Hi All, I am building a TT and using a broken Infinity Black Widow tonearm. I am going to 309MM (12") and I don't think the anti-skate increaments will be accurate: as it is indexed for a 9" arm. So, I can I tell when I have it right?

The nub of the tonearm wand is .206 OD and the ID of the carbon graphite tube I am using is .209. I am also making my own headshell out of the shank of a 5/16 aluminum bolt. Cheers.

http://i9.photobucket.com/albums/a60/djnagle/IMG_3631.jpg

I read somewhere 'bout, using record with a long runout and adjust so it doesn't run to the end but also does'nt return all the way to the info grooves.

A blank record is a good starting point, and there is a three sided Johnny Winter Live album that had a fine blank side, which I used to use. But blanks don't cause the same skating force that a groove does, so its only a starting point. Thorens suggested using a record you don't care about, and headphones, and lowering the tracking force till you have noticeable distortion in both channels. Adjust the antiskate until the distortion is equal in both sides. And then restore tracking force.
I think that the antiskating needed will be less for longer arms than shorter ones, since the offset angle will be less. That might give you a WAG for starters.

Thanks G & N. Yes the offset angle is only around 17 degrees. Now that I read about the blank vinyl, I seem to remember a test album that had three or four blank spots in various places just for adjusting skate. I don't have headphones on this system but I'm sure I can hook something up. Cheers.

Thanks G & N. Yes the offset angle is only around 17 degrees. Now that I read about the blank vinyl, I seem to remember a test album that had three or four blank spots in various places just for adjusting skate. I don't have headphones on this system but I'm sure I can hook something up. Cheers.
The force is caused by the groove. Blanks have no grooves, therefore exert no force, so I don't see how that's a good starting point.

The problem with reducing the TF and listening for equal distortion is that the higher the TF, the higher the skating force, so when you restore the TF to where it should be, the anti-skate will be insufficient. But that's still a more logical starting point, and will probably suffice for the long arm.

Thanks Howard. I am expecting the new tube tomorrow and hope to have the arm done this week. I'll post pix as I progress. Cheers.

Skating is caused by the offset angle and the friction between the stylus and the vinyl. Certainly its true that the stylus in a groove will have more friction than the stylus point on flat vinyl, but its a starting point.
It also has the merit of being relatively absolute. Different records are made of different combinations of material (virgin vinyl, you hope, but also carbon, mold release, and ground up old vinyl, sometimes in the 70s with bits of label paper visible, etc.) so the friction will be slightly different, but the force produced by the grooves depends on the amount of modulation, which, with real music, is changing constantly.
I think its generally agreed that too much antiskate is worse than not enough, and that a little is better than none. So the blank groove gives a low reference, and a high modulation record would give a high reference. Somewhere between would be a good approximation.
Since skating force also depends on tracking force, I suspect that the Thorens test would give you a lowish reading -- my memory is that it wasn't too much different than a blank groove (which is a hell of alot easier). Perhaps the Thorens idea is to then increase the tracking force and adjust by ear (in which case, why not just start with the regular value and adjust by ear, though maybe its to teach you what to listen for).
Djnagle -- you can use speakers rather than headphones, but the more seperation and the less room reverb the better -- makes it easier to distinguish channels. Maybe move the speakers so they are on either side of your head and close?

adjusting anti skate is never simple...the rotating groove causes a centripetal(inward) force to act upon the stylus assembly and tonearm... however this force varies in intensity depending on where the stylus is located on the rotating record,the downforce acting on the stylus,warps,how level the turntable is and also whether the groove rotates at 33&1/3 or 45 rpm...

at best you can only hope/guess that the antiskate force applied is enough to exert a sufficiently 'equal' centrifugal(outward) force to prevent audible mistracking and unequal groove wear in either left or right channels ...

rega used to specify using a couple tenths of a gram less antiskate than downforce setting...yet their antiskate gauge on the rb300 arm is far too crude for such fine adjustments anyway...and most antiskate devices are innaccurate within the first 0.0 - 1.0 gram range as the antiskate spring is often ineffective until the tonearm moves to take up the slack in the linkage

easiest approach is to set antiskate and downforce to the same settings..and fine tune by ear at the first and last track to find a compromise...while observing the 'stance' of the stylus to see if it 'skews' to the left or right when subject to a rotating groove... ideally it should veer either way and remain dead vertical in relation the front of the cartridge...

