This circuit was found in a Popular Electronics from the 90's. The output signal can be applied to a headphone or speaker. The microphone can be a piezoelectric tweeter capsule or other type.
This circuit was found in a 90’s 303 Circuits. The components are from the period and the heating...
This circuit was found in a 1987 magazine. It consists of an oscillator controlled by the...
This circuit was obtained in a 90s American documentation. The integrated circuit used is uncommon...