This circuit lets through the 300 Hz to 3kHz range that corresponds to the human voice. We found it in the Radio Electronics magazine of February 1990. The circuit uses both parts of the LM381.
This second amplifier is based on the integrated LM108 and has a differential input. The resistor...
Other amplifiers of the series like the MC3301, MC3401 and LM2900 can be used in this circuit. We found...
In the figure we have the circuit of a bistable using two relays. We found this circuit in an...