What are Pre-Amp outputs?

Answer 1

They are RCA type connectors on the back of your Head Unit (Radio). There are 2 connections, usually blue and white, the cord for this has the same connectors on both ends. The Pre-Amp outputs are a direct line for the Signal from your Head Unit to go directly to an Amplifier (you will see similar connections on your Amplifier as you see on the back of your Head Unit), so when you run speaker wire from your Amplifier, the speakers will play the sound (Music) your Head Unit is producing no matter if its from the CD or FM/AM tuner or AUX input like from an I-Pod.

Another Answer

A pre-amplifier, which is also known as a 'control unit', a high-fidelity unit which is separate from, but which must be used together with, a 'power amplifier'.

Pre-amplifier/power amplifier units are normally regarded as 'high end' equipment and tend to be very expensive. The pre-amplifier unit is equipped with inputs for phono, CD-player, tuner, and various other auxiliary units and (usually) provides a single pair (right- and left-channels) audio outputs for connection to the power amplifier. The pre-amplifier is the unit which provides the volume control, tone controls, filters, etc., while the power amplifier simply amplifies the output from the pre-amplifier unit. The output usually takes the form of a pair of RCA connectors, usually colour coded white and red.

Some 'home theatre' amplifiers provide a 'pre-amplifier' output, which bypasses its internal power amplifier, for the purpose of adding external power amplifiers, if desired.