Direct drive vs belt vs rim vs idler arm

Halcro. Thanks ... will have another look at your results. I've read about the Dual eds motors and have long contemplated a DIY using one of these. I still have a couple of these so the next project will involve using one of these motors. I managed to pick up a cosmetically trashed Revox B790 with a broken arm so scavenged all the working bits. The motor looks to be based on the dual with an identical upper casting but the electronics are much more complex and use quartz locking. I replaced the thrust pad and changed all the capacitors on the boards and housed the power transformer in an outboard enclosure ... no other mods except for the platter. I picked up an acrylic Feickert platter with brass inserts on German eBay and decided to chance using it as it is MUCH heavier than the Revox one. Decided to use acrylic for the plinth as I had a Basis Vector and figured that tonearm had been voiced on acrylic. I have used it over 6 months now with no problems. I pulled it apart a couple of months ago and the bearing seems to be holding up so far. I'm very happy with how the tt sounds.

Tonywinsc, thanks for your comments. As far as centering the record goes, I didn't do anything so I think I'm just lucky to have one with a reasonably well centered hole. When I did the test I was actually at first disappointed. as the pitch waver was still quite audible. Goes to show while we debate the minutiae of 0.008 % speed errors the record itself is much more to blame for wavering pitch than most good tt's regardless of drive system. Halcro, when I made my tt , the fact that I used a much much heavier platter than the Revox tt it came from caused some anguish but have had no real issues in practice , the tt comes up to speed quickly and seems to hold speed pretty well even if I use a record brush. I still need to somehow rig up a second arm and do the test I proposed in my previous post to see what happens when playing music just to make sure the servo isn't going crazy with the added mass. Finally , I apologize if my posts come up in the wrong spots in the thread as the powers that be took almost 24 hours to put up my previous post.

Keep in mind too, like I said before; the Timeline needs to run for several hours on your tt in order to get a reasonable data set for evaluation. You need thousands of rotations to conclude anything in the 0.01% range or else you will be seeing those fairies dancing around.

Tony,

I said this earlier in the thread:

If your Timeline was 31" from a wall, a speed error of .01% would appear as a 0.02" (0.5mm) laser deviation per revolution.

So, if you played a 20 minute record side, the platter would have made 666.66 revolutions. 666.66 * 0.02" = a total deviation during that one record side of 13.3". What if the total deviation was half that (6.65")? Your speed error is 0.005%. What if it was a quarter (3.25")? Your speed error is 0.0025%.

You guys are making me feel.... normal.

Hi Ketchup,
The fewer data points that you have, then the higher the standard deviation which let's say is increased uncertainty. Just the fact that you are going to make two 0.100" pencil marks 0.02" apart is going to add to the measurement error. A few hours of running time will make the marks far enough apart to at least minimize the pencil mark measurement error.
Ok, you have a measurement after 666 revolutions. Go ahead and let it run for a few hours and see if your results are the same. The results might look worse, or they might look better, but I doubt they will be exactly the same. (I've been known to eat my words before). :)