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Old 15th January 2011, 10:51 AM   #11
volken is offline volken  Netherlands
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Default 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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Old 15th January 2011, 03:06 PM   #12
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Is your TD124 being driven by real (distorted) mains or a lab supply? The harmonics on mains can make synchronous motors produce far more vibration
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Old 15th January 2011, 04:55 PM   #13
volken is offline volken  Netherlands
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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
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Old 16th January 2011, 12:42 AM   #14
jlsem is offline jlsem  United States
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Quote:
Originally Posted by kevinkr View Post
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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Old 16th January 2011, 02:46 PM   #15
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Default Td 124

Not that the TD124's motor doesn't vibrate, but the motor is a shaded pole induction motor, not a synchronous motor.




Quote:
Originally Posted by davidsrsb View Post
Is your TD124 being driven by real (distorted) mains or a lab supply? The harmonics on mains can make synchronous motors produce far more vibration
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Old 16th January 2011, 03:37 PM   #16
kevinkr is offline kevinkr  United States
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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+ ) 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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Last edited by kevinkr; 16th January 2011 at 03:46 PM.
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Old 16th January 2011, 05:12 PM   #17
Pano is offline Pano  United States
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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.
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Old 17th January 2011, 04:08 AM   #18
jlsem is offline jlsem  United States
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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.

Quote:
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

Last edited by jlsem; 17th January 2011 at 04:14 AM.
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Old 17th January 2011, 09:04 AM   #19
volken is offline volken  Netherlands
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Default 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 !
Attached Images
File Type: bmp Motor FFT Thorens TD124 cold start.bmp (104.1 KB, 37 views)
File Type: bmp FFT Thorens TD 124motor after 10 min..bmp (104.1 KB, 30 views)
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Old 17th January 2011, 04:15 PM   #20
Pano is offline Pano  United States
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Quote:
Originally Posted by jlsem View Post
The actual noise level is really not relevant when doing comparative testing.
Yes, agreed. If we could turn back the clock a bit and get some before and after measurements of Kevin's work, that would be cool. Maybe on his next victim.
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