VPI Classic tweak

Captain_winters,
I don't quite get how you reached the conclusion that "each position is a different diameter." I agree that each position might result in slightly different speeds, which two belts might or might not even out without the SDS. But why couldn't you dial it in with the SDS whatever the effect of using two belts? Regardless, it seems to me that the effect of using two belts would be more complicated than reducing it to an assertion of "fighting," assuming the belts are of identical length.

The pulley has three possible positions for each speed so it is certainly possible to put two belts on the top and bottom groove respectively.

This is interesting and I'm tempted to try it myself. Out of curiosity, those who have the SDS, do you use the the 33 or 45 diameter? Either one is possible since the SDS will adjust the speed so I'm wondering which diameter would offer the best speed stability. The 45 being thicker would grab more of the belt; the 33 being thinner less of the belt and more of the platter. Any thoughts?

You mean since different pulley positions render slightly different speeds without the SDS? With the SDS this should be a non-issue; I just wonder about the physics of pulley thickness and how it affects the speed and ultimately the sound.

Interesting. I'd think that the pulley is manufactured to very tight specifications and differences, if any, between different positions in the same speed diameter would be too insignificant to affect the speed. I attributed the small variances in speed among the different positions to the differences in the pull on the platter and bearing caused by the different height relative to the bearing. I would think that without the SDS using two belts would result in a certain speed that could then be dialed in precisely with the SDS if necessary, rather then the belts fighting. In other words, whatever the result of their "fighting," it could be adjusted perfectly by the SDS.

Perhaps we're both have a different basis from which we extrapolate. I'm talking about a different belt position on the same speed grooves; there are three of those for 33 and three for 45. So 33 has three possible positions, each apparently resulting in some small speed variance at 33 rpm, which I accept. But to contend that the DIAMETER of each of those positions is different on the pulley seems to me to be quite a bit of a stretch. With tools you mentioned you can test the speed, but not the diameter. Using two belts on the top and the bottom 33 rpm pulley grooves should result in a net speed that should be able to be dialed in by the SDS. Both belts are subject to the same forces so the net speed should be perfectly stable.

Ok, so that I understand you, you maintain that each of the three grooves on the 33 rpm (and 45 rpm diameter) that are millimeters apart have a different diameter? As I stated, the pulley is manufactured to such high specifications that the miniscule differences, if any, should have an absolutely negligible effect on the platter speed. I believe the differences in speed are caused by different belt positions relative to the platter bearing; i.e., the pull is different when the belt is higher or lower on the platter.

It totally makes sense, if true, and would perfectly explain the speed difference among different pulley positions. However, I'm still unclear why using two belts would not result in a net speed that could be adjusted by the SDS since both belts would be subject to the same forces with each rotation.