Thorens TD124 measurements

[volken]

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

JaapThorens TD124_2 ser.74632 Speed Original motor.bmp

Thorens TD124.2 ser.74632 Speed new motor bearings.bmp

[kevinkr]

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.

[Pano]

Kevin, do you have a soundcard that you can use for measurements? Would love to see here what you find.

[kevinkr]

Originally Posted by panomaniac

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.

[jackinnj]

Originally Posted by kevinkr

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 --

[Pano]

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?

[kevinkr]

Originally Posted by jackinnj

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..

[kevinkr]

Originally Posted by panomaniac

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..

[user510]

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

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

[jackinnj]

It would be interesting to see the results with X=time and Y=tt speed using some very dynamic program material (1812 Overture, Verdi Requiem?).