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'''3.5mm TRS''' (Tip-Ring-Sleeve), also known as a '''mini jack''', '''⅛" jack''', or '''minijack''', is a common audio connector used for headphones, portable audio devices, and auxiliary audio connections. It is one of the most widely produced and recognized electrical connectors in the world, found on everything from CRT televisions and professional equipment to smartphones and laptops.<ref name="wp-phonejack">[https://en.wikipedia.org/wiki/Phone_connector_(audio) "Phone connector (audio)"], Wikipedia.</ref>

== History ==

The phone connector family dates back to 1878, when it was developed for use on manual telephone switchboards — making it one of the oldest electrical connector designs still in active use. The original connectors were ¼" (6.35 mm) in diameter.<ref name="wp-phonejack" />

The 3.5 mm miniaturized variant was introduced in the 1950s, initially for use with transistor radios and other portable electronics where the full-size ¼" connector was too bulky. It gained widespread adoption through the Sony EFM-117J transistor radio (1964) and subsequent portable devices. By the 1980s, the 3.5 mm jack had become the universal standard for portable headphones and personal audio equipment, cemented by its adoption on the Sony Walkman (1979).<ref name="wp-phonejack" />

== Design ==

The 3.5 mm TRS connector consists of a cylindrical plug with three conductive sections separated by insulating rings:

* '''Tip (T)''' — carries the left audio channel
* '''Ring (R)''' — carries the right audio channel
* '''Sleeve (S)''' — serves as the common ground return

The plug diameter is 3.5 mm (approximately ⅛"), and the barrel is typically 14–17 mm long. The female jack (socket) uses spring contacts to make electrical connection with each section of the plug when inserted. A detent mechanism provides a tactile click when the plug is fully seated.

== Specifications ==

{| class="wikitable"
! Parameter !! Value
|-
| Plug diameter || 3.5 mm (0.138")
|-
| Contacts (TRS) || 3 (tip, ring, sleeve)
|-
| Signal type || Analog audio (stereo)
|-
| Typical output impedance || 16–600Ω (headphone); 1–10kΩ (line level)
|-
| Coupling mechanism || Friction fit
|}

== Variants ==

* '''TS''' (Tip-Sleeve) — 2-contact mono variant; used for mono audio, instrument cables, and some microphone connections
* '''TRRS''' (Tip-Ring-Ring-Sleeve) — 4-contact variant adding a fourth conductor, typically used for combined stereo audio + microphone on smartphones and headsets. Wiring standards vary — CTIA/AHJ (used by most modern devices) places the microphone on the second ring and ground on the sleeve, while the older OMTP standard reverses these two.<ref name="wp-phonejack" />
* '''2.5 mm''' — a smaller variant (sometimes called "sub-mini") found on some older mobile phones, cordless phone headsets, and certain professional equipment

== Use on CRT Equipment ==

On CRT televisions and monitors, the 3.5 mm TRS jack is most commonly found as:

* '''Headphone output''' — provides a stereo audio output for private listening, typically on the front or side panel of the set. Plugging in headphones usually mutes the internal speakers.
* '''Auxiliary audio input''' — some CRT sets include a 3.5 mm input for connecting portable audio players or other devices with headphone-level output
* '''Audio output''' — certain CRT televisions use a 3.5 mm jack as a fixed-level or variable-level audio output for external speakers or amplifiers, particularly on smaller sets where space for full-size [[RCA (connector)|RCA]] jacks is limited
* '''External speaker output''' — some portable and compact CRT sets use a 3.5 mm jack for connecting external speakers

The 3.5 mm jack is also found on many devices commonly connected to CRT televisions, including game controllers (for headset audio), portable game consoles, and computer sound cards.

== Adapters ==

Common adapters include:

* '''3.5 mm to dual RCA''' — converts a headphone-level stereo output to left/right [[RCA (connector)|RCA]] plugs for connection to a TV or amplifier's audio input. One of the most common audio adapters in use.
* '''3.5 mm to ¼" (6.35 mm)''' — adapts between mini and full-size headphone jacks
* '''3.5 mm to Mini-TOSLINK''' — some devices use a combined 3.5 mm / Mini-[[TOSLINK]] socket that accepts either an analog audio plug or an optical digital audio plug

== See Also ==

* [[RCA (connector)]] — standard consumer audio/video connector
* [[TOSLINK]] — optical digital audio connector (Mini-TOSLINK variant shares similar form factor)
* [[Binding post]] — screw-type speaker connector

== References ==
<references />

[[Category:Connector types]]