Abstract: An active band-pass filter comprises at least one unit consisting of two filter sections connected in tandem via capacitive coupling impedances, each section including an operational amplifier with an R/C network in its feedback path. The network has two parallel branches, one of them being divided into two series capacitances whose junction is grounded through a shunt resistance and is also connected to the output of the other section through one of the coupling capacitances acting as a feedback impedance. One of these series capacitances, lying between that junction and the inverting input of the operational amplifier, is also in series with an input impedance which in the case of the first section is a high-ohmic resistor and in the case of the second section is the other coupling capacitance. In a modified unit, constituting the dual of the first one, all the capacitances of the former are replaced by resistances and vice versa.