In the common synchronous gear drives for phonograph or talking picture turntables there is at least one driven gear which makes the same average revolutions as the turntable and which is driven by a higher speed gear (or worm). Commercial gears have slight but appreciable errors in both tooth spacing and shape, which necessitates a variation in the relative angular speeds of the two gears. These irregularities may introduce disturbances of frequencies corresponding to the frequency of revolution and its multiples.

The effect of the higher harmonics can be easily reduced by filtering, but to filter the lower frequencies the turntable must be prohibitively massive or the couplings must be so flexible as to put the table speed at the mercy of the irregularities of its bearings and endanger the synchronism of sound and picture.

The planetary gear system, to be described, increases the speed of the lowest‐speed gear with respect to the gear meshing it, thereby increasing the frequency of the disturbance and greatly facilitating mechanical filtering.

The main turntable bearings are also run at higher speed with similar effect upon disturbances arising from frictional irregularities. Damping is also provided to dissipate transient disturbances of speed.

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