Mini Megaphone (CB8952E)

Found in Popular Electronics' 90s, this small megaphone is based on LM386. The circuit uses a high impedance microphone.

Low distortion sinusoidal oscillator (CIR21117E)
Found in National Semiconductor documentation from the 1980s, this circuit can be implemented with...
3 to 11 MHz VCO (CB21494E)
This circuit was found in a 1968 EEE. The circuit makes use of logic gates of the time and can be...
3 kHz Notch Filter (CB13567E)
We found this circuit in a publication on operational amplifiers from 1978. The circuit is made...