Thorens TD124 measurements

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Hello Kevin, Steve and other Thorens 124 lovers !

As a long time TD124 lover and a lot off renovation work on about 50 124 tables .
I have done a lot off measurements to get a better picture from this remarkably turntable.
The measurements are done with a HP 35665A Dynamic signalanalyzer with test records, Thorens rumblekoppler and B@K accelerometers.
The measurements I made are always before and after revision work. Because a turntable is a mechanical device with a motor you can calculate for some turning parts the resonance frequence and the amplitude is a indication for the state off it, and off course the harmonics it deliver.
So I have measured a couple OEM idlers, belts , bearings and consoles with this FFT analyzer.
I have attached two speed measurements pictures one asis with the motor and old bearings the second after motor revision.
Motor revision is the first thing to do that means new bearings, felts etc.
I use for 90% parts from Juerg Schopper they give good results but use also some parts van several Ebay supplyers.
On the picture you can see the drift in absolute speed ,3khz ref, and the 100 hz motor
coil vibration and 23 hz motor resonance .
The second plot can be made better with carefull revision work on main,idler,steppulley bearings .

Next time some more pictures

Jaap View attachment Thorens TD124_2 ser.74632 Speed Original motor.bmp

View attachment Thorens TD124.2 ser.74632 Speed new motor bearings.bmp
 
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Thanks for posting Volken.. Would also be very interesting to see how the TT noise and speed performance compares to a modern reference.

If I am interpreting your results correctly the improvement in motor performance with an overhaul is pretty significant. I've done a lot of other tweaking in the areas mentioned, and my table seems to perform well.
 
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Kevin, do you have a soundcard that you can use for measurements? Wold love to see here what you find.

Hi Mike,
I have a pretty good sound card, unfortunately what I don't have are accelerometers and a rumblekoppler so it will be quite a while before I could get all the bits and pieces together to do it..

I still want to change out the motor bearings (again) and see whether or not that has an effect on motor noise. The motor in mine certainly isn't as quiet as I would have hoped, but the turntable with SME 3009 arm isn't generating any audible rumble either.
 
Hi Mike,
I have a pretty good sound card, unfortunately what I don't have are accelerometers and a rumblekoppler so it will be quite a while before I could get all the bits and pieces together to do it..

You can use an old cartridge as a very sensitive motion sensor! Decades ago Scientific American had an article in the Amateur Scientist in which they used 3 phono cartridges as accelerometers for a seismograph.

ancient history --
 
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You can use an old cartridge as a very sensitive motion sensor! Decades ago Scientific American had an article in the Amateur Scientist in which they used 3 phono cartridges as accelerometers for a seismograph.

ancient history --

Hi Jack,

Sounds like an interesting idea.. Certainly plenty of inexpensive new cartridges I could pick up for the experiment.. No old ones that I would want to dedicate to this usage unfortunately..
 
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And of course the recording soundcard will give you an idea of what noise is coming thru your cartridge.

Unless the TT is very noisy, that's all that should matter, right?

I'm pretty interested in seeing the motor noise spectrum.. I should look for a rumblekoppler or make one for the other half of the experiment. I think I will get a few cheap phono carts on eBay for this purpose, would hate to roach my zu/denon doing this.. :D
 
Hello Kevin, Steve and other Thorens 124 lovers !

As a long time TD124 lover and a lot off renovation work on about 50 124 tables .
I have done a lot off measurements to get a better picture from this remarkably turntable.
The measurements are done with a HP 35665A Dynamic signalanalyzer with test records, Thorens rumblekoppler and B@K accelerometers.
The measurements I made are always before and after revision work. Because a turntable is a mechanical device with a motor you can calculate for some turning parts the resonance frequence and the amplitude is a indication for the state off it, and off course the harmonics it deliver.
So I have measured a couple OEM idlers, belts , bearings and consoles with this FFT analyzer.
I have attached two speed measurements pictures one asis with the motor and old bearings the second after motor revision.
Motor revision is the first thing to do that means new bearings, felts etc.
I use for 90% parts from Juerg Schopper they give good results but use also some parts van several Ebay supplyers.
On the picture you can see the drift in absolute speed ,3khz ref, and the 100 hz motor
coil vibration and 23 hz motor resonance .
The second plot can be made better with carefull revision work on main,idler,steppulley bearings .

Next time some more pictures

Jaap
An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.

Hi Volken.
Thanks for posting. This is interesting.
I must confess. I'm a complete noobie when it comes to vibration analysis. I presume that the method is more complex than one might first surmise. Please let me attempt to understand your charts. Forgive if I state what is obvious.

chart type: x-y where X= frequency in khz, Y = amplitude in db
in the two charts we see a spike at roughly the same frequency. Around 3 khz. But there are differences in amplitude between them. The original motor spikes up to approximately 12 db (positive) where the refurbished motor spikes to approximately 10.6 db (positive). Seems rather noisy for both motors.

