The configuration of this circuit was suggested by an old English publication that comes to projects with the operational amplifier 741. Since the 741 is still very popular today, the viability of the project remains. The circuit is intended originally crystal microphones, but these types no longer exist. However, its characteristics allow its use with ceramic high impedance microphones. The power supply 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. The output impedance is 1 k, and enough signal level to excite most common amplifiers. Consumption is very low, allowing its use with battery. Input cables and output signals must be shielded, and if used source, must have excellent filtration.
