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Old 8th March 2006, 04:19 PM   #11
EC8010 is offline EC8010  United Kingdom
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gpapag: I fixed your link to Vinylengine, but I couldn't seem to find the John Wright article. Your link to the RIAA standards doesn't work, but I don't understand why. When I searched for Aardvark mastering, I found the RIAA standard and it had the address you used. Odd.

As for my bias design, the main requirement was that it should work without upsetting the unipivot. As has correctly been said earlier in this thread, it's easy to upset a unipivot with off-centre forces. My arrangement applies the force at the pivot height to avoid this problem. I used constant bias force because I had no evidence at the time (fourteen years ago) that anything else would be better. There's no reason why my design couldn't be adapted to produce a nonlinear force simply by fitting an eccentric sleeve around the existing arm pulley. I suspect the outer surface would have to be cut by hand, but it wouldn't be too difficult.
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Old 8th March 2006, 04:42 PM   #12
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Default Bias

Gpagag,

The aardvark site shows a diagram that confirms what i find with a lot of records

http://www.aardvarkmastering.com/riaa-1.gif

that is a dip towards the centre. You might be familiar with Stan Rickers interview at Cardas Audio

http://www.cardas.com/content.php?ar...+Ricker+Part+I

He talks about records there being made in a kind of U shape for stacking purposes.

the problem with of using grooveless records to gain information is of course that they bear no real relationship to real grooved records. Its practically impossible to decide whether the different forces at work on a grooveless record originate from the vinyl, other centrifugal forces, or from the arm. Using a grooved 'run-in'record like the clearaudio is pretty useless as well, because its mastered not to produce sound or calibrate real life bias.

The problem with bias is that the complex dynamic forces operating on the stylus vary. The bowl shape or dip in the record has different shape with each record, and if the record is also eccentric, will be all the more complex to calculate. Its no suprise to me that Harry Weisfield of VPI removed antiskating from one of his arms completely. In my experience some cartridges are much more 'bias' sensitive than others. A good tracker with relatively high compliance can usually get by with much less bias than others. I also find that needing to use more bias can be a sign that the cartridge needs retipping.
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edward
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Old 8th March 2006, 04:58 PM   #13
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'I sacrificed a Carpenters LP to science by sawing it diametrically in half and measuring thickness at various points. Some LPs are observably flat, but the one I chose was not. I don't seem to have the numbers to hand, but the slope was very gradual and I posted numbers on this forum.'

Its always the Carpenters who get sacrificed . The bias issue only really gets critical imo when either the cart mistracks, or its audibly favouring a groove, or if there's long term wear to one side, pushing the cantilever over. Air bearings are i guess the most likely to mistrack, because they are so level, and their lateral mass changes at the point where the dip changes. Some people prefer to align their air bearings out of level for this reason. That's also true for the Clearaudio/Souther. In practice this can make for even greater problems if the record is eccentric (and to some extent it usually is).
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Old 9th March 2006, 02:00 PM   #14
gpapag is offline gpapag  Greece
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Dear all
Trying to find data about modulation velocity changes versus groove radius, i fell over this sitehttp://www7a.biglobe.ne.jp/~yosh/sitemap.htm
I just went through the titles.
It seems like the puthhy cat has already been under a japanese microscope. I have quite a lot work to do ( i mean work), so i don't find it prudent to withhold such wealth of information not for a moment.
Enjoy.
I will be back in a few days with comments

P.S. It seems that John Wright's article has dissapeared from VinylEngine site. Nevertheless, i have it in my hard disk. It is ~500kB. I would e-mail it to anyone interested. By the way, if someone has the second part of this article in his possession, i would be very interested to have a copy

Regards
George
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