Bias/anti-skate advice(wanted:))

Discussion in 'Audio Hardware' started by frimleygreener, Jun 26, 2018.

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  1. frimleygreener

    frimleygreener "It 'a'int why...it just is" Thread Starter

    Location:
    united kingdom
    I have a Rega RP6. Rega owners will be aware that "dialing in" both tracking force and anti bias are pretty much guesstimates due to the marked range of the counter balance for tracking and the slider for anti skate: tracking force is easy to set via a digital scale(done) but anti skate?
    I have a hifi news test record that allows for bias to be correctly set,but how do you use it properly? Is it a matter of lower,listen,raise adjust until the parameters are met, or being a "locked groove", do you lower and adjust whilst the test band is playing?
    Thank you in advance for any pointers:)
     
  2. Leonthepro

    Leonthepro Skeptically Optimistic

    Location:
    Sweden


    This is the best video and info about anti skating and how to set it that I have found yet. Ledermann knows his stuff and it makes sense.

    The funny thing is as a Rega owner I used to set anti skating mostly by ear, trying to find the least distortion in intensive 1 channel passages of records. I used to end up at 0.9 for my Nag 110 before I tried this method and it yeilded the best results for that. When I tried the deadwax method and reset it I later ended up on about 0.8. Pretty convincing for me, but logically that was mostly just luck I think.

    But in short I wouldnt recommend using a test record for anti skating in general.
    The reason why you dont want to set anti skating for any 1 segment on a record, just like what a proper test record is is because its just taking 1 sample as the average for your whole playing future. You want the best average for your whole record on all your records and this video tells you how thats possible.
     
    Last edited: Jun 26, 2018
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  3. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    Adjustment is similar to other tonearms. They've given an adjustment range between 1-2, which should be set to match the tracking weight you've set:

    SETTING UP YOUR RB303 TONEARM
    Push the bias adjustment slider to the same number as the tracking force control. ie a recommended 2.0g tracking force = 2.0 on the bias slider.

    The HiFi news doesn't really have an antiskate track. The better test would be a Shure tracking record, where you have several different acceleration levels to test tracking, and when mistracking first occurs, you can see if it can be improved with antiskate adjustment.

    However, test tracks with high levels are not a good way to adjust antiskate either, as high-volume tracks will themselves create more skating force then the average LP's music.

    What I wrote a while ago, but can't properly quote due to old locked threads:

     
  4. frimleygreener

    frimleygreener "It 'a'int why...it just is" Thread Starter

    Location:
    united kingdom
    "Bands 6 + 7 + 8
    Bias setting (300Hz tone L+R at +12dB / +14dB / +16dB)

    These tracks are for setting anti-skate. If the 300Hz test tone is heard distorting or buzzing on either channel then your 'anti-skate' or 'bias compensation' should be adjusted to compensate. Most cartridges seem to sail through the first track regardless, but fine tuning will be needed to successfully complete the 14db and 16dB tracks. Increasing VTF towards the top end of the cartridge manufacturers scale can improve tracking here.

    It's interesting to note that advanced stylus profiles like the Gyger S on the Goldring 1042 have a smaller 'sweet spot' during bias adjustment . A Goldring 1006 and Audio Technica AT110E where equally indifferent to bias setting over a larger range of the scale and where unable to track the final band as well the 1042.

    Band 9
    Bias setting (300Hz tone L+R at +18dB)

    The famous torture track - just another 2dB rise over band 8 but this is very difficult for a cartridge to track cleanly. If you've got through this far with reasonable results then consider this a test of your cartridges suspension design and tonearm control"
    What are these anti skate settings for then on the test record?
     
  5. Leonthepro

    Leonthepro Skeptically Optimistic

    Location:
    Sweden
    This only applies to the cartridge thats designated for that arm. My Rega Carbon cart worked with exactly 2 grams and 2 anti skate as settings. This changes as soon as you try other cartridges with different VTF settings, cartridge weights and such.
     
