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back to the Thorens TD124 Dept

Project No. 13943; A TD124 done differently.

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The external finish was chemically removed using a product called "Aircraft Remover".  The name will be familiar to those who have worked with automotive finishes.  Particularly those working in auto body shops and in auto body supply stores.  Painters who work in the aviation field will also know it. After the beige enamel finish is removed we are left with the bare metal.  This chassis is an aluminum die casting.  There is evidence of some touch-up and surface prep work having been done at the foundry.  Nothing ugly.  For my part, and after having stripped the paint from the aluminum, I found it necessary to go around the external surfaces with a 6 inch board and 400 grit wet/dry sand paper.  This was needed to smooth out some rather coarse grinding having been done at the foundry.  Following the 400 grit I scuffed the outer surfaces with #000 steel wool, and then followed that with more scuffing using a 3M nylon scuff pad (green) to finish off the cleaning process.

Now I just have to decide what color to paint this unit.  I do have some piano black acrylic lacquer that I am tempted to use. Or I could just leave this one in bare aluminum.  It kind of reminds me of vintage aircraft with aluminum skins.  The practice with aircraft was to occasionally polish the aluminum, which was left bare to the elements....even at high altitudes. Ahh, the gold ol' days.

Critical components:

  1. The motor: There are some options here. 
  2. Upper clutch operated platter
  3. Iron flywheel
  4. platter mat


re: The motor..........The Papst.  It had been Thoren's practice to supply spare E50 motors to customers upon request.  But then there came a time when the motor manufacturer was unable to produce any more without investing in new tooling.  The old tooling had worn out.  So Thorens Export Company, still located in Switzerland, chose to look for an alternate motor to offer its customers as a replacement.  Long story short, they turned to Papst and found the little Ausenlauffer motor.  More details about that at this link.

papst_1.jpg (197825 bytes) Link to my notes on using the Papst 3-phase motor on 13943

short summary; For a month I experimented using one of these (Papst) motors on 13943.  Toward the end of that month I came to the conclusion that this motor does have some potential with the TD124.  But I also came to the conclusion that the unit took too long to come up to speed on a cold start-up*. But once up to speed, sound quality seemed just as good as with the E50.  Perhaps even a bit more energetic.  It was the lengthy warm-up times made me want to go back to using the E50.

*(by using the method described in the Thorens "service bulletin No. 22" to implement the 3-phase Aussenlaufer motor to operate on single-phase)

re: The motor......There is more to the E50, however. It has been known for some time that the E50 motor did evolve during the production run of the TD124.  Forensic evidence suggests that it was sometime late in the run of the original version that Thorens became aware that not all was perfect with the E50.  The motors tend to run hot and sometimes "cook" their windings.  An undocumented revision was made.  They began using larger gage copper wire in the coil windings.  Otherwise, same as original.  One source suggests that the changes were made around SN# 40000.*

*Simone Lucchetti http://www.audiosilente.com/  (text is in Italian.  Use translator to view in English)

The result of the coil revision was a cooler running motor and one that produced greater power.  The motor went from 10 watts to 15 watts with this change.  The revised E50 will reach operating speed quicker on a cold start and then run with more torque throughout the day.  Additionally, the coils will stay cooler while the motor runs.  What's not to like!  As it turns out the above link (audiosilente.com) does produce, and make available, an upgraded windings set for the E50.  These can be installed into any E50.  The price is agreeable for me, so I ordered one set of coils to be used on 13943. 

4/28/2014  5/1/2014Delivery from Italy took exactly two weeks.  Not bad.  Simone sent the coils via registered mail.  He also attached an installation instruction in pdf to an email to me.  The instructions are in English as well as Italian, complete and easy to follow.

Here's a copy: coils installation pdf

DSC_0751.jpg (313898 bytes) two new coils next to an old one. The disassembled core in the background

DSC_0752.jpg (235229 bytes) side by side. old (left) new (right).  The new coils from Simone are slightly larger and fit a bit tighter inside the core.

DSC_0753.jpg (314692 bytes) Wherever the core makes contact with the coil, sharp edges are dressed smooth.  That way we don't cut into the insulation and accidentally cause a short!

