Amplifiers are sometimes called amps or separates. An amp can be used when your receiver is not getting the dynamic range or power required to drive your speakers. For example, your receiver may only output 100 WPC (Watts Per Channel) and you want 250 WPC for your left and right speakers. An amplifier set between your receiver and speaker connection will be able to fix this problem, and allow you to add more dynamic range and power to your speakers.
Amplifiers are especially useful in large rooms where more power is required in order to fill the room with sound. Due to the extra power, amplifiers are also known to give a cleaner better sound than receivers . Another application for amplifiers is to amplify the zone 2 or zone 3 output from your receiver.
Note that amplifiers only amplify audio signals. They don’t process any signals and only take analog audio inputs. Therefore, a receiver or preamp will be necessary to precondition your digital and analog signals.
See the Biamping and Biwiring section for information on how to increase the Amp power output to your speakers.
Preamps are similar to receivers. They both take audio/video inputs and they both condition audio signals. The function of a preamp is to process the audio signal, allow switching between inputs, control the volume, and maintain constant output impedance. The difference between a receiver and preamp is that preamps are meant to be connected directly to amps, while receiver can connect directly to speakers. Preamps are mostly used for non–hometheater applications such as a music only system.