  6. daytona600

    daytona600 Forum Resident

    Location:
    UK
    Roughly 50% of tracking weight & dial in by test record / ear

    Rega dialing in" both tracking force and anti bias are pretty much guesstimates same as azimuth & vta
    shame on you rega
     
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  7. Leonthepro

    Leonthepro Skeptically Optimistic

    Location:
    Sweden
    Pretty much agreed. But again, Rega is a very plug and play company so the cart supplied with the table will most likely be a 1:1 setting to the VTF, that is 2 anti skate if its 2 grams.
    But maybe I just got lucky with my old RP1.
     
  8. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    Not really. Arms don't "designate" a cartridge. It is more about the geometry that creates the skating force, than what you stick on the end.

    The tangential direction that vinyl is moving under the cartridge is not in line with the arm's pivot point. This creates a force that pulls the cartridge towards the center spindle.

    I was unable to find an adequate diagram online, so I made one.

    [​IMG]

    This is a free body diagram that demonstrates where the skating comes from and why anti-skate is needed.

    In red, we have the friction of the needle being pulled through the groove. The actual amount of friction force generated can depend on several factors as I described in the quote in the prior post.

    In blue, we have the only direction that the tonearm can resist the friction with it's own tension force: towards the pivot point. Regardless of the shape of the tonearm or even which direction the cartridge is pointing, we only care about the point of contact vs the pivot point when calculating this force.

    Since the friction is not parallel to the resisting force, when they are subtracted from each other that still leaves some amount of non-negated force towards the center of the rotation (purple). Without any other mechanism, this force could only be counteracted by the stylus, applying more pressure to the inner groove wall, or if that wasn't sufficient, the needle jumping out of the groove and skating over the top of the record.

    Therefore, the turntable manufacturer has added an antiskate mechanism which applies a torque to the tonearm from the pivot point (green), which becomes a counter force to balance the free body equation. This way, the forces on the cartridge are in equilibrium when playing a record.

    We see the particular friction force is what needs to be cancelled by both tonearm tension and the antiskate mechanism components, and so the amount of antiskate required depends on the friction. This is why a higher tracking weight requires more antiskate - the heavier pressure of the needle creates more friction.

    So what can affect the friction besides weight? First, the rotation speed. If the turntable isn't rotating, there is no friction. Then the music - when the cartridge is tracking a waveform, this creates more distance for the needle to travel with the same amount of rotation. The formulation of the vinyl, and it's coefficient of kinetic friction in contact with diamond. The stylus contact profile is also one factor (elliptical vs conical), but it is the shape of the diamond that dictates this, not so much any characteristic of the cartridge.

    This isn't really a "test by ear" or "fine tune by the seat of your pants" adjustment. Manufacturers use more sophisticated methods, such as piezo pressure sensors, or even a pivoting headshell that dramatically demonstrates when the forces are not in equilibrium. With this experimental information, they provide you the calibrated antiskate adjustment, scaled to match the weight setting.
     
    Last edited: Jun 26, 2018
  9. John Moschella

    John Moschella Senior Member

    Location:
    Christiansburg, VA
    Honestly, I didn't think that video was very convincing. First he gets tongue tied trying to explain skating force without a sketch. Bad idea.

    Next the proposed method is highly subjective in that you are supposed to adjust until the tone arm moves slowly toward the spindle and you do it at the very end of the pressed grooves. If you want to use this method it would be better to use a blank side, or a blank track in the middle of the record. But my real problem with this method is the friction force will not be the same on a blank space (or track) vs. a real groove.

    Lately I adjust by ear and I find that using center mixed (or even better mono) sibilant vocals is easy and accurate for real world conditions. When the anti-skating is set correctly the distortion remains centered with the vocal, if is leaks to the right then lower the anti-skate, if it leaks to the left then you need to add a little more. Give it a try.
     
  10. Leonthepro

    Leonthepro Skeptically Optimistic

    Location:
    Sweden
    I know how anti skating works already thanks to the video posted above. I suggest a watch of it to explain why any 1 mechanism cant optimally adjust the antiskating for you on average.
     
