may have guessed, a lower-resistance pot, like 250K, allows more high frequencies to leak through to ground. More resistance, like 500K, means less of the signal can push through.
Since the signal in an electric guitar is so weak, a 1 Meg pot is almost like a brick wall when it’s on 10. There is almost no high-frequency leakage.
Because tone controls are wired in differently than volume controls, the resistance only effects how quickly the tone rolls off. This is a more subtle difference that many players would never even notice.
Should I Change the Pots in My Guitar?
There are only two main reasons why you should consider changing the pots in your guitar:
1. Your pots are broken or problematic
If the shaft broke off or you burned out a pot while soldering new pickups, you need a new pot.
On the other hand, scratchy, noisy pots can usually be fixed with a little DeoxIT contact cleaner spray. If you’ve tried cleaning them and they still don’t work right, it might be time to replace them.
2. The guitar is too bright or too muddy
Low-output pickups like a Fender-style single coil have lots of treble. Rather than keep the tone control rolled off, a low-resistance pot can send some of those harsh frequencies straight to ground.
Most Fender guitars come with 250K pots.
High-output pickups, such as a P90 or a humbucker, tend to have less treble. If that little bit of treble leaks off though the pot, it can result in a dull or muddy tone. Darker pickups can benefit from 500K pots.
While these guidelines may help you decide between 250K or 500K, there are other options available.
Gibson guitars built from the mid-1970s though the early 2000s they used 300K volume pots. This provided a mellower tone that left many players wondering where those classic scorching Gibson tones went. Gibson used 500K pots for P90 and humbucker guitars until about 1973.
Some players prefer the darker sound of the 300K Gibsons. It’s really a matter of preference.
There is also the Fender Jazzmaster and Jaguar. Although these guitars feature bright-sounding single coil pickups, both guitars feature 1 Mega-ohm pots in the lead circuit. This provides a wide range of tones just by fiddling with the volume and tone controls.
Which Pots Should I Buy?
There are several things to consider when replacing the pots in your guitar.
- Resistance Value – 250k, 500k, 1M, etc.
- Shaft Type – Split shaft versus solid shaft.
- Shaft Length – CTS pots come in 1/4-inch (for pickguard mount), 3/8-inch (for rear-route guitars), and 3/4-inch (mostly for older Gibsons with a ground plate). (Note: The shaft length measurement refers to the threaded portion only.)
- Tolerance – How much does the true resistance of your pots matter to you? Would you care (or notice) if it was plus or minus 10 percent? 15 percent? 20 percent?
If you are replacing a broken pot, find one with the same resistance as that old one. Then make sure you get the correct shaft type and length.
Keep in mind that import guitars (those from China, Japan, Korea, and Indonesia) typically have pots with metric-sized shafts. That means upgrading to a brand like CTS or Bourns will require widening the holes in your guitar body.
Mike Eiman 