Turntable speed accuracy

Hi Lewm. Papst made a huge variety of motors. I think the company still exists and now makes industrial fans. I haven't seen the external rotor type being implemented for dd nor do I think it would be a good idea to try. They did make a number of dedicated dd motors though . The SOTA turntables (as well as many other brands in the 80's & 90's) used a papst dc 'pancake' motor up to series iii . I did have a star iii as well and now now use the platter, bearing and vacuum pump in a DIY tt but with a different motor.

Pabst is indeed a company name and does not refer to a type of motor. The AC motor in our 208 is indeed the eddy current AC model and was also used by Rek-O-Kut and a variety of tape machines. With its external rotor, its flywheel effect is prodigious! As good as it is, IMO/IME their servo DC motors left much to be desired. Were it not for the motor in the 208, I'm not sure I would even be messing with belt-drive at all.

Hi Lewm. Papst made a huge variety of motors. I think the company still exists and now makes industrial fans. I haven't seen the external rotor type being implemented for dd nor do I think it would be a good idea to try. They did make a number of dedicated dd motors though . The SOTA turntables (as well as many other brands in the 80's & 90's) used a papst dc 'pancake' motor up to series iii . I did have a star iii as well and now now use the platter, bearing and vacuum pump in a DIY tt but with a different motor.

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)