Prime motor construction

Prime motor construction

Postby Mr_Putty » Wed Sep 12, 2018 12:16 pm

A bit of history. I have determined that my Prime motor is adding noise to my TT via my belt. With a string belt that is tight the noise sounds like rumble. Same for the rubber belt. It is audible at normal listening levels. If I reduce the tension on the string belt the noise goes away! But, the belt is so loose I suspect slipping and speed variation. If I ignore the “rumble” there are sonic improvements that are desirable with a tight string belt. With the rubber belt the speed is really too fast, and always has been, on any of the pulley settings. With the string belt the speed is slow. I should add that lifting the motor off its base did not affect the rumble I want to eliminate. Now to my motor. When I got it there was enough vibration that I wondered if it was bad. After the recommended break-in it felt much better, and after about 40 hours it seemed fully seated and smooth. The pulley and brass collar are both tight. And the pulley looks true when spinning. SO, what to do? Is there a diagram of the motor showing it’s bearings? Are they user replaceable? I have seen there are precision ceramic bearings online. Would they be recommended? I know a speed controller would be useful, but the concern here is the unwanted noise. Are other Prime users having this problem or solved it? BRF, your comments please.
Thanks,
JTA
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Re: Prime motor construction

Postby 10ovr » Wed Sep 12, 2018 1:01 pm

Try putting a mouse pad under the motor see if it changes,,,
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Re: Prime motor construction

Postby Mr_Putty » Wed Sep 12, 2018 2:53 pm

10ovr wrote:Try putting a mouse pad under the motor see if it changes,,,

I stopped using a mouse pad a long time ago. Mine were unreliable, and I recently lifted the motor by hand while listening with no change in rumble. So it’s not coming from the motor through the TT platform and back to the stylus. I just switched back to the rubber belt to confirm and it’s still audible.
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Re: Prime motor construction

Postby spinblackcircle » Wed Sep 12, 2018 3:09 pm

There have been cases of motor magnets being damaged in shipping. While I could pickup the sligtest motor noise/vibration when I had a Classic. the motor on my Prime is the quietest VPI motor I've had.

If your table is under warranty, I would get your dealer involved. If it isn't, maybe a new motor will fix you up.

http://www.hurst-motors.com/papbdirectdrive.html#buy

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Re: Prime motor construction

Postby Mr_Putty » Wed Sep 12, 2018 3:34 pm

spinblackcircle wrote:There have been cases of motor magnets being damaged in shipping. While I could pickup the sligtest motor noise/vibration when I had a Classic. the motor on my Prime is the quietest VPI motor I've had.

If your table is under warranty, I would get your dealer involved. If it isn't, maybe a new motor will fix you up.

http://www.hurst-motors.com/papbdirectdrive.html#buy

3201-001

What’s odd is that I just did the motor lift test with rubber TT belt again, with the same record as last night and headphones to eliminate ambient noise, and now hear the rumble decrease when the motor is lifted. The motor also seems very smooth, but last night it had some roughness I could feel. So, I guess it’s possible it’s in the last stages of break-in. The variation in vibration is what has me wondering about the bearing condition and replacement with better ones. If the bearings are serviceable I’m willing to try cleaning them, which should only help with smoothness. I can do the string belt test later tonight for a second comparison.
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Re: Prime motor construction

Postby Brf » Wed Sep 12, 2018 3:39 pm

Unfortunately, the Hurst motors used by VPI suffer from manufacturing inconsistencies. I know that VPI tries their best to screen out the poor performers, but sometimes a perfectly good Hurst motor will start to vibrate and get noisy. This is because the Hurst motor is only supported from the top by a single friction bearing (sorry no roller balls used, therefore, nothing to upgrade) and the heavy magnet structure that hangs below the bearing can start to vibrate when out of balance. A better design would have both the top and bottom supported by a roller bearings.

As you have pointed out, there exist a brass collar just under the pulley. The brass-collar serves two purposes 1) it locks the shaft to aligns the rotor with the windings, and 2) provide a small flywheel affect to help filter and damp cogging. You can attempt to adjust the rotor/winding alignment by releasing the brass collar set screw and move the pulley shaft to fine tune the rotor/winding alignment. I’ve done this successfully to help reduce both noise and vibration.

Sometimes the noise and vibration will dissipate when you lift the motor up, but this could be a result of realigning he rotor/winding with a non-perpendicular gravitational force. Make sure that your motor is on a level surface.

