This filter for frequencies from 300 Hz to 3.4 kHz was found in the February 1995 Radio Electronics magazine. Other operational amplifiers can be experimented, and the source must be dual.
In the figure we have the way to implement a 5 to 45 V zener diode with 50 mA of maximum current...
This circuit is from a Radio Electronics magazine from December 1958. The indicator instrument is analog...
These integrated ones consist of class B amplifiers with gain fixed 24 internally for better...