    Last edited: Jun 26, 2018
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  11. Leonthepro

    Leonthepro Skeptically Optimistic

    Location:
    Sweden
    You misunderstand completely like most people when it comes to this. The blank space is not representative of any one groove in existence. Your records are not 1 groove of constant loudness, frequency and modulation, they are changing constantly. This means that no one anti skate setting is ever correct, thats the first thing to realize.
    Second is that the best course of action is to find a happy median for the anti skate, the average skating force, that is where most music spends its time in general.
    This turns out to be 70% modulation for the grooves. Its by far the closest to average skating.
    Now finally all you need is to find a force equal to the 70% groove modulation that pulls the arm in and apply it outwards. This turns out to be the arm on a blank surface very slowly skating inward.
     
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  12. frimleygreener

    frimleygreener "It 'a'int why...it just is" Thread Starter

    Location:
    united kingdom
    So....could anyone help with the query I posted?
     
  13. Jeffreylee

    Jeffreylee Rock 'n' Roll Typist

    Location:
    Louisville
    Haha. Welcome to anti-skate land, which is a very special kind of hell.

    When using the test record, you listen, then lift the tonearm and make adjustments, and then listen again. Repeat until you give up and decide to leave well enough alone and just play some damn records.
     
  14. Linto

    Linto Mayor of Simpleton

    don't worry about it, really, near enough will do, especially if everything else is set up correctly

    I used to work at a Rega dealer

    and the last thing to use is a HIFI News test disc, made to show off the tracking ability of a certain cartridge. The best carts in the world can't track jack on that record.
     
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  15. John Moschella

    John Moschella Senior Member

    Location:
    Christiansburg, VA
    Everything is great up to the part
    "Now finally all you need is to find a force equal to the 70% groove modulation that pulls the arm in and apply it outwards. This turns out to be the arm on a blank surface very slowly skating inward"
    To me this is pure conjecture. Better to use real records as I described, which BTW, is completely consistent with all your other points.
     
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  16. The FRiNgE

    The FRiNgE Forum Resident

    An outstanding tutorial by Mr. Lederman, very clearly explains the nuts and bolts of anti-skate. Just one point I have a question about however, about the method to set anti-skate by tone arm designer Frank Schroeder. Lederman explains friction and the "pull" on an angled headshell, which causes an inward skating force. He further explains how the groove pitch can vary the pull (friction) on the stylus, and the practical objective to set anti-skate for a best average. All of this is good. But.. Schroeder says to set the anti-skate very close to the label, at mid-point of the lead out area (before the lead out groove picks up the stylus) .. that the arm should glide slightly inward toward the label. As correctly pointed out by Mr. Lederman, the groove increases friction. So, a slight under bias on a blank section with LESS friction would be not accurate under actual playing conditions. If anything we need overbias on a blank section, as the groove will exert more pull. On that blank section (lead out area) the arm should glide slowly to the RIGHT, not to the left. (Right would be movement toward the outer rim of the record)

    I am not a fan of setting the anti-skate on a blank section anyway. It can be a "ballpark setting", but isn't accurate as the groove will require MORE anti-skate.

    I hate to say this, I disagree with Frank Schroeder. (famous people are not infallible)

    Furthermore, Mr. Lederman didn't discuss another important variable, aside from varied groove modulation and varied pull on the stylus, the outer part of a 12 inch LP record pulls harder on the stylus. Therefore we need more anti-skate on the first track. The inner groove pulls least on the stylus, so less antiskate needed there. A well engineered antiskate mechanism compensates for the change in skating force as the arm moves closer to the label. To repeat, more anti-skate is needed at the first track, less on the last track, (approximately 1/2 the antiskate bias needed on the last track) To repeat again, a well engineered anti-skate mechanism automatically compensates for this difference.

