This circuit is from an ancient American documentation. The integrated circuit is 741 and the power supply must be symmetrical. The passing band is centered at 1 kHz.
We found this circuit in a 90's EDN. The circuit is based on a control integrated that is still...
In the figure we have the way to use the transistors of an old-paired pair as a trigger circuit. The...
This very high input impedance JFET circuit was found in the 1995 Encyclopedia of Electronic...