Abstract: Apparatus for detecting at least one predetermined angular position on rotating devices, having a tachogenerator with a stator part and a rotor part for producing a tacho signal with speed-dependent frequency. The stator and rotor parts of the tachogenerator form at least four circumferentially directed, substantially equidistantly spaced pole areas. For the purpose of an angular position-dependent amplitude modulation, a pole clearance is provided in at least one of the pole areas in both the stator part and the rotor part of the tachogenerator. An envelope amplifier with a threshold value stage is preferably connected in series with the tachogenerator and essentially only permits the passage of the angular position signals resulting from the coincidence of pole clearances in the rotor and stator parts of the tachogenerator.