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 4-transistor signal tracer or follower was found in Radio Electronics magazine from May 1960....
This sound effect circuit uses only one integrated. We found it in a 90's EDN. The effects can be...
This is one of many power control or dimmer configurations that we have found on this site and in...