Audio amplifiers work by converting small electrical signals into larger electrical signals. This is done by passing the electrical signal through a transistor. The transistor is like a gate that allows the current to pass through when the voltage is sufficient. The larger waveform is then passed to a transformer, which reduces the current and increases the voltage. This then gets passed to another transistor or directly to the speaker. The role of the transformer is to change the current into voltage because speakers need high voltage but low current to work. This process is called amplification because the output of the amplifier is larger than the input.