Spindle oil

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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Herman...Confusion is not the issue. It's just that you are citing the kinds of problems that a slipshod servo design might exhibit.

By the way, the reason that relatively inexpensive linear tracking systems did not become very popular is that:
1. For low end systems they add significant cost relative to a simple pivoting arm.
2. For high end systems, they eliminate all the exotic designs, precise setup,tweeks, and endless adjustments that are dear to the heart of audiophiles. Just plop the record down and push the button. How boring!

El, eplain to me how your arm can keep from cogging over to catch up when the groove spacing is wider than average. You can't. If the arm is moving at a constant speed and the groove's relative motion toward the spindle is faster, the arm has to either make periodic corrections or keep getting further and further behind. Either we're talking about 2 different things or one of us is wrong.

These aren't the "problems of slipshod design." They are the issues that any arm has to deal with. I'm not saying that your system might not be the best solution to the problem, but to deny that it exists is ludicrous.

Sean, I don't think my example of an off center record is extreme. El tells us his sylus won't deviate from the center line more than .006 inches. That is less than 1/128 of an inch, about the width of the markings on my ruler. Not much. I just tried a number of random records and several of them were easily moving back and forth more than 1/128 of an inch.

Since it pivots it can track deviations up to the .006 limit without any correction. After that it is either making corrections or it is deviating more than .006 inches. You can't have it both ways.

Herman & El: You guys are discussing something in specific that i'm not really super fond of i.e. servo-driven linear tracker. Based on past experiences, i still believe that such a design has the potential to be better than most conventional pivoted designs.

Having said that, my thoughts are that the servo-driven mechanism is still going to be closer to the center of the groove more of the time than ANY pivoted arm over the duration of the LP. We already know that a pivoted arm can only be "centered" twice on an LP. We also know that this figure is based upon optimal cartridge installation / alignment.

With that in mind, how often do you think that the stylus is going to be centered on a pivoted arm as the off-center record yaws back and forth? On top of that, you have the inertial mass of the arm following that rotational irregularity, supported only by the cantilver of the cartridge up front and the bearing at the back of the arm. This not only causes the arm to follow that motion with NO form of correction, you're introducing more horizontal deflection into the stylus than should be there. My guess is that under these conditions, the stylus of a pivoted arm would be centered a big fat "ZERO" times on a record like this. That's because even when the arm gets to the point where the stylus should be centered, the stylus is probably going to be being pitched about sideways as the record wobbles around its' rotation.

Now how often do you think the linear tracker is going to be out of the center of the groove? Not only can the arm measure and correct for this ( to some extent ), but the arm starts off with the stylus following the grooves rather than pivoting across them? Before answering that, ask yourself how a record is originally cut i.e. with a pivoted arm or with a linear tracking cutting head? Now factor in how that cutting head is driven i.e. with a servo-driven motor.

If common sense has any input into your thought process, the law of averages will tell you that it is with the "inferior" servo-driven linear tracker, flaws and all. Pivoted designs came about because they were FAR more cost effective and easier to design and produce, not because they worked better. Sean
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PS... Most of the early motorized linear trackers put the money into the mechanics of the table's arm, meaning that the rest of the table i.e. the attention to motor vibration and the platter suspension were highly compromised. The fact that many of the motors driving the platter were also driving the arm compounded the vibration problem, which was already poor to begin with.