Thorens TD-124 noise diagnosis - diyAudio
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Old 16th January 2011, 08:08 PM   #1
dls123 is offline dls123  Canada
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Default Thorens TD-124 noise diagnosis

Hi all,
A few months back I lucked into a free TD-124 Mk I from a friend who inherited it and knew I would like it. It appears relatively unused. I made a multi-ply baltic birch plinth, oiled the bearings, and mounted an AT 1005 Mk2 arm. I have both a V15 type V and Decca cart, each in their own SME headshells. I have been running the Decca and the TD124/AT1005/Decca combo is amazing. More lively than my old TD125 Mk2/SME/V15 combo. Could never run the Decca in that SME arm. So anyway, the sound is amazing, the bearings dead quiet, speed is steady within 3 - 4 minutes and it hits speed within 3-5 secs of turn on. Also it rotates for a good minute after turn off. So it seems to work well. There is this annoying amount of surface rumble or other noise (you tell me) when the needle is down and the motor on. If the needle is down and the motor off the noise is gone. I cannot tell you the frequency, but it is low. It would seem the noise is motor/bearing related, yet motor is dead quiet, you cannot hear any motor or belt noise even with your ear to the table and cannot feel any vibrations. Clearly it is coming in through either the platter or the arm. Here is what I have done so far to diagnose:

1. installed the motor suspension kit to convert to a Mk2 suspension. This one is from Mirko on ebay. Installation was easy. Result was absolutely no change in the noise level, but it looks nice...

2. removed the arm board screws and let the arm board rest on a layer of very thin cork I have around for insulating wires from chassis in old tube restorations. I just rested the arm board on the cork and put the needle down on the lead in groove and noise was the same. I know there are better ways to isolate the board from the chassis, but this was a quick experiment. My reasoning was that if this was the problem there should have at least been a reduction in noise. Again, no change in noise which leads me to believe the sound is not coming into the arm through the board...?

3. I neglected to mention that noise level is the same with both cartridges, so it is not a Decca issue (Lord knows there can be many of those, but this one works fine in this arm).

So, does anyone have a suggestion as to what to do next? The motor runs perfectly quietly and cool and holds speed well, accelerates well, so I am loathe to take it apart. Idler wheel is original, but is true and silent, but maybe it is the source? Or the main bearing? Or other bearings? Belts seem just fine, again, no audible noise from anything. You can not even tell the table is on with your ear near it. Given the cost of some of these replacement parts I don't want to just start replacing things? The mushrooms are original. My feeling is that replacing them will not solve the problem, but perhaps I am wrong? The amount of noise is not bad at all when music is playing, but you can hear it in a quiet passage with the volume up. The TD125 has no similar issues being belt drive. While I understand the idlers will be noisier, I think this is probably excessive. So any suggestions as to what to try next will be appreciated. I do see what the fuss is about, this thing has amazing dynamics and sound stage with that AT1005 Mk2 arm and Decca cart. Phono preamp is a completely restored and "McShaned" Citation I. I am Jim McShane's authorized installer/tech in my spare time, so I do know how to tinker and rebuild. I would just appreciate advice before rebuilding anything else on it! What should be my next move or diagnostic?

Thanks in advance!
Don
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Old 16th January 2011, 08:18 PM   #2
Pano is offline Pano  United States
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this should go into one of the existing TD-124 threads. Will figure out which one and move it.
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Old 16th January 2011, 08:30 PM   #3
dls123 is offline dls123  Canada
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Sure, I was reading some of them. Let me know wherever you decide to move it.

thanks,
Don
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Old 17th January 2011, 06:36 AM   #4
volken is offline volken  Netherlands
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Hi Don,I think these are vibrations from the motorcoils 100hz ,see my measurements .
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Old 17th January 2011, 01:13 PM   #5
dls123 is offline dls123  Canada
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Hi
If so, then do I rebuild the entire motor, or just motor bearings? It would seem you are correct because turning the motor off stops the sound with the stylus down and coasting. It isn't a 60 Hz hum, higher. Also if it were a hum then it would still be there with the stylus lifted just off the surface. The belt is original I think, but in good shape. Very loose, just tight enough to make the table work properly. So what should I replace?

Thanks!
Don
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Old 17th January 2011, 01:52 PM   #6
oshifis is offline oshifis  Hungary
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Remove the belt and see if you still can hear the noise. It could be some problem with the motor suspension.
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Old 17th January 2011, 01:57 PM   #7
dls123 is offline dls123  Canada
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Hi
I replaced the motor suspension, upgrading to Mk II kit. Made no difference. Motor is dead quiet with or without belt. Only noise is heard on lead in groove or between cuts or silent passages with stylus down. Other than that you cannot hear the table running with your ear to it.

Don
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Old 17th January 2011, 03:08 PM   #8
BaMorin is offline BaMorin  United States
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Quote:
Originally Posted by dls123 View Post
Hi
I replaced the motor suspension, upgrading to Mk II kit. Made no difference. Motor is dead quiet with or without belt. Only noise is heard on lead in groove or between cuts or silent passages with stylus down. Other than that you cannot hear the table running with your ear to it.

Don
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Old 17th January 2011, 03:09 PM   #9
volken is offline volken  Netherlands
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Don rebuild the motor with new bearings, felts, bearing plate and ball, oil and most important
correct alignment during building up if you have no expirience let some one do it for you its a nasty job for the first time !!!
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Old 17th January 2011, 03:13 PM   #10
BaMorin is offline BaMorin  United States
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sounds like you have a main bearing issue, even though you can't hear it. Which really means nothing........I'll explain. Most any phono cart can read movement down to .01 micron.....not much volume at that little of movement, but none the less. If the main bearing is putting as much as 1 micon (10 times what a cart can read) of rumble into the platter you will certainly pick that up in the electrical sense, but the platter isn't moving enough air at 1 micron (of movement) for your ears to pick it up. Just my 2 worth
Marc
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