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Turntable speed stabilty
Turntable speed stabilty
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Old 27th June 2017, 11:41 AM   #21
luckythedog is offline luckythedog  United Kingdom
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Quote:
Originally Posted by Kay Pirinha View Post
How did you record the angle/x axis
It's based on 'correct' time, ie the time when perfectly constant 33 1/3 rpm would present at that angle/location on the rotation. I think that's fine, even if it means there's always some error in exact angle/location - we're not that interested in finding exact position. Whereas we are interested in accurate frequency relative to real time, reasonably locally on the rotation.

LD
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Old 27th June 2017, 12:14 PM   #22
Kay Pirinha is offline Kay Pirinha  Germany
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So, e.g. in your graph from #4 the eccentricity would move in contra-rotational direction (assuming that the record is spinning a little slow) if you'd record more than one turn?

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Old 27th June 2017, 01:54 PM   #23
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by Kay Pirinha View Post
So, e.g. in your graph from #4 the eccentricity would move in contra-rotational direction (assuming that the record is spinning a little slow) if you'd record more than one turn?

Best regards!
Yes. However, in a healthy TT error is often small enough to tolerate and I try to do that. However, I also have the option to vary start point of 2nd revolution display based on average frequency of the first. This is why I only display 2 revolutions, BTW, since errors accumulate.

It's also why I standardise on 3150Hz test tones, though 3kHz is supported. Actually, pretty much any frequency would work, but to avoid this issue one has to know what the original frequency was meant to be in the first place...

LD
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Old 28th June 2017, 04:42 AM   #24
Hiten is offline Hiten  India
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Thanks Bill and LD.
Quote:
Originally Posted by luckythedog View Post
Also, focus on accurate motor speed control is typically misplaced, IMO, because that's seldom a dominant factor in overall pitch stability, it seems.
LD
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Originally Posted by luckythedog View Post
I like the idea of displaying a servo signal where there is one, if nothing else, for a health check......!

But pitch stability is only partly about platter speed stability. Typically factors like spindle centering, platter vertical run-out, warp, and cart-arm stability contribute far more in an otherwise healthy TT. So this is where bang-for-the-money is, and is well within most DIYers capabilities methinks.

LD
Kindly explain platter vertical run-out. Also what do you mean by Cart-arm stability affecting constant speed ?
TTs having good sonics are not related to pitch stability is little surprising. Do cutting lathes have perfect speed? How is it achieved ? I think beyond certain point it does not matter as much as rumble noise. But achieving it or measuring it is interesting. Do you or anyone else have polar plots of classic tables mentioned earlier ?
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Old 28th June 2017, 04:47 AM   #25
Hiten is offline Hiten  India
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Ok just read in other thread about Lathe speed stability. But how it is achieved ?
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Old 28th June 2017, 06:09 AM   #26
xx3stksm is offline xx3stksm  Japan
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Here's FFT of my turntable PL910(kyocera late1980).Testrecord is "stereo reviiew's model sr12".When FFTsize is 32768, calculated data is about 0.3second.When 8192,about 0.085second.

I can't measure speed drift from FFT.But I suppose peak level of successive small size FFT(8192) is referrence to average turntable speed.They are fairly stable more than predicted.
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File Type: jpg record1.jpg (180.0 KB, 513 views)
File Type: jpg record3.jpg (174.3 KB, 501 views)
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Old 28th June 2017, 06:43 AM   #27
planet IX is offline planet IX  Germany
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Some thoughts about the correlation of sonics and pitch stability...

Pitch stability is measured with a discrete frequency and amplitude, so there is a (more or less) constant drag on the motor.
I think any TT motor can handle a constant drag satisfactory.

With music playing the drag on the needle changes permanently. So maybe we should look at the dynamic behaviour of the motor and the motor controller. A testrecord with a frequency that changes the amplitude abruptly could probably give a better prediction of the sonics...
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Old 28th June 2017, 12:30 PM   #28
gpapag is offline gpapag  Greece
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Turntable speed stabilty
Quote:
Originally Posted by planet IX View Post
With music playing the drag on the needle changes permanently. So maybe we should look at the dynamic behaviour of the motor and the motor controller. A test record with a frequency that changes the amplitude abruptly could probably give a better prediction of the sonics...
I agree on this Boris.
But also remember that there is vinyl –mat interface, mat material and mat-platter interface.
The more lossy the two interfaces are and the more compliant and thick the mat is, the more decoupled the vinyl is from the platter.
This is good for acoustic decoupling but not good for torque transfer under dynamic drag changes.

George
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Old 28th June 2017, 02:18 PM   #29
super10018 is offline super10018  United States
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To LD,

Your plot is very clever and informative. I wish you can add user interface so we all can measure our own tables.

I am thinking if I can export a set of data, i.e. time and frequencies, from recording of a test tone 31Hz. Then, I may import the data into some kind of polar plot software. I may get same measurements as yours. Do you know any polar plot software I can use?

Thank you!
Jim
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Old 28th June 2017, 04:09 PM   #30
msdin is offline msdin  United Kingdom
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Originally Posted by luckythedog View Post
It works with any test record that provides a continuous sine tone at about 3kHz or 3.15kHz, and just needs a short recording of 10s or so in any lossless format at any reasonable level.

So, over a few years, I collected together recordings of test sample tones that people have posted on forums, but usually I don't know and it doesn't matter what the actual test record was.

I don't mind running a few examples here, if anyone likes?

The software is a set of VB modules I wrote a few years back for myself to diagnose and improve pitch stability on my rigs. I never got round to making a proper user interface, so I still have to run them them manually.

Meantime, here's another good example from the archive. This is from a Micro Seiki SX-777. Red and Blue traces are for 2 consecutive revolutions.

LD

Here is a 3150hz sample from a Phonosophie No3 turntable.

Phonosophie P3 3150Hz Tone /Phonosophie_P3_3150Hz_Tone.wav

msdin
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