Restoring and Improving A Thorens TD-124 MKII - Page 63 - diyAudio
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Old 9th December 2012, 05:17 PM   #621
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Click the image to open in full size.

This is an interesting approach and one, I think, that could serve to illustrate something I am coming around to think.

First, an observation about the tinkering I've done on my own:
The quieter the motor runs. The quieter and smoother the belt/stepped pulley/idler wheel runs. The less one is tempted to categorize this model in the same league with other idlers known to produce obvious rumble.

Why? Because at a certain level of performance, it becomes apparent that this model does not produce any obvious rumble. At least not rumble that can be heard through the speakers on a needle drop into the lead-in groove.

Once the TD124 is operating to this level of performance, plinth selection becomes less of an issue. High mass. Medium mass. Naked? To mushroom or not. These things matter less to the sound output of the turntable.

And the key to obtaining this level of performance in my early model units has been centered around the motor and its bushings and thrust.

So the first I would check on the above pictured Thorens is to find a record to play and then drop the stylus down into the lead-in groove to see/hear if there is any evidence of rumble. And this would tell me if the experimenting that ultimately lead to this design of support, was chasing substantial audible improvements or if it had been chasing ghosts down blind alleys.

If no rumble, then the process that led to the design might be valid and worth a try. If rumble, then the result was achieved on false information and the sound quality of it being touted would not be comparable to that of a properly running TT in any design of plinth.

About the missing outer platter:
It is common to find these players with damaged or lost outer platters. The lightweight aluminum shell is easily dented and by minimal force. So among the latest generation of tuners it becomes somewhat popular to simply discard the outer platter and work without.

But this outer platter was more than just a disc jockey tool. It served to isolate the record from the bearing. A true-spinning outer platter on fresh rubber pucks and with a good standard mat should not be discounted. This piece may not be the "weak link" that some would suggest that it is.

-Steve
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Old 9th December 2012, 08:35 PM   #622
kevinkr is offline kevinkr  United States
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I use the upper aluminum platter with a Merill-Scillia mat (cork, rubber and lead amalgam) and am very happy with the result. I do recommend running with the upper platter if available. Sadly I do not have one for my second 124, but it would have it if I did.

I will second the rumble comment, my 124/II is extremely quiet, no audible rumble that was not there on the original recording. It took quite a lot of effort to get it there, the second one was much easier..
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Old 15th December 2012, 07:21 PM   #623
kevinkr is offline kevinkr  United States
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Have a lead on a stamped upper platter for my series I table, wish me luck!
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Old 15th December 2012, 10:36 PM   #624
Nanook is offline Nanook  Canada
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Default Vibrating motor solution.

Quote:
Originally Posted by kevinkr View Post
Not shown in the previous pix is my pride and joy ( ) a very mint TD-124/II. It was almost as if it had spent the past 40yrs in a time capsule - which in a sense it had since it was in a console with a lid that the owner never opened after the very early 1970s..

The motors in these tables vibrate pretty badly, but the belt, good motor mounting bushings and a massive plinth keep the whole thing pretty quiet. Careful tweaking does help. Lots of torque comparatively speaking, when warm it is fully up to speed in about 1 revolution of the platter.
Kevin,

As per everything AC a solution can be had after rebuilding the motor to reduce any possible vibration to essentially "0".

And for all that think that it is virtually impossible, consider that the well known Airpax/Thomson motors typically sound best when fed 72-85 VAC. Hmmm, wonder what it could be.
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Old 16th December 2012, 02:53 AM   #625
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Quote:
Originally Posted by kevinkr View Post
Have a lead on a stamped upper platter for my series I table, wish me luck!
Luck.

Interesting about the upper platters. I've seen some that appear have been formed by "spinning". Others appear to have been stamped. The spun ones will indicate concentric tool marks typical of that process. The stamped ones will not have any tooling marks.

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Old 16th December 2012, 03:59 AM   #626
kevinkr is offline kevinkr  United States
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@ Steve:
I've noticed the variation in upper platters as well, mine has concentric tooling marks consistent with your description of a spun platter.

