On one hand, an audio amplifier can comprise electrical components like resistors, capacitors, inductors, transistors, integrated circuits, power supplies or batteries, and vacuum tubes or power transistors. On the other hand, an audio amplifier can comprise a block of wood. It is not entirely clear how a block of wood can amplifier an audio signal. In fact, your run of the mill block of wood cannot amplify sounds. But if the block of wood has a certain shape then yes, it amplifies quite nicely.