DSC_0754.jpg (283378 bytes) I used a pattern maker's file in combination with 400 grit emery cloth.

DSC_0755.jpg (224884 bytes) Core assembled.

DSC_0757.jpg (285085 bytes) motor assembled with new cores.

The windings offer operation at 3 different voltages, just like the original.  The only real difference is that the magnet wire in these new windings is a slightly larger gage.  I did not measure this since it would require surgery.  Rather, I followed Simone's instruction sheet, soldered the new windings to the Thorens AC terminal and then went through the usual motor-rotor alignment process while the refurbished motor ran under its own power.  As I type this 13943 is playing an Lp.  Paul Simon, There Goes Rhymin' Simon.  I will observe the operation of the player with new coils over the next couple of days then write down any observations I have to this page.

5/1/2014....I've had a couple of days to listen to 13943 using the new motor windings.  Here are some observations about the operation and sound quality of the deck...

DSC_0758.jpg (246042 bytes) 13943 on the rack.  Plinth in use is for temporary utility.  Tonearm: Zeta.  Cartridge: DL103R SS ruby/FL and in a  Uwe Panzerholz body.

13943 is in an open box plywood plinth, on the rack and playing records. No mushrooms.  I've taken no measurements.  When it comes to determining any increase/decrease in motor power or torque I can only note how quickly it starts up from cold, how well it maintains pace and what if any changes I hear to sound quality.   During the assembly and then the bushing alignment-tuning process I did notice that motor did not vibrate quite so much as before.  This is a subjective observation based on holding the motor in hand while it runs.  And also listening to the casing with a stethoscope as it runs.  It does seem quieter.
From a cold start 13943 takes a couple of platter revolutions before the strobe indicates arrival at speed.  When it does hit steady at 33-1/3rd rpm, it almost seems to snap in.  Right after that episode the strobe indicates a slight amount of slowing over the next few minutes.  Afterward, its steady.  It seems to hold speed throughout the day without any significant deviation from nominal.  Wow.  The strobe holds steady all day.
Listening. It sounds just like a healthy TD124.  Nice snap-to rhythm lines.  It has a sharp sense of pace that seems rock steady.  Nice open detailed and large sound fields.  I've been listening to rock, classical and jazz so far.  No complaints.

5/6/2014.....its been 6 days since my last notes.  There are some changes.

Motor operation has gradually changed its start-up behavior over the past several days.  Instead of a taking a couple of platter revolutions to arrive at speed, it now takes less than one revolution.  It comes to speed with a sense of deliberateness and holds a steady strobe position for a couple of seconds, then the strobe starts to indicate a slight slowing of rpm.   Over the next few minutes, it recovers its speed loss and then finally comes to a steady strobe position.  And it holds this for the rest of the day, but with only the occasional need for a very minor pitch correction. This seems to be a predictable pattern.  .

Listening.  Sound Quality is getting better in several ways.  Mostly it is a more solid and steady sense of pace.  Really good pace.  Keep in mind that I have an SP10 mkII standing next to the Thorens.  The SP10 provides a very strong reference when it comes to holding a steady pace.  And the TD124, with the new coils from Simone, is moving closer into SP10 territory on this one aspect.

There is a greater "jump factor" than before.  Instruments and notes tend to pop out of the speakers in front of me.  Where before it was a bit less energetic this way.  The music tends to seem more palpable, ripe and in front of me.  Closer to touching me from where I sit or stand.  Did I just take a view into the recording space?  It does seem to be getting closer to that goal.

Quietness.  This TD124, with its mkII conversion motor mountings installed, and with the new coils, is as quiet as they come.  A really good sense of silence between the notes.  During the blank space between tracks.  Lead-in grooves, etc.  Detail delivery.  Inner details, the quieter ones, are now in crisper articulation than before.  It delivers both the big energetic parts as well as the delicate softer bits with equality.  I've heard this before with 2729 but now, with the new motor coils installed and working in, I'm getting more and better.  Crisper.  Sharper.  Yet organic in overall character.