if the stylus assembly seems upright to the record surface when viewed from the front and while it is playing at both the beginning and ending of the record... then i suppose that is as close as you can get it without actually listening or taking accurate output readings from a mono recording...

all of the above is useless unless the cartridge is quite accurately aligned anyway..and ideally you would observe how perpendicular to the record surface the cartridge when it is playing the single groove that is closest to the null points that the arm and cartridge is aligned to...and then you would listen for any obvious mistracking in either channel where visual alignment is no longer possible to determine..

not an easy task without specialist equipment i've yet to hear of..:scratch2:

I think the problem is that Djnagle is making his arm longer, so the markings on the antiskate mechanism will no longer reflect the forces the arm is being subjected to.
Coral or Neat and a couple of other companies actually made a antiskate measuring device that was substituted for the cartridge and actually showed the resulting force, so you set the antiskate when the little line was centered. They come up on ebay now and again. Easy, but which one is it accurate for -- conical, elliptical, or line contact?

Yep Nat, the longer arm is the problem. The spring in the anti-skate adjuster is so delicate that I don't think the markings will be right. However, now that I think about it, they might be a good starting point.

My guess, based on the diminishing of the offset angle possible with a longer arm, is that the original markings would be high, but probably not too much.

The replacement tube I bought is 42" long. Maybe I should start with that and work down. Probably not my offset at 42":D

The blank piece of vinyl method is not the real way to go. You need to use your ears, and here is how.

Use a record with good inner dynamic contrasts. Not the huge dynamic swings, but something that has some pop and pace and drive to it, and vocals across both channels.

The basic premise is that anti skating increases will slowly increase this level of dynamics until there comes a point where it will drop off very sharply and significantly. This dynamic will also not sound balanced in both speakers, showing a prominance in the left speaker initially.

So start with a very low anti skate and listen to the left and right speakers. You should probably hear more dynamics in the left speaker.

Now increase the anti-skating gradually, a wee bit at a time, then go back and listen again. Keep doing this in very small increments until you begin hearing more dynamics in the right speaker. They should start to sound more balanced between the L-R speakers too.

Now continue increasing this slowly. At some point you will hear a pretty noticeable drop off. Back up the anti-skate a wee bit and you should get those dynamics back again.

There you go. You have maximized it.

+1 on the technique that BobM described. I used it when I was setting up my AVA-modified Grado. The difference in sound when you pass the optimum point is not subtle. I ended up with the anti-skate set slightly below where it would have been if I had trusted the scale on the adjustment dial.

If you know the original geometry the anti-skate scale was made for, and the new geometry, a correction factor for the scale can easily be calculated. This does not assure that the anti-skate force will be correct, simply that the same force will be applied at the stylus with the new geometry as with the old. The skating force on the stylus creates a twisting moment about the tonearm pivot. The magnitude of the moment is directly proportional to the distance between the stylus and the pivot. The anti-skate scale is set up to show the anti-skate force required to counter the twisting moment for the original distance. If the new arm is 20% longer, multiply the original scale by 1.2 to find the equivalent new setting. If it is 50% longer, use 1.5 for the multiplier and so forth.

Edit: As I think about this, what I wrote above is not strictly accurate. You need to create an imaginary line perpendicular to the tangential intersection of the stylus and the groove. Approximately, this is a line that passes through the stylus and the center of the record. Create an imaginary line parallel to this that passes through the tonearm pivot. The perpendicular distance between the two lines for the two geometries is the distance from which the correction factor should be calculated.

Second edit... I've made an error in this explanation... I will post a correction tomorrow. Sorry for the confusion.

Denis: I bought a Realistic Test Record at a garage sale, have not played it, but it appears to be in good shape. I have read the supplied pamphlet and there is no anti skate test. There is however some tracking and distortion test. If you’re interested I’ll truck it to our next gathering.

