This 50 Hz rejector or notch filter was found in a 1975 documentation. Other frequencies can be obtained by changing components. The filter uses a Wien network and must use a symmetrical power supply.
In the figure we have an interesting protection bridge against power polarity inversion of a...
This amplifier was found in an old publication of 1990. With the changes, it may still be...
Obtained from an English publication, this circuit actually needs a current limiting resistor,...