When it comes to signal versus noise it seems to be working into belt drive territory.  In ways I can still remember it plays with a greater sense of quietness (in the parts where it is suppose to be) than I got from my old Teres 145.   In this sense the player delivers on its original design promise.... to be an idler driven turntable that does not at all suffer from what plagues almost all other idler drives.....rumble. 

The sound field is as wide and open as I've heard any of my TD124 motor units deliver.  It plays big but now with a better sense of articulation, pounce and pop.

Time for review.  Lets consider what work the drive train has had done, and what I might yet do with its various components.

Upper platter and clutch:   to be addressed.  This component is at once a weakness and a strength of the TD124.  The clutch operation is a very nice utility that one gets used to quickly and will be missed when operating other players.  But the thin upper aluminum shell of a platter often comes to us having been bent in a previous life.  Yes it can be straightened into a condition where the clutch parts won't rub against the spinning shell during play, but......the shell doesn't always lie flat on the rubber pucks of the flywheel.  It doesn't provide a perfectly flat, true running surface to spin records on.  I'll explore some options in this regard.  But with the requirement that original clutch operation remain a part of this player.

Iron Flywheel:    to be considered.  How shall I upgrade this, or does it really require attention!

Platter mats:  Is there anything better than the original Thorens rubber mat?  Let's try a few ideas.

Platter bearing:  

The original nylon platter bearing sleeves have been replaced with new Oilite bronze.  The platter bearing shaft itself was carefully examined for evidence of wear.  Using a micrometer, the shaft was measured for evidence of out-of-roundness and of taper.  In both cases it turned out that there was no measurable evidence for either.  However there was some visual indication of where the bushing sleeves and shaft had been running against one another.  A very fine-grit strip of Crokus cloth (a rubberized abrasive) was used to put a new pollish all over the 50 year old bearing shaft.  Once done, the shaft was measured once again with the micrometer and found to be still uniformly round, straight and the same original diameter (out to 4 decimal places).  In this condition it was ready for the next 50 years.

The bearing ball at the tip of the shaft was also removed (unclipped) and examined for evidence of wear.  This, like the shaft, showed no measurable evidence of wear.  It was cleaned and placed back into its countersunk socket at the tip end of the shaft (with a dab of lube) and retained by a bronze clip retainer, which snaps into place.

The bottom thrust cap, attached to the bottom of the bearing housing by three machine bolts, has been upgraded with one of my gunmetal bronze caps.  This very solid end plate provides a solid, non flexing thrust point for the bearing thrust.  Currently I'm using a Teflon-infused Delrin thrust pad in place of the original Nylatron one that Thorens provided.  According the material specification, it has 15% teflon mixed in with the Delrin.  Wear rates with this material appear to be better than I've noticed when using plain Delrin or Nylatron as a thrust pad.*

* I've had approximately seven years to experiment with different bearing thrust pad materials and observe wear rates.

I still use the same type of oil that Thorens recommended in the main bearing.  A straight 20wt. turbine oil.  But a modern equivalent and from the same oil company that provided the original. (Texaco)  


Discussed above.  Having tried a Papst Aussenlaufer* motor, with some slight disappointment, I moved on to an E50 renewed not only with new rotor bushings and thrust pad, but also with new upgraded mk2 coils from Simone Lucchetti.  See notes above for how well this worked.  Based on my experience so far I'll likely stay with the E50 as described on this page.

* I know of one individual who is currently designing and building a dedicated 3-phase controller for the Papst Aussenlaufer.  In fact, this individual has the exact same  motor I worked with.  I will report his results as he lets me know them.  I do expect to hear of results far better than what I experienced while using this 3-phase motor on single phase power per Thorens bulletin 22.  That method employed a hack to fake the motor into working.  (timing capacitor) No way a motor like that can run as smoothly as it should.  We think the dedicated 3-phase PS will take a TD124 to new heights using the Papst in combination with a proper power source.

Motor Controller:  (for the E50)

Yet to be tried.  As far as I know, no one is actively offering a standalone motor controller specific to the needs of the TD124.


