Turntable speed accuracy

I found a website where the owner installed a Papst motor in his Thorens TD124 and compared its performance to that of the turntable with its original motor. He liked the musical "drive" with the Papst but preferred the Thorens motor for its lower noise floor. However, he did also comment that with a true 3-phase AC synchronous motor controller (so you can throw away the phase-splitting capacitor), the Papst would have been MUCH quieter and therefore might outperform the Thorens motor in all other respects. So, Ralph, have you ever used such a motor controller with your Atmasphere 208 turntable?

I hope this is only slightly OT. :<)

I found a review posted by 'grimagog'? for a Mark Kelly controller applied to a Papst 3-phase motor. His claim was that having the ability to "tune" the current via the conroller leads to a quieter motor and (back on topic) improved speed stability.

Mark Kelly posts over at the DIYaudio forum occasionally and appears to be extremely motor-knowledgable. Jim Hagerman was toying with the idea of a new 3-phase motor controller as well.

I've got to believe that a multi-phase AC motor should be easier to design for speed stability compared to a 2-phase or single phase motor. More continuity of pulse per revolution, for sure. Certainly much of heavy industrial motors are 3-phase, so I think the math is pretty well-understood. But since most of us live where the power coming in over the wires is not 3-phase, some kind of controller is needed.

The Papst motors discussed above use a 4uF cap to provide the appropriate phase delay, to "trick" the motor into sync. I wonder if atmasphere has any tricks for improving the motor performance on his tables?

I've had good success with some of those grand old tables by micro-polishing the bearing balls, and improving the sleeve's ability to retain oil via fine cross-hatching at 1500 grit. The Rabco tables were interesting in that they had a spiral groove to "pump" oil back up the sleeve to keep a nice continuous lubrication film. With the right lube viscosity, these things would spin for several minutes down from 78rpm. I think the Empires were the same way.

So a nice even motor and nearly frictionless bearing = speed stability? (carefully avoiding the drive question here)

Atmasphere: "Were it not for the motor in the 208, I'm not sure I would even be messing with belt-drive at all."

I share that sentiment.

Lewm: " I actually thought that the term "Papst" (Pabst?) refers to a particular motor configuration, patented or invented by someone named Papst, not to a company that makes a wide variety of different kinds of motor."

I am surprised that you did not know Papst is a company that made motors. Yes, it's Papst with the P. and the same Papst model is used inside the Empire 208, Fairchild 412, various Rek-O-Kut belt-drive and idler-drive tables such as K33H and L33H. Different motor models are used in Thorens 124 as replacement, smaller motor in the Empire 598, etc...

It's also possible the Audio Note TT3 three-motor turntable uses Papst motors. http://www.audionote.co.uk/products/analogue/tt-3_01.shtml#

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Dear Lewm,
Yes it is Exactly as you described. Modern manufacturers have better toolings and usually better preconditions but most do not make proper usage of it. Continuum is a positive exception. Nowadays high quality bearings seem to be too expensive which means we are offered more and more crap.

Best & fun only

Dear Thuchan, I just this past month ordered the bearings for my new turntable design and the costs are - with a limited edition of 12 units for 2012 and 2013 - USD14,800 + 19% VAT for the bearing alone (no joke - for each single bearing).
But then this bearing is a custom-made bi-planar air bearing of outstanding precision, capable to lift and spin a 110 lbs platter with ease.
If one want to go all the way it get's expensive.
But there are many good standard bearings out there, for far less money and of high quality.
Cheers,
D.