Vintage DD turntables. Are we living dangerously?

Henry, Just for the record, I stated long ago that while I would agree with the hypothetical aspects of Richard's analysis, I do not and did not think your pods were in fact being moved by stylus drag, but like you say, it is a question open to experimentation.

I performed the analysis of thermal expansion using F degrees and inches. (By the way, I left out a minus sign on the exponent; the coefficient is 1.3 X 10^-6.) By this analysis, an alu bar that is 9 inches long at 68 degrees F (roughly the pivot to spindle distance of an L07D) would expand to 9.000468 inches at 72 degrees F. The expansion of .000468 inches is equal to .0119 mm. This is less than insignificant, even if the construction of the L07D were to be of pure alu, which is not the case (see above). So let's put that to rest, just as I am willing to put to rest the idea that your pod moves strictly due to stylus drag.

Fleib, Try to see the point that if the tonearm and platter move at different times due to differences in resonance or susceptibility to spurious energy sources, then those movements are added to distortions produced by spurious movement of the stylus. Whereas, if the tonearm and platter are well coupled and must move together, then such external sources of energy are cancelled, in effect. For this reason also, we are told to wear seatbelts. I once saw a short movie in which a porcelain cup was put into a small barrel. Then the barrel was thrown down a set of stairs. Of course, the cup inside the barrel was shattered. Then the experimenter strapped the cup firmly to the side of the barrel and repeated the experiment. This time, the cup emerged intact. Keeping the tonearm and platter in consonance has the same beneficial effect. You may disagree, but that is the basis for my thinking, not to mention the thinking of 9 out of 10 designers of commercial turntables.

Lewm,
I see your point, but what you fail to see is, it's completely dependent on design. Any pod rigidly coupled to the base is connected to the platter, assuming the platter is rigidly coupled. Suppose you have one of those pneumatic vibration isolation stands or a lead balloon under your table. What difference would it make? Complicate matters with a subchassis and you're just as likely to insure spurious resonance as avoid them.

**Whereas, if the tonearm and platter are well coupled and must move together, then such external sources of energy are cancelled, in effect.**
Cancelled? This is the mantra of the suspended. What external forces, sound pressure? You're just as likely to increase consequences, as cancel. Extraneous vibrations should be dissipated, not perpetuated.
Regards,

I don't know where the subject of a sub chassis came up in this discussion. Whatever you want to put under your tt should affect the tonearm and bearing/platter equally and simultaneously, is all I say. Yes, if you bolt the outboard pod to a shelf, and you also fix the tt base to the same shelf, you do get a semblance of the same effect I favor. Henry was not about to do that at the outset of this thread. I am not sure he espouses that approach even now.

You also wrote, "Cancelled? This is the mantra of the suspended. What external forces, sound pressure? You're just as likely to increase consequences, as cancel. Extraneous vibrations should be dissipated, not perpetuated."

OK. Whatever happens to the tonearm, from whatever source of spurious energy of any kind at all, should also "happen" to the platter/bearing at the same point in time. You can choose whatever base you want, whatever source of spurious energy you want. I don't like suspended tables for other reasons. I think we're talking past each other. But I see you disagree, and that's fine. Thuchan asked for opinions, and I am certainly not alone in mine.

For a long time I agreed that the tonearm and the platter should resonate in unison to avoid added distortion. But after reading about good results from the separte armpod approach, I started to question my original thinking. I realized the tightly coupled arm to platter approach would work only if the stylus is also tightly coupled to the arm, that is, extremely low or no compliance at all. But most cantilevers are attached to a piece of compliant rubber and that automatically decouples the stylus from the rest of the arm so the separate armpod becomes really inconsequential and therefore it's not surprising that it can sound good reported by those users. That's just my current thinking and I'm open to other possibilities.


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Fkeib. I agree, 100% torque conversion is not possible.

That is why I listed this assumption..."TDs motor only provides enough torque to maintain original speed before stylus is lowered, after it is lowered."
I have assumed that the motor plays no part in dealing with stylus drag. It is only delivering enough torque to overcome windage and bearing friction.
Any additional friction in the form of stylus drag is resisted by the stored energy in the rotating platter. That is why I needed to calculate its moment of inertia.
This makes my calcs conservative, since there will be some restorative torque from the motor. Since we don't know how much, it was considered best to ignore this parameter.

The info I did find online relating to calculating stylus drag used a free wheeling platter, running at rated speed. Timed to stop without and then with the stylus lowered. My calcs are a derivative of that method.

I don't think that Maynard and I would agree on very much at all!