The purose of an amplifier is to receive a small eletrical signal and enlarge or amplify it.In the case of a pre-amplifier the signal must be amplified enough to be accepted by a power amplifier .In the case of a power amplifier ,the signal must be enlarged much more ,enough to power a loudspeaker.Although amplifiers appear to be a mysterious "black box",the basic principles on which an ampligier operates are relatively simple .Simply stated,an amplifer receives an input signal from a sore (CD player or other source) and creates an enlarged replica of the original smaller signal.The power required to do this comes from the 110-volt wall receptacle.So,an amplifier has three basic connections:an input from the source ,an output to the speackers and a source of power from the 110-Volt wall receptacle.