Spindle oil

Herman..."Crab walking"? I'm not sure what you mean. The Sony PS X-800 arm actually does have a pivot. However, the arm angle is constantly measured, (Hall effect sensors) and the pivot point is moved as necessary to keep this angle tiny. The pivot movement is biased to match the nominal LP groove spacing. Only if the groove spacing changes from nominal does an arm angle develop, and the pivot movement speed varied so as to get the arm angle back to zero (plus or minus 0.05 degrees). At all times the arm is free to pivot, so the servo activity is not seen by the pickup.

Bottom line is that it works flawlessly, and the biotracer vertical servo (not on all Sony linear tracking TT) will handle warped records that would be unplayable on most systems. Another nice feature of the biotracer arm is that the VTF is applied as a bias to the servo, and can be adjusted WHILE a record is playing, so that sonic effects of VTF can be evaluated.

El: I think that Herman meant that the servo controlled linear arm would be cogging side to side ( crab-walking ) trying to constantly correct for the center of the groove. Sean
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Sean...But it doesn't. This servo system was not designed by amateurs.

El, it has to have some amount of cogging, otherwise there wouldn't be any need for the sensors. Every time it makes a correction it cogs and with an off center record it would be doing so continuously. Of course it is another matter whether this detracts from the sound.

I'm curious where the sensors are mounted in relation to the pivot point. Your spec of .05 degrees seems like an awfully low figure. With a 3 inch arm that would be about 70 microns at the stylus. I'm not saying it can't be done, but that does seem awfully low for a consumer table.

While I agree that it is an interesting exercise in engineering, one has to wonder why nobody builds such a system anymore. In the cost is no object world of high end audio things like stepper motors, hall effect sensors, and microprocessor controllers are dirt cheap. Perhaps it is a matter of perception given the amount of trashing they took early on.

Herman...Your assumption that there is "cogging" really means that the control process exhibits overshoots. It is entirely possible to design a control process that does not overshoot at all.

Regarding off center records...remember that the arm pivots, and this pivoting takes care of following wobbly grooves. Remember that the arm servo is biased so as to move at the speed necessary for nominal groove spacing, so the servo does not need to follow the instantaneous arm angle. There is filtering, and probably a notch filter at the 33.3 Hz frequency. Again I say that the Sony engineers knew what they were doing.

I agree that the 0.05 degree tracking error is very very small. Probably smaller than it needs to be. Pivot to stylus measures 7 inches, so 0.05 degrees represents 0.006 inches. An angle of 0.05 degrees is 180 arcseconds. This is easily measured. In the inertial guidance systems that I used to work with we routinely implemented angular measurements on the order of 1/10 arcsecond.