Apart from the large spikes within the line graph we see lots of amplitude variation with the original motor showing a wider range of amplitude. These noises, however, are within the - 60db range. And thusly not really audible or apparent without appropriate instruments to measure them.

How's that?

Look forward to more similar input. I'd really like to develop my own method of vibrational analysis as applies to turntables in general.


-Steve
 
Speed Thorens TD 524 direct drive for reference

Hello Steve,Kevin

For comparison I did a measurement on a Thorens TD524 this is the professionally Thorens player with the EMT938 direct drive motor in it.
You can see there is no 100hz motor vibration and the speed stability is better !
The rumble is in the -60 db range and usally you not hear this.

Next comes the rumble FFT plots !

Jaap
 

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I did the measurements with 220 volt mains supply and also with my own TD124 motor supply with his own 50hz oscillator and isolation transformer the vibration is the same because this kind off motor produce a 100Hz vibration !
The difference between the old motor and after revision you can clearly see in my first spectrum plots the 100Hz harmonics are gone !

Jaap
 

Attachments

  • Thorens TPS1 en Thorens TD124-EMT 997 003.jpg
    Thorens TPS1 en Thorens TD124-EMT 997 003.jpg
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Hi Mike,
I have a pretty good sound card, unfortunately what I don't have are accelerometers and a rumblekoppler so it will be quite a while before I could get all the bits and pieces together to do it..

I still want to change out the motor bearings (again) and see whether or not that has an effect on motor noise. The motor in mine certainly isn't as quiet as I would have hoped, but the turntable with SME 3009 arm isn't generating any audible rumble either.

The easiest and most practical way to do comparative measurements of the intrinsic noise in an analog playback system is to use a high quality and very clean test record with an unmodulated groove. There are several ways you can reduce noise by taking into account the thing as a whole. For example chassis and plinth modifications can damp a good deal of motor noise, as well as using a platter made of a material that damps better than aluminum.

John
 
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I have one of those test records courtesy of Pano, so eventually (as it suits me) I will get around to doing some objective evaluation of the noise levels. All I can say is this particular TD-124/II subjectively is extraordinarily quiet. I hear nothing except tracing noise even at very elevated spls (100dB+ :eek:) on lead ins and lead outs of records that were mastered on quiet cutters. (Speaker f3 is in the low 30s)

Also WRT to the 100Hz are you absolutely sure this is not magnetic field coupled from the motor into your measurement device? My calculations indicate that at 50Hz motor vibrations should be in the vicinity of 23Hz and at 60Hz around 27Hz? Can you elaborate?

In any event I am quite satisfied with the noise performance, it's significantly better than the medium it is meant to reproduce.

I'm using geltec bushings on motor and plinth as well as the dots on the platter. I also have a Merill-Scillia lead, cork, and rubber mat. Also using a Bren1 record weight which with the mat adds significant moving mass of about 1kg. (FWIW I probably would not go with geltec again except on the platter, but we will see how they hold up.) The down side of that extra mass is that is harder on the geltec pads and the platter brake.

I eventually plan on a Schopper platter as I have observed that a table with iron platter is mechanically quieter.
 
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Hey Kevin, on that test LP there should be a blank groove for you to test noise with.
Don't know how noisy the cutter was for that disc, but I do know that major efforts were made to keep it quiet.

You should be able to capture the noise signature with your soundcard. PM me if you need help with that.
 
The actual noise level is really not relevant when doing comparative testing. It's just for seeing if a particular tweak has resulted in any improvement. It's fun to quote absolute quantitative figures but not necessary in the quest to improve the system overall.

I eventually plan on a Schopper platter as I have observed that a table with iron platter is mechanically quieter.

The cast iron platter damps vibration much better than any aluminum platter, especially if it has very high graphite content. If it's demagnetized after machining it's unlikely to has any negative effects on the cartridge as well.

John
 
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Shaded pole motor

The TD124 E50 motor is a shaded pole motor so you have to deal with two kinds off vibrations the mechanical freq. from the rotational speed off the rotor with mains 50hz about 23 hz , depending from the slip and externe forces on the motorpulley , and the magnetic vibration from the statorcoils with 100 hz at a mains freq. 50Hz and by yours 120 hz.
The lattest you can clearly hear with stethoscoop on the motor and when the motor is in a bad shape you hear this ,,hum,, when you place the needle on the record in a silent groove during play !!!
The measuring is done with the cartridge itself but also with the accelerometer results are the same its quite normal to measure these components .
When you done a good revision job you normaly not hear this vibration in the music!!
The Schopper platter is very good indeed I use it myself it gives a quiet background you here more inner details .
The inclosed spectrum is from a motor asis with the cold start and after a 10 minutes warming up !
 

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  • FFT Thorens TD 124motor after 10 min..bmp
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