An amplifying device is an electronic apparatus used to increase the amplitude of an electrical signal. There are several synonyms for an amplifying device which include power amplifier, signal amplifier, audio amplifier and preamplifier. A power amplifier is an amplifying device that can boost the level of an electrical signal to drive a speaker or other high-power load. A signal amplifier is used to amplify signals in a communication system. An audio amplifier is designed to amplify audio signals from a source to power speakers or headphones. A preamplifier is used to amplify weak signals from sources to a level that can be further amplified by a power amplifier.