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Anti-Skate

heidcase music

heidcase music

pfm Member
Never been able to understand which way the record pulls the stylus
So .. which will cause more long term damage .. under anti-skate setting .. or over anti-skate setting in context with the tracking weight
 
The stylus "wants" to travel towards the centre of the record, due to friction between the stylus and record. Anti-skate tries to counteract that so that the stylus has a radial (to the record) force in neither direction.

If the anti-skate is out, the sylus will "hug" one side of the groove or the other.

If you look at any toenarm using a falling weight anti-skate, you'll see that it is pulling the tonearm away from the centre of the record.

Tracking weight is simply the downward force on the sylus.
 
Turntable-Anti-Skate.jpg
 
^^^^^ Not actually true.

The force on the stylus is actually back along the groove - friction acts to oppose motion, and motion is obviously along the groove.
 
Vinny said:
^^^^^ Not actually true.

The force on the stylus is actually back along the groove - friction acts to oppose motion, and motion is obviously along the groove.
Click to expand...

The OP wanted to know "which way the record pulls the stylus", and in the simplest terms without getting into the finer details of it all the pic shows correctly that the stylus gets pulled towards the inside diameter -centripetal- of the LP under normal playback.
 
The record does not pull the stylus in any direction,
Friction does that, and it acts along the groove.

The reason that the stylus would naturally move towards the centre of the record is due to the offset angle of the cartridge to the arm axis. If the cart' could be used so that the axis of the cart was parallel to or coincident with that of the arm, there would be no force, either direction, just along the axis of the arm.

Parallel trackers produce no skating force on the sylus, so have no need for anti-skate.
 
I remember a clear demonstration that the stylus wants to move to the centre.
A moment of clumsiness on my part caused the pickup to jump from the runout grooves onto the label where there are no grooves to guide it. It immediately shot off to the left to be stopped short by the centre post. No doubt about it!
The arm was an SME 3009 and the anti skate line and weight couldn’t cope with the forces involved when out of the grooves.
 
So where did the reason come from that setting antiskate to match the tracking force applied?
I track at 2g but only use 1,5g on the antiskate dial on my 309.
 
Until the penny dropped, none of this made any sense.....................

The coefficient of friction of MANY material pairs is quoted as 0.7 - it is just convenient and close to real life. Stylus-vinyl is no different.

So, the frictional force is going to be AROUND 0.7 x the tracking force.

From there, you need to do some very basic geometry to work out the force on the stylus on the inner side of the groove. Assume zero friction in the arm bearing.

Most people reckon to set by ear anyway, and lots of tonearms have no calibration - ARO, Hadcock, Schroder...................................... In fact, calibrated anti-skate is probably in the minority.
 
If I "play" an unpressed blank side of an LP with no anti-skate, the arm wants to move towards the centre, albeit quite steadily, so I fail to see how it can be a stylus-groove friction effect. I seem to remember reading aeons ago, that a good way to acheive a base line setting for anti-skate was to use such a flat un-grooved disc, setting the antiskate such that the arm does not move and fine tuning with a pressed disc afterwards. My DL110/Ittok was set up this way. VTF 1.8g, antiskate dial 1.4 gives the best performance.
 
With fixed offset pivoting tonearms, the skating force vector is half way between the lines of friction and resistance to friction. The friction vector is equal to tonearm offset, whereas, the resistance to friction vector is equal to the pivot to stylus line. As offset is inward, skating is inward at exactly the angle that is halfway between offset and the pivot to stylus line (i.e. a right angle to offset, and therefore only on a direct vector with the record spindle at the two nulls). With typical anti-skating mechanisms the compensation vector isn't exactly opposite that of the skating vector, nor is it applied in a straight line. Of course, this is looking at things horizontally, when we also look in the vertical, we see that VTF is applied at a vector that is between straight down and laterally straight inward. Very few anti-skating mechanisms have been developed that fully account for this, with the A.R. Sudgen and Co. Connoisseur SAU 2 being the most elegant solution I know of, with down force being biased toward the opposite angle to the net affect of skating force on the distribution of VTF between the two grooves; IOW there is more VTF applied on the Rch outer groove wall side than there is applied on the Lch inner groove wall side. SAU 2 looks wrong, and certainly feels wrong, but it is the only skating compensation mechanism that actually does what it says on the tin, it negates the affects of skating on equal groove wall pressure by directly compensating in the appropriate vector. It could just as easily have been dubbed 'Tracking Force Equalizer'.

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Pine Marten said:
I fail to see how it can be a stylus-groove friction effect
Click to expand...

That would imply that you believe that there is no friction between the stylus and flat vinyl. Guess what - there is.

That apart - what force do you imagine there might be other than friction? Guess what - there isn't.

Pine Marten said:
I seem to remember reading aeons ago, that a good way to acheive a base line setting for anti-skate was to use such a flat un-grooved disc, setting the antiskate such that the arm does not move and fine tuning with a pressed disc afterwards.
Click to expand...

Try it - it will be miles out as, at the simplest level, the contact area, and hence the frictional force, will be very different flat v groove. You should find that you need far more anti-skate on flat vinyl as the stylus will also "carve" a scratch into the vinyl, which produces an even greater force on the stylus.
I have seen that too and tried it. That was before the penny dropped as to why there is a skating force at all.

The maths is moderately complicated - I beleive it is on Vinyl Engine for anyone interested, but due to the changing geometry of stylus axis v groove as the arm tracks across the record, skating force varies. In most tonearms, anti-skate is constant across the record. Falling weight systems are not and can come close to matching the change in skating force.

The maths is interesting, if you like that sort of thing, but in real life it is all a compromise as friction varies due to groove shape variation (ie the music).
 
Craig B said:
Very few anti-skating mechanisms have been developed that fully account for this, with the A.R. Sudgen and Co. Connoisseur SAU 2 being the most elegant solution I know of, with down force being biased toward the opposite angle to the net affect of skating force on the distribution of VTF between the two grooves; IOW there is more VTF applied on the Rch outer groove wall side than there is applied on the Lch inner groove wall side. SAU 2 looks wrong, and certainly feels wrong, but it is the only skating compensation mechanism that actually does what it says on the tin, it negates the affects of skating on equal groove wall pressure by directly compensating in the appropriate vector.
Click to expand...

Fascinating arm, I’ve never seen one up close so never realised how radical its thinking. I’m surprised it hasn’t been copied as that bearing alignment and weight certainly looks like a pretty logical answer. Clever stuff!
 
For me the first thing to realise is that anti-skate is impossible to get right. The amount of drag will vary depending on how violent the modulations in the groove are so a rough approximation is all you can hope for. The only way you can be sure you've got it right to examine a used stylus to see if the wear is even.

I've found the method of finding the right value adopted by Soundsmith to work quite well. I'm sure it's still a best guess but I'm happy with it. As a general rule it seems that the best anti-skate always ends up being a lot less than the tracking force value. So if the tracking force is 1.6 the anti-skate will be about 0.6.
 
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