The filter presented is from 1994 but can be implemented with a more modern equivalent. We found this setting in the National Semiconductor Linear Applications Handbook.
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...