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From: rcd@opus.UUCP (Dick Dunn)
Newsgroups: net.audio
Subject: Re: How do you check antiskating?
Message-ID: <405@opus.UUCP>
Date: Thu, 26-Apr-84 02:37:10 EST
Article-I.D.: opus.405
Posted: Thu Apr 26 02:37:10 1984
Date-Received: Sat, 28-Apr-84 08:27:03 EST
References: <2469@watcgl.UUCP>
Organization: NBI, Boulder
Lines: 51

<>
>I KNOW the antiskate calibration scale on my arm is incorrect for my
>cartridge.  Doesn't the required antiskate force vary from one cartridge
>(and stylus) to the next anyway?

Yes, somewhat - but the variation is related to the required tracking
force.  That's why some tonearms have an anti-skate scale calibrated the
same as the tracking force, and others do the anti-skate adjustment
automatically.
Backing up a bit, why does it skate?  (Why do I ask?  Because understanding
this makes it easier to figure out what to do about it.)  It skates
because the end of your tonearm is bent:
	   *
            \
             \
              +-------------------------------------------o---|

* = cartridge, o = pivot
The record obviously "tugs" on the stylus ever-so-slightly as it moves
underneath.  If the tangent to the groove at the stylus went toward the
pivot, the force would be directly out from the pivot and no anti-skate
correction would be needed.  (In fact, this is the case with so-called
"linear-tracking" turntables - and they don't need anti-skate force.)

Since in the case above the tangent goes wide of the pivot (below in the
drawing), there's a component of the force that acts to turn the tonearm
toward the center of the record.  [Why, you may ask, is the damn tonearm
bent, anyway?  To allow a reasonably short tonearm, yet keep the stylus
reasonably aligned in the groove across the record.  And so you ask, why
not just use a longer tonearm?  Because it's heavier, more subject to
resonance problems, it looks stupid, and your wife doesn't want it in the
living room.]  So you add a little force to counteract the inward tendency.

What determines the skating force?  First, tracking force - remember your
physics; frictional force is proportional to how hard you sit on it.
Second, cartridge compliance interacting with the type of material you
play.  (At this point, the problems become intractable, but you've got
something to worry about and spend a lot of money for someone else to
fix.)

Another comment (Jeff Frey) on the same topic:
>...Spring-adjusted anti-skate leads
>to difference force at the inside and outside radii of the disc,
>however, so no setting will really be optimum.

Yes, although you can get rid most of this - you just don't let the spring
stretch very much over its travel and you can easily get the variation
below a few percent.
-- 
...Cerebus for dictator!				Dick Dunn
{hao,ucbvax,allegra}!nbires!rcd				(303) 444-5710 x3086