Jim

Hey Jim, that sounds great. I am really hoping to get this TT done by then. The only thing that is holding me back is finding someone to drill the 5" and 2" holes in the marble. I am really looking forward to the next meet. I will also have your Xover progam with me....thanks for lending it to me. Cheers.

If you know the original geometry the anti-skate scale was made for, and the new geometry, a correction factor for the scale can easily be calculated. This does not assure that the anti-skate force will be correct, simply that the same force will be applied at the stylus with the new geometry as with the old. The skating force on the stylus creates a twisting moment about the tonearm pivot. The magnitude of the moment is directly proportional to the distance between the stylus and the pivot. The anti-skate scale is set up to show the anti-skate force required to counter the twisting moment for the original distance. If the new arm is 20% longer, multiply the original scale by 1.2 to find the equivalent new setting. If it is 50% longer, use 1.5 for the multiplier and so forth.

Edit: As I think about this, what I wrote above is not strictly accurate. You need to create an imaginary line perpendicular to the tangential intersection of the stylus and the groove. Approximately, this is a line that passes through the stylus and the center of the record. Create an imaginary line parallel to this that passes through the tonearm pivot. The perpendicular distance between the two lines for the two geometries is the distance from which the correction factor should be calculated.

I'm not sure if I am reading this right. I am extending the arm out 33 percent more. So do I just move the anti-skate slider out 33 percent as well, or do I need to measure the pressure on the spring and increase that pressure 33 percent. Or are they both the same thing?

I sketched a generic tonearm. Imagine a line perpendicular to the stylus. Imagine another line parallel to the first that passes through the tonearm pivot point. The distance between these two lines is the basis for the correction factor. It is not simply the distance from the stylus to the pivot. I hope the sketch explains it better than I can!

I've made a big error in this explanation and in the sketch. I removed the sketch and will post a correction tomorrow. Sorry for the confusion. I will still be able to provide a sketch of the measurements you can use to create a correction factor for your anti-skate scale.

If the arm were infinitely long, you wouldn't need antiskating (or for that matter, offset) since there would be no difference between the direction of the friction -- perpendicular to the radius -- and the pivot to stylus direction (since a 5 inch arc traced by a line of infinite length is a straigth line (as is the radius of a circle of infinite diameter)). Its when the arm has real dimension that there is a difference, since the arm is tracing an arc of radius equal to pivot to stylus dimension. With a 9 inch arm, the difference between the arc and a straight line is quite noticeable.
If, however, the stylus is offset, that difference can be lowered a good deal, but the penalty is that the arm is now being dragged in a different direction than the pivot to stylus direction, so it skates.
All of this pedantic stuff to support my belief that the longer the arm, the less antiskate needed. So I would think lessening the antiskating force would be desireable.

using the Johnny Winter "Second Winter" blank (grooveless) side is definitely not the way to go. i totally agree with BobM....use your ears to gauge and zero in on the antiskating....or go out and buy the TELARC OMNIDISC....there is a test signal that helps you to accurately dial in the antiskating.

Denis: I bought a Realistic Test Record at a garage sale, have not played it, but it appears to be in good shape. I have read the supplied pamphlet and there is no anti skate test. There is however some tracking and distortion test. If you’re interested I’ll truck it to our next gathering.

Jim
This is what I use - the tracking torture test. I've found tracking is best with little or no antiskate. I wish I could say it depends on the arm/cartridge combo, but I've found this to be repeatable with a wide range of 9" setups.

I've read that transcription arms don't require side bias, but I wouldn't know personally.

Here's the correct sketch.

The dimension labeled "A" is the basis for calculating the correction factor for the anti-skating scale. The correction factor would be equal to new tonearm dimension A / original dimension A.

Sorry for the prior confusion. I'm happy to offer further explanation (and hopefully not further confusion!)

Here's the correct sketch.

The dimension labeled "A" is the basis for calculating the correction factor for the anti-skating scale. The correction factor would be equal to new tonearm dimension A / original dimension A.

Sorry for the prior confusion. I'm happy to offer further explanation (and hopefully not further confusion!)
So the hypotenuse is the effective arm length, but how do you determine the other two sides? Seems you need one more value.

