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Old 20th March 2012, 12:43 AM   #1
gpapag is offline gpapag  Greece
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Default Grooves

Hi all
I would appreciate your comments on the attached doc.
It has to do with estimating (calculating) dimensions of vinyl record groove modulations
If you can spot any mistakes in the reasoning, please let me know.

Regards
George
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File Type: zip Groove 1.zip (348.5 KB, 29 views)
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Old 20th March 2012, 02:14 PM   #2
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Looks interesting.
It becomes somewhat clear now, why a spheric tip should be used and why it has a radius of 16,5 um for stereo and 25 um for mono records following the norm.
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Old 21st March 2012, 09:44 PM   #3
gpapag is offline gpapag  Greece
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Groove-T
Thanks for reading.

Stylus shape/radius.
This is I guess something that will surface up when I will dig a bit deeper further on, but for now, I can not find anything in the text and the graphs of the previous attachment that relates to it.
Do I miss something?

George
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Old 22nd March 2012, 09:49 AM   #4
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Basically record grooves are 50 um wide when no modulation is there.
With modulation they can be reduced down to 10um.

The spheric tip stay still in the groove when tracking this, since he is round and thus the contact surface is much smaller than the stylus radius. But we always have a pretty much constant contact surface. So we are in need of a little bit more tracking force around 2,2 to 2,5 gramms to get a proper tracking.

Any Cantilever changes the tracking angle dependent of modulation.
Its the same geometric law like for tonearms which are not tangential.

Thus there is a phase error L / R, no matter which kind of stylus.
Long cantilever have lesser error than short ones.

If the tip is elliptical, the ellipse changes the diameter in modulated grooves and this results in variable contact surface and thus the stylus creates his own modulation distorsion, depending of the music signal modulation.
(Its somehow like the ellipsoid ball for american football.
Depending where fromyou look at him, he has a different size. When touching the floor with speed, you cannot predict in which direction he fly away, but with a round ball you can pretty good predict the direction.)

The phase error is also there with spheric tips, but it can calculated. The result to reduce the phase error was the Dynagroove System with precompensation of the effect.

Spheric tips with 16,5 um radius can track 40 kHz!

Another advantage with spheric tips is, that the stylus has lesser wearing, since the contact surface has a constant size, but! the contact area is not always the same due the phase error.
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Old 22nd March 2012, 08:53 PM   #5
gpapag is offline gpapag  Greece
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OK
As I have suspected, you are going into some deep details.

You may find a serious study here (middle of page and down) Note on Record Specifications

Although this Japanese fellow humbly calls his work “junk science” , he is some light years ahead from what I will ever be able to do (not that I ever tried science ). Thanks for giving me the impetus to look at his work.

Something that I have to mention to anyone having read my previous attachment.
I have used the term “RIAA deemphasis” to describe the RIAA equalization that is applied to the recording phase.
I used this term because my understanding is that the main problem during recording was the taming of the cutter’s large excursions at low frequencies, thus de-emphasizing the low frequencies would alleviate the issue.
But now I realize that in literature, the term used for recording equalisation is “RIAA preemphasis”, while the term “RIAA deemphasis” is applied to the playback equalisation. . (Confusion )

George
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Old 23rd March 2012, 03:38 PM   #6
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Wow, exquisite link, tons of information and it seems to be far away from junk science.

If you are interested, i can email you a pdf with everything explaining abouth spheric tips, but is in german only. But it is really the essence!


And yes, for vinyl we have to go into details, a record groove is extremely full of details
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Old 23rd March 2012, 06:54 PM   #7
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by Groove-T View Post
And yes, for vinyl we have to go into details, a record groove is extremely full of details
I never implied the opposite

Thank you. You have PM

George
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