[Syrah]

So I seem to have taken up another project that is beyond my skills and my time, a garage sale Thorens TD126 Mkii.  It seems to be in pretty good shape - it runs anyway.

I’ve managed to partially take it apart.

My first question is, does anyone know how to undo the strain relief shown in the attached photo?  I’m baffled.  I’d rather not just break it open, but I’m on the edge.

So here’s my grand plan.

1.    I’m going to have the electronics sent to someone to re-cap everything, as I’ve read that the caps go with time.

2.   I’ll set aside the arm and armboard.  I’ll keep an eye out for a used VPI tonearm or something – I’m partial to unipivot.

3.   I’ll make a custom armboard using CLD, with sheet aluminum on the outside and maybe a mix of closed cell foam and MDF or hardboard, like a mini Symposium shelf.

4.   Remove the power supply from the bottom metal chassis (see photo) and put it in a separate box with an umbilical cord to the table.  It just can’t be good having a transformer coupled to the metal chassis on which the sub-chassis springs sit.  Maybe I’m wrong, but that doesn’t seem right.

5.   Since, without the power supply, the chassis will be straight sheet metal with a few cutouts for the motor and the spring adjusters (see photo), I’ll glue closed cell foam to the metal chassis and effectively turn the bottom into a Symposium Svelte type shelf, I’ll put sheet aluminum under the foam, then ball type footers.

6.   I’ll make a new plinth that has a gap so that it doesn’t touch the chassis.  It will just be decorative.

My thinking is that this will make for a lightweight chassis that is constrained layer dampened, rather than a chassis with a transformer that is just screwed into a wooden frame.  I know from my experience with an LP12 that this design typically favors lightweight shelves, so why not a lightweight but rigid chassis.  I will cut holes in the foam and metal sheet to be able to access the motor and adjust the springs.

Any thoughts as to this strategy?  Obviously it will no longer be a stock vintage TD126.

[neobop]

Hi,
Sounds very ambitious, but you have some problems.  You say you're short on skills and time, but those two things will become mandatory.

First of all, you say it runs.  That's good, but what shape is the main bearing in?  What about the motor?  It's 30 yrs old. 
Secondly, if the transformer is part of the sprung weight you can't just remove it and expect the suspension to act as designed.  It will be tuned to a low frequency and you'll mess that up.  I guess you could substitute a similar weight, but you might have enough problems with the suspension as is.  The springs are 30 yrs old as well.  You want to swap arms - if the armboard/arm are different weight than stock, it complicates the problem. 

Is that 2 transformers in the photo?  The 126 is an electronically controlled servo drive.  I suspect that transformer should stay where it is and not be separated from the circuitry, but I'm not sure. 

Here's an alternate plan you might consider:
Go to Vinyl Engine Library and download a free copy of the service manual.  See if you can get it sounding good as a stock unit - lube the bearing, clean the pulley, get a new belt.   If the arm bearings seem sluggish you can hit them with a blast of no residue contact cleaner. 
Then, if you want to replace the electrolytic caps you'll have a copy of the service manual for the tech. 

I don't agree about a lightweight chassis being advantageous, or an armboard for that matter. 
Good luck with the project,
neo

[Syrah]

Thanks Neo.  Much appreciated.

I don't plan to touch the suspended sub-chassis part, other than to change the armboard.  I've weighed the stock armboard with the stock arm on it, so my plan is to stay in that general weight vicinity.  The arm is light, but the complicated mechanism for cuing and auto arm return are pretty heavy, so I've got some play to put a heavier arm in.

The bearing actually looks pretty good.  I've read that if it's out of oil, that's the sign of a problem, and it is.  But it looks clean.  I'm not entirely sure what it's supposed to look like new, so it's tough to say.  I'll post a photo tomorrow.

The transformer and the other part (which has a cap, maybe something to clean up the power) have a few wires back and forth, so it probably is a servo mechanism.  I don't see why all wires can't be extended by a few feet so that it can be mounted in an external box.  I was going to contract out that part plus the cap replacement to my audio expert, since those parts are indeed beyond me.  Both of those sit on the chassis below the suspended sub-chassis, so there shouldn't be any weight issues with the sprung parts.

The part I was going to couple to either closed cell foam or a MDF-Foam-MDF sandwich is the metal chassis below the sprung sub chassis.  Right now it screws into the wood outside structure with wood crossbars.  I was just thinking that coupling that base with a CLD base might help isolate vibration yet not overly deaden the sound - it seems popular to stick on 3M or that car stuff on the metal surfaces but I think that will just deaden the sound of the TT, whereas CLD might isolate vibration yet keep it snappy.

Thanks.

[neobop]

Syrah,
I never owned a Thorens , maybe someone with more experience can give you specific info.  Download the service manual.  You'll find it invaluable, so will your tech.  It should tell you how to do such mundane things as open the strain relief clamp, and such essential things as test voltages on a circuit board and a parts list w/values. 

If you tuned the suspension on your LP12 you have a good idea of what's involved.  Freeing an arm from auto features involving cams and connecting rods will  boost performance.  Some semi auto arms only have a mechanism which triggers the arm lift - a better way to go.  Some of the weight of that mechanism might be borne on the other side of what it's connected to.  I guess you'll find out.

Your fascination with constrained layer damping could work out, I don't know.  With table design and energy management you dance the damping vs. dissipation samba.  High mass goes a long way in killing vibrations.  I think an armboard must be rigid and transmit any stray vibrations out.  A relatively light armboard designed for damping will be less affective IMO.   One way to lighten an armboard and make it work better is to make it thinner and use a material like aluminum or oak with standoffs to make up the difference in thickness.  That worked out much better for me than thick MDF. 

It could be the bearing oil just dried up after all the years.  Most people never service the bearing.  If it doesn't look scored and works, I'd clean it up with lighter fluid or gasoline, clean the well and inspect the thrust plate best you can, and oil it.  Check for wobble.  Probably fine.

Any chassis mass under the subchassis will benefit from rigidity and high mass IMO.  You're going to extend the bottom of the cabinet?  Will this be a bigger hollow space, an echo chamber, or like a mounting base?  With the metal chassis I might brace it better with the cabinet - use steel L braces or corner braces, even extra crossbars.  This seems like a good place to make the cabinet more rigid.  I don't think rubber spray will do much of anything here.  It's said to work good on the underside of ringing platters.  Denon uses it like that. 

Let us know how it's progressing.
neo