This is simple circuit for Guitar Pre-Amplifier. This circuit has some advantages such as it will work under tough conditions, very simple and has high input impedance. This circuit will not load down electric guitars because of the high input impedance. This circuit can be used to amplify microphones. Here is the circuit:
A 9-volt battery is typically used as power source, however the circuit will tolerate 6 to 30 volts. At idle, Battery drain is about 1milliamp. The two red LEDs used as voltage reference. they are used to set the operating point of the op-amp. The op-amp that is used in this circuit is non inverting op-amp. A fair amount of abuse will be tolerated by the output and the headphones can be plugged into it in pinch.
This circuit uses Rg to determine the gain. 100 Kohms will give 12dB gain and 1 Mohms will give 30 dB gain. The op-amp that is used in this circuit is LM741. It can be replaced with TlQ81 if the circuit is used for “sizzle”. [Source: Bob Blick Electronic Consultant]