A power amplifier (PA) converts a low-power signal to a higher power one. Two common examples are audio amplifiers, used to drive loudspeakers and headphones, and RF power amplifiers, such as those used in the final stage of a transmitter. An audio power amplifier is an acnic amplifier that amplifies low-power acnic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspeakers or headphones. The amplifier principle is to generate an output signal that is a replica of the input signal with an increased higher magnitude. Note: Amplifiers strengthen or boost the weak signal without changing any input or information. Negative feedback is used in amplifiers.

