Some amps include circuitry that allows you to boost the bass output, ranging from a knob or button that provides a set amount of boost, to a built-in parametric equalizer with many possible configurations and adjustments.
If an amp generates a large amount of heat, a cooling fan can regulate the temperature to prevent the amp from overheating.
Preamp outputs are RCA outputs that let you pass the preamp audio signal from one amp to additional amplifiers.
Useful if you're adding an amp to a factory radio, or don't have enough preamp outputs on your aftermarket receiver. Speaker Level Input Types: Harness, Speaker Terminal, RCA.