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Active balancers are attractive to be used in applications where rotational imbalance is frequently varied. For example, in media level servo track writers used in hard disk drive industry, a set of blank disks is loaded on spindle motor for purpose of servo writing. Since servo writing is performed at high speeds, imbalance introduced by disks and spacers results in significant vibrations that can affect the quality of servo writing process. This paper proposes a new configuration of active balancer that enables to compensate for rotational imbalance each time a new set of blank disk is loaded into servo track writing machine. The active balancer is in a shape of ring with a number of grooves displaced around axis of rotation. Steel balls are placed inside the grooves and held by permanent magnets. Imbalance compensation is achieved by electromagnetically activated release of the steel balls. Main advantage of the proposed configuration is in large compensation range. Presented 3-D finite element analysis results and experimental results demonstrate and prove effectiveness of this novel configuration.