They Type O is a letter-series plug-in that contains two op-amps. The input and feedback networks of the op-amps can be configured from the front panel using knobs and/or user-supplied components. There are sockets on the front panel for banana plugs. The Type O also has a regular signal input that does not involve the op-amps. A mode switch selects which op-amp's output will be displayed, or the regular signal input.