Hi JonL, in your sketch is seems to me that the offset would change as the arm moves inward. It also seems (I am not good at math so I am just going by my eye) that the "A" value diminishs as the arm moves inward as well. So where would I adjust skate for?

So the hypotenuse is the effective arm length, but how do you determine the other two sides? Seems you need one more value.
I used a sheet of ink jet paper. Align the long edge along the center line of the head shell, move it back or forth until the short edge crosses the bearing axis, and mark it with a pencil. That distance is the linear offset.

Not super accurate, but you'd be surprised just how accurate it is (within a mm or 2 is possible).

The geometry stays the same no matter where the tonearm is. You basically need to project a line along the axis of the cartridge and then measure perpendicular to that line to the tonearm pivot. I suppose you could make this measurement (carefully) with a big enough carpenter's square. You can probably get light plastic squares or draftsman's triangles and measure that way. If you pretend that the triangle is part of the tonearm you can see how it won't change no matter what position the tonearm is in since the headshell angle doesn't change as the tonearm moves and the tonearm length doesn't change either.

You can also use some very basic trigonometry, probably easier than the measurements. You need to know accurately the headshell angle. Measure the length from the center of the tonearm pivot to the point of the stylus, ignoring any curves or angles in the tonearm. Just the straightline distance between those two points. (Howard, is that the "effective length?") That is the hypotenuse. We'll call it "h." Call the headshell angle "x." Then the length "A" that we're looking for is simply h sin x.

You can see that A will change depending on both h and the angle x.

Edit: Or do it the way Ripblade suggests. Just as good.

If you already know these parameters, I'll be happy to punch the numbers for you.

I'm sorry but did I miss something here...

any kind of ciphering correction factors for anti-skate are futile. All this assumes anti-skate calibrations on a given arm are true and that you want to go the route of one to one with your VTF, which in most cases is incorrect, so in other words it is most definitely false. Fact is there are arms and TT owners that don't use anti-skate at the extreme.

The force is caused by the groove is not correct either, anti-skate is to counter the effects of inertia of the spinning disc pulling the mass outward. I think a basic 101 physics book will clear that up.

Also any output that isn't mono from the playing of a record will not offer an accurate outcome. Funny though, this one is almost on the right track. Besides your ears and looking down the length of the arm, toward the cartridge (with a good bright light and magnifying glass) to roughly eliminate the cantilever from tipping inboard or outboard, a voltage measured off the cartridge tone arm cable of the output, left to right, comparing groove sides from a mono, or like source in other words, is going to get you on target.

Refer to Fremer's TT set up DVD. If ya don't know of someone with one Dennis, I can lend you mine. In the end though your ears are the final, fine tune, it has to sound right regardless!

Happy (Analogue) Listening! :beatnik:

Also any output that isn't mono from the playing of a record will not offer an accurate outcome.
Quite! Neither will lateral groove modulations. Vertical tracing in mono is quite revealing of any tracking distortion....and the correct side bias.

I'm not a turntable expert, but I am an engineer and I have to take issue with some of these statements both for overall accuracy and as they relate to the context of this thread.

I'm sorry but did I miss something here...

any kind of ciphering correction factors for anti-skate are futile. All this assumes anti-skate calibrations on a given arm are true and that you want to go the route of one to one with your VTF, which in most cases is incorrect, so in other words it is most definitely false. Fact is there are arms and TT owners that don't use anti-skate at the extreme.

While this *might* be a true statement, the OP posed a question as to how to set his antiskating for a modified tonearm based upon the scale from his unmodified tonearm. I am confident that the methodology I proposed accomplishes this.

The force is caused by the groove is not correct either, anti-skate is to counter the effects of inertia of the spinning disc pulling the mass outward. I think a basic 101 physics book will clear that up.

