All the LPs that I've looked closely at have some run-out. Even my 1958 and 1967 Decca test LPs (boot-sales). I've had numerous decks. The most recent two are Standard Goldring GL75 and an '88' with 3012 SME and two carts. These have filament-and-weight anti-skate. The arms' lateral bearings show no obvious friction.
There will be friction as the anti-skate filament moves over the guide. With the A-S friction present on either deck the stereo image seems to wander. Without it it doesn't.
Listening to a 3k W&F test tone on the '58 LP the wandering effect is extreme. There's even some 2nd harmonic in it! Pulling the weight up (sharp image movement) and then ease back t'other way (gentle). I don't think F=ma comes into it given the very small accelerations of the weight.
Polishing the wire supports and adding light oil to the filament didn't help much, if at all.
Then there's the angle of dangle. At least the GL75 design has the filament bend through 90 degrees. The unnecessarily high support on the SME bends it through over 100 degrees. Daft. Why not a bit less than 90? (I feel an alternative SME wire support coming along soon...)
So compromise. Use the weight but at abt half or less of that indicated by the 'calibrated' grooves in the anti-skate booms or by the much maligned blank disc method.
Any other ideas ???
Back in the day my mate's TD160 had magnetic bias correction. I can see why now! Always thought that odd because mag force varies with the fourth power* of separation distance. Must use interesting cam geometry...
* https://en.wikipedia.org/wiki/Force...e:Cylindrical-magnet-force-diagram_loglog.svg
This came up at work where it's the fifth power for electrical power transfer when separating audio coupling coils.
There will be friction as the anti-skate filament moves over the guide. With the A-S friction present on either deck the stereo image seems to wander. Without it it doesn't.
Listening to a 3k W&F test tone on the '58 LP the wandering effect is extreme. There's even some 2nd harmonic in it! Pulling the weight up (sharp image movement) and then ease back t'other way (gentle). I don't think F=ma comes into it given the very small accelerations of the weight.
Polishing the wire supports and adding light oil to the filament didn't help much, if at all.
Then there's the angle of dangle. At least the GL75 design has the filament bend through 90 degrees. The unnecessarily high support on the SME bends it through over 100 degrees. Daft. Why not a bit less than 90? (I feel an alternative SME wire support coming along soon...)
So compromise. Use the weight but at abt half or less of that indicated by the 'calibrated' grooves in the anti-skate booms or by the much maligned blank disc method.
Any other ideas ???
Back in the day my mate's TD160 had magnetic bias correction. I can see why now! Always thought that odd because mag force varies with the fourth power* of separation distance. Must use interesting cam geometry...
* https://en.wikipedia.org/wiki/Force...e:Cylindrical-magnet-force-diagram_loglog.svg
This came up at work where it's the fifth power for electrical power transfer when separating audio coupling coils.
I have been exploring anti-skate after ignoring it for years.
I found that the WALLY TRACKER has opened what I call Pandora's Box of Worms. Sometimes one would rather not know too much.
I am using the very fine sounding SUPATRAC tonearm and when I needed to get the cartridge a new cantilever I thought I should look into the anti-skate conundrum. Not for sound quality but for cantilever longevity. I had not been using anti-skate at all since I thought I could get away with not using it. I do not detect any problems with the sonics.
With this tonearm there are three basic regions - in the middle of the record there is neutrality - at the beginning of the record lots of bias is needed - the arm wants to swing to the middle of the LP - and as you already have guessed the last third has natural bias - it, also, wants to swing but to the middle at just about the right amount for anti-skate.
The SUPATRAC comes with an anti-skate that allows the amount of bias to vary due to where the pivot point is along with the amount of weight used - this can get close but the last third of the record the thing needs to be "turned off" which I figure could be done with a very deft application of magnetism which is what I am going to attempt.
I do not doubt anti-skate is important but I am beginning to understand why many ignore it since it would require more than a weight and length of string to make it close to linear across the record. A non-unipivot arm would be more naturally linear. I tend to think what makes the SUPATRAC sound so good is also what conspires against it having a simple anti-skate set up. I tend to think a traditional uni-pivot would be impossible to compensate with the typical anti-skate mechanism due to interfering with the uni-pivot's azimuth. One would thing there is only the choice of using some kind of string bundle attached above the unipivot to create a bias force by twisting the strings.
Then there is the option of a servo-motor controlling the bias ...
