Jack Connectors: jack plug; jack socket

Jack or phone connectors have been in use for many years and versions including the basic connector as well as TRS and TRRS are used in many areas today.

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The jack plug and socket are a very common form of connector. They may also be referred to as the phone plug, audio jack or phone connector.

The jack, phone, or telephone connector has provided reliable service for many years, and is currently widely used in audio applications.

Initially the standard was for a quarter inch diameter, which is known as the standard jack, but miniature and sub miniature versions are also available.

The jack or phone connector is chiefly used for guitar, microphone and PA style applications, and has been widely used for headphones, although when Apple decided to discontinue its use on their phones, this tended to indicate their use would decline in this area.

 TRRS jack plug
A 3.5 mm jack plug
TRRS - Tip Ring Ring Sleeve

Jack plug & socket history

The jack connector is one of the oldest forms of connector that are still in use. The classic quarter inch jack is believed to date back to 1877 when the first telephone switchboard was installed. This was located in Boston, USA.

However the development can be traced to an earlier patent of 1874 by C.E. Scribner for what he termed a jack-knife connector. This gave rise to the term jack.

The jack connector was developed to be used in the manually operated telephone exchanges of the nineteenth century. Operators would have banks of jack sockets on a panel, and operators would make the connections by plugging a jack plug in a lead into the required jack socket.

 A switchboard from 1882 using jack connectors
A telephone switchboard from 1882 using jack connectors

Although this might seem archaic today, the telecommunications was in its infancy, and electronics as we know it today did not exist. Even the thermionic valve or vacuum tube which was probably the first electronic device was still a few decades away.

What is a Jack connector

The jack plug has a single cylindrical barrel, with a grooved tip to provide retention in the socket. Rather than having multiple pins for different contacts, the jack connector is unusual in that it uses different sections of the cylinder insulated from one another to provide the different contacts.

The original jack connectors only had two contacts and hence two rings, but later versions had, three, four and even five rings.

There are a number of standard sizes for jack connectors in use these days:

  • 1/4" jack (6.35 mm) or standard jack:   This was the first type of jack used and it is still widely used for applications including guitar and microphone audio leads - these are typically only the two contact varieties.
    Stereo jack plug jack plug
    A stereo quarter inch jack plug
    High quality audio headphones also use quarter in jack connectors, and as they are required to carry stereo, the three contact versions are normally used.
  • 3.5mm also known as the miniature jack:   The miniature jack is widely used for smaller headphones and earpiece sets used with mobile music players and mobile phones.
  • 2.5mm also known as the sub-miniature jack:   The sub-miniature jack connector is less widely used than its miniature counterpart, but nevertheless finds many uses in equipment where size is of the essence.

Basic two line jack connections

The most basic of the jack connectors uses just two connections: the tip and the sleeve.

This type of jack is often used for microphones, guitars and for many other applications. Probably the most widely used format in this version is the quarter inch jack, as for many audio applications, the connector needs to be relatively robust.

 Basic two line jack / phone connector pin configuration
Basic two line jack / phone connector pin configuration

Basic Two Line Jack Phone Connector Connections
Pin Function
1 Ground
2 Signal

TRS jack connections

The letters TRS are commonly seen when describing some jack / phone connectors. The letters TRS stand for Tip, Ring, Sleeve and they apply to jack connectors with three connections.

The connections that are normally used for TRS jack connectors are given in the table below. By adopting this convention it is possible to plug almost any item using one of these connectors in to a relevant item of equipment and it will work.

 TRS jack / phone connector pin configuration
TRS jack / phone connector pin configuration

Standard Jack Phone Connector Connections
Pin Unbalanced Balanced Stereo
Tip Signal Signal +
i.e. 'hot' signal
Ring Not present Signal -
i.e. negative phase
Sleeve Ground / return Ground /shield Ground / shield

TRRS jack connectors

As indicated by the name, the TRRS jack connector has a total of four lines that can be connected using the Tip, first Ring, second Ring, and the Sleeve.

This configuration of jack connector is widely used with 3.5mm jack connectors for headphone and microphone connections for mobile phones, although now that Apple has gone away from using them, they are starting to be used less.

