AF signal injector and tracer

Signal injector and the tracer is a very useful device when troubleshooting electronic audio equipment. We decided to build this signal injector by inspiring the article available in June 2016 - Everyday Practical Electronics (EPE) Magazine (Audio Signal Injector and Tracer by John Clarke - Page 22 to 29).

The signal injector design in EPE magazine is simple but we got few issues while constructing that circuit. The main issue is that LMC6482 is not available to buy in the local market. After few months wait we got a couple of ICs from eBay for LKR 600.00. The second issue is its output is not enough to drive most of the loudspeakers. After prototyping EPE design we decided to build similar sort of signal injector and tracer with commonly available ICs and with more powerful power amplifier stage.

For our design, we use the LM358 operational amplifier IC which is commonly available in the local market (for LKR 15 to 20). For the power amplifier, we use LM386 low voltage power amplifier IC (which also costs around LKR 10 - 15). Our design is almost similar to EPE design and the only major addition is LM386 AF power amplifier stage.

3D view of signal injector & tracer PCB.

We build this signal injector and tracer on a single side PCB. Compare with original EPE design this unit consumes more power and it is not designed to drive using a battery. The AM RF demodulator probe (Page 30 - 31 on the same magazine) also works well with this unit.

In supplied PCB we do not include attenuator circuit and in our prototype, we build it using point-to-point wiring method (on top of the selector switch).

Our signal injector and tracer schematics and PCB designs are available to download at google drive. For a more detailed overview please check the June 2016 issue of Everyday Practical Electronics magazine.

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