Transformer

An electrical device in which two or more separate and electrically isolated coils of wire are wound around a common ferromagnetic core. Alternating Current passing through one coil creates a varying magnetic field which induces a corresponding current in the other coil(s). In audio applications transformers are often used to convey a signal without a direct electrical connection, thus providing 'galvanic isolation' between the source and destination. Winding a transformer with different numbers of turns for each coil allows the output voltage to be increased or decreased in direct proportion – a feature widely employed in mains power-supply transformers to reduce the mains voltage to something more appropriate for the circuitry, for example, or in microphone preamp step-up transformers.