Spindle oil

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.

J.A. Michell recommends to use the Mobil 10W30 motor oil. I use it with my Rega P25 and I'm very happy with it.

El, one of us is confused and I think it is you.

Consider a record where the spacing is wider than average. You lower the stylus into the groove, the arm is perpendcular to the rail, and begins moving toward the spindle. However, it is traveling too slowly for the wide groove spacing and soon finds itself lagging behind. The sensors see this and before the arm can get more than .05 degrees away from perpendicular the arm speeds up momentarily to recenter. It just cogged over. This will continue all the way across the surface.

Consider an off center record. From the point of view of the arm, the off center record presents a groove that is on average moving toward the spindle, but also constantly wandering back and forth. So to maintain the perfect angle the arm sometimes has to speed up when the grove is wandering toward the center and actually back up when it is going the other way. The pivot will allow the arm to move back and forth with the groove to a certain extent, but when the angle approaches .05 degrees it will cog.

The only way for your table to keep the arm at the perfect angle is to know in advance which way the groove is going. It doesn't. It senses when the arm is not centered and then reacts to this.

If the arm was tracking the groove perfectly then there would be no need for it to pivot and no need for sensors. The very fact that it does proves that it is not always at the perfect angle and cogs to correct anytime the arm approaches an angle of .05 degrees. I'm not saying it overshoots. I'm saying that Sony biases the arm to move at a rate that will track the average record, and that any record that is not average will require the arm to cog.

Herman: your example of an off-center record is a bit extreme. While this does happen, even a pivoted arm is "wallowing around" in the grooves as it the disc shimmies and shakes in an oblong rotation. There's only one TT made that actually deals with this in a very thorough manner and it is a Nakamichi.

The ReVox TT's with the "brick-like" linear tracking arm uses some type of optical sensor that reads the groove spacing and adjusts accordingly. I don't know the specifics of this system, but you can very clearly see the light shining down on the disc from within the "cartridge carrier" ( for lack of a better term ). This was my first linear tracking table and quite honestly, i was not the only one impressed by this $150 Ebay purchase. Everyone that heard it after i set it up in one of my systems commented on how good vinyl sounded.

As a side note, Kavi Alexander of Water Lily records uses a ReVox ( as far as i know ). I remember that he was looking for one of these, so i dropped him a line and gave him some background as to the differences between the various models that ReVox made. He was so grateful that he offered me a free disc from his label, but i declined his gracious offer. After all, if we can't help each other out without expecting to get compensated for basic info, we are a doomed breed. Excuse me while i park my dinosaur : ) Sean
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