This circuit produces the sound of a motorcycle or an outboard motor. The frequency is adjusted in the pot. For supplies above 9 V the BD136 must be equipped with a small heat sink.
This is one of the many versions of amplifiers with LM386. This was achieved in an old publication (1981). The...
This circuit uses unijunction transistors and drives a small speaker through an output...
This circuit can also be used as a shield if the excitation is made with 5 V and the output stage...