I found that the WALLY TRACKER has opened what I call Pandora's Box of Worms. Sometimes one would rather not know too much.
I am using the very fine sounding SUPATRAC tonearm and when I needed to get the cartridge a new cantilever I thought I should look into the anti-skate conundrum. Not for sound quality but for cantilever longevity. I had not been using anti-skate at all since I thought I could get away with not using it. I do not detect any problems with the sonics.
With this tonearm there are three basic regions - in the middle of the record there is neutrality - at the beginning of the record lots of bias is needed - the arm wants to swing to the middle of the LP - and as you already have guessed the last third has natural bias - it, also, wants to swing but to the middle at just about the right amount for anti-skate.
The SUPATRAC comes with an anti-skate that allows the amount of bias to vary due to where the pivot point is along with the amount of weight used - this can get close but the last third of the record the thing needs to be "turned off" which I figure could be done with a very deft application of magnetism which is what I am going to attempt.
I do not doubt anti-skate is important but I am beginning to understand why many ignore it since it would require more than a weight and length of string to make it close to linear across the record. A non-unipivot arm would be more naturally linear. I tend to think what makes the SUPATRAC sound so good is also what conspires against it having a simple anti-skate set up. I tend to think a traditional uni-pivot would be impossible to compensate with the typical anti-skate mechanism due to interfering with the uni-pivot's azimuth. One would thing there is only the choice of using some kind of string bundle attached above the unipivot to create a bias force by twisting the strings.
Then there is the option of a servo-motor controlling the bias ...
Use a small bellcrank on a precision bearing to transmit the A.S. force round that corner? I doubt the friction actually affects the stereo image directly (*), but solid friction is stick/slip so it could be causing its own characteristic noise - to evaluate that use a silent groove in an off-centre pressing? It strikes me such weight/cord anti-skate mechanisms provide damping to the arm in the horizontal plane, don't know if that's actively been investigated.
Exactly 90 degrees is what you want as the cord should be horizontal in the plane of the arm movement, and vertical in the gravity section.
(*) I wouldn't expect the cantilever movement to affect the friction dynamics on the cord over its guide. However the stick/slip of friction could affect the lateral bias on the cantilever. However the effect is minimal on a well centred pressing as there is only slow and one-way movement of the cord in the ideal case.
You mean something like this?:
https://en.m.wikipedia.org/wiki/Bellcrank
I think the friction is due to the small radius at the point where the thread changes direction. A suitable small bearing would help. Even the bellcrank needs some kind of bearing.
https://en.m.wikipedia.org/wiki/Bellcrank
I think the friction is due to the small radius at the point where the thread changes direction. A suitable small bearing would help. Even the bellcrank needs some kind of bearing.
It most certainly does affect stereo imaging - see the originl post. I don't know exactly why but using the two carts that I have, removing the weight stops the image drift described. Sadly most pressings are not well centred. Not even HiFi test records from a respected company.
The answer to my problem is blindingly obvious. Things hiding in plain sight usually are. Belcrank would work but easier to just run it over a pulley! A big thank-you to the forum contributors would be in order at this point.
This is my plan so far but plans rarely survive execution:
An e-bay miniature ball-race plus an internally taper-reamed aluminium pulley tyre, interference-fitted onto it. El-cheapo tapered reamer available anywhere. Tyre made from an Excellite hobby knife handle - good source of small ally stock, easy to get and cheap. Could make it from any material. I do have a lathe but this sort of thing could be done using just an electric drill hacksaw and file...
The supporting structure could be a piece of simple heavy plain copper single-strand house wiring wire. I have a 0.100" dia piece handy.
Mounting could be via an electrical eyelet or fork soldered to the wire end and held under the same SME screw - not enough clearance for looped wire (unless it's hammered flat - bit unsightly and there would be a stress concentration at the point it went back to round).
Its other end hammered sufficiently out of round to form an interference fit to the inner diameter of the ball-race.
Happy days.... I hope.
Next problem will be to sort out the crappy slightly intermittent pogo-pin arrangement from the arm to the heaadshell.
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Actually a bell crank doesn't have enough range of motion, thinking about it - a pulley could be a good answer, larger radius is better for bearing noise and least distortion of the cord.
I have found a decent solution to my problem - since the anti-skate needs to be variable: the only way to do this is with magnets unless one is exceedingly clever and could design a servo which would have even more problems.
