This preamp is very simple, and will work under tough conditions. The input impedance is pretty high, so it won't load down electric guitars. It will also amplify microphones. When I have a moment,
I'll make some additions that will optimize it for microphones, and also show how to power a condenser microphone.
The power source is typically a 9-volt battery, but the circuit will tolerate 6 to 30 volts. Battery drain at idle is about 1 milliamp. The two red LEDs are important in the circuit - they act as a voltage
reference to set the operating point of the opamp.
The output will tolerate a fair amount of abuse, and you can plug headphones into it in a pinch.
Please note that I have shown a generic symbol for a jack both at the input and output. Use whatever you need, or none at all.
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