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-   -   What does anti-skating achieve? (http://www.diyaudio.com/forums/analogue-source/5269-what-does-anti-skating-achieve.html)

bm_mode 16th August 2002 10:03 AM

What does anti-skating achieve?
 
I know anti-skating is there to prevent the cartridge from swinging in towards the centre, but why is this necessary? Would this not push the stylus up against the outer edge of the groove, emphasising that channel of the stereo at the expenxe of the channel encoded on the inner groove?

I can't hear any real difference on my turntable with anti-skating applied or not, but then again it not the greatest of turntable front-ends (Lenco L78 and a cheap ortofon cart fed into an even cheaper op-amp phono pre-amp kitset job).

peranders 16th August 2002 02:15 PM

The question has puzzled me since I was kid, never got a good answer intil now.

It's unimportant if you have a very long and (straight) arm!

If you have a completely straight tone arm, what happens if you apply a force exactly away from the suspension point? Nothing, just a force in the same direction as the arm, no skating!

But, normal arms 10-12" long must have some angle of the pickup in order to get a decent tracking error, minimum at the centre (of the engraved surface) on the LP. This angle creates a force (due to friction in the vinyl) which direction is NOT from the suspension point. One composant of the force is straight in the arm direction and the other one is towards the LP center. This force must eliminated with a contra force (force the arm out) in order to prohibit the arm to dance "jenka" over the tracks.

Did anyone understand my explaination?

The purpose of anti-skating:

1 Prevent skating, not very pleasant for the LP, or your ears.

2 Prevent wear in the inner wall of the track.

My question to the expertice: Why does a elliptical stylus need more anti-skating force than a round one?

dice45 16th August 2002 07:20 PM

Ok folks,
peranders is right, but his statement is not complete.
So i take another swing on it.

Imagine a flowing river. Now hang a paddle into it. Angle different to flow direction. The river's flowing water will exert friction and stream forces on the paddle. AS the flowing direction is not aligned parallel with the paddle's blade, stream force exert a momentum trying to rotate the baddle until its blade is aligned with the flowing direction. Then the momentum becomes zero and the only forces remaining are the friction forces trying to pull the paddle out of your hand.

So: the skating force's origin (in fact the SF is a momentum referenced to tonearm pivot) is exactly the same of the momentum caused by stream forces described above. "Flowing direction" is the groove tangent thru the stylus tip. As the tonearm has a headshell with an offset angle to minimize lateral tracking error and as the phono cartridge is aligned to that heasdshell, the groove tangent has a distance to the tonearm pivot. So a momentum develops turning the tonearm towards the spindle. Like the paddle in the river.


The purpose of anti-skating:

1st
Prevent skating, not very pleasant for the LP, or your ears.

2nd
Prevent wear in the inner wall of the track.

3rd and sonically important
horizontally bias the generator system of the phono cartridge.

The phono cartridge has its cantilever suspended in rubber. This rubber acts like a pair (or quad) of highly progressive springs (and that damping is built-in is secondary for tis consideration) which menas that the sping forces rise more than linear with excursion. If now the cantilever is biased out of its center position, acceleration forces spindle-wards and edge-wards become different. Different enough to spoil sonics.

Obvious the same has to happen in vertical direction ; proper adjustment of tracking force yields in similar sonic benefits as proper AS adjustment does.

To give you a figure, actual skating force is almost constant over the tonearm's sweeping angle and it is about 8 to 10% of the tracking force.

peranders, you ask why elliptic styli have different AS forces than conical ones. I have no comprehensive answer for that. IMO each stylus has a slightly different AS force/tracking force cocktail because friction differs. According to what i described below, i would not trust any AS scale printed on a tonearm. I would trust my ears only.

Sonic mess caused by improper AS adjustment becomes apparent in microdynamics, macrodynamics, transients. Left and right channel behaves different.
I decribe below a possible approach to adjust AS by ear. But before you get lost, consider this adjustments are well audible on a top-notch TT. I have no experinece if and how the sonic changes expose themselves on a Lenco.
------------------------
(copied from an earlier JoeNet post)

short advice to adjust the cartridge:
let's presume that overhang and offset angle are already correctly aligned, estimated tracking force and skating compensation adjusted.

1. Adjust correct azimuth by slighltly turning your headshell and listen to a stereo recording how soundstage changes its size, perspective and balance or: measure the crosstalk between left and right channel: adjust so that crosstalk L=>R is *EQUAL* to R=>L crosstalk. If you find the Ortofon Test Record 0002, you can do this by ear.

2. select a mono recording with female voice (dynamic!!) and a lot happening around. Relax and concentrate.

3. Wrong vertical tracking angle (VTA) lets her voice go wider and wider as she sings louder. Real wrong VTA lets her voice go cinemascope from left to right speaker.

Adjust VTA so that the voice has the maximum focus (minimum size and maximum shape of virtual sound sources). The louder she sings/screams the smaller her mouth has to appear; this is clearly audible at the right VTA position. This optimum is very narrow: within 2/100 of a millimetre of vertical tonearm position.

4.Find the tracking force with best dynamics and micro dynamics and most believable sound colours. This optimum also is very narrow.

5. Have a rest. You may have to repeat steps 3 and 4 : you need the maximum resolution for the following.

6. Have a rest. Select a premium stereo recording. Relax and concentrate again.

7. Adjust the skating force to zero and prepare yourself for a mean experience. The right channel will not show dynamics at all; it will sit in the corner totally bored and ignoring you. The left channel will sit in its corner like an evil ghost, considering to attack you in the next moment. It will sound very dynamic in a way that numbs the left half of your body. However, the dynamics will be nightmare-like artificial.

Now you increase the skating force to a quarter and then to a half of the expected value. You will sense that the right channel comes more-and-more alive and the left channel sounds less dynamic, intimidating and artificial. This reduction is less than the increase of dynamics in the right channel; the while system becomes more dynamic. You increase now the skating compensation by *very* small steps until you reach a point where left and right channel sound equally dynamic. Then you increase further very small steps; both channels will grow more dynamic. One step too far and both channels loose their dynamics completely and sound dead. So you go back to the position where dynamics and microdynamics were maximum.

8. Note down *all* positions, scale readings, input impedances/capacitances and so on (you may want to mount another cartridge later and then find you loathe it) .

Done.

I never had the skating compensation's scale read above the
tracking force scale, always below!
Usually 60-70% of the value expected by the scale prinited on the tonearm.

wuffwaff 16th August 2002 07:39 PM

peranders,


a complete straight tone arm would have to be a linear tracking one where the pivoting point is somewhere far away (for you it probably would be in Spain):D


For setting antiskating force I use a somewhat easier method (although I will try the one mentioned by Berhard).
Use a test record with a tracking test. Normally at 70, 80 or 90 mu the cartridge starts to misbehave (i.e. distort). Now I adjust the antiskating until the distortion starts at the same time in the right and left channnel.

william

dice45 16th August 2002 09:38 PM

William,

so i did before AllenWright showed me this method to do it by ear.
The test record brings you in the ball park, not more. And you never know if your test record survived the last mistracking :)
BTW, also the test record will disagree with the tonearm's AS scale.
And the blank band test, too; surpisingly the blank band test agrees closely with the adjustment by ear.

wuffwaff 17th August 2002 06:17 AM

Hi Bernhard,

the blank test once drove me crazy with my Lyra Lydian. The form of the needle doesn't seem to like blank tests:( The scale of my SME IV wasn't big enough to dial in enough antiskating.

william


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