This is a false statement. Since the stylus is not rotating with the platter, it is not subject to the kind of rotation induced centrifugal force we experience on a carousel. The skating force is actually a torque on the tonearm caused by the friction of the stylus in the groove. This friction force acts tangential to the groove at the point of contact with the stylus, it attempts to pull the stylus out of the cartridge. Looking at my sketch, you will see that the line of action of this force does not pass through the tonearm pivot (unless there is no headshell angle). The line of action of the force acts at some distance away from the pivot. A torque, or moment, is created about a point by a force acting at a perpendicular distance from that point. Much like pulling on a wrench to loosen a nut. The skating "force" is actually this moment (or torque) acting about the tonearm pivot and trying to rotate the tonearm inwards as the record turns. Counterintuitive, but true. The friction force on the stylus is generated by the coefficient of friction in the groove, and the normal force of the stylus against the groove walls. The normal force is proportional to the vertical tracking force, varying a tiny bit in operation by the dynamic effects of record warping, tonearm mass and friction, and *possibly* by groove modulation. The coefficient of friction is the big unknown and probably depends on many factors - vinyl composition, quality, dirt, temperature, humidity, frequency content, stylus shape, stylus material, stylus condition, etc. The antiskating adjustment is set to match the VTF, since that directly changes the normal force. The tonearm manufacturer has assumed a coefficient of friction at the stylus to create their unique scale. For the OP question, the only thing that has changed is the perpendicular distance of the line of action of the force to the tonearm pivot, and my method calculates the difference and corrects the original scale to suit.


Also any output that isn't mono from the playing of a record will not offer an accurate outcome. Funny though, this one is almost on the right track. Besides your ears and looking down the length of the arm, toward the cartridge (with a good bright light and magnifying glass) to roughly eliminate the cantilever from tipping inboard or outboard, a voltage measured off the cartridge tone arm cable of the output, left to right, comparing groove sides from a mono, or like source in other words, is going to get you on target.

Refer to Fremer's TT set up DVD. If ya don't know of someone with one Dennis, I can lend you mine. In the end though your ears are the final, fine tune, it has to sound right regardless!

Happy (Analogue) Listening! :beatnik:

I have no comment on the rest except that I concur with the last sentence:
Happy (Analogue) Listening! :beatnik:

Just to add to the fun, the linear velocity decreases as the arm moves inward -- the groove modulations get close together as you move inward, which I would guess increases friction -- certainly tracking gets more challenging. Velocity isn't a factor in the simplified version of friction taught in first year physics, but the coefficient of friction certainly is. I don't know how these two values (and the change in the relationship between offset and distance from the spindle) interact, but I suspect its a complex one and is part of the reason that trial and error, rather than equations seem to be most useful in determining the proper amount of antiskate force.

Just to add to the fun, the linear velocity decreases as the arm moves inward -- the groove modulations get close together as you move inward, which I would guess increases friction -- certainly tracking gets more challenging. Velocity isn't a factor in the simplified version of friction taught in first year physics, but the coefficient of friction certainly is. I don't know how these two values (and the change in the relationship between offset and distance from the spindle) interact, but I suspect its a complex one and is part of the reason that trial and error, rather than equations seem to be most useful in determining the proper amount of antiskate force.

I agree that the coefficient of friction is likely to be highly variable -- from one disc to the next, and possibly within one disc, as well as for all the reasons I listed in a previous post. I'd guess the coefficient of friction could vary over a 2:1 range, possibly more. This variability and the inability to measure it is what drives the success of trial and error methods. The physics of the situation don't change, and hence the equations don't lie. Once again, if the OP was satisfied using the original scale to set anti-skating with the original tonearm, the methods I presented will provide an accurate correction factor to use with the original scale to achieve the same magnitude of anti-skating effect with the new tonearm geometry. I don't understand your comment about the relationship between offset and distance from the spindle... the offset is a fixed quantity for any given tonearm design (except articulating headshells like a Zero-100) and doesn't change with tonearm position on the record.

I've always used a blank section, and jsut adjusted it so that the TA skated out slightly. Try as I might, I've never heard any mismatch of tracking from L_R with this method. I think the additional friction from side groove contacts component of the skate is small compared to the overall effect as transfered to the stylus tip. When you use a blank section, the very tip of the stylus is plowing into the vinyl. You can easily see minute lines where the stylus has been. I'd suspect, (and, yes, I have no quantitative proof) that that plowing friction is very close to the sliding friction that a stylus sees while cradled in a groove. Naturally, a highly complex groove modualtion will have more friction that a silent groove, but if you correct for mistracking during high transiet pieces then it is only correct for that groove friction value, and "over" corrected for less complicated pieces. It is always an approximation.

