Belt tensioner makes wonders!

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I saw herr Schroeder's smart implementation of the belt tensioner principle while back at Audio Asylum. Advantages seemed so obvious, so it made me try on my own. My design is rather straightforward: constant gravity force is applied to the rocker sector with the tensioner pulley on it, by means of the weight hung on the silk thread.
It was a real PITA to adjust the mechanism to get two pulleys axles exactly parallel (otherwise belt runs up or down); I should make the basis adjustable. Eventually, it was all set; two seconds after the needle dropped on the record, I knew I have a major sonic improvement!
Week of intense listening only proved the first impression: each and every component of the sound picture got better, especially:
- lightning speed with razor sharp leading edges and proper decay (crucial importance for piano records),
- no smearing between single notes during arpeggio(never heard it before),
- large scale orchestral music became clearly delineated between instrumental groups and between players within each group,
- much better defined bass,
- sound color scale and texture largely improved.
And all this because of simple tensioner? It keeps to amaze me.


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Hi Michael,
Very nice!!! I can’t open the picture but I’ve seen it on audioasylum.
I made precision motor distance adjustment for my TT and it is not enough - I found out I need some kind of belt tensioner. Thermal expansion of platter changes belt tension too much to ignore it. I also like your idea of increasing belt contact surface with the pulley.
What weight do you use?

Thanks Marek,
The weight is about 100 gramm, and since the tensioner pulley sits twice closer to the rocker axle than thread connection point, it gives 200 gramm on the pulley. By simple math it is equal to 65 gramm of the belt tension force, 130 gramm of side force on the motor axle and 84 gramm of side force on the platter bearing.
I belive this mod may be easily implemented by average DIY'er and for the profound effect it makes, it's a killer tweak!
One tip: use the Maccormik 1/2'' mylar tape for belt; it is thicker than VCR tape and suit this tweak nicely. I tried to use it with no tensioner - it slips!
OK, I think if I am to make this I will use a tensioner from a tape machine of some sort. Maybe use a spring loading instead of the counterweight if I can find something that easy to adapt.

BTW, where did you buy the McCormick tape from? I'm using some 1/4 clear tape leader at the moment, but have a 1/2" pulley installed.

Here is the link:

It depends. With all being equal, you have to have certain wrap angle to preclude the mylar tape from slipping on driver pulley (unless you are not using rubber belt - the worst option). To obtain this angle, motor is usually placed rather far away from the platter. With the tensioner, the idler pulley is getting much closer to the platter, increasing the angle between belt "tangents", and the forces parallelogram got "squeezed". So for the same minimum belt pre-tension force required to eliminate slipping, the platter bearing side loads become smaller.
I have tried holographic mylar from mccormick - it wasn’t straight and the edges were wrinkled - the tape is meant to be used for decoration. You may like what I use - ½” poly leader tape (audio product, made in Germany) a bit heavier, stronger and straight. I bought it from eBay store run by seller “xiat”. I got a remnant for a penny, normally he sells it on a big spool hence the high price.
"Where can you find the idler pulley and shaft?"

The pulley is machened from delrin and the shaft from stainless steel (then polished) at local machine shop. Light machine oil for lubrication. Not a rocket science and rather inexpensive. I tried to lower the idler weight to reduce inertial response delay.
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