Cogging!

Thanks for the info!

I have DDs whose motors 'cog'. Theoretically awful — but I hear no deleterious effects, sounds utterly smooth and pitch-stable to me.

Bardo
anti-cog

Cogging is a bad thing in any turntable motor, regardless of how it drives the platter.  With belt-drive, it could be even more annoying and noticeable than with DD.  But the fact is that in most any modern turntable of reputable design, motor cogging should not be an issue, even if it's happening. 

bimasta, If you hear no issues with the turntables you own, then how do you know the motor is guilty of cogging?  Is it merely because they are iron core motors?

To reduce or even eliminate cogging, try using a variostat between the wall outlet and the turntable.  For turn-on, use full 120v (or your local wall current).  Once the platter reaches speed, reduce the voltage to just above the minimum required to keep the motor spinning the platter.  I don't know how effective this will be with a quartz-controlled dd table, but for AC synchronous motors, particularly VPI motors.  It's a LOT cheaper than a VPI SDS or other motor controller and just as effective.