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Old 18th March 2018, 01:02 AM   #1071
Shhh its me is offline Shhh its me
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Quote:
Originally Posted by luckythedog View Post
I have a polar plot for an LP12, attached below.

LD
With these plots, how is the location of say 0 and 90 degrees determined?
Are these assumed locations on the platter that can't be pinpointed so as to make corrections?

This is of relevance for setting up a dynamic balance rig.

DIY motor dynamic balancing
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Old 18th March 2018, 10:29 AM   #1072
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by Shhh its me View Post
With these plots, how is the location of say 0 and 90 degrees determined?
Are these assumed locations on the platter that can't be pinpointed so as to make corrections?

This is of relevance for setting up a dynamic balance rig.

DIY motor dynamic balancing
You could make a light scratch on your test LP and line it up with a marking on your platter.
Recording and analysing the LP 4 times, each time 90 degrees shifted, you may be able to discriminate between LP eccentricity and spindle/platter misbehaviour.


Hans
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Old 18th March 2018, 02:47 PM   #1073
luckythedog is offline luckythedog  United Kingdom
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Quote:
Originally Posted by Shhh its me View Post
With these plots, how is the location of say 0 and 90 degrees determined?
Are these assumed locations on the platter that can't be pinpointed so as to make corrections?

This is of relevance for setting up a dynamic balance rig.

DIY motor dynamic balancing
OK, I'll check that thread out, thanks.

Meantime, as Hans says, you need a marker in the test file that identifies location on the record if absolute reckoning is required.

Note that convention has time moving clockwise on the polar plots, whereas absolute location on the record has opposite sense when you think about it...........

LD
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Old 27th April 2018, 09:56 PM   #1074
ThomasA is offline ThomasA  Sweden
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LD,

nice to see development of some polar plot tools of turntable speeds. You do not have any analysis of FM and AM components as well? Some 10-15 years ago some person made measurements of an LP12 and files from my Linn Axis at rec.audio.

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Old 28th April 2018, 12:43 PM   #1075
ThomasA is offline ThomasA  Sweden
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Found the original thread at rec.audio.tech here:

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Old 28th April 2018, 01:54 PM   #1076
Pano is offline Pano  United States
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Turntable speed stabilty
Thanks for digging that up. No mention in the thread of the software used. Good to see some other analysis, tho.
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Old 28th April 2018, 02:14 PM   #1077
ThomasA is offline ThomasA  Sweden
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Yes, I recall there was an analysis at Sterophile by John Atkinson at the same time, and they used the same files.

Linn LP Playing System Measurements | Stereophile.com

Goofballs "software radio" never became open or available though. Good however that there are interests enough to pursue and develop these measurement tools.

Since 1990 I have used the 10 g Akito arm, but changed to a light-weight 4 g arm (Moerch UP-4) 2016. Vertical resonance increased from 8 to 10,5 Hz, but I really want to go higher for the vertical direction. The DP-8 arm is on my wish-list but very expensive. I am also still hesitant to the published measurements made so far with the DP-8 (vertical resonances between 16-19 Hz).

Nevertheless, the change from 8 to 10,5 Hz decreased the warp-induced noise by 5-6 dB.

Dropbox - Tonearm mass and noise LP playback.pdf
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