Understanding Potentiometers in Guitar Effects

Potentiometers feature in the vast majority of guitar effects circuits that’ll you’ll encounter. Poteniometers allow you to control the volume and intensity of your effect but what are they and how do they work?

What are potentiometers?

At it’s simplest a potentiometer (pot) is just a variable resistor. Like all resistors, potentiometers are measured in Ohms, usually with values between 1k and 10M. Turned fully counter clockwise the potentiometers value will be zero. As you turn the potentiometer the value will increase until you reach the maximum value.

A standard pot will usually have three lugs. In most build documentation you’ll see these lugs numbered 1, 2 and 3 (or A, B and C in some cases). The orientation depends on whether you’re viewing the pot from the top or bottom.

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How do potentiometers work?

Inside the pot there is a resistive track that connects lug 1 with lug 3. Lug 2 is connected to the ‘wiper’, by turning the shaft the wiper moves between lug 1 and 3, increasing or decreasing the resistance value as it goes. In my illustration below, the blue line connecting lugs 1 and 3 represents the resistive track while the red line from lug 2 represents the wiper.

Types of potentiometers

While pots are identified by their resistance value they are also defined by there taper. In terms of potentiometers, taper refers to the relationship between the rotation of the pot shaft (or movement of the wiper) to the change in the resistance value.

In terms of guitar effects pedal building the two types of pots you’ll come across most often are Linear and Logarithmic (also known as Audio).

The difference between the two is in the resistance rate as the wiper moves along the track. Linear pots, as the name suggests, causes the wiper to maintain a constant rate as the pot turns, and therefore a constant increase in the amount of resistance. With logarithmic pots, the wiper moves less at one end and then ramps up at the other, so a far greater increase in resistance at once end compared to the other.

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Logarithmic pots are often preferred for volume controls (particularly if you’re wiring up an actual guitar) because of the way our ears perceive volume. For our ears to perceive a halving of volume with the control at the midway point, the pot actually needs to be logarithmic. So, log pots are generally preferred for volume because signal level ramps up and down more smoothly to the human ear than it does with linear pots.

Most pots have a letter on them that identifies their taper. Depending where they are made, the identifier can vary.

Taper	String	Asia (common)	America	Europe	Vishay
Linear	LIN	B	B	A	A
Log / Audio	LOG	A	A	C	L

There is a third taper type called Reverse Logarithmic, although it is far less common. Reverse log pots are commonly labelled with a ‘C’, although those manufactured in Europe can come marked with an ‘F’.

You can buy pots with two main types of connecters, lugs and PCB mounts. If you’re using a PCB, PCB mount pots will usually result in a neater build however pots with solder lugs can be placed anywhere and connected via wire so you’re not constrained to a PCB for positioning.

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