Preouts
Preouts, short for preamplifier outputs, are line-level audio outputs that carry the signal from the preamplifier section of a stereo or AV device to external equipment. They are distinct from the device's main speaker outputs, which feed power amplifiers and loudspeakers. In practice, pre-outs allow users to add external amplification, signal processors, or subwoofers without relying on the device’s built-in amps.
Most pre-out jacks are RCA connectors labeled left and right; some equipment provides dedicated subwoofer pre-outs
The level and behavior of pre-outs vary by device. On many receivers, the pre-out level tracks the
Common applications include bi-amping with a separate power amplifier, routing the signal through external processors or