Low cost Mic Mixer

  
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This is the schematics of a low cost mic mixer that can be assembled from the components in your junk box. This two channel mike mixer is designed for handling high impedance dynamic microphones. Transistor Q1 can be any general purpose pnp transistor like BC177 or BC157B. Resistor R5 biases the transistor while R3 and R4 provides channel isolation.
Low cost Mic Mixer - schematic

How ever better the transistor quality better the performance. C1 and C2 performs the job of input coupling and DC isolation while C4 is the output DC decoupling capacitor. Resistors R1 and R2 can be used for the level control of input signals. Avoid using power transistors for Q1. This is because power transistors have high leakage current and it adds to the noise which is not suitable for our purpose here I am an entrant in a 12 day 6, 500 km car rally through Europe. The organisers have recommended that we use an intercom between driver and navigator as we will need to be talking to each other almost continuously for ten hours a day whilst map-reading and driving. Professional systems are available for close to $1, 000 but I feel that I should be able to get away with a couple of PC headsets and an appropriate amp. That said, I am a mechanical engineer and so am out of my depth on this website! Would this circuit work with the two 3. 5mm microphone jacks plugged in as the microphones and the output simply wired to the two headsets If so, and given that I have no junk box, what would be the best transistor Could I put a pot on each headset output to control volume Would it work wired directly to 12V



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