Hurst Motors: 300 RPM vs 600 RPM--Upgrade or Myth?

The Hurst motors are pretty limited as far as what you can do about vibration. The rotors are not dynamically balanced and can oscillate as they spin. A lot of this will depend on the condition of the bearing. I've tried to ameliorate this with thick oil in the bearing, but it doesn't help much (I went as high as 600K cst, but it didn't seem to make any difference). Part of the problem is the rotor is only supported on the top by a friction bearing. The bottom, where the magnet and most of the mass is, can flop around freely if it is not balanced. It would be much better if there were a bearing on the base of the rotor as well as the existing bearing where the shaft exits the motor housing.

VPI adds a brass collar to the shaft that allows you to cinch the rotor up against the wave washer to try to minimize the vibration, but with varied results. The windings can also "float" within the metal pole pieces so they can vibrate at the line frequency. I've had some improvement by adding silicone "washers" (0.0625" thickness, shore 50 high temp silicone) the size of the winding bobbins between the bobbins and the pole pieces, but this was most effective on the 60 series motors where I could replace the bottom plate with a thick aluminum one and compress everything to damp the vibrations. The stock 59 series motors are hit and miss it seems and they have a cheap "snap-on" bottom plate that won't work to compress a damping assembly. Some of them run fairly well, others vibrate terribly and there doesn't seem to be much you can do to stop it. Damping material and mass are just a band-aid; if the motor is prone to vibration, there isn't much to be done other than replace it and hope the new one is better.

The measurements I posted show the primary vibration response is from the cogging of the PM rotor with the metal pole pieces (120Hz). The only thing that can be done to reduce this vibration source is to reduce the drive current, but that also reduces the torque. No free lunch I'm afraid.
 
For just a second I was going to suggest the thrust bearing mod that I've seen mentioned for Rega motors, but then I remembered that the Hurst motors don't have the bottom of the shaft exposed the way those Philips or Premotec motors do (unless it's just covered by the label sticker... Hmm). I'd have to pop open the motor pod again to see whether I could even do anything useful at all to the actual motor. I think the motor used on the Player could potentially benefit from a thrust bearing, though, but that doesn't help with a Scout.
 
Stumbled across this: 9904 111 31813 - ALLIED MOTION PREMOTEC - Motor, Reversible, Synchronous, 31813 Series, 110 Vac, 250 rpm, 18 mA | Newark element14

These are the motors used in a lot of British decks (Rega, etc.). Would this have the necessary torque for a VPI platter? Would it have better vibration characteristics than the Hurst motor? And assuming a suitable pulley could be machined (Enjoy life with LP's and Turntables seems a good potential source) and base/housing cobbled together, would anything else be necessary to wire it up to safely use with a Falcon? Or would this motor be just as noisy as the Hurst or too weak for a VPI deck?
 
It should be able to turn a Scout platter with no problem. They have 3mm shafts (or possibley 0.125") so you will need a new pulley. When the motor is spinning in your hand, it will have some vibration, but mounting it in a heavy case like the SAMA housing will quiet it down. They are rated at 2 Watts and constructed better than the Hurst motors IMO, so it should run fairly quiet.
 
Stumbled across this: 9904 111 31813 - ALLIED MOTION PREMOTEC - Motor, Reversible, Synchronous, 31813 Series, 110 Vac, 250 rpm, 18 mA | Newark element14

These are the motors used in a lot of British decks (Rega, etc.). Would this have the necessary torque for a VPI platter? Would it have better vibration characteristics than the Hurst motor? And assuming a suitable pulley could be machined (Enjoy life with LP's and Turntables seems a good potential source) and base/housing cobbled together, would anything else be necessary to wire it up to safely use with a Falcon? Or would this motor be just as noisy as the Hurst or too weak for a VPI deck?

Hi there,
Some months ago, I purchased this same motor from Element14 to replace a worn 1980s Philips Airpax motor (now known as Allied Motion/Premotec). The new motor model number is exactly as you've mentioned. For some reason, the old motor had different phase capacitor (0.68uf) and the new motor would have to use 0.22uf (this is for 250rpm/50hz here in Asia). Nevermind this. What I found is the new motor have much less torque and need minimum 90V at the phase for starting up the Systemdek 11X platter which is almost an identical glass platter as Rega turntable. The old motor would happily start up the platter at 80V without trouble.

