This traditional circuit was obtained in a 1974 documentation, but can be mounted today with the transistor BC549, and small changes we made in the original design. Powering can be done with 9 volt battery, as the consumption is very low. If power supply is used, it must have excellent filtration. Input cables and output signals must be shielded. It is recommended to mount into a metal box to serve as a shielding. Two units can be powered by the same source in a stereo version. The signal level of the output is sufficient to excite most amplifiers. The input is high impedance.
