An amplifier takes a relatively weak audio signal from a source such as a CD player, music streamer, DAC or pre-amplifier and increases its power so it can drive a pair of loudspeakers.

Inside the amplifier, the incoming audio signal is processed by electronic circuits and combined with power from the amplifier's power supply. The amplification stage increases the voltage, current or both while attempting to preserve the shape of the original audio signal.

In a typical integrated amplifier, the unit combines several functions. The pre-amplifier section selects the desired source and controls the volume, while the power amplifier section provides the electrical power required by the speakers.
The amplified signal is then sent through the speaker outputs. The loudspeaker's drivers convert this electrical signal into physical movement, producing the sound that you hear.

Amplifiers are available in different designs, including Class A, Class AB and Class D. Each uses a different approach to amplification and has its own characteristics in terms of efficiency, heat generation, size and circuit design.

When choosing an amplifier, it is important to consider its power output, speaker impedance, connectivity and compatibility with your loudspeakers. The goal is to provide enough clean power to control the speakers without unnecessary strain or distortion.