VPI Classic tweak

All the grooves on the flywheel of the HRX drive station have the same diameter, which is probably why it works well in my setup.

Good Listening

Peter

Use a micrometer and measure the various pulley positions.

We all know the Harry is a marketing genius, you just confirmed it. My marketing course work rings a bell here, you know the classic 'repeat' on the shampoo bottle. I am sure Harry is planning belts in different colors, that will improve the sound. What's your color choice?

The belts will be binding, one belt will try and turn the platter faster in each rotation than the other. Therefore one will have to slip. The belt with the most torque will probably win. Hard for me to visualize how this could be an improvement in sound.

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.

I believe the position on the platter is irrelevant, the platter is machined to the same diameter up and down its sides. I believe the pulley is machined intentionally with a larger diameter on each groove progressively to accommodate those enthusiasts without a SDS. This is the only way they have to compensate for AC frequency differences, which is how speed is determined on an AC motor.

I used to have a Scout turntable for which I bought a straight, non variable speed pulley, which was close to the diameter of the 33rpm portion of the stock Scout pulley. With the SDS I could adjust for correct speed and also switch between 33 and 45 rpm. I was also able to use multiple belts without the potential problem of varying belt speed rotation.

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.

How else could the speed be different? The pulley is machined to a different diameter at each of the pulley positions.

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.

The actual diameter of each position is different. It allows enthusiasts without a SDS to dial in the speed as close as possible to 33 or 44. Check it out with the friekert app and test disk. It gets faster in one direction and slower in the other. Just by moving the position of the belt on the pulley. You can't notice it with the naked eye, but it is true.

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.

VPI does that for enthusiasts like me that don't have SDS,and no control over AC frequency, so we can obtain correct speed by changing belt position on the pulley, to go faster or slower.

I don't agree. Check it with the friekert app and test disk, each position is a different diameter resulting in a different platter speed. Whether you use a SDS or not, the 2 belts will be spinning at 2 different speeds.

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.

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.

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 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.

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?

Don't see how that can be done on classic series pulleys. Every pulley position is a different diameter, to allow for speed adjustment for variable AC frequencies. Multiple belts will each be at a different speed.

Bifwynne

No have run 4 belts for many years

Good Listening

Peter

Just a thought. I wonder if putting an extra belt on the platter/motor mount could prematurely wear the motor bearings because of extra tention on the drive shaft and bearings. I'm not sayin' ... just asking.

I run with 4 belts on my GrooveMasters which utilize the HRX drive station from VPI GrooveMaster

Good Listening

Peter

I might give this a try, I never thought about running two belts. We Shall see.