Like the previous circuits, this one uses a small speaker as a microphone and has two amplification stages with 600-ohm output.
This circuit was found in the July 1998 issue of Electronis Now magazine. It is a traditional...
The diagram, obtained in an old European documentation, shows the ways to trigger and to shut down...
We found this circuit in a Poptronics from 1998. The circuit can be extended to more competitors...