I've tried several different belts.  I have some notes on this elsewhere on the site.  After some experimentation with original Thorens (with logo) belts, and with a few different aftermarket belts available cheaply on Ebay, I've settled, for now, with a belt supplied by Schopper.  The Schopper belt duplicates the length, width, thickness and elasticity of the original Thorens belt, but with a more modern compound material that leaves far less material residue onto the drive and driven pulley surfaces.

Stepped pulley:

Thorens changed the stepped pulley design three times over the production run of the TD124.  The stepped pulley design on 13943 is the first version. It has a precision ground solid steel post anchored to the chassis from below by two set screws.  The stepped pulley, containing sleeve bushings (bronze) and a spherical cup at the very top of its housing to hold a bearing ball ( 4mm).  The stepped pulley with its bronze sleeve bushings, and bearing ball within, slides over the upright post. Gravity holds the stepped pulley over the post and against the bearing ball perched at the very top of the upright post to provide a vertical thrust point. For lubrication, the TD124 service manual is followed and straight 20wt turbine oil is applied liberally to the the bushing and shaft.  It should be noted that within the bushing is a groove, centrally located, that holds a felt oil retainer.  It is made certain that this felt is thoroughly saturated in the above noted lube.

The stepped pulley receives drive from the motor-driven belt at the large ring on the very bottom.  Above the belt ring are 4 stepped ring registers of different diameters to provide platter speeds from 78 to 16 rpm.  The rubber tire of the idler wheel drives against one of these while being slightly pinched against the inner rim of the iron platter.  This is how the platter is propelled.  The stepped pulley might also be termed as a capstan. Like a pinch roller,  but with 4 different rings for 4 different speeds.

The question becomes one of what can be done to maintain design integrity of this part of the drive train.  My experience so far is that this earliest design of stepped pulley does not provide any significant problem to be overcome.  The examples that have come across my workbench have not shown evidence of significant wear on either upright post or inside the bronze bushing sleeves.  And the ring registers that drive the idler tire seem to have held up very well.  

The 4mm bearing ball at the top can be replaced with a new one.  But close examination by measure (micrometer) and by magnified vision (10x Loupe) have not shown any significant evidence of wear to these original parts.  So I've only had to clean, re-lube and re-assemble the stepped pulleys that I've seen so far.  I have experimented with using different bearing ball materials on this assembly.  For instance I have used Silicon Ceramic bearing balls (gr 5) in place of the original hardened steel one.  I can't say that I have heard, or measured, any significant difference in sound quality of the motor unit when comparing between thrust ball materials at the stepped pulley.

Idler Wheel:

At this point I've tried two kinds of idler wheels.  The original 50 year old ones found on the Thorens motor units as they come to me.  On some cases I've seen these with the rubber showing cracked surfaces and a hardened surface all over the rubber.  Others, however have appeared to me with still soft rubber, no cracking or crazing and no evidence of any flat-spotting out on the rim where the rubber drives against the platter and stepped pulley rings.

It is possible to have an existing idler wheel recovered in new rubber by one company that specializes in doing just that.  http://www.terrysrubberrollers.com  If you go this route you retain the original steel parts of the wheel and also the bronze bushing sleeves within that may, or may not, have some wear in them.

Another option is to buy a new replacement idler wheel from Mirko at http://www.classicturntables.com  The Mirko idler wheel duplicates the shape and dimension of the Thorens idler wheel.  Mirko uses a slightly softer rubber material on his reproductions.  And, it is important to note that the new wheel from Mirko comes with new bushing sleeves within it.  This results in a completely new replacement wheel.  I've used several of these and continue to like this option.

A third option is a new design of idler wheel that I'm currently seeing around the web.  This version is a solid steel wheel that employs a Silicone O-ring out on the perimeter of the wheel to deliver the drive.  This will be a much heavier wheel.  I've no experience with this type of design and have nothing to report on them at this time.

A fourth option.  I may explore a different design of idler wheel.  When I have something I'll report that to the TD124 Dept.

Idler Wheel thrust washer.

This is the tiny little ring that slips over the upright precision ground steel post.  The post that the idler wheel slips over and spins against.  This little thrust ring takes the vertical thrust from the spinning idler wheel and gets ignored by all of us.  It shouldn't be neglected.  So far I've found my original thrust washers to be in good usable condition.  I know this because I look them over with magnification and sharp lighting.  But this could also be a point worthy of experimentation.  Upon assembly, I just make sure that there is ample lube on this location.


