A type of signal interconnecting jack, used mainly in the musical world as the standard interconnection on modular synthesizer modules that conform to the Modcan-A format. In addition, it is used on synths made by Buchla and Associates to route control voltage signals (but not audio signals). It is also frequently seen on test equipment such as voltmeters, as the jack that the test leads plug into. As in the case of the phone jack, the interconnection cord is nearly always equipped with male plugs at both ends, while the equipment being connected always uses female jacks.
Banana jacks are sturdy, inexpensive, and reliable. A useful characteristic is that many of the male plugs have a female jack molded into the back of the plug. This allows cords to be "stacked", which makes it possible to route a single output to two or more inputs without needing a Y-cord or a multiple module. The main disadvantage of banana jacks is that the provide only a single contact surface, which means there is no provision for a signal return conductor. In the test instrument world, this problem is handled by combining two or more plugs/jacks into a single molded piece, which connects to a multi-conductor cable. But modular synths which use banana plugs only use one plug and jack, and the patch cord only has one conductor; they rely on the power supply providing internal interconnections between modules for the signal return path. This causes a problem when interconnecting two modules that are in different cases, or when it is necessary to connect to some equipment that uses a different connector standard. Modular synth manufacturers who make equipment that uses banana jacks usually offer an interconnection module that makes it possible to establish a ground connection between cases, so that a signal return path exists.