A push-pull arrangement with two strings over two pulleys with a small piece of steel (I mean really small - 0.25 " square) and neodymium magnets (disks from AMAZON - ordinary quality) set to a height that gives a good result. Once you get it going it is pretty easy to get it adjusted. You can easily move the magnets around to fine tune cantilever deflection while the record is playing. Strings level with the SUPATRAC's "thrust box" using the hole in the arm for the right side hoist string: one going "backwards" for the main and one going to the "front" for the negating side.
I have ordered a valve spring adjuster from AMAZON to make it easier and more precise for the main anti-skate magnets.
https://www.amazon.com/gp/product/B08B8CSSB5/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
Fasten the magnet to the top and attach to a base of some weight. I will use superglue. For the moment I have made a platform with a wine cork and a small piece of copper plate. Using pieces of card stock beneath the plate to make adjustments. Very tedious. The copper plate will be retained. The base has to be of more weight that you might think is needed. On the negate side the magnet is not secured. Not enough force is generated to require it in my case. I can either tape it down or leave it loose to be able to move it for fine adjustment.
The downside is you need to be able to make room for this. My plinth had a hole in it right where I needed the string to go for the negating magnet. And plenty of room to the side for the main. Not elegant in any way. I suspect it would be impossible to do it compactly. I cannot get the anti-skate magnets near the arm since the back of the arm is of a material that is magnetic.
As you can imagine/know the weight does not move very far with the the swing of the tonearm.
My strings are about 10 inches. My plinth sits up high and the underneath is easily accessible.
Using WALLY TRACKER I am getting a steady 11% across the scale for a 2 grams tracking force.
A much smaller force is used to negate the unneeded force from the main anti-skate for the latter third of the record which is obvious!
I wonder if a further refinement would be to have the weight and magnet in a thin silicone bath? One can see the metal pieces (cut from a small alligator clip - whatever those are made from) wiggle - whether this imparts some errant force on the tonearm?
I have been doing this with a cartridge I will not be using while waiting for my cartridge to come back from Andy Kim for a new cantilever and wanted the tonearm to be right before installing it. A long way of saying I have not heard what this arrangement does. My phono stage is transimpedance , my other cartridge is a Zu Denon 103 and its high coil impedance does not work well with this kind of stage.
Middle of the week I should know if it works at all (sonically), works OK or works very well. I have played records but I cannot hear them - so I know it works smoothly.
For those with non-linear horizontal bearings could be worth a try - the bearing on the SUPATRAC is of exceedingly low friction - it is how the arm is hung that brings these anomalies. Even with this, the arm sounded great with no anti-skating. I could never get the anti-skate to do what I needed it to do and this was before I got the WALLY TRACKER so I had no idea what I was up against. Please do not take my comments as a condemnation of the SUPATRAC. This is a great tonearm but with compromises as all tonearms have. The standard setup on the SUPATRAC would work better if there was some way to get the anti-skate to stop for the last third of the record - but I cannot get this to happen without the anti-skate then not allowing the tonearm to return to rest. I am hoping that my obsession will be of use to others.
A push-pull arrangement with two strings over two pulleys with a small piece of steel (I mean really small - 0.25 " square) and neodymium magnets (disks from AMAZON - ordinary quality) set to a height that gives a good result. Once you get it going it is pretty easy to get it adjusted. You can easily move the magnets around to fine tune cantilever deflection while the record is playing. Strings level with the SUPATRAC's "thrust box" using the hole in the arm for the right side hoist string: one going "backwards" for the main and one going to the "front" for the negating side.
I have ordered a valve spring adjuster from AMAZON to make it easier and more precise for the main anti-skate magnets.
https://www.amazon.com/gp/product/B08B8CSSB5/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
Fasten the magnet to the top and attach to a base of some weight. I will use superglue. For the moment I have made a platform with a wine cork and a small piece of copper plate. Using pieces of card stock beneath the plate to make adjustments. Very tedious. The copper plate will be retained. The base has to be of more weight that you might think is needed. On the negate side the magnet is not secured. Not enough force is generated to require it in my case. I can either tape it down or leave it loose to be able to move it for fine adjustment.
The downside is you need to be able to make room for this. My plinth had a hole in it right where I needed the string to go for the negating magnet. And plenty of room to the side for the main. Not elegant in any way. I suspect it would be impossible to do it compactly. I cannot get the anti-skate magnets near the arm since the back of the arm is of a material that is magnetic.