General notes about the E50

Type: Shaded Pole Induction
no. poles: 4
wattage: 10 watt (first version)

What makes it work;  It runs on AC current.  Within the motor coils are several different windings designed to allow the motor to operate at different voltage ranges as follows: 100/120 , 125/150, 200/250.  These different voltage ranges are user selectable by means of a commutator board with an insulated screw that is threaded into one of the three voltage taps desired. 

The motor will operate on either 50hz or 60hz mains frequencies.  60hz will result in 17% faster motor rpm than 50hz.  The speed difference is compensated for by using a two ended drive pulley where one end is a diameter appropriate for the one frequency and the other end for the other frequency.

It's terminal speed is determined by a combination of factors approximately as follows:

mains frequency:  90%
load: ~2%
drive voltage 5%
slippage at the poles: ~3%


I found some short calculations in Machinery's Handbook to determine motor rpm when the outer platter is rotating at 33-1/3rd rpm. I've put one to use below.

known data:

  1. 60hz drive pulley diameter is 1.177 inches

  2. the belt-driven step pulley diameter at the belt interface is 2.755 inches.

  3. the 33-1/3rd ring diameter on the step pulley is .470 inches

  4. the idler-driven platter at its inside rim is 9.682 inches diameter

(platter rpm is 33-1/3rd.)

(a) to know step pulley rpm:  9.682dia x 33.333 / .470dia = 686.66 rpm

(b) to know motor shaft rpm: 2.755dia x .686.66rpm / 1.177dia = 1607.rpm


Unloaded and at 60hz 110/120 vac the motor has been measured at 1750 rpm

Using the above method to calculate motor rpm I can estimate that the loaded motor must rotate at 1607rpm to turn the platter at 33-1/3rd rpm. This indicates a  ~1%  drop in motor rpm when driving the platter at 33-1/3rd rpm.

Some observations.  By changing the AC mains voltage coming into the motor,  the rpm will either increase or decrease with voltage change. More volts = more rpm.  Less volts = lesser rpm.

Using my Viz IsoTap Wp-27A variable output voltage isolator, I can either decrease or increase voltage to the motor in 5 volt increments. A 5 volt change to the operating turntable will result in a visible difference in speed as seen at the strobe window. Perhaps on the order of a 1% speed change. (rough visual estimate)

If a variable frequency power supply were employed. Motor speed could be regulated by altering mains frequency to attain the desired platter rpm.  To date, it is unknown if anyone has produced such a power supply for the TD124.


A minimal plinth for 13943

Design goals:

maximize rigidity
minimize mass (by today's standards)

rationale: To study audible effects of plinth design with regard to; mass, material and rigidity.  The material is baltic birch multi-ply.  The mass in this design is greater and denser than that of some of the early open box style plywood plinth designs seen from the period.  The perimeter features stacked layers of baltic birch multi-ply.  This is popularly thought to function as additional dampening for the chassis that is coupled to it.  However the area and height of the design is kept to a minimum in terms of functionality.  When compared against currently popular thinking in TD124 plinth design, the "minimal plinth" is indeed minimal. 

Concept sketches:

First prototype, slightly rough.

DSC_1061.jpg (187221 bytes) DSC_1062.jpg (140144 bytes) DSC_1063.jpg (263258 bytes) DSC_1065.jpg (186872 bytes) DSC_1067.jpg (193969 bytes) hint: click on thumbnail to view image full size.

Subjective Impressions: No negatives so far.  Listening time has been brief.  Size-wise the assembled turntable and plinth take up  little rack area compared to some other turntables I have.  Presently, I'm listening without the rubber mushroom isolators.  Rather, the TT chassis is fastened directly and solidly to the top of the plinth via the 4 fasteners. 

Next plinth: min_lt_2.  Same sense of size and shape but one more layer in the vertical build and different materials.

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Back into Slate...

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That Zeta tonearm is hard to photograph.  The black seems to suck up all of the light.  However it sounds nice