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Hurst motor rumble?

I have an HW19-IV with the stand alone motor.
When I drop the stylus onto a stationary object next to the platter, there is rumble as soon as the motor is turned on. Turn it off, the rumble goes away.

I removed the drive belt and tried again. No rumble. This means the noise is not coming through the platform on which everything sits.

Next, drive belt still disconnected,I dropped the stylus and spun the platter by hand. No rumble. (The bearing appears to me to be tight and well lubed so I don't think the noise can stem from disaligning of the platter bearing by the pressure of the belt.)

It seems obvious that the noise is coming from the motor through the drive belt to the platter. I am using a standard Hurst 600 rpm motor.

I always thought, apparently erroneously, that the drive belt itself damped motor noise. If any of you has a belt drive turntable, I would like to know what happens when you perform the aforementioned test. You need deep bass and may have to turn up the gain.
Can anyone verify that a "quieter" motor might reduce or even eliminate this rumble?
Has anyone done actual measurements of this effect and what are they?
rpfef
rpfef OP
110 posts
 
The rumble is masked by surface noise when a record is played. As we all know, unheard vibration can cause audible effects elsewhere.
The fact of this vibration getting into the signal matters, I would think especially at higher volume.
It is irrelevant what I should or should not do when placing my stylus on a plinth mounted cleaning device. The fact of the rumble remains.
The vibration is clearly low-frequency. That's why I suggested you would need speakers capable of some bass. Also, since this noise is pretty low level, you'd need, in all probability, to turn up the volume to hear it well. I listen at pretty high volume but this noise can be heard (but only with the belt in place!) at low levels, also.
If you tried this test on your "custom" HW-19 with negative results with the drive belt connected and turning the platter and the needle resting on something attached to the plinth but not the platter, like a stylus cleaner, and your speakers reproduce 60hz signals and you tried the gain at high, then I conclude that my problem is solvable with a motor that has less vibration.
This is what I am trying to determine before putting money into it.

The secondary question, then, becomes what motor can I get at reasonable cost that has lower vibration than the standard Hurst 600RPM motor.
mofimadness's avatar
mofimadness
4,982 posts
 
I know that VPI is now using a custom made 600rpm motor.
Still from Hurst, but not available from Hurst directly as a
replacement, you have to order it from VPI. I've read that it
is supposeably better, (not sure in what regards). You
could contact VPI and ask them.
brf
1,715 posts
 
Two suggestions.

1) install a rumble/subsonic filter http://www.kabusa.com/rf1.htm

2) try isolating the SAMA better with a compliant material like sorbothane. It is possible that motor vibrations are being transfer to you table via the platform.
melm
1,074 posts
 
It's hard to figure out what is going on.

But if you want a quieter motor, you can try the 300 rpm one. You can get it less expensively directly from Hurst (IIRC it's exactly what VPI uses) but you would have to get a new, larger, pulley from VPI.
bpoletti
1,552 posts
 
I've never thought about "dropping the needle" onto anything that didn't have some kind of spiraling groove toward the center of the turntable. My tastes in music don't venture out that far.

If the noise doesn't happen during playback, who cares?
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