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. A male connector, is mated into a female connector, 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 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:
| Abbreviation | Contacts | Typical uses | Plug appearance |
| TS | 2 | mono audio | |
| TRS | 3 | stereo audio | |
| TRS | 3 | mono audio | |
| TRS | 3 | MIDI | |
| TRRS | 4 | stereo headset with mono microphone | |
| TRRS | 4 | video with stereo audio | |
| TRRRS | 5 | stereo audio |
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 for full-sized connectors, for "mini" connectors, and only for "sub-mini" connectors. Rings are typically the same diameter as the sleeve.
Other terms
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 The Institute of Electrical and Electronics Engineers in 1975 also made a standard that was withdrawn in 1997.The intended application for a phone connector has also resulted in names such as audio jack, headphone jack, stereo plug, microphone jack, aux input,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. 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.
Historical development
The original version descends from as early as 1877 in Boston when the first telephone switchboard was installed or 1878, when an early switchboard was used for the first commercial manual telephone exchange in New Haven created by George W. Coy.Charles E. Scribner filed a patent in 1878 to facilitate switchboard operation using his spring-jack switch. In it, a conductive lever pushed by a spring is normally connected to one contact. But when a cable with a conductive plug is inserted into a hole and makes contact with that lever, the lever pivots and breaks its normal connection. The receptacle was called a jack-knife because of its resemblance to a pocket clasp-knife. This is said to be the origin of calling the receptacle a jack. Scribner filed a patent in 1880 which removes the lever and resembles the modern connector and made improvements to switchboard design in subsequent patents filed in 1882.
Henry P. Clausen filed a patent in 1901 for improved construction of the telephone switchboard-plug with today's inch TS form still used on audio equipment.
Western Electric was the manufacturing arm of the Bell System, and thus originated or refined most of the engineering designs, including the telephone jacks and plugs which were later adopted by other industries, including the US military.
By 1907, Western Electric had designed a number of models for different purposes, including:
| Code No. | Description |
| 47 | 2-conductor plugs for use with type 3, 91, 99, 102, 103, 108, and 124 jacks—used for switchboards |
| 85 | 3-conductor plugs for use with type 77 jacks—used for the operator's head telephone |
| 103 | twin 2-conductor plugs for use with type 91, and type 99 jacks—used for the operator's head telephone and chest transmitter |
| 109 | 3-conductor plugs for use with jack 92 on telephone switchboards |
| 110 | 3-conductor plug for use with jacks 49, 117, 118, 140, and 141 on switchboards |
| 112 | twin 2-conductor plug for use with jacks 91 and 99—used for the operator's head telephone and chest, with a transmitter cutout key |
| 116 | 1-conductor plug for use with cordless jack boxes |
| 126 | 3-conductor plug for use with type 132 and type 309 jacks on portable street railway sets |
By 1950, the two main plug designs were:
- WE-309, for use on high-density jack panels such as the 608A
- WE-310
- B-Gauge standard BPO316
- EIA RS-453: Dimensional, Mechanical and Electrical Characteristics Defining Phone Plugs & Jacks standard of diameter, also found in IEC 60603-11:1992 Connectors for frequencies below 3 MHz for use with printed boards – Part 11: Detail specification for concentric connectors .
Military variants
- M642/1-1
- M642/1-2
- M642/2-1
- M642/2-2
- M642/4-1
- M642/4-2
- MIL-P-642/2, also known as PJ-051.
- MIL-P-642/5A: Plug, Telephone and Accessory Screws, and MIL-DTL-642F: Plugs, Telephone, and Accessory Screws, with diameter, also known by the earlier Signal Corps PL-68 designation. These are commonly used as the microphone jack for aviation radios, and on Collins S-line and many Drake amateur radios. MIL-DTL-642F states, "This specification covers telephone plugs used in telephone, telegraph, and teletype circuits, and for connecting headsets, handsets, and microphones into communications circuits."
Miniature size
The 2.5 mm or sub-miniature sizes were similarly popularized on small portable electronics. They often appeared next to a 3.5 mm microphone jack for a remote control on-off switch on early portable tape recorders; the microphone provided with such machines had the on-off switch and used a two-pronged connector with both the 3.5 and 2.5 mm plugs. They were also used for low-voltage DC power input from wall adapters. In the latter role, they were soon replaced by coaxial DC power connectors. 2.5 mm phone jacks have also been used as headset jacks on mobile telephones.
The in and in sizes, approximately 3.5 mm and 2.5 mm respectively in mm, though those dimensions are only approximations. All sizes are now readily available in two-conductor and three-conductor versions.
Four-conductor versions of the 3.5 mm plug and jack are used for certain applications. A four-conductor version is often used in compact camcorders and portable media players, providing stereo sound and composite analog video. It is also used for a combination of stereo audio, a microphone, and controlling media playback, calls, volume and/or a virtual assistant on some laptop computers and most [|mobile phones], and some handheld amateur radio transceivers from Yaesu. Some headphone amplifiers have used it to connect balanced stereo headphones, which require two conductors per audio channel as the channels do not share a common ground.