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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Broadband IR Receiver TDA3047 (CB15396E)
This receiver for infrared remote control was found in the Philips Databook of 1990, The circuit...
Flood alarm (CB20728E)
Found in an English publication from the 1980s, this circuit uses components that are still common...
Crystal tuned amplifier (CB7453E)
This circuit was found in Maxim's documentation from the 90's. The frequency of the circuit is...