TRS jack

A quarter-inch connector with three contacts, tip, ring and sleeve, used where a signal needs more than one conductor plus ground.

In guitar equipment it appears as a stereo output, an effects send and return on a single socket, a balanced line on a smaller connector, or the control connection for an expression pedal, which uses the additional contact for a variable resistance. The extra contact is why a mono cable in a TRS socket can cause problems: the ring connection may be shorted, which breaks a stereo signal but is normal for some switching arrangements.

Example: an expression pedal connected with a stereo jack uses the ring and sleeve to send a variable resistance back to the effect.

TRS jack

See also