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Turntable speed stabilty
Turntable speed stabilty
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Old 28th June 2017, 07:36 PM   #31
luckythedog is offline luckythedog  United Kingdom
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Quote:
Originally Posted by msdin View Post
Here is a 3150hz sample from a Phonosophie No3 turntable.

Phonosophie P3 3150Hz Tone /Phonosophie_P3_3150Hz_Tone.wav

msdin
Here's the polar plot for that file from your Phonosophie P3. Also, another plot from a Phonosophie P3 file I had in the archive, for reference which happens to be at 4kHz but with the same scale so it's easy to compare. The archive one is the 2nd attachment.

Overall I would say your P3 is good and healthy. If you wish to improve it, something seems going on around 6Hz or so, which also occurs on the archive P3 so might be drive related. Also you have something going on at just over 2Hz which doesn't seem to crop up on the archive P3.

You have far more stable 'once per revolution' eccentricity like rotation speed variation than the archive P3, and also your cart/arm resonance seems more stable.

BTW, the y-axis on the inset spectrum auto-scales. So when there's a lot of eccentricity, as in the archive P3, it looks as though all other contributions are smaller, whereas that's just an artefact of the scale.

Hope this is interesting/helpful ?

LD
Attached Images
File Type: jpg Phonosophie P3.JPG (230.9 KB, 371 views)
File Type: jpg Phonosophie Archive.jpg (224.4 KB, 365 views)

Last edited by luckythedog; 28th June 2017 at 07:38 PM.
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Old 29th June 2017, 07:03 AM   #32
waltzingbear is offline waltzingbear  United States
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For those wishing to read more on flutter analysis and diagnostic methodologies I can recommend Dale Manquen's site, M A N Q U E N . N E T - A U D I O

Dale isn't with us anymore but his site lives on. In it (among other things) he explains how to take the data like you have on the last post and use it to identify the cause(s).

Cheers
Alan

Last edited by waltzingbear; 29th June 2017 at 07:06 AM.
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Old 29th June 2017, 08:21 AM   #33
billshurv is offline billshurv  United Kingdom
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Turntable speed stabilty
That it all tape related though? Can't see any vinyl information.
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Old 29th June 2017, 09:11 AM   #34
billshurv is offline billshurv  United Kingdom
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Turntable speed stabilty
Found another option for the test tone. Tacet-Vinyl Check-180 Gram Vinyl Record|Acoustic Sounds . A report I have seen says this is one of the more useful current production test records with a suggestion its a quieter and better centred pressing than the Feickert one.
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Old 29th June 2017, 04:01 PM   #35
waltzingbear is offline waltzingbear  United States
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math is math
flutter is flutter
rotational elements are rotational elements

apply it to the problem at hand

Cheers
Alan
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Old 29th June 2017, 05:12 PM   #36
diyrayk is offline diyrayk  United States
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Default Is it "turntable" speed stability or is it "record player" speed stability?

Quote:
Originally Posted by luckythedog View Post
This LP12 example is actually quite good as these things go. One can readily see mostly there's a once per platter revolution 'eccentricity', which might well be record mis-centering. Otherwise, one can see contributions around the 8-12HHz region which might well be cart-arm resonance - often this can dominate stability in a good TT, IME, as it appears here.

So in this case although the underlying TT seems good, the cart-arm resonance might well be dominant in determining pitch stability, or there might be something else TT drive-wise that contributes the 8-12Hz instability. LD
Quote:
Originally Posted by luckythedog View Post
Stylus-groove friction isn't steady, it varies with time in a 1/f flicker noise like profile about an average value IME. This variation causes variation in skate force in an offset arm, and in downforce due to VTA on all arms. This is a stimulus that can cause the headshell to move which is a source of FM or pitch variation. What happens next depends on the cart-arm resonant system, and how much damping there is around. LD
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 testrecord with a frequency that changes the amplitude abruptly could probably give a better prediction of the sonics...
The effects of speed stability cause a pitch fluctuation or Frequency Modulation (FM) of the audio signal in the groove. A bent motor shaft on an idler or belt drive turntable will have a similar effect on the sound as an eccentric capstan on a tape recorder or a bad drive component in a movie film projector. These are all mechanical reproducers and have rotating parts which can cause cyclic and/or transient speed variations. The topic has been extensively researched and documented in technical papers and journals. The British Broadcasting Company published an excellent research paper “The Subjective Discrimination of Pitch and Amplitude Fluctuations in Recording Systems” in 1955 in Britain, and reprinted in the US by the AES in 1957. The BBC research built on other research references dating back to at least 1941. The BBC researchers found that the sensitivity threshold for FM among groups of listeners was broadly centered in the range of about 4Hz to 10Hz. Many arm/cartridge combinations have a mass/compliance resonance frequency within the 4Hz to 10Hz range. Bruel & Kjaer published a paper “Audible Effects of Mechanical Resonances in Turntables” in 1970. B&K mounted three different tonearms on the same turntable. Using the same turntable/motor and same cartridge moved in turn to each of the three arms, the weighted % wow and flutter B&K measured varied by a factor of 3 to 1, depending on the tonearm being used in the test setup. If you were the manufacturer of that turntable, which wow and flutter number would you use for the spec’s in your sales brochure?

