This circuit from the 1980s uses an operational amplifier that is uncommon today. The circuit can be designed with modern operators. The gain is 40 dB.
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...