Active audio filter (CB21770E)

This circuit was found in a 1977 documentation for radio amateurs. Integrated circuits are common operational amplifiers.

Simple sound bridge (CB6069E)
This simple bridge circuit can be used for impedance or resistance measurement using a high...
1,000 V Voltage Source (CB522E)
This circuit can source up to 1,000 V from a 9 V battery. Output current is very low, some...
Changing the frequency of the LED blinking (CB24661E)
The figure shows how to change the frequency of a 5 V LED blinking. The capacitor can have other...