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VPI Classic tweak

So I ordered a spare belt for my Classic One to have as a spare and when I got it I looked at the table and thought...Hmm why not try 2 belts? After a little research I did find a post on another forum from Mike at VPI who stated that a second belt should open things up a little bit and it did. A little bit more focus and imaging is what I observed. I found no discernible difference in platter speed. At 26 bucks it's a relatively cheap tweak plus the platter looks pretty cool with 2 belts.
mjm1124
captain_winters
133 posts
 
How else could the speed be different? The pulley is machined to a different diameter at each of the pulley positions.
actusreus
733 posts
 
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.
captain_winters
133 posts
 
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.
actusreus
733 posts
 
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.
captain_winters
133 posts
 
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.
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