I have a schematic for an audio amplifier that states that the volume potentiometer is 20KA. What does 20KA mean in the context of a potentiometer? I don't see anything else that states its total resistance.
The "A" part stands for audio taper.
- "B" would be linear taper and
- "C" is a reverse audio taper: -
Image from this website
Audio Taper Potentiometers are log taper potentiometers that are specifically designed for use in audio applications.
Audio taper potentiometers are the potentiometers that are used for volume control in audio devices. This includes headphones, headsets, computer speakers, or any volume-altering devices. The main thing differentiating audio taper potentiometers from others is that audio taper potentiometers are log tapers. Most potentiometers used are linear tapers, meaning any turn in the wiper of the potentiometer changes the resistance linearly. Audio Taper Potentiometers are log tapers, which are potentiometers that change resistance logarithmically as you turn the wiper.
This is crucial for audio applications because logarithmic change in resistance, not linear change, is what is desired. Ours ears perceive sound in a logarithmic fashion. If you were to use a linear potentiometer for volume control, increasing and decreasing sound, the volume changes would not turn out right. A linear taper's adjustment grows far too rapidly as the pot is turned up from zero. This means that the volume levels shoot up too high right when you beginning turning it up. Volume control then is very difficult. For linear tapers, the volume control is squeezed into the first 60 degrees or so of rotation, while the rest of the rotation has little effect of audio. Linear tapers are just not built to manage audio. Log tapers, though, are perfect for audio applications. Its characteristics are suitable to the way our ears receive increasing or decreasing sounds. It gradually increases sound as the wiper is turned.
Thus, audio tapers are potentiometers that are log tapers. This is the key separation from linear tapers.
Wiki says this in addition to the above: -
A logarithmic taper potentiometer is a potentiometer that has a bias built into the resistive element. Basically this means the center position of the potentiometer is not one half of the total value of the potentiometer. The resistive element is designed to follow a logarithmic taper, aka a mathematical exponent or "squared" profile. A logarithmic taper potentiometer is constructed with a resistive element that either "tapers" in from one end to the other, or is made from a material whose resistivity varies from one end to the other. This results in a device where output voltage is a logarithmic function of the slider position.
The 20K" part stands for 20 kohm i.e. the end to end resistance of the pot.
"20K" is the resistance - 20 kilo-ohms.