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Rumble question- Thorens/black widow

Hello, I've been a reader  for a while but this is my first post. Thanks in advance for any help/advice!

my turntable makes a very soft rumble sound mostly audible between the tracks or in very soft passages of music. I know the noise floor will never be like a cd but I would like to address this as I don't hear it in my previous  turntable which is a cheapie. 

I have a thorens td125mkii w an infinity black widow tonearm. I suspect the sound is actually due to the tonearm. That's because it seems to be microphonic, because if I gently rub my finger on any part of it, you can hear the gentle rubbing sound get picked up. This is the first black widow- it doesn't have damping trough.  

-do you think the rumble is from lack of damping or maybe not?
-can I diy damp the arm easily to test it?
-or what else might be the problem? It has original wiring but theres no hum or feedback at all. 

Thanks and sorry if this post was long!
-David 

128x128mugrug12

Showing 7 responses by mugrug12

mugrug12's avatar
mugrug12 OP
10 posts
 
It's definitely originating in the motor, but due to the microphonics I observe I've the tonearm, I think that is why it's being picked up maybe. The motor can be heard with your ear directly next to the pulley w no platter on which I figured was normal probably?
mugrug12's avatar
mugrug12 OP
10 posts
 
Thank you guys...

the cart is an ortofon super om30. I just got an nos adc xlm ii so I can see if that makes a difference but it seems like it's the arm. For instance if I lift the arm and gently slide a finger down the tube with my other hand I can hear the sound of the finger running come from the speakers. Is this the kind of microphonics that damping mitigates?

the motor doesn't really make noise. Your ear has to literally be an inch from the pulley w no platters on to hear it. I figured that was par for the course, is that wrong?

Dave 
mugrug12's avatar
mugrug12 OP
10 posts
 
Thanks that's helpful guys. Is bearing chatter possibly what I'm experiencing then? Or I'm barking up the wrong tree maybe. Have you guys ever owned a thorens td125mkii or BW tonearm? Time to google "bearing chatter" here I go....
mugrug12's avatar
mugrug12 OP
10 posts
 
Yes- The music itself sounds awesome and i think w the xlm mkii it will be even better.  I just think the noise floor should be lower. Is tomearm damping strictly to fix resonance from the music, or is it also for mitigating mechanical vibes from the turntable itself? Could it be damped externally somehow?
mugrug12's avatar
mugrug12 OP
10 posts
 
I think also maybe I don't fully understand the purpose of tonearm damping. If the mass/compliance is well
matched producing the correct recosnance, like my setup is, then what's the damping fluid for on the later models?
mugrug12's avatar
mugrug12 OP
10 posts
 
It tracks great w the ortofon and im excited for the xlm (though a little nerve racking using thise tiny wires!) 
maybe my issue is the thorens itself. But this model is known for having really low rumble I thought...
mugrug12's avatar
mugrug12 OP
10 posts
 
Hi Norman,
dont apologize, all the responses are very much appreciated and I like problem solving!
I did squeeze some oil under the pulley and worked it down, however I should hit the bottom bearing good call. 
However- I think I just figured out from an experiment that it's not the motor causing the rumble:
I took the belt off and put the platter back on. Threw on a record and lowered the stylus onto it. I turned on the (beltless) motor. Total silence from the stereo. Does that suggest the noise is not from the motor, or is my logic flawed?
-Dave 
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