This circuit was found in a 1990 English magazine. It is a system in which the audio signal from input 1 (normal) passes until a signal at input 2 (priority) switches the circuit. At that moment it is that signal that passes. In a surround sound system, we put music on input one and when someone speaks into a microphone connected to input 2, switching occurs automatically, passing the sound from the microphone to the output. The source must be well filtered, and the transistor can be the BC558.
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