@ Nanook:
I tried operating the E50 (shaded 4 pole induction motor) in my table on reduced line voltage to see what effect it had on vibration, it helped slightly, and completely killed the dynamics.. Same effect could be achieved by operating the motor on the next higher voltage tap.. (125V - 150V tap) I've managed to quiet both of my TD-124 to the extent that most recordings have a much higher LF noise floor than either of these tables. From a performance perspective I've found running at normal line voltages results in the best overall perceived performance.
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Old 17th December 2012, 02:50 AM   #627
Nanook is offline Nanook  Canada
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Default "Oo, oo, oo I wanna be just like you..." (a quote from King Louie)

Quote:
Originally Posted by kevinkr View Post
@ Nanook:
I tried operating the E50 (shaded 4 pole induction motor) in my table on reduced line voltage to see what effect it had on vibration, it helped slightly, and completely killed the dynamics.. Same effect could be achieved by operating the motor on the next higher voltage tap.. (125V - 150V tap) I've managed to quiet both of my TD-124 to the extent that most recordings have a much higher LF noise floor than either of these tables. From a performance perspective I've found running at normal line voltages results in the best overall perceived performance.
A very wise man suggested to me to use 2 variacs for AC induction motors. One for each pair of windings on an induction motor. Adjust both variacs (let's call the first one #1, the 2nd one with the capacitor call #2) to the same level where the motor quiets down significantly. Obviously there should be no interconnection of the winding pair at the motor. Just ensure that both variacs are fed from the same input voltage source. Then adjust #2 until less noise (again). This should provide almost the "ultimate" way of driving the AC motors. But the cost of 2 variacs is not cheap by any means. Now full current capability of #2 windings will be improved and be more efficient.

These are only my thoughts and could be completely wrong, however I don't think so. Another possible way would to use a 2 channel digital signal generator at the correct 50Hz/60Hz as needed that can allow for phase adjustment and output of both channels individually (perhaps a digital mono volume for each variac?).

I've decided that when I grow up, I wannabe just like you

As always a great thread to read.
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Old 17th December 2012, 03:52 AM   #628
kevinkr is offline kevinkr  United States
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Nanook, interesting idea.. And I have plenty of variacs and a spare motor to experiment with once I rebuild it.. So at some point as schedule permits I will have a look at it.

I believe in fact that it would be possible to run one winding fixed and vary the other one +/- a few percent to see what effect that has..(Each winding independently end to end can operate from 100 - 125V)

The individual windings are tapped and connected in series at the taps selected for the required voltage operating range, but it is imminently doable without permanent alterations to the motor.

I posted some actual details regarding motor wiring on another TD-124 thread here: Thorens TD 124 power question...
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Old 17th December 2012, 08:09 AM   #629
volken is offline volken  Netherlands
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This only works with the synchrone motor where you need a capacitor to get the 90gr.lead for the second coil then you can get much lower noise if you tune this .
I have done this for the Thorens TD160 motor with very good results.
The main vibration with the E50 motor comes from the ,,twice line frequency vibration, at your place 120 hz .
This vibration is always there and get influenced from the airgap between the stator and rotor, eccentricity of the rotor , bearing play etc.
If you carefull align the upper and lower bearings you can minimize it .

regards Volken
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Old 23rd January 2013, 04:10 AM   #630
kevinkr is offline kevinkr  United States
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Default Those Eddy Current Brake Magnets...

Worked on a 1962 vintage TD-124 tonight, one of the complaints the owner had was that no matter what he did it just ran too fast. He had adjusted the magnet to the point where there was no more than 10 mils (0.25mm) of clearance between the magnet and the stepped pulley and still it ran too fast.

I decided to test it by substitution with a known good magnet which worked fine with a spacing of about 0.2" (5mm).

These magnets are usually strongly attracted to the vane in the eddy current brake assembly as the retaining screw is loosened - this one exhibited no such tendency.. It was extremely weak.

So if the table runs way too fast no matter what you do you might want to have a look at that magnet.

I suspect the typical speaker repair shop could probably remagnetize these magnets
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