A known form of disc player apparatus or phonograph, which may be used for example and more particularly in broadcasting studios, comprises an oscillating or floating support chassis which is resiliently mounted or suspended in or on a base means. The chassis carries a sound pickup assembly and a turntable which is driven by a motor, directly or for example by means of a belt.
A regular or scheduled broadcast is under pitiless pressures of time, as for example, the transmission must be precisely blended in to programs in the course of being transmitted, or it must be possible directly to start connection operations without any loss of time. It is therefore essential that the time required for the turntable of a record or disc player to reach the required rated speed or rotation is as short as possible. The use of the most modern drive principles, that is to say, using a light turntable, a low-inertia rotor in the drive motor and direct drive, permits optimum rapid starting and rapid stopping of the turntable. It will be appreciated however that, in the event of rapid starting and rapid stopping in this way, considerable reaction moments occur, and these may give rise to a detrimental rotational oscillation of the support chassis on its resilient suspension or mounting, about an axis (generally referred to as the Z-axis) perpendicular to the turntable and on the axis of rotation thereof.
Purely lateral or vertical moments can always be compensated by a dynamically balanced pickup arm. On the other hand, it has not been possible hitherto to compensate for rotational moments as referred to above because the mass of the pickup arm cannot be kept at zero. The above-mentioned rotational oscillatory or vibratory movements have an interference effect on the sound pickup operation and produce unpleasant fluctuations in synchronism or smoothness of motion or in the pitch produced, particularly in the starting operation.