This voice scrambler and descrambler circuit was found in a Radio Electronics from July 1963. Transformers are common types at the time with impedances according to telephones and line.
This is a project that can easily be adapted for other purposes such as counting people, objects,...
This circuit is from a PopularElectronics of June 1992. The magazine no longer exists, but the...
This circuit makes use of a mechanical delay line to produce the reverberation effect. This is a...