This circuit was found in a publication by Edelman from 1924. The power comes from the battery and the listening is through a high-impedance headphone.
This 1/2 hertz high selectivity filter was found in the December 1990 issue of Radio Electronics...
The two power steps below are intended for use with the SAA1027 stepper motor control but can be...
This interesting circuit, found in a 1986 publication, includes a powerful audio amplifier. Being...