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RCA jack

An RCA jack, also referred to as the ¼ inch phono jack, is a type of electrical connector which is commonly used in the audio/video market.

For many applications it began to replace the older phone jacks used in the audio world when cassette tape players started becoming popular in the 1970s.

The corresponding plug is called an RCA plug or a phono plug, as opposed to a phone plug which refers to a telephone jack plug.

A panel of four RCA jacks, and three RCA plugs of various quality

In the most normal usage, cables each have a standard plug on each end, consisting of a central male connector, surrounded by a ring. The ring is often segmented for flexibility. Devices mount the jack, consisting of a central hole with a ring of metal around it. The ring is slightly smaller in diameter and longer than the ring on the plug, allowing the plugs ring to fit tightly over it. Connections are made by pushing the cable's plug into the jack on the device.

The jack has a small area between the outer and inner rings which is filled, typically with plastic. They are often color coded, yellow for composite video, red and white for right and left stereo audio. This trio (or pair) of jacks can be found on the back of almost all audio and video equipment.

One problem with the RCA jack system is that each signal requires its own wire. Even in a simple case of attaching a cassette deck you'll need four of them, two for input, two for output. In any common setup this quickly leads to cable spaghetti, which is made worse if you consider more complex signals like component video (another three cables each way). There have been numerous attempts to use combined connectors in both the audio and video world, but none of these have ever become universal.

As with many other connectors, the RCA has been adopted for other uses than originally intended, including as a power connector and as a connector for loudspeaker cables. Its use as a connector for composite video signals is extremely common, but provides poor impedance matching.