This circuit was obtained from an 80's EDN. The components used are still common. The circuit can be used as a shield and the frequency is approximately 775 Hz.
This circuit was found in a Mullard transistor manual from 1960. Note the symmetrical power...
With the shadow over the sensor, it is possible to interrupt the sound of your amplifier using this...
This circuit puts the battery in the circuit when the voltage of a source is cut, preventing it...