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Setting anti-skate

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Setting anti-skate

Postby crofk » 11 Jun 2010 02:33

I finally got around to buying a test record. On it is spot of blank vinyl for setting your anti-skate. As most of you know, you just set your stylus in the center of the blank spot and set the atni-skate so that it stays in one spot neither moving in or out. That said, I am curious as to if there is a great variation in what the VTF is set at and what the anti-skate is set at? Is there variations between cartirdges? Is there variation between tonearms and/or tonearm length (9 - 12) ? The reason for asking is that on two of my tables the numerical setting is way different than the VTF. They are both 12" arms though. Even between the two 12" there is a sizable difference in settins but one has a Denon DL160 and the other has an AT150ML. The third is a 9" arm adn is running an AT OC9. It is fairly close to what I had presumed to be the correct setting before the test record.

Guess the numbers on the dial don't really mean anything - just more of a reference. But I found it rather curious. Anyone else notice this?

Kim
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Re: Setting anti-skate

Postby fscl » 11 Jun 2010 04:30

crofk wrote:I finally got around to buying a test record. On it is spot of blank vinyl for setting your anti-skate. As most of you know, you just set your stylus in the center of the blank spot and set the atni-skate so that it stays in one spot neither moving in or out.

Guess the numbers on the dial don't really mean anything - just more of a reference. But I found it rather curious. Anyone else notice this?

Kim


Yes, this has been covered quite extensively here on VE. The past topic which may be most informative is this one:

http://www.vinylengine.com/phpBB2/viewt ... b4d973e4d5

On my conventional pivoting active tonarm turntable, I find the anti skate setting is lower than the manfacturer's recommended setting, whether maintaining the cartridge stationary on the blank area OR adjusting so that the cartridge moves VERY SLOWLY towards the lead out, as recommended / adjusted at the Soundsmith turntable clinic.

The active tonearm makes anti skate experimentation very easy. Currently running a Pickering with dust brush and in this configuration, the actual anti skate force is greater than recommended (ASF > VTF), to offset the added skating effects from the brush.

Search "anti skate anti bias" for more topics.

Good luck.

Fred, the AR stays put as mentioned in the link and the rest are linears.....:D
Music is Everything....Except Predictable....WFUV Fan.
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Postby zharca » 11 Jun 2010 10:56

As has already been said, the subject has been discussed very thoroughly here a number of times, but a couple of quick observations:

Settiing up with a blank disc will give you a very wrong setting - too little antiskate. You must factor in groove friction and also drag from the groove modulation.

Because stylus profile, vtf and cartridge compliance are also factors the amount of antiskate needed will vary a lot between cartridges.
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Postby luckydog » 11 Jun 2010 11:59

I'm still exploring the 'instantaneous' skate force that AS is trying to compensate. Due to modulation, skate force can instantaneously be much larger than a typically AS setting, and point the 'wrong way' to be compensated by AS for some of the time !

IMO the best that AS can do is compensate the average skate force, which has only limited value. It also helps extreme instantaneous trackability in a relatively small way, sort of in a 'straw and camel's back' improvement situation.

So IMO AS is not critical, but might as well optimise it if the mechanism is there.

Average skate force arises from average friction acting along a line different from the tonearm axis. It can be possible to measure the average friction, using a simple method, most recently posted here http://www.vinylengine.com/phpBB2/viewt ... g&start=82.

[BTW, ignore the correction posted afterwards, the original was correct !]

Once one obtains a measured value for friction coefficient Cf, the average skate force, SF, is approx

SF = VTF * Cf * sin(tracking offset angle) [gf]

In principle, the AS should be set to equal SF.

Cf is typically in the range 0.22 - 0.55, say 0.35 typ. Tracking offset angle say 20 degrees. VTF typically 1.5 gf. Then optimal AS might typically be 0.18gf.

HOWEVER Cf varies from disc to disc, across the surface, and dependant on modulation level at which it is measured. So I wouldn't get too hung up about exact AS setting.

Using blank (ungrooved) vinyl often gives a way too high value for Cf, as it depends on the base of the stylus digging into the vinyl. It's so different from the normal mode of stylus/vinyl contact as to be generally useless, IMO.

Bottom line IMO : Don't get too hung up about AS setting. It's only an average in a wildly fluctuating dynamic situation. Even zero is a respectable number.
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Postby Paladin » 11 Jun 2010 15:09

I remember cars. There is static versus dynamic alignments. Dynamic means the alignment is set while simulating rolling on the road. My tires and front-end parts last longer, the car drives smoother, corners better, and I’m happier. It sure beats eyeballing and guessing.

Using the blank spot 2/3 of the way to the center of the record, up and rolling, most of the time my AS ends up around half of what the dial says. Rarely do I get close to what the dial recommends and never over. Beats eyeballing and guessing.

I set it then don’t worry about it sitting straight. No record wear and the tips last a very long time.
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Postby luckydog » 11 Jun 2010 15:59

Paladin wrote:No record wear and the tips last a very long time.
Hi Paladin. That is as true for any reasonable setting of AS, i reckon. Well, normal sort of wear.
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Postby Paladin » 11 Jun 2010 16:13

Yeah, I really do not have wear issues. I bend them first. So I have no proof the AS differences do anything.
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Postby analogaudio » 12 Jun 2010 00:02

The point of antiskate is not to change the wear rate, the point is to offset unequal forces acting on the stylus in the groove because the head of the tonearm is offset at an angle of somewhere around 20 degrees.

