How an integrated amplifier works

An integrated amplifier is a preamplifier and a power amplifier in one box. The preamp half picks the source you want to hear and sets the volume. The power half takes that small signal and gives it enough current to move the speaker cones.

Most of the weight inside belongs to the power half. The transformer and the big capacitors keep current ready for loud moments, and the heatsink carries away the heat the output devices make.