Phone Connector (audio) - Modern Connectors

Modern Connectors

Modern phone connectors are available in three standard sizes. The original 1⁄₄ in (6.35 mm) version dates from 1878, when it was used for manual telephone exchanges, making it possibly the oldest electrical connector standard still in use. The 3.5 mm or miniature and 2.5 mm or sub-miniature sizes were originally designed as two-conductor connectors for earpieces on transistor radios. The 3.5 mm and 2.5 mm sizes are also referred to as 1⁄₈ in and 3⁄₃₂ in respectively in the United States, though those dimensions are only approximations. All three sizes are now readily available in two-conductor (unbalanced mono) and three-conductor (balanced mono or unbalanced stereo) versions.

Four- and five-conductor versions of the 3.5 mm plug are used for certain applications. A four-conductor version is often used in compact camcorders and portable media players, and sometimes also in laptop computers and smartphones, providing stereo sound plus a video signal. Proprietary interfaces using both four- and five-conductor versions exist, where the extra conductors are used to supply power for accessories. The four-conductor 3.5 mm plug is also used as a speaker-microphone connector on handheld amateur radio transceivers from Yaesu and on some mobile phones – see below for details.