Bodine motor rumble: capacitor? [and more Presto 6N...]

[markrob]

Hi Steve,

Its interesting that its mostly vertical. Have you tried to narrow that down? If you play back a silent cut with a stereo pickup, you can see the vertical vs. lateral rumble by creating two tracks. The sum of L+R will be the lateral rumble and the difference L-R will be the vertical component. If its more vertical than lateral, you might be able to see if there is something mechanical with the motor mount that is causing the vibration. Something else to try would be to cut a silent groove with the motor running normally. Unplug the power while cutting and let the platter spin down. If the noise is due to mains based motor torque ripple, then it should stop at the time the power is removed. If its due to some mechanical issue (e.g. eccentricity), then it will remain on playback during the spin down. This may not be a useful test if the time to spin down is too short.

If you determine that the motor torque ripple is the main cause, you might be able to make a big improvement by going to a servo controlled brushless DC motor. Not sure its worth the expense though.

Mark

[Steve E.]

Hi Steve,

Its interesting that its mostly vertical. Have you tried to narrow that down? If you play back a silent cut with a stereo pickup, you can see the vertical vs. lateral rumble by creating two tracks. The sum of L+R will be the lateral rumble and the difference L-R will be the vertical component.

Yes. Did more or less this. Simply, summed L+R and most of what I am hearing disappeared. Also, when I look at "silent" groove under microscope, the bottom of the cut is straight, but the depth of cut wavers rhythmically.

Unplug the power while cutting and let the platter spin down. If the noise is due to mains based motor torque ripple, then it should stop at the time the power is removed. If its due to some mechanical issue (e.g. eccentricity), then it will remain on playback during the spin down. This may not be a useful test if the time to spin down is too short.

I did this, too, and indeed the symptom went away when the motor was cut.

It's almost certainly coming through the idler wheels. That's the only point of contact that I can't isolate. The main thing I can think of that would help would be a better platter mat (different or thicker rubber, or cork?) plus rubber material on the center flange. The flange has none, right now. And, either a more viscous damping fluid in the dash pot, or perhaps no dash pot at all?

[alexdw5]

Hey guys, did you ever find a fix for this? I just picked up a 6n and it has some formidable low-bass rumble when I switch the motor on to turn the platter. The funny thing is, it only happens at 33rpm. When I try 78, there's no rumble whatsoever. Thinking about ordering some of those aforementioned Grainger grommets and trying those out, and maybe trying to re-set the motor via the two adjustment screws on either side, above the motor.

[Jccc]

I have a rumble on my Presto 6N as well. it does not come out in the recordings but it is kinda loud.
I am wondering if its the rubber wheels?

either way I will just let it be as its not effecting the recordings or the platter speed.
I uploaded a video of it

IMG_4197.MOV

[MEGAMIKE]

ive always wondered why the rumble in my prestos and the vacum on my vr never comes out on recordings

[trailerparkjesus]

ive always wondered why the rumble in my prestos and the vacum on my vr never comes out on recordings

Vacuums do on t560! Only way to get rid of most is to remove the pot from the machine and mount it away from it all. Still will get some regardless. But to say there is none means your not blasting your silent test cuts loud enough.

[MEGAMIKE]

sounds like a worn diamond to me ..and blasting blank cuts louder has nothing to do with vacum volume...maybe if i had mr tuffnills "11" amp from spinal tap