An audio amplifier is an electronic device that boosts the amplitude of an audio signal for clearer and louder output. It typically has low-level inputs, such as a microphone or audio source, and outputs to speakers or headphones. The amplifier has two main stages: the pre-amplifier, which amplifies the low-level audio signal, and the power amplifier, which amplifies the signal to a level that can drive speakers. It also has tone controls and volume knobs to adjust the characteristics of the sound. Amplifiers come in different types and sizes, from small portable ones to large ones used in concerts and sound systems.