Direct drive vs belt vs rim vs idler arm

Ha ha,
Never seen or heard of that idler before?
In fact......didn't know that Fidelity Research made ANY turntables?

Dover

I do not think that the published specs for the SP10 are wrong.....There is no measurable speed change due to stylus drag.
I have alluded to another problem with speed stability in DD TTs that is unrelated to stylus drag or cogging. See my earlier posts. This problem can be fixed. It is related to the method in which the TT measures its own speed. Get this wrong and we have problems. It occurs at much higher frequencies and at a much lower level than the overt cogging and stylus drag phenomena.
Taking it away however is dramatic.
It also shows that we can perceive timing problems well below the threshold of measuring instruments.

What a great thread! I tune out for a couple of weeks and almost miss the best thread in ages.
Halcro: Here are the results from my DIY dd turntable. I used the motor and electronics from a Revox B790 which is based on the dual eds but with more sophisticated electronics with a platter from a feickert tt. https://picasaweb.google.com/114629926159017275364/MyPictures?authkey=Gv1sRgCLqX-P6Iw6SUdA#
Hope the link works.
Your results for the tt101 are interesting but more telling (as you have multiple arms) would be to place the smaller feickert test disc on top of a (heavily modulated?) 12" lp and play the lp with one arm and the test disc with another. This will give us a picture of what's going on in real time under dynamic conditions.
I proposed this a while ago on the tt speed accuracy thread.

Hi Lespier,
Very impressive results. Congratulations on your tt design. I am also amazed at the unfiltered results. Your test record is centered nearly perfect based on the extremely low Wow&Flutter results. Did you do anything special to your test record to center it? I think we all want to know how to do that.

Dear Ct, The copper mat cannot really "damage" the servo permanently. It's just that the servo is operating suboptimally. Excessive platter mass can only damage the bearing in the long run.