Matt circuit

A simple test circuit to fault find audio and radio equipment. Can be used to inject a square wave signal, rich in harmonics, or used with headphones as an audio tracer. Signal Tracer and Injector Circuit diagram a single pole double throw sitch is used to switch between inject and trace modes. The diagram is drawn in trace mode, the earpiece being connected to the collector of the last transistor. Both transistors are wired as emitter followers, providing high gain. DC blocking is provided by the 1n capacitor at the probe end, and the two stages are capacitively coupled. When the switch is thrown the opposite way (to the blue dot) both transistors are wired as an astable square wave generator. This provides enough harmonics from audio up to several hundred kilohertz and is useful for testing AM radio Receivers.

The circuit described here is of a dual audio-signal tracer. An audio-signal tracer is a simple device used to troubleshoot for audio signals in radio and other electronic circuitry. The device is a battery-powered stereo amplifier with two loudspeakers, packaged into a small handheld unit with test probes. An optional diode detector can be incorporated for the detection of amplitude-modulated signals. A test signal (audio) is injected into the tracer at CON1/CON2 from various points of the circuit under test. So long as the signal is heard, the circuitry up to that point is (at least minimally) functional. However, if the signal disappears, a fault can be assumed to be present in the stage of the circuit just preceding it. Fig. 1: Circuit diagram of the dual audio-signal tracer The simple external diode detector is not only sensitive to amplitude modulation but even circuits that are normally used for other modulation schemes (such as FM radios) can be tested in some cases. Circuit an...