Phone connector (audio)

A phone connector is a family of cylindrically-shaped electrical connectors primarily for analog audio signals. Invented in the late 19th century for telephone switchboards, the phone connector remains in use for interfacing wired audio equipment, such as headphones, speakers, microphones, mixing consoles, and electronic musical instruments (e.g. electric guitars, keyboards, and effects units). A male connector (a plug), is mated into a female connector (a socket), though other terminology is used.

Plugs have 2 to 5 electrical contacts. The tip contact is indented with a groove. The sleeve contact is nearest the (conductive or insulated) handle. Contacts are insulated from each other by a band of non-conductive material. Between the tip and sleeve are 0 to 3 ring contacts. Since phone connectors have many uses, it is common to simply name the connector according to its number of rings:

The sleeve is usually a common ground reference voltage or return current for signals in the tip and any rings. Thus, the number of transmittable signals is less than the number of contacts.

The outside diameter of the sleeve is 6.35 millimetres (1⁄4 inch) for full-sized connectors, 3.5 mm (1⁄8 in) for "mini" connectors, and only 2.5 mm (1⁄10 in) for "sub-mini" connectors. Rings are typically the same diameter as the sleeve.

The 1902 International Library of Technology simply uses jack for the female and plug for the male connector. The 1989 Sound Reinforcement Handbook uses phone jack for the female and phone plug for the male connector. Robert McLeish, who worked at the BBC, uses jack or jack socket for the female and jack plug for the male connector in his 2005 book Radio Production. The American Society of Mechanical Engineers, as of 2007, says the more fixed electrical connector is the jack, while the less fixed connector is the plug, without regard to the gender of the connector contacts. The Institute of Electrical and Electronics Engineers in 1975 also made a standard that was withdrawn in 1997.

The intended application for a phone connector has also resulted in names such as audio jack, headphone jack, stereo plug, microphone jack, aux input, etc. Among audio engineers, the connector may often simply be called a quarter-inch to distinguish it from XLR, another frequently used audio connector. These naming variations are also used for the 3.5 mm connectors, which have been called mini-phone, mini-stereo, mini jack, etc.

RCA connectors are differently shaped, but confusingly are similarly named as phono plugs and phono jacks (or in the UK, phono sockets). 3.5 mm connectors are sometimes—counter to the connector manufacturers' nomenclature—referred to as mini phonos.

Confusion also arises because phone jack and phone plug may sometimes refer to the RJ11 and various older telephone sockets and plugs that connect wired telephones to wall outlets.