We found this circuit in a documentation from the 70s. The circuit uses amplifiers from the time, but it can be implemented with modern equivalents.
In the figure we have a simple way to produce tone in a piezoelectric transducer. The frequency depends...
This absolute value amplifier was found in a 90's EDN. Equivalent amplifiers can be used. The...
The integrated circuit used in this configuration for noise reduction on FM radios is not common...