This amplifier in common mode was obtained in an Electronic Design from the 90's. The circuit is valid for any operational, remembering that the power supply must be symmetrical.
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...