The original version of this circuit was found in an old English publication that comes to projects with the operational amplifier 741. However, we made several changes to the circuit to make viable its assembly today, working mainly with component values. The circuit is for low impedance microphones and has a good gain. The output signal is sufficient to excite the input of most amplifiers. The circuit can also be used with magnetic pickups for electric and acoustic guitars. The source need not be symmetrical and both input and output signals must be made with shielded wires. The unit consumption is low, on the order of a few milliamperes. If power supply is used, it should have excellent filtration.
