A very weak signal that needs to be boosted to the same level as other signals by a preamplifier, before it can be processed by another device like a mixer, receiver or amplifier. Pre-amplifiers are designed to process and control audio signals before they are amplified and distributed in a public address system.

The primary function of a commercial PA preamplifier is to provide audio routing, mixing, and signal processing capabilities to enhance the quality and control of the audio signals in a commercial setting.