Active audio filter (CB21770E)

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

Microphone Pre Mixer (CB18095E)
This circuit, from a 2005 documentation, brings together in a single device a mixer and a...
Electronic Die (CB17701E)
We found this circuit in a 2002 documentation. This die shows numbers 1 to 6 on a common anode...
Mixer with voice effects (CB25401E)
We found this circuit in the October 1991 issue of Radio Electronics magazine. The circuit uses...