As an exercise, I modeled my SME 3009 in a CAD program and ‘flexed’ the arm sideways to empirically measure what the stylus point does in the groove under dynamic conditions:

Click the image to open in full size.

For a sideways displacement of about the thickness of a credit card, give or take, about 40% of the sideways displacement of the stylus goes into scrubbing motion along the groove, causing FM distortion. At mass/compliance resonance frequencies the scrubbing-induced FM shows up as measurable, and often audible, flutter. The amount and character of the scrubbing depends on the magnitude of the displacement, arm geometry, and stylus shaft length.

Click the image to open in full size.

The usual measure of turntable speed stability, i.e. wow and flutter, includes the mechanical stability effects of the tonearm/cartridge, and is a speed stability measure of the record player, not just the turntable by itself. The two contributions need to be analyzed separately. A single numerical value for the wow and flutter that’s going into the preamp is meaningless. Dynamic stylus drag variation could cause a transient pitch variation (FM) in the turntable drive or does the dynamic stylus drag variation cause a sideways displacement of the cantilever which translates into transient pitch variation (FM) from the resultant scrubbing? Each of these sources requires a different remedy.

Thoughts?

Ray K

AES E-Library Subjective Discrimination of Pitch and Amplitude Fluctuations in Recording Systems

https://www.vinylengine.com/turntabl...p?f=46&t=58101
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Old 29th June 2017, 05:16 PM   #37
diyrayk is offline diyrayk  United States
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Quote:
Originally Posted by Hiten View Post
Any other method other than test records ? Since offcenter and warps can not be avoided any modern method to measure speed stability ?
A Postscript printer can print precise dots (or markings) we can make perfectly center thick white sheet with such markings and optically measure the speed variations. Right ?
How do classic tables like Thorens, Garrard, Lencos and Technics compare with regards to speed stability. Any one has measured them and have data on them ?
Regards.
The advantage to your optical dots method is that it measures the pitch stability of the turntable, and is free from the mechanical stability effects of the tonearm/cartridge. By comparing the results of an optical method signal with the results from the arm/cartridge signal one could segregate the contribution of the turntable speed stability effects from the arm/cartridge resonance and mechanical stability effects. Put the printed dots pattern on the Feickert disc while running the test and both method signals could be measured simultaneously, as an added measure of controlling all the test variables. Now, if the Feickert discs were pressed with the dots printed right on the disc label, or stamped or laser etched on the outer perimeter lead-in area, hmmm…

Ray K
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Old 29th June 2017, 05:22 PM   #38
diyrayk is offline diyrayk  United States
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Quote:
Originally Posted by billshurv View Post
That it all tape related though? Can't see any vinyl information.
He explains the effects of AM modulation and FM modulation generated by a mechanical reproducer. When you read through his website, focus on the discussion and portions of his graphs that cover the spectrum “Lower bandpass - .5 Hz to 250 Hz to isolate components due to rotating tape drive members”. His website is more comprehensive than the AES paper that it was built upon, plus the technical info on his website is free.
A record player is a mechanical reproducer, just as a tape deck is. The FM effects from an eccentric tape deck capstan at 10 Hz is the same thing as FM effects of stylus scrubbing with an arm/cartridge system excited at a 10Hz resonance frequency. Take advantage of the research that's already been done by others and build on it. Don’t spin your wheels re-researching something that’s already been done.

M A N Q U E N . N E T - A U D I O

Oh, and while you’re at it, check out his electronics bench and model train set. He has DIY skills too:

The Magic Portal

Ray K
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Old 29th June 2017, 07:40 PM   #39
gpapag is offline gpapag  Greece
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Turntable speed stabilty
As the lowest tech possible , no math approach, I tried heterodyning a single frequency vinyl playback file with a computer generated test tone of the same frequency and same level.
I made a new file. L channel is the vinyl playback tone, R channel is the synthesized tone.
I synchronized the two tones at the beginning of the file.
Then I saved the file as a mono (L+R) file.
See the outcome for a 3150Hz track from the JVC QL-A2, for which Lucky kindly provided the polar plot in post #1257.
I measured the period T in sec of each pattern .
1/T is the frequency component of this pattern.
The more times the same pattern appears, the stronger it’s freq component is.
1.8sec frame length is one revolution of the platter.
This way I can locate all the modulating components, i.e. the Cartesian Freq-level inset from Lucky’s analysis.

George
Attached Images
File Type: png Heterodyning.PNG (123.2 KB, 314 views)
File Type: png 1 turn slices JVC+synthesized 1350Hz.PNG (60.6 KB, 92 views)
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Old 29th June 2017, 07:55 PM   #40
billshurv is offline billshurv  United Kingdom
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Turntable speed stabilty
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