    Also not mentioned by Mr. Lederman in his detailed, well thought out tutorial, skating force causes the cantilever to deflect off-center. This an extremely critical point, as an off-center cantilever, caused by skating force, throws the stylus out of line. Likewise after a careful setup, an incorrect anti-skate setting negates the setup. When a cantilever no longer remains centered during play, as it did on the protractor grid, the setup means nothing. It's no wonder so many get so frustrated setting up their cartridges, and do not hear the results in a sound check (distortion, channel imbalance, etc)

    So what does all this mean?

    The cantilever MUST remain centered as the stylus tracks the groove.
    How can we tell? Look at it!
    Observe as the stylus settles in the groove, does the cantilever remain centered?
    When the bias (anti-skate) is off, the cantilever will deflect left or right.

    Looking head on to the headshell.. observe:
    1) if the cantilever deflects to your left, there is too much anti-skate, apply less antiskate
    2) if the cantilever deflects to your right, there is too little anti-skate, apply more antiskate.

    The cantilever deflects in the OPPOSITE direction of the skating force. ie: assume you have no no anti-skate, (set at zero) and the arm wants to skate in, the cantilever deflects to your right, toward the outer rim of the record.

    An experiment: (as confirmed by yours truly) proof the cantilever deflects opposite of the skating force...
    1) Place the stylus guard on the stylus, or use a spare headshell
    2) tape a piece of thread or string on the front of the headshell, above where the stylus would be.
    3) the string is a simulation of the cantilever, and what happens as pull is applied to the stylus (your hand is the pull)
    4) pull on the string in line with the headshell a light pull slightly upward , just enough to float the arm above its rest. The idea is to simulate pull on the stylus
    5) be sure to pull in line with the headshell angle
    6) observe the angle of the string, does it remain in line with the headshell?
    7) It will not be in line... as much as you may try to pull exactly in line with the headshell , the string will always angle to your right.
    8) Why does this occur? Why does the string angle? (Mr. Lederman answers this in the turorial, but never posed the question)
    9) as referenced to the cantilever the pivot does not shift to a pahanom point to the right. In practice the pivot remains the same (the actual pivot point) but the cantilever "wants to" align in a straight line to the pivot point, and NOT the headshell.

    One of these days I am going to post a You Tube demonstration.
    This may be TMI, but valuable. I agree with Mr. Lederman on all points except two:
    1) a blank disc isn't the best method to set anti-skate, and the arm should be slightly over-biased when using this method (slight movement outward not inward)
    2) The geometry referenced to the cantilever, the actual pivot point remains the same.. the cantilever "tries" to align to the actual pivot point.

    Anti-skate is complicated business. No matter where it is set, there will be small errors record to record, and what part of the record played.
    As advised by some, just play the dang record.. set the bias to the tracking force and enjoy the music.
    Steve VK
     
    Last edited: Jun 27, 2018
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  17. The FRiNgE

    The FRiNgE Forum Resident

    I have to congratulate you on this beautiful diagram! This really illuminates the cause of skating, why the arm wants to swing in.
    Also this diagram illustrates my point above, in my precious post.
    With no anti-skate, (or not enough of it) the stylus tugs on the cantilever in the direction of the RED arrow, however, the cantilever does not remain centered to the headshell. Yes the arm wants to swing in, but also the cantilever "wants" to align with the pivot.. in the direction of the BLUE arrow. The cantilever does not actually align exactly, but will tend toward the blue arrow. So again, the skating force of the arm causes the cantilever to follow (forced to follow) a straight line with the pivot. With ample anti-skate, the cantilever is counter-forced to remain in line with the headshell.
    Steve VK
     
    Last edited: Jun 27, 2018
  18. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    That's an interesting question, a lab experiment an undergraduate might have had to perform. Generally the conclusion the experiment would reach is that the kinetic or sliding friction force of dry materials is the same regardless of speed.

    However, there are materials where the friction becomes less as the speed difference increases between the materials. Alternately, materials that deform elastically may have more heat dissipated via friction at a higher speed, and also, macro-scale rougher surfaces have more interface friction until they reach speeds where bumps are skipped over. I think vinyl will be in the latter category, with more friction at the higher tangential speed through a wiggling groove, but not a directly proportional relationship like one might assume.

