This variable filter circuit was found in July 1975 Radio Electronics magazine. The circuit uses 3 general purpose op-amps like the 741 and must use a symmetrical source.
Using the LM380, this circuit provides a power of the order of 200 mW. In it we have a stage of...
I found this circuit in an article in a 2003 publication. The circuit is an example of how to...
We found this circuit in a Radio Electronics from October 1965. The pickup coil can be of the...