Modest power audio amplifiers for driving small speakers or other light loads can be constructed in a number of ways. The first choice is usually an integrated circuit designed for the purpose, which is so-called audio amplifier IC. Discrete designs can also be built with readily available transistors or op-amps and many designs are featured in manufacturers' application notes. Older designs employed audio interstage and output transformers but the cost and size of these parts has made them all but disappear. As a general rule, transformerless low power speaker projects will work better with 4.5 or 6 volt battery packs of AA, C, or even D cells than 9 volt rectangular.

       One simple type of audio amplifier can be constructed using an integrated circuit called an operational amplifier. An operational amplifier, the audio amplifier IC (also known as an "op-amp") serves as the active component in the audio amplifier circuit. In some cases, we can use an integrated circuit with 10 transistors to amplify much better with much less power drain on the batteries than our simple amplifier.

       Audio amplifiers are used to amplify sound waves that have been converted into electrical signals. It must amplify the input signal without introducing signal distortion. Important applications of audio amplifier include public address systems, theatrical and concert sound reinforcement, and domestic sound systems. The sound card in a personal computer contains several audio amplifiers (depending on number of channels), as does every stereo or home-theatre system. Instrument amplifiers include guitar amplifiers.