Audio amplifier circuits

An audio amplifier is a circuit that increases the strength of a sound signal so that it can drive a loudspeaker or feed a later stage. The signal from a source such as a microphone, pickup or media player is usually too weak to produce useful sound on its own, so one or more amplification stages raise its voltage and current. The ratio of output to input is called the gain, and a good audio amplifier increases the signal while keeping its waveform faithful, so that the reproduced sound matches the original as closely as possible.

Audio amplification is often split into two roles. A preamplifier handles the small signals from a source, providing voltage gain, input selection and sometimes tone or volume adjustment, and presenting a clean signal to the next stage. A power amplifier then supplies the larger current needed to move a loudspeaker cone, delivering the watts that produce audible sound. In more elaborate systems an electronic crossover divides the signal into frequency bands — for instance bass, midrange and treble — so that each can be amplified and sent to a driver suited to that range.

Amplifier circuits are built around transistors, operational amplifiers or, in some designs, vacuum tubes, arranged in stages that each add gain or buffering. Important design concerns include low distortion, adequate output power, a flat frequency response across the audio band, and stability. Hobbyist collections of audio amplifier circuits range from simple single-chip designs for small speakers to multi-transistor power stages, and they remain a popular entry point for learning analog electronics.

Frequently asked questions

What is the difference between a preamplifier and a power amplifier?

A preamplifier boosts and conditions weak source signals, while a power amplifier supplies the larger current needed to drive a loudspeaker.

What does gain mean?

Gain is the ratio of an amplifier's output signal to its input signal, describing how much the signal is increased.

What does a crossover do in an audio system?

It splits the signal into frequency bands so that each can be sent to a loudspeaker driver suited to that range.