This variable filter that lets frequencies from 500 Hz to 1500 Hz pass through was found in a Popular Electronics from the 90's. The operational amplifiers are the 741.
This circuit was published in an Italian magazine Radio Elettronica in February 1976. The...
Found in a Popular Electronics from the 90's, this circuit converts a 40 V symmetrical source to a 5...
This high selectivity circuit for single tone decoding was found in 1970s documentation. The coil...