A number of designs have been proposed for ridge filters and range modulators used in proton therapy to modify the beam in order to spread out the Bragg peak. Despite the variety of solutions, no simple design capable of providing large fields and easy variation of the spread out Bragg peak (SOBP) length in a pulsed beam has been developed. We propose a compact ridge filter that can be used in a proton beam of any time structure. It allows the production of depth dose distributions that meet the requirements of therapy dose fields.