This filter, with a cut-off frequency of approximately 1 kHz, has a high Q and employs two operational ones. The power supply must be symmetrical.
This circuit is from a Radio Electronics from October 1963. The LDR and transistors are from the...
The figure shows how to use an operational circuit as a voltage divider. The circuit is from a...
This is the basic configuration of an operational amplifier as a current regulator. We found it in...