A control circuit controls current through a voice coil motor (VCM) during retraction
of a transducing head from the surface of a recordable medium. The transducing
head is carried on movable member actuated by the VCM. The control circuit includes
a measuring circuit for measuring a back electromotive force (back EMF) from the
VCM. The control circuit also includes a driver circuit connected to terminals
of the VCM for providing the VCM with a drive current having a magnitude based
on the back EMF from the VCM. The control circuit further includes a chop clock
to alternate between measuring the back EMF from the VCM and providing the VCM
with the drive current at a random frequency within a range of frequencies around
a median frequency.