As you can imagine/know the weight does not move very far with the the swing of the tonearm.
My strings are about 10 inches. My plinth sits up high and the underneath is easily accessible.
Using WALLY TRACKER I am getting a steady 11% across the scale for a 2 grams tracking force.
A much smaller force is used to negate the unneeded force from the main anti-skate for the latter third of the record which is obvious!
I wonder if a further refinement would be to have the weight and magnet in a thin silicone bath? One can see the metal pieces (cut from a small alligator clip - whatever those are made from) wiggle - whether this imparts some errant force on the tonearm?
I have been doing this with a cartridge I will not be using while waiting for my cartridge to come back from Andy Kim for a new cantilever and wanted the tonearm to be right before installing it. A long way of saying I have not heard what this arrangement does. My phono stage is transimpedance , my other cartridge is a Zu Denon 103 and its high coil impedance does not work well with this kind of stage.
Middle of the week I should know if it works at all (sonically), works OK or works very well. I have played records but I cannot hear them - so I know it works smoothly.
For those with non-linear horizontal bearings could be worth a try - the bearing on the SUPATRAC is of exceedingly low friction - it is how the arm is hung that brings these anomalies. Even with this, the arm sounded great with no anti-skating. I could never get the anti-skate to do what I needed it to do and this was before I got the WALLY TRACKER so I had no idea what I was up against. Please do not take my comments as a condemnation of the SUPATRAC. This is a great tonearm but with compromises as all tonearms have. The standard setup on the SUPATRAC would work better if there was some way to get the anti-skate to stop for the last third of the record - but I cannot get this to happen without the anti-skate then not allowing the tonearm to return to rest. I am hoping that my obsession will be of use to others.
Rick, your problem makes me think of compound bows.
These are bows where as you draw the arrow, the bowstring passes over a cam arrangement at each end of the bow. The result is instead of aiming while holding back the maximum force the bow can give, the cams make the force much lighter at that point of the draw.
From your text and reading up on what the arm is and how it uses a below-the-record pivot point for the arm, the arms advantage is increased tracking down-force when the record is fighting back against the cart in loud passeges. ...and you make the point that this plays havoc with anti skate forces needed and again in your unique case - in both directions.
You say a force is already applied, which needs cancelling over part of the arc of the arm. Why not have a weighted 'string' come off a non-round cam-pulley attached to the rotation axis of the arm? The tangient it comes away at and the effective diameter of the pulley at that point could be arranged to absolve a multitude of sins!
These are bows where as you draw the arrow, the bowstring passes over a cam arrangement at each end of the bow. The result is instead of aiming while holding back the maximum force the bow can give, the cams make the force much lighter at that point of the draw.
From your text and reading up on what the arm is and how it uses a below-the-record pivot point for the arm, the arms advantage is increased tracking down-force when the record is fighting back against the cart in loud passeges. ...and you make the point that this plays havoc with anti skate forces needed and again in your unique case - in both directions.
You say a force is already applied, which needs cancelling over part of the arc of the arm. Why not have a weighted 'string' come off a non-round cam-pulley attached to the rotation axis of the arm? The tangient it comes away at and the effective diameter of the pulley at that point could be arranged to absolve a multitude of sins!
I discovered the same thing when i was tweaking my Schiit Sol which uses the typical threaded weight hanging over a hook. I believe the reason for the blurred imaging is because the friction of the thread on the hook is applying a side force that is not constant, upsetting the stability of the stylus/groove interaction. The Sol arm is a unipivot which may be more susceptible to this unbalancing force, making the sonic smearing more apparent.
My solution was to clamp a pulley to the existing hook and drape the thread over the pulley instead. I also clamped another pulley to the bearing so that the thread converted lateral force to vertical force in a true, linear fashion. There is a small counterbalance attached to the vertical pulley to help compensate for skating variation due to angular error.
Altogether, this arrangement is essentially transparent, that is to say, the images are no longer blurred as though the antiskate was disconnected. There's plenty of room for improvement but it works well enough as is I'm in no hurry to refine it.
What this has taught me is that discussion surrounding the use of antiskate often ignores the unintended consequences of the various techs used. The dual pulley arrangement itself is not ideal, but it works better than other systems. It could be improved further by using larger pulleys to increase leverage, thus reducing friction further and allowing for the use of a smaller, lower EM weight. But for now...,
