Direct drive vs belt vs rim vs idler arm

Motor speed control circuits have to be designed for the various types of drives. For belt drive tt's the circuits must likely be tuned specifically for the belt compliance/platter mass being used. DD tt's must have altogether different speed control circuits as compared to idler or belt drive. Back to belt drive; I think changing belt types on a tt affects the sound because the spring rate of the belt has changed thereby affecting the dynamic response of the system. The speed control circuits are designed around a specific set of parameters including the belt type. Changing belt types alters the spring rate side of the equation and may make the table sound better or possibly worse. It might be hit or miss. The same goes for adding mass to the platter.
You have to try the Dr. Feickert Analogue iPhone/iPad app. I think it is a killer app. You need a test record with a 3150Hz test tone. You can order one through the maker of this app or in my case, I have a test record with a 3150Hz test tone. This app does three things; it lets you dial in platter speed while the cartridge is tracking in the groove, it analyzes and computes your table's Wow&Flutter (it automatically filters out the record's runout which can accentuate Wow&Flutter) and it charts your platter's speed over time. My particular tt has Wow&Flutter measuring +0.02%/-0.03%. That is within specifications. The speed plot over time shows a small, smooth sinusoidal wave. That might be motor cogging smoothed out by the platter mass, but I think it might be the motor speed controller cycling about the setpoint. I measured the speed of an old Oracle tt and it did a little better than my tt. It had a Wow&Flutter measurement of +0.01%/-0.01%. It also had a smooth, low frequency sine wave for speed vs. time. The Oracle was harder to adjust and dial-in an exact speed of 33 1/3. I would really like to hear from others how their idler drive and direct drive tt's compare with the speed vs time plotted by this app. It might give us some insight into why the different drive systems sound different.

I also meant to mention that by setting platter speed with this iPhone app, it significantly improved the PRAT of my tt. I had been using the little strobe disc for years to set platter speed. The speed was off by a significant amount using the little manufacturer supplied strobe disc.

I respect all of our opinions, and really being happy with one's turntable is all that counts. For me, in practice, there is such a thing as "good enough". The theoretical discussions are a separate bit of play.

Well said, Lewm, and a welcomed reality check in a discussion verging at times toward angel-counting on a pinhead.

Tony, Is Dr. Feickert a psychiatrist? He must be, to play with the minds of audiophiles in such dangerous ways.

As to Dover's post, belt creep is not caused from stretching the belt. Find Mark's writing on the subject because he explains it far better than I ever could, and he backs it all up with the proper math. It is a physical limitation of a belt drive system that generates an inherent tracking error.

As far as I know, Mark doesn't address tape drives or string drives, however. I don't look at a string drive the same way as a belt drive, but tape may be a viable way to avoid the problem. String drives have a limited slip that has always intrigued me.

Syntax discounts the idler drive out of hand, but I assure you that all the problems that he mentions have been addressed. It has a lower tracking error than a belt at around one part per million, and it has fewer maintenance worries than a string. Not only that, but with a proper controller it is more speed accurate. However, that's not to discount the string because I believe similar outcomes can be reached with a string when the system is designed correctly and built well. It can be fiddly, though.

.