Minor correction to trigonometry method... the hypotenuse should be the length measured from the tonearm pivot to the intersection of the headshell centerline and tonearm centerline. In other words, to the point at which the headshell angle begins -- technically the vertex of the headshell angle. The error with the way I had stated earlier would be very small though, less than the uncertainty in the coefficient of friction. Sorry once again!

JonL
My comment about the relationship between offset and actual distance from the spindle is based on my memory of it as being a topic in the early articles on antiskating (which can be downloaded at Vinyl Engine). I think that its more than simply the error that results from the stylus tracing an arc rather than a straightline, but I think I remember something about relative error.
Bye the bye, my reference to first year physics is to place my level of expertise, not to rank on anyone else's.

Hi Nat,
I'll see if I can find the articles at V.E. when I have some time (pretty busy for the next few days...)

I didn't read anything into the first year physics remark. First year physics covers about 95% of what's important in the world anyway!

OK, you guys are talking way above my head, but I am enjoying the reading and trying to figger it out.

Minor correction to trigonometry method... the hypotenuse should be the length measured from the tonearm pivot to the intersection of the headshell centerline and tonearm centerline. In other words, to the point at which the headshell angle begins -- technically the vertex of the headshell angle. The error with the way I had stated earlier would be very small though, less than the uncertainty in the coefficient of friction. Sorry once again!
Then the only way to do this is to measure directly since that is not a published measurement.

The only thing worse than a know-it-all engineer, is an engineer who keeps changing all that he knows. :D

Yeah, I'm sorry. I've been doing this stuff at night, usually with a beverage or two by my side. I agree that measuring directly would be best. It shouldn't be too difficult, and absolute accuracy really isn't required because anti-skate, as has been pointed out, is probably something of an estimate and compromise anyway. Are headshell angles normally published?

OK, you guys are talking way above my head, but I am enjoying the reading and trying to figger it out.

If you know or can measure the headshell angle, and you can measure the distance from the tonearm pivot to the point where the headshell joins the tonearm (where the angle begins) I can do the math for you.

Yeah, I'm sorry. I've been doing this stuff at night, usually with a beverage or two by my side. I agree that measuring directly would be best. It shouldn't be too difficult, and absolute accuracy really isn't required because anti-skate, as has been pointed out, is probably something of an estimate and compromise anyway. Are headshell angles normally published?
I'm just ribbing you. Very few mfrs publish the headshell angle. For cartridge alignment, differences of a tenth of a degree are significant. For this, that's obviously not the case, so a plain old protractor would work fine.

Thanks JonL. Howard and I have been talking off line and we have the geometry of the arm figured out. The normal stuff - mounting distance from spindle, effective length, off set angle. I just didn't know how to interpret the change in arm length to the already set anti-skate marks on the arm.

It will be interesting to see how much the arm changes in respect to mass weight and effective weight but as that arm was one of the highest compliance arm made, adding weight shouldn't hurt anything.

P.S., thanks Howard for your off line help.

I'm not a turntable expert, but I am an engineer and I have to take issue with some of these statements both for overall accuracy and as they relate to the context of this thread.

My apologies. I DO need a bit of engineering study.

I am glad we agree about...

Happy (Analogue) Listening! :beatnik:

Thanks JonL. Howard and I have been talking off line and we have the geometry of the arm figured out. The normal stuff - mounting distance from spindle, effective length, off set angle. I just didn't know how to interpret the change in arm length to the already set anti-skate marks on the arm.

It will be interesting to see how much the arm changes in respect to mass weight and effective weight but as that arm was one of the highest compliance arm made, adding weight shouldn't hurt anything.

P.S., thanks Howard for your off line help.

I hope I was able to help and that my couple of false starts didn't just hopelessly confuse the issue instead. If you want to give me any measurements, before and after, I'll be happy to calculate the anti-skate correction you'll need.

My apologies. I DO need a bit of engineering study.


No problem. Going through the explanation was actually useful for me as well.


I am glad we agree about...

Happy (Analogue) Listening! :beatnik:

:yes: