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.

Frequently Asked Questions:

Q:

The scan is pretty bad and I canít tell what parts are near the input. Got a parts list?

A:

No, but starting from the input jack is a 10K resistor, a 220pF capacitor to ground, a 1M resistor to ground, and a 0.047uF capacitor to the opampís non-inverting input

 

 

Q:

The scan is still really bad, and I also want to know how to hook a condenser microphone up.

A:

OK, Iíll redo this page in 2002.

 

 

 

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