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 

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Could be the thorens motor? I used to have a td320mk2. Only unwanted noise came from this part. It might amplified by the plint, table it connects on.
There seems to be a modkit for mk125..
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?
What cartridge are you using? That arm has a super light mass of 3 grams!
http://www.theanalogdept.com/bw_adc.htm
It may make sense to address the motor noise/vibration first? Admittedly it has been a long time since owning a Thorens turntable, but I don’t recall it having as much audible noise as you describe.

 

The first generation Infinity Black Widow tonearm with knife-edge bearings requires the use of a low mass/high compliance cartridge for it to perform at its best. (Back in the day think Micro Acoustics, ADC, Grace, etc.) I would not recommend a “home brew” damping strategy. This does not necessarily address your issue but should provide the opportunity for best tonearm/cartridge performance.Watch those original wires, super fragile as you probably already know.


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 
That Ortofon is a good match with that arm,here are the results from vinyl engine,a perfect resonance of 11 hz.
The problem is not with the arm and cartrige compatibility!  https://www.vinylengine.com/cartridge_resonance_evaluator.php?eff_mass=3&submit=Submit
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?
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?
then what's the damping fluid for on the later models?


To allow more flexibility in choice when using lower compliance cartridges.
The arm in its early iterations was susceptible to what was called at the time “bearing chatter.” As totem395 mentions the damping fluid tray served to increase cartridge compatibility. It also helped to alleviate the potential for bearing chatter.
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....
Yes, absolute first-hand experience with the Infinity tonearm many years ago. One of the best combinations was with the ADC XLM II that you mentioned purchasing NOS. My turntable at the time was a Kenwood KD-500, which was direct drive and having a fixed suspension. So, very different from the Thorens. Since what you’re describing is while the tonearm is not in use it is unlikely having to do with the bearings.
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,

I have a Grace 747, which isn't unlike your BW arm.  The Grace is dead silent, and is my favorite.  I have it mounted to an old Dual 1229 and their is no rumble or noise anywhere.  I would suspect that the noise you are hearing is motor related, not arm related.

I'm not so familar with your Thorens, but if you're handy I would pull the motor and open it and inspect the top and bottom bearings.  If you havent serviced it recently it's probably starving for a little oil.

Also, inspect the motor shielding and power cable.  This too can cause what you are experiencing, as can poor tonearm leads.

Sorry, but their are several things to consider.  Oh, the ADC is an excellent cartridge.  I have one in my stable and do enjoy it from time to time..
N.

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