A vibrator for generating vibrations. An exciter cell having rotationally drivable unbalanced masses that are rotatably supported in an exciter cell housing and having an adjustment unit for adjusting the phase position of the unbalanced masses relative to one another. The adjustment unit is configured as a planetary gearing that has at least two input trains to which the unbalanced masses of the exciter cell are coupled that are adjustable in phase relative to one another and that has an adjustment input train for changing the phase position of the output trains of the planetary gearing.