Designing a turntable.

The task of a turntable seems to be simple. At audio frequencies, the arm should be kept locked above the groove, without any extraneous motion relative to the cartridge. And the groove should be dragged at a constant angular speed underneath the stylus. This means that over the whole frequency band of 10Hz up to 20kHz and beyond, the whole loop made by record, platter, bearing, (sub)chassis, arm board, tone arm, and cartridge body should behave in an utterly rigid and non-resonant fashion. Any flexing of the same dimensions as the microscopic undulations in the groove detracts from sonic fidelity.

At lower-than-audio frequencies, the arm should be made able to freely follow the groove’s warps and excentricities, so as not to damage LP or cartridge, and this without inducing any spurious signals into the cartridge’s generator.

Only when these demands are fulfilled can the stylus trace the actual information embedded in the record’s groove walls.

A simple task, you said?

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