Saturday, October 3, 2009
PRE AMPLIFIER
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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