Having said all that, I looked into the last model (shortly before product discontinuation) of VPI Classic 1 and found a different Hurst motor (Model AB-SP Part# 3005-003, 5W/24V/600rpm) in place instead of the bigger 10W PA/PB 59mm series. Obviously, the pulley is different size but drive the same 20lb Classic platter. This Classic 1 is also fitted with a custom 24VAC motor drive board for this model. The new motor seems similar size and wattage with some difference. American made motor shaft diameter would be imperial inch size and European motor being metric measurement. Hope my info is of help.
 
I would like to add that USA market VPI Classic 1 would be fitted with Hurst PA/PB 59mm 110V/60hz/600rpm and standard pulley to suit. What I own here is a Asia Pacific export model with Hurst PA/PB 230V/50hz/500rpm and a different diameter pulley to suit 500rpm to 12" platter. In any event that I need to buy a spare 500rpm motor pulley, I can't buy this online nor use HRX pulley option from USA VPI dealerships. At this point in time I'm having a custom metal pulley machined out for 2-3 belt drive to be fitted to my Classic 1. Due to my lack of pulley design skill, I hope my local machine shop can clone the original pulley for a 3 belt drive. If I can't match it 100%, then my upcoming SG-4 controller will compensate for any shortcoming.
 
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Jasmine TM-R501 Turntable Motor | eBay

This is also an intriguing product, though I wonder if it would be much/any better in the long run. It would certainly be easier to control than the Michell motor, with the dial on the motor pod itself, but I have no idea the quality of the assembly. And again, the downside of the DC motor is not really being able to auto-control it with the Falcon. That said, given the description, I wonder if it could be possible to modify it for some kind of external control...
 
Pyramid,


Would it be possible for you to measure the Hurst motor vibration when driven by the two phase generator that you have made while driving the platter.
My experience is that this way of motor drive results in less noise compared to the simple cap that is mounted as factory standard.


Hans
 
Pyramid,


Would it be possible for you to measure the Hurst motor vibration when driven by the two phase generator that you have made while driving the platter.
My experience is that this way of motor drive results in less noise compared to the simple cap that is mounted as factory standard.


Hans

Hans-

The plots below were made with the same 5.5W 600 RPM motor in the same SAMA housing with the accelermeter located at the same point on the SS ring of the housing, with pulley attached but no belt (or platter). Adding the platter to the equation seems to reduce the vibration levels about 3dB.

The first plot is with the motor driven from single phase wall power with factory phase cap; the main response is at 120Hz (cogging) at ~-52dB.

The second plot is with the motor driven from a dual phase supply set to 90° phase offset and full voltage. The cogging response is down ~9dB.

The third plot is with dual phase drive, but the voltage reduced to 90VAC. The cogging response is about the same, but the motor started vibrating at ~40Hz at a level of -36dB. The response at 60Hz also came up dramatically at a level of ~-52dB. This got worse the lower the applied voltage was.

The motor has the brass collar on the shaft and in the past, I was able to reduce the random vibration that seems to occur with these motors, but it is mostly hit and miss. YMMV...
 

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Well that's curious... I experimented with the Voltage Output Mode on the Falcon, using a db measurement app with my iphone placed directly on the motor pod housing. Dropping the voltage down to 75V from 99V led to about a 2.5db drop on both 33 and 45 settings. Are you saying that dropping the voltage might actually be counter-productive, or just when using the phase offset?
 
Well that's curious... I experimented with the Voltage Output Mode on the Falcon, using a db measurement app with my iphone placed directly on the motor pod housing. Dropping the voltage down to 75V from 99V led to about a 2.5db drop on both 33 and 45 settings. Are you saying that dropping the voltage might actually be counter-productive, or just when using the phase offset?

On the earlier plots I did (OP), the lower the power the lower the vibration, but those were all single phase drive. This is the first time I've seen this (with dual phase) and I'm not sure where it is coming from. The primary response (40Hz) doesn't seem to be related to the drive frequency. It may be the rotor oscillating (think a spinning top that creates a counter-rotation wobble), but I don't know why it happens only at dual phase or why it is affected by lower voltage.

I've had motors that would exhibit lots of vibration until they were smacked sharply against the table top; they would quiet down remarkably until hit again or shook. I think the Hurst motors are not precision built and can lead to a lot of mechanical problems like this.
 
Is anyone else having trouble posting to this site?

When I start typing, the screen display starts to lag behind what I type. By the time I get a hundred words into the queue, I can type entire sentences before they show up.

I tried to reply to Han's post earlier today, but the site got so sluggish, I had to close the browser and try again (3x). The last attempt this morning was so bad, I clicked on "Preview" post and the screen locked up for more than 20 minutes. I finally had to reboot the computer as the browser stopped responding.
 
Is anyone else having trouble posting to this site?

