Abstract: An audio system and circuit are disclosed that are operable in either a first configuration and a second configuration. The first configuration includes sound processing circuitry, a primary connector, and a header. The second configuration adds an optional secondary connector to the header. The system and circuit mutes or turns off the audio signal at the primary connector and the main output contacts (if any) upon insertion of a plug into the secondary connector in the second configuration. The system and circuit also optionally mutes or turns off the audio signal at a main output contact upon insertion of a plug into the primary connector in each of the first and second configurations. The system may also employ logic switches or FETs to interrupt the audio signal upon insertion of a plug into the secondary connector. The system uses a simple switchless interconnection between the secondary circuit and the main system.