The wire used in a transformer is usually solid copper magnet wire with an insulated coating, in order to electrically insulate adjacent turns in the coil from each other to ensure that current travels through the entire winding. Extra tape insulation is usually provided between winding layers in larger transformers.
Windings on both the primary and secondary coils may have taps to enable adjustment of the voltage ratio. A centre tapped transformer is often used in the output stage of an audio power amplifier in a push-pull type circuit. Tapped transformers are also used as amplifier components. Transformers can also be manufactured with multiple primary and secondary windings, to allow for multiple step-up and/or step-down ratios in the same device. A variable transformer can also be made by providing a moveable arm that sweeps along the length of the winding, making contact at any point along its length.