There has been a variety of different standards for TRRS jack or phone connectors:

  • OMTP:   This standards for Open Mobile Terminal Platform. It was created by mobile network operators to define various standards for mobile phones and other mobile devices. During its lifetime, the OMTP included manufacturers such as Huawei, LG Electronics, Motorola, Nokia, Samsung and Sony Ericsson, with Nokia as a leading light.
     TRRS jack / phone connector pin configuration
    TRRS jack / phone connector pin configuration

    OMTP TRRS Jack Phone Connector Connections
    Pin Function
    1 Ground
    2 Microphone
    3 Audio right (earpiece)
    4 Audio left (earpiece)
    The OMTP TRRS jack pin configuration is used with: Old Nokia devices, old Samsung, old Sony Ericsson including 2010 and 2011 Xperias, Sony (PlayStation Vita), etc.
  • CTIA & AJH:   CTIA is the Cellular Telecommunications and Internet Association and AJH stands for American Headset Jack. CTIA replaced the AJH although the two connection standards are the same. Nowadays CTIA is the adopted standard which is used across most mobile phone and similar devices.

    Apple uses a CTIA/AHJ connector arrangement, but uses a its own proprietary microphone and volume control signalling system. However, simple commands like Play/Pause and Skip however should work across modern mobile devices.
     TRRS jack / phone connector pin configuration
    TRRS jack / phone connector pin configuration

    CTIA TRRS Jack Phone Connector Connections
    Pin Function
    1 Microphone
    2 Ground
    3 Audio right (earpiece)
    4 Audio left (earpiece)
    The CTIA TRRS jack connector format is now used by virtually all smartphone manufacturers who use jacks. Apple, up until iPhone 7, HTC, LG, Blackberry, latest Nokia devices, latest Samsung devices, Sony , Microsoft (including Surface and Xbox One controller with chat adapter), most current Android phones.
  • CTIA - AV style:   There are some differences required for AV devices as they need to be able to carry composite video (CVBS) signals. Accordingly they are often slightly different.

    CTIA AV Style TRRS Jack Phone Connector Connections
    Pin Function
    1 CVBS video
    2 Ground
    3 Audio right (earpiece)
    4 Audio left (earpiece)
    This standard is used with the Apple iPod (up to 6th Generation), Raspberry Pi (2014 onwards), Xbox 360 E.
  • Audio Video:   Many camcorders need to use a different standard in view of their requirements.
    General AV Style TRRS Jack Phone Connector Connections
    Pin Function
    1 Right audio
    2 Ground
    3 CVBS video
    4 Audio left
    This configuration is widely used with Sony and Panasonic camcorders as well as those from many other manufacturers.

Jack / phone sockets with switches

Many jack sockets incorporate switches so that when the plug is inserted some switch contacts are made or broken. The original requirement for this arose so that when the jack plug was inserted to enable headphones to be used, then the speaker output was disconnected. For switched jack sockets, there is one set of contacts for each channel, i.e. one for a mono socket, and two for a stereo socket.

Using jack connectors

Jack connectors are normally very reliable. Even when they are used in a comparatively rough area like that of music and audio use for stage and performances, etc, they perform well. Even the smaller connectors used for headphones and other AV equipment like camcorders, etc perform well.

As might be expected there are a few hints and tips for their use.

  • Soldering:   The plated finish on the jack connectors can make them very difficult to solder. The only way to enable the solder to take is to roughen the surfaces required for the solder. Often a small file may help for this as it needs to significantly scratch the surface to be soldered to enable the solder to take.
  • Occasional bad contacts:   With use, these connectors, like any other can become dirty and this can lead to poor contacts in some instances. Often it does not appear that the contacts may be dirty as the plated finish does not show the dirt. It can help to wipe the connector over with a paper towel or paper handkerchief (unused!). The paper has sufficient abrasion to remove the dirt and leave the contact of the plug much cleaner.

The jack connector or phone connector has been around for very many years. Whilst its use in smartphone technology may reduce, the jack connector is still a key connector format for wired headphones, general audio work and in many other areas. It will remain in use for many years to come.

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