VPI Classic tweak

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?

interesting to see what speed you will end up with, since the belts will be fighting each other, with my AC frequency and I don't have a SDS I run at the top groove for 33, it is the closest using freickert android app and the test disc.

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.

No different with the SDS, different pulley positions are different diameters and will yield different speeds. You can verify it with the friekert app and test disc. The different pulley positions are for those that don't have the SDS to get as close as they can to 33 or 45 since without the SDS you have no control over AC frequency. With the SDS you don't need all the different pulley diameters since you can control AC frequency and optimize any of then for perfect speed. Adding another belt at different pulley diameter just upsets that balance.

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.