A potentiometer consists of a three-terminal resistor and a moving contact, all of which form an adjustable voltage divider. These devices form one component of (typically) analog electronics, and their name comes from the fact that they serve as a voltage divider that varies electrical potential.
While digital potentiometers exist, they are not “true” potentiometers; instead, these devices use digital signal processing to imitate the effects of analog potentiometers.
In practice, potentiometers – which we often refer to by their shorthand, “pots” – act as controls for electronic devices because they allow the user to manipulate electronic signals easily. As a result, pots are well-suited to frequency attenuation, volume controls, or as a complement to a filter network to fine-tune other audio signal characteristics.
Use of Potentiometers
You’ll see potentiometers in use to control volume in audio devices, electric musical instruments, and live sound. Pots may control absolute output or volume by frequency as part of a graphic equalizer.
In the past, you could also find pots in analog televisions, where they controlled most display settings such as color, contrast, and display brightness. In analog computers, pots could set conditions for a calculation. While you won’t see these applications in modern electronics, it’s helpful to see how potentiometer technology has developed.
Potentiometer Types
We can categorize pots according to several variables, the most obvious of which is the form factor: slide or rotational.
Rotational vs Slide Potentiometers
- Rotational potentiometers: A rotational pot offers control using a spinning knob that adjusts the point of contact between the wiper and a nearly-circular resistor. The rotation is limited to one revolution, and the resistor is an almost-complete circle with a small notch removed.
- Slide potentiometers: You can find slide pots commonly on lighting and soundboards. These devices feature a small handle that can slide either horizontally or vertically – depending on installation – to control the point of contact between the wiper and the resistor.
Linear vs Logarithmic Potentiometers
The other important way to categorize potentiometers is whether they offer linear or logarithmic attenuation.
- Linear potentiometers: These pots use the resistance between the wiper terminal and the terminals connected to one end of the resistor to determine the signal. That resistance is proportional to the distance between them.
- Logarithmic potentiometers: Log potentiometers use an asymmetric profile for the resistor, either by physically tapering the resistor or by constructing it of multiple different materials with varying resistances. Either way, log pots attenuate according to an exponential curve.
Audio and amplifier volume controls almost always contain logarithmic potentiometers because the human ear perceives sound volume logarithmically anyway. Only with a log pot will a setting of 5 out of 10 sound half as loud as 10 out of 10.
Pros and Cons of Linear Potentiometers
-Pro: Intuitive visual feedback. By putting an array of slide pots next to each other, it’s easy to compare the levels visually. This quality is why you’ll typically see linear pots in soundboards and graphic equalizers. The visual appearance of the array of sliders translates easily into a working idea of the tonal effect created.
-Con: Vulnerability. These pots feature an open slot that runs the entire length of the slider, making them relatively easy to contaminate, harder to keep clean, and often shorter-lived as a result.
Pros and Cons of Rotational Potentiometers
-Pro: Space-saving. These pots rotate in place, which may make them better suited to small applications or devices.
-Pro: Easy to seal. These pots seal well for two reasons: the knob naturally forms a sort of cap and the only point of entry for contamination is the small space between the knob and the housing in which it turns
-Con: Hard to read. These devices offer little visual indication as to their positioning, making it difficult to read or compare them. Rotational pots may have a small indicator mark, but that may not be very intuitive for comparing or reading absolute levels.
Potentiometers are used extensively in audio devices, especially for electric musical instruments and live sound, to control volume, whether absolute output or volume by frequency as part of a graphic equalizer.
Conclusion
Both linear and rotational potentiometers are common in a variety of applications, but we see them most frequently in audio signal processing. They allow the user to manually adjust volume and other sound properties by adjusting the position of contact between a wiper and a resistor, with the signal varying in proportion to the point of contact. Each configuration type offers distinct advantages and disadvantages that make them appropriate to different applications.