Thorens TD-124 noise diagnosis

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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
 
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
 
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
 
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
 
Thanks Marc. Yet another possibility. Yet, why wouldn't I hear it when I shut off the motor and let it coast with stylus down? Or are you talking about main motor bearing? If bearings in the spindle were a problem then wouldn't I still hear it with motor off? Or does it require the torque of the motor running to reproduce it..?

cheers,
Don
 
Thanks Marc. Yet another possibility. Yet, why wouldn't I hear it when I shut off the motor and let it coast with stylus down? Or are you talking about main motor bearing? If bearings in the spindle were a problem then wouldn't I still hear it with motor off? Or does it require the torque of the motor running to reproduce it..?

cheers,
Don

Mainbearing has a wow component in the range < 1 Hz !!give speed problems !
 
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In a recent Stereophile review (Schick arm) Art Dudley had a similar problem with his TD-124 but not with the EMT arm he usually uses. I would try swapping the SME and Shure V15 onto the TD-124 and see whether or not you still have a problem. The solution in the case of the Schick is to not mount it on the extended arm board, but to the (slate) plinth.

Yours is a 9.5" arm, and it might be possible to mount it off of the arm board directly on the plinth and maintain the required pivot to spindle mounting distance. Not sure how practical this would be, but I would think your arm a fair match to the Decca so I can see why you went that way. I'm making two assumptions, one is that your plinth is heavy and lossy, and two that your TD-124 is not mounted on bushings.

I am using an SME 3009 Series II (not the improved) with Zu/Denon DL-103 on my TD-124/II and it is hard to imagine it being any quieter. I am however using the occasionally maligned geltec bushings on mine and if anything they do seem to be pretty good at keeping all motor vibration out of the chassis. I also have geltec dots on the lower platter, and between the plinth and chassis as I have a light, flimsy plinth at the moment.

You many have a minor arm/cartridge/chassis resonance issue that is amplifying the 120Hz component of the motor noise.

Note: If you have one of the early main bearings using plastic sleeves you should either replace the bushings with sintered bronze ones or replace the entire housing with one of Mirko's (sq38s) soon. These have a tendency to seize up and also as they wear if not outright seized they distort causing serious speed variations.
 
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Hi
Thanks for the detailed response. I am afraid there is no space on the plinth to mount the arm. I made the plinth to be just a bit larger than the table. Yes, the AT1005 Mk2 arm is a very good match for the Decca. It will play a V15 fairly well too, but is magic with the Decca. The noise is the same with both carts. I could mount the SME as an experiment, but I haven't got an arm board that is drilled for it. It might fit the current one, might not. Still, it won't track the Decca so would only be good for experimentation. Mine has the bronze bushings, not plastic. I may ship the motor off for a rebuild. I suppose it is worth it as it probably needs to be done eventually anyway. But the thing holds speed perfectly and is very quiet. Still, that may be the problem. If you kill the motor and let it coast, the noise vanishes. I doubt it is electrical because then you should hear it with the stylus just above the record and you don't. If it were a platter bearing then you would expect to hear it even with the motor off. All of this points to the motor, even with the new Mk II suspension upgrade kit in place. That made no difference. So I will consider a motor rebuild. Fabulous table/arm/cart combo. Music just leaps out of it!

cheers,
Don
 
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Hi
Thanks for the detailed response. I am afraid there is no space on the plinth to mount the arm. I made the plinth to be just a bit larger than the table. Yes, the AT1005 Mk2 arm is a very good match for the Decca. It will play a V15 fairly well too, but is magic with the Decca. The noise is the same with both carts. I could mount the SME as an experiment, but I haven't got an arm board that is drilled for it. It might fit the current one, might not. Still, it won't track the Decca so would only be good for experimentation. Mine has the bronze bushings, not plastic. I may ship the motor off for a rebuild. I suppose it is worth it as it probably needs to be done eventually anyway. But the thing holds speed perfectly and is very quiet. Still, that may be the problem. If you kill the motor and let it coast, the noise vanishes. I doubt it is electrical because then you should hear it with the stylus just above the record and you don't. If it were a platter bearing then you would expect to hear it even with the motor off. All of this points to the motor, even with the new Mk II suspension upgrade kit in place. That made no difference. So I will consider a motor rebuild. Fabulous table/arm/cart combo. Music just leaps out of it!

cheers,
Don

Hi Don,
My suspicion is that the motor rebuild may help very little, please read this article about what sounds to me like the identical issue: Listening #87 | Stereophile.com

I would strongly encourage you to swap arms and try the experiment with the SME/V15. Should the problem then persist at that point I would go ahead with the motor rebuild which you can actually do very successfully yourself - saving some coin for other upgrades. Check over at "The Analog Depot" for availability of motor bearings as IMLE his are the best precision bearings I have tried so far. (They were out of stock before Christmas so may not yet be available)

I'd say the geltec motor mount bushings might be worth a shot at this time as well, but YMMV, and they're not without controversy.

My concern is that there does seem to be an issue with certain arms (ytbd) on the TD-124 and noise. No one has conclusively identified the cause yet, but I suspect a resonance issue is to blame.

Edit: Rebuilding the motor is always a good idea, but based on your description of motor performance I'm not sure that the rebuild of itself will solve your issue. The motor is the root cause, but arm choice seems to play a role as well.
 
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HI
Very interesting reading. It appears to be the same problem. Too bad, as that arm and that cartridge are a perfect marriage with that TD124 except for the noise. I seem to recall other folks having that exact same arm on the TD124 with no mention of this issue. One of the reasons I traded for the AT1005 Mk2 arm when I got the TD124. I suspect you are right in that rebuilding the motor may make things a bit better as may trying other mother mounts, but probably will not eliminate the problem. I shall have to think on this one a bit, and will try the sme arm swap when I get a chance. It has been mounted on my TD125 since I bought it used in 1979, so I sort of hate to remove it.....

cheers,
Don
 
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Edit: I was wrong, the headshell is not an Orsonic, but probably is a stock AT headshell. I would try the other cartridge and see if that has any effect. Anything that changes the mass of the arm may affect this untoward behavior, and perhaps a heavier headshell might work.

What headshell are you using on the AT-1005?

The Orsonic headshell is a high mass, and extremely rigid design that is prized by many for use with older high mass arms, and low compliance cartridges. (It is, umm, supposed to be effective at controlling "vibration" and might help.) This might be worth a shot as well, in particular I am thinking of the Orsonic AV-101. These are rather expensive and since I will be trying to acquire one for my soon to be ordered Schick I should probably keep my mouth shut.. :D
 
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Hi
I am using a standard SME black headshell. I have several. The AT shell that came with the arm is too narrow for the Decca. I think I will mount the V15 in it though and see if the noise is reduced. A simpler experiment than swapping arms at this point. It that does it then I can investigate other head shells. Thanks for the suggestion.

Don
 
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