Turntable speed accuracy

The argument between measured performance and audible performance must be as old as our hobby. Both sides of that coin are being described here regarding speed.

I don't have any musical training and I expect my perception of timing (tempo) is better than my sense of pitch, which is certainly not absolute. A few years ago when I bought my SP-10 Mk 2A I had a tech friend go through all the calibrations described in the Service Manual. The strobe showed steady speed but when I listened to any recording with a sustained piano cord I could clearly hear a wavering. My friend could not find a correction for that so I took it to a professional tech. With the aid of one of my observed recordings he was able to find another adjustment that eliminated the wavering. After that there was not observable difference in the strobe but there certainly was an audible difference.

Thus I don't feel any need to investigate this Timeline device.

This is an interesting discussion! Thanks all who have participated. I'm particularly interested in the role of the type of motor as it relates to speed stability. It seems that DC motors require a lot of fancy/expensive control mechanisms to achieve speed stability, many with a feedback loop of some sort for control. And as with any feedback loop, there is an opportunity for oscillation, which is certainly a problem.

On the AC motor front, you have synchronous motors, but perhaps the best performance came from the 3-phase motors, like the old Papst pancake motors that a number of high-end turntable makers used to use. I think technically they are eddy-current motors, and hugely inefficient. But their design with the spinning outer rotor and inner coils gave the motor a bit of flywheel effect regardless of the type of platter being used. It seems to me that the Papst motor is what is in the turntable that Atmasphere was raving about earlier.

Are there other 3-phase eddy-current turntable motors still in use today? I know that Papst ceased production of theirs, and it was problematic in several areas (the vanes make a whirring sound, for instance, and the bearing technology is 1950's era).

What other types of motors are best for speed stability?

I think you have it a bit backwards. Generally the motor chosen is related to the intended drive system. Plus there is a time-related effect. With regard to my first point, direct-drive motors pretty much must use some speed corrective mechanism, e.g., the well known quartz-linked servo. There are many ways of implementing this kind of circuit, and I am certainly no expert. The science of motors per se is amazingly arcane. However, just about all DD motors are either 3-phase AC synchronous types or DC types. Even within those two categories, there are many different ways to build each, which also will affect how the tt "sounds". Modern belt and direct drive turntables are still using the same technology, only with perhaps faster electronics. As regards my second point, 1960s and earlier turntables tended to use cruder single-phase or two-phase motors, e.g., Thorens, Garrard, and Lenco. But these were idler-drive and the motor is suited to that application. I just mean to say that you have broached a very complex subject and that in general it is not accurate to generalize on what type of motor per se is "best". You would not use a Pabst motor in a direct-drive turntable, for one example. There is more that I don't know about motors than what I do know. That much I am sure of. There are websites like this one where eggheads chat about motors 24/7, for example. Their jargon is at least as obscure as the one I work with all day long as a molecular biologist.

How do TT bearings in motors from the 50s differ from those used now?

Ketchup,
TT bearings of the 50is are bigger, more stable and usually in good TTs of a much superior built quality than those of most modern concepts.

best and fun only