This circuit with the HA2400 was found in the March 1980 Radio Electronics magazine. The circuit has digital-gain control and must be powered by a symmetrical 15 V source.
This circuit is suggested by the National Semiconductor Linar Applications Handbook, controlling a DC motor...
This circuit was found in an Electronics Now of the 80s applying to NiCad batteries of the time....
Other operational amplifiers can be used in this conventional filter that rejects only one...