A variable amplitude vibration generator especially adapted for use with compacting machines in which a primary weight is eccentrically fixed to a power driven rotatably mounted shaft and a secondary weight eccentrically freely rotatably mounted on the shaft is releasably securable to the shaft by activating a remotely controllable detent connection, in an in-phase relationship with the primary weight to provide high amplitude vibration, and in which - upon rotation of the shaft in either direction though slightly less than 180* - with the detent connection deactivated, an out-of-phase relationship is established between the primary and secondary weights to provide for low amplitude vibration.