Another alternative is to replace the Hurst motor with another motor or another motor design design like a BLDC motor.
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Re: Prime motor construction

Postby Mr_Putty » Sat Sep 15, 2018 2:19 am

Brf,
Thanks for the detailed comments. I found a bit less motor vibration after loosening the pulley set screws a bit. I may try a rebalance by rotating the pulley a bit. A superior motor replacement would be welcome but I have no knowledge of which specific one would be a good choice. And I’m only about nine months in using this TT. I made some changes to my Prime isolation blocks and really like what changed. I also removed the string belt and went back to two rubber belts. So far every record I have played sounds more musical. Maybe the motor was resonating a bit in addition to being rough, as it is also is not as noticeable. Only time will tell if the changes I made are stable. I have an idea about isolating the motor so that it does not rest on the TT base, but need to work out the details before proceeding. It would be suspended above the TT base.
Cheers,
Oktoberfest is here!,
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Re: Prime motor construction

Postby Lewisranchmike » Thu Sep 27, 2018 10:06 pm

Brf wrote:Unfortunately, the Hurst motors used by VPI suffer from manufacturing inconsistencies. I know that VPI tries their best to screen out the poor performers, but sometimes a perfectly good Hurst motor will start to vibrate and get noisy. This is because the Hurst motor is only supported from the top by a single friction bearing (sorry no roller balls used, therefore, nothing to upgrade) and the heavy magnet structure that hangs below the bearing can start to vibrate when out of balance. A better design would have both the top and bottom supported by a roller bearings.

As you have pointed out, there exist a brass collar just under the pulley. The brass-collar serves two purposes 1) it locks the shaft to aligns the rotor with the windings, and 2) provide a small flywheel affect to help filter and damp cogging. You can attempt to adjust the rotor/winding alignment by releasing the brass collar set screw and move the pulley shaft to fine tune the rotor/winding alignment. I’ve done this successfully to help reduce both noise and vibration.

Sometimes the noise and vibration will dissipate when you lift the motor up, but this could be a result of realigning he rotor/winding with a non-perpendicular gravitational force. Make sure that your motor is on a level surface.

Another alternative is to replace the Hurst motor with another motor or another motor design design like a BLDC motor.

Hello BRF:

May I ask if you know of a motor than would be an upgrade to the Prime. I just had some issues and got a new Hurst motor from VPI but it still seems to vibrate a little. Is there an upgrade drop in I can try.

Best,

Mike in Austin
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Re: Prime motor construction

Postby Mr_Putty » Fri Sep 28, 2018 2:09 am

Mike,
Is your motor already in it’s case? Either way is your impression of smoothness given time to break-in? I suggest you hold the motor while running it and move it around. You will likely feel some positions are smoother than others. Keep it moving it and try to encourage it to find smoothness. My Prime motor was pretty rough when I got it. I think it had some dirt in it as there was some dark grease like oil around the shaft that worked its way out. If you see any clean it off. Mine took way more than the typical 20 hours of running to get smooth. However, there was a noticeable improvement at the 20 hour point. I also tried to discourage its vibration patterns by using/altering various types of support pads and adding mass to the top of the housing via a stainless block that I could move around. All this helped smooth out what I think are “average” bearings. I can barely feel my motor vibrate now. The wait was a pain and uncertain. So, I too would like a better motor, someday. The Number9 motor controller claims to greatly improve motor cogging. But it’s not cheap. And any bearings that are not clean and broken in will still be a problem. I can confirm audio improvement as my motor got better. I guess that was part of the risk I took in buying a B-stock table. FWIW, I was told the only difference in new and b-stock was appearance. I can only say to me budget was the deciding factor. No regrets, still tweeking...and liking the results.
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Re: Prime motor construction

Postby Packgrog » Fri Sep 28, 2018 10:31 am

I would recommend trying out some Herbie's Tenderfeet in place of the standard rubber feet. I have something similar under my motor: stacks of Herbie's extra-thick grungebuster dots on top of Herbie's square big fat dots. These are much better at mitigating vibration transmission than rubber and mouse pads, and more stable as well.

Another thing that I did with my Scout Jr. motor that may not be possible with the newer cylindrical motor housings is that I placed some thin grungebuster material between the top and bottom housing plates to prevent them from ringing like crazy and thereby amplifying the motor vibration. This also worked quite well. Another thing that I tried that worked very POORLY was to try adding mass to the motor pod using either brass weights or a baggie filled with sand. Both dampened vibrations but had an audibly negative impact on the sound. Steel or lead ball bearings might be more effective and synergistic, but I have not tried them, as just the grungebuster damping seemed to work best for me, and I didn't want to risk causing a short by adding conductive material to the inside of the motor housing.

One good way to see if you can benefit from some simple damping would be to gently place your hand on top of the motor housing while listening to music. Can you hear the difference? If so, investigate damping options. If not, there may be something else going on.

Hope that helps a little.
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