When I start typing, the screen display starts to lag behind what I type. By the time I get a hundred words into the queue, I can type entire sentences before they show up.

I tried to reply to Han's post earlier today, but the site got so sluggish, I had to close the browser and try again (3x). The last attempt this morning was so bad, I clicked on "Preview" post and the screen locked up for more than 20 minutes. I finally had to reboot the computer as the browser
stopped responding.

Pyramid,


Thanks a lot for the published results.
It fully confirms my findings.
And no, I have no problems with a sluggish response while typing.


Hans
 

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> typing, the screen display starts to lag behind what I type

The edit-box runs on *your* computer. Ask what else your computer is doing at the time.

In older Windows, "Task Manager" is useful to see which programs or background processes are chewing-up a lot of time. Windows Update can be very greedy. So can viruses.

Here's TaskMan on my machine. I keep few background processes. Jiggling the mouse in FireFox browser bumps it to 6% (but I can't get back to TaskMan fast enough to screen-grab). My Google Photo Backup pops to a few % every minute. I recall Windows Update eating 50%-99% of a Pentium. I've found viruses by them hogging the CPU.
 

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Pyramid,


I was shocked reading the "Chernobyl" thread referred to in posting #5.
For a reputedly company like VPI, the choice of words is utterly beyond any form of communicating with your market.
I'm also surprised that they never went the road that others took like Linn to generate a two phase signal with their SDS / ADS frequency generators, reducing noise by some respectable 9dB or to offer a BLDC motor as a further upgrade option.
I can only agree with Harry's comment that at the end it's the sound that counts, but for the rest IMHO his reply is completely embarrassing.


Hans
 
Pyramid,


I was shocked reading the "Chernobyl" thread referred to in posting #5.
For a reputedly company like VPI, the choice of words is utterly beyond any form of communicating with your market.
I'm also surprised that they never went the road that others took like Linn to generate a two phase signal with their SDS / ADS frequency generators, reducing noise by some respectable 9dB or to offer a BLDC motor as a further upgrade option.
I can only agree with Harry's comment that at the end it's the sound that counts, but for the rest IMHO his reply is completely embarrassing.


Hans


It's never fun to read something that contradicts a premise that you believe, but the data I presented was accurate, factual and easily verified (or refuted) by simple measurements, which Mat indicated they would do, but as of yet have not done.

Harry's response is actually pretty typical for him, from what I've seen on their forum as well as others such as Audio Asylum. I think embarrassing is a fairly good assessment.
 
There's blame to spread around for the hostility on those threads. Too much historical resentment on both sides, I think. A damn shame, since both sides have produced some wonderful hardware, and could have done some amazing things together. :(

One thought occurred to me on why the 300RPM motor might seem better in practice: The larger pulley diameter and subsequently greater contact area between the pulley and belt might allow for better damping of the vibrations. I could certainly be wrong, but that might provide SOME help. I also wonder if that also puts less stress on the motor itself.

Or maybe there's no practical difference between the two. I don't know.

What I do know is that the VPI motor pod is kind of noisy. I'll get to find out tomorrow if the voltage reduction is good enough, or if switching to a DC motor (and possibly back to my Michell deck!?!) is ultimately the better option.
 
I measured just the 5.5W 600 RPM and 7.5W 300 RPM motor when connected to the platter of a VPI Scout via a single factory belt. Surprisingly, both motors did quiet down ~3dB when measured at the motor housing.

I also measured the vibrations at the plinth for both motors and they showed similar reductions, but not as much as I would have expected. (~7-8dB attenuation).

I also noticed that the higher frequency vibrations (harmonics?) of the 120Hz fundamental were reduced in the 300 RPM motor when connected to the platter and belt.

The first 2 slides are the 600 RPM 5.5W motor measured at the motor housing (slide 1) and at the plinth (slide 2).

The last 2 slides are the 300 RPM 7.5W motor measured at the motor housing (slide 3) and at the plinth (slide 4).
Hi Pyramid,

It's a while ago since you compared motors, but maybe you would like to add my measurements to your collection.
For my VPI, I have two motors, a 250rpm 6W Hurst motor and a 500rpm 10W Hurst motor.
The motor is (of course) driven by 2 phases shifted exactly 90 degrees, each having a distortion of less than 0.5%.
I have recorded through my Cart, needle on the record with the belt removed and the motor turning.

As you can see below, the 500rpm motor has a strong 200Hz vibration that is 20dB less with the 250rpm motor.
At 50Hz they are comparable and below 50hz the 250rpm motor makes a bit more noise.
So in this case I would say that the 250rpm is the better one of the two.


Hans
 

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