Second order active voice filter (CB7568E)

This filter for the 300 Hz to 3 kHz range was found in an American documentation from the 90's. The operational amplifier is a double 741.

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Regenerative receiver (CB22273E)
This simple 1 transistor circuit was found in an American documentation from the 60's. The...
Code practice oscillator (CB7314E)
Found in a magazine 73 for radio amateurs, this circuit makes use of general purpose transistors and...
Automatic Faucet (CB18147E)
The presented circuit allows to control the valve of a tap. The positioning of the emitter and the...