    Turntable designers of old may know the answer experimentally, and have given this some thought when designing the cam profiles that also keep the force of a anti-skate spring relatively constant throughout the tonearm range.
     
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  19. The FRiNgE

    The FRiNgE Forum Resident

    Yes,
    Here is a simple and very accurate method of setting your anti-skate:
    Observe the cantilever as the stylus settles in the groove. Ideally, we want the cantilever to remain centered. Very slight deflection to the left or right, means the antiskate needs adjustment. The deflection, if any, is very easy to observe, as the eye can pick up even the slightest deflection in either direction (in other words the eye isn't calibrated per se, but highly sensitive to relative movement off-center)

    Looking on squarely with the headshell, lower the stylus and observe the cantilever just as the stylus settles in the groove:

    1) if the cantilever deflects to your right, the arm is skating in, apply more anti-skate
    2) if the cantilever deflects to your left, the arm is skating out, apply less anti-skate
    3) if the cantilever remains centered, the arm is neutral
    4) skating force varies across the record, more skating at the outer edge, least at the inner track. Start this procedure about 1 cm from the outer edge, then repeat at the canter of the record, then again at the inner track, choose the best compromise, or adjust mostly to the inner track.

    The blank disc isn't accurate. Use my suggested method. It is accurate under actual playing conditions, verify by ear to make minor adjustments.

    Good luck, seems complicated written out, but in practice this is very easy :)
     
  20. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    A better way to picture it - if there is no anti-skate mechanism, the cantilever has to offer the green anti-skate force itself.

    By pressing harder against the inner wall, the cantilever is moved out of true, out of optimum magnetic placement, as well as the pressure between groove sides being unequal.
     
  21. The FRiNgE

    The FRiNgE Forum Resident

    The higher tangential speed vs lower speed would be one factor. The pitch of the groove, a higher pitch at the inner track would be another factor. The higher speed between materials would exert more friction, however the increased groove pitch at the inner track (at lower tangential speed) presents a tougher obstacle course for the stylus. This is a problem for calculus to solve. Does the higher speed exert more friction vs groove pitch? I assume it does.
     
  22. Leonthepro

    Leonthepro Skeptically Optimistic

    Location:
    Sweden
    But you have no way of knowing if the record is even close to 70% groove modulation at the point you use it for, dont you see what I mean?
     
  23. Leonthepro

    Leonthepro Skeptically Optimistic

    Location:
    Sweden
    I only care about 1 thing when it comes to setting anti skating. Setting it so that it as closely equals the force of 70% groove modulation.

    If there was a machine that fulls the arm to the left with a force equal to 70% groove modulation then I would set the anti skate to where the arm stands still.

    With the math that has been done thats all I care about because it will mathmatically speaking be optimal. I can not do anything about varying skating forces because of different placements on a record.
    I should also not use 1 single groove on a random record to test for skating because I have no idea of its modulation in that area.
     
  24. Thomas_A

    Thomas_A Forum Resident

    Location:
    Uppsala, Sweden
  25. Bob_in_OKC

    Bob_in_OKC Forum Resident

    Location:
    Dallas, Texas
    Differences in speed, groove radius, and location on the record are negible in their effect on skating force. It’s primarily tracking force and overhang. Also causing changes in skating force are tip shape and the hardness and smoothness of the surface. Groove modulation in theory affects the smoothness of the surface, so it’s in there as a cause, but it’s being overrated in this thread.

    When it comes to methods like the one proposed in the video, the orientation of the surface to the stylus, the number of contact points, and the indentation of the surface under the stylus are all different than in a groove. Skating force is higher on the flat surface with a sharp tip, so at least the method proposed in the video gets that part right. But the video offers no explanation why that is, why the stylus should move slowly, or how slowly it should move. A better video would’ve been to condense it to 2 minutes and just demonstrate.
     
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