Systemic Development > Analog Devices

Turntable belt length

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S Clark:
If you have an outboard motor on a belt drive table, does length matter?  I can't see why it would.  What about tension?  Should it be just enough to keep it from slipping?

James Edward:
My completely unscientific but thoughtful answer- I like your thought about just tight enough, because otherwise too tight would cause the belt to stretch around the pulleys when at rest, maybe causing some uneven belt elongation.

Folsom:
If it's too long then it'll have less grip. But in general, no.

Some people like string the best for a belt. That doesn't work with all turntables as you may imagine.

BobM:
I have a VPI platter and motor and of course it came with the rubber belt. Try this ... put your finger lightly on the belt "before" the capstan on the motor. Place it lightly there and you will not feel much, because the belt it being pulled by the motor. Now place your finger on the other side, where the motor is pushing the belt to the platter. I bet you will feel quite a bit more bounce and vibration on the belt.

That vibration is being transmitted to the platter and ultimately to the stylus. 2 solutions.

(1) place something solid and heavy there so it touches the belt and absorbs some of that vibration before it gets to the platter. Maybe a brass weight or something similar.
(2) replace the rubber belt with silk string. The string won;t vibrate like the rubber and silk doesn't stretch. Any other kind of string will stretch and cause speed anomalies. Caveat ... you can;t do this second method unless you have a speed controller because the diameter of the silk string is much smaller than the rubber belt and will sit lower in the groove of the motor capstan and your platter will spin at something other than 33 1/3. Second caveat - getting the length of the sting correct takes some trial and error, because you have to tie that simple knot in it just right.

In my opinion the silk sting sounds much better than the rubber belt. You do have to start the platter turning by hand though, but that's a slight inconvenience.

Enjoy

tmazz:

--- Quote from: S Clark on February 23, 2021, 06:59:11 PM ---If you have an outboard motor on a belt drive table, does length matter?  I can't see why it would.  What about tension?  Should it be just enough to keep it from slipping?

--- End quote ---

I think you are correct about just tight enough so it doesn't slip. What you want to avoid is making the belt tight enough to put sideways pressure on the platter bearing or the motor shaft . if you pull them with enough force perpendicular to the shaft you run the risk if making the shaft rub against something on the side of it. In my mind the less sideways force the better. This can cause some slippage when the platter is initially starting from a dead stop, but I agree wit Bob and give my platter a little hand spin before I hit the power button. I do this not only to avoid belt slippage but also to help avoid any undue wear and tear on the motor as the highest amount of torque required from it is at startup. I figure anything I can do to reduce the strain on the motor can only help increase its longevity.

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