The R channel, on the outside, gets less VTF than the L channel and because of this it has a lower threshold for mistracking, as the recording level increases it mistracks sooner. The mistracking is heard as sudden gritty distortion on loud sections on the Right channel more than the Left.

Antiskate allows both channels to track loud sections equally well.

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Postby luckydog » 12 Jun 2010 00:50

analogaudio wrote:The R channel, on the outside, gets less VTF than the L channel and because of this it has a lower threshold for mistracking, as the recording level increases it mistracks sooner.
Hi analogaudio. Yes, but not by much, and only some of the time, i think. Only at extreme tracking limit is there a benefit from optimal AS, and more effect is available from a similar increase in VTF, IMO.

Skate force derives from an average friction force that instantaneously varies greatly, both in magnitude and direction, as groove angle changes with modulation. It is the instantaneous situation that determines trackability, not the average. Applying AS can even up the forces affecting extreme trackability on inner and outer groove excursions. But instantaneously, this correction is a relatively small part of the peak forces. Even optimal AS only offsets a small part of the peak forces. So optimal AS can extend trackability limit a little, but not as much say as adding the equivalent to VTF.

With zero AS, the average load imbalance on the two groove walls is c 25% i reckon. Which isn't necessarily a primary problem. But is worth correcting, without being too fussy about it, IMO. Failure to do so at all might result in a few dB of overall peak trackability impairment. Getting it crudely right, but sub-optimal, perhaps less than 1dB. That's possibly as good as it gets.
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Postby LPspinner » 12 Jun 2010 03:50

Hi guys:

Setting anti skate or Bias can be a vexed issue. As a rough guide the makers indicated setting generally get you in the ballpark but no necessarily spot on. Under most conditions this is generally good enough.

How ever, like it has already been stated, setting the bias by using an un-modulated (blank) disc is not correct and would produce incorrect results. I once had a test record that used a constant and steadily increasing signal that was used to set the bias, and it was a snap to use.

The user would first set the down force or tracking force, then approximately set the bias up according to the arms markings. The user would then play the test track listening to the test signal until the signal became so loud (heavily modulated) that is caused the stylus to miss-track. The side that miss-tracked first was the side that needed more bias (Right channel miss-tracking first means more bias, Left channel miss-tracking first means less bias). When the test miss-tracked equally in both channels the Bias was set correctly.

In my experience the arms markings on the arms I used usually got pretty close. In the end I never bothered and I don’t think my enjoyment suffered because of slightly “off” bias settings.

My important observation through all this though, is don’t use and un-modulated disc. Hope this makes sense.

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Postby Paladin » 12 Jun 2010 04:30

I believe what Shure researched and publicized in their heyday. They were colossal and one misstep and the whole world would see it. Shure stuck to their guns and the tech manuals agreed. And it worked for me. Later the magazine with fresh writers decided the old ideas were wrong and eventually told us CDs are better. I haven’t found it necessary to change.

From one of my dusty tech manuals:

“The inward skating force causes the inner wall of the groove and tip to wear faster than the outer wall and, consequently, the frequency response of the inner wall will deteriorate rapidly. The left and right channels of a stereo system are inscribed, respectively, on the inner and outer groove walls. Therefore, the skating force selectively degrades the left channel.
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Postby luckydog » 12 Jun 2010 09:43

Paladin wrote:From one of my dusty tech manuals:

“The inward skating force causes the inner wall of the groove and tip to wear faster than the outer wall and, consequently, the frequency response of the inner wall will deteriorate rapidly. The left and right channels of a stereo system are inscribed, respectively, on the inner and outer groove walls. Therefore, the skating force selectively degrades the left channel.

Hi Paladin. Yes, i think one can see how a 25% average load imbalance (zero AS) might lead to uneven wear for the stylus in the long run. On the other hand, perhaps a more typical 5% imbalance (estimate typ AS) might be reasonably undetectable........ Perfect correction results in reduction of only half of the imbalanced load i.e c 12.5% of VTF for zero antiskate, that might be only 2.5% typ for normal AS setting. Much might depend on to what extent wear and force are related, and if so, to what extent peak force rather than average is the principle wear factor. It's one of those unopposably sound ideas, in the absence of counter information. However, IMO wear is so slow for a well aligned stylus that a typ benefit of perhaps only 2.5% wear life (typ AS), is not a primary concern. Perhaps 12.5% wear life for zero AS would seem something to get concerned about though, IF that estimate is true.

This L and R wall business...........the trackability limit at issue affects the inner groove wall (for undercompensated SF), and specifically mistracking by riding up it. That riding motion is pure 45-45, that's why it appears firstly in one channel, i think. In fact both groove walls are involved in encoding even pure L & pure R signals. The bottom of the groove moves both laterally and vertically even for a pure L sinusoid. Splitting hairs perhaps, but a useful concept IMO is that the stylus must stay in contact with both groove walls at all times. If tracking distortion appears purely in one channel it is because the mistracking involves stylus riding up on one groove wall, it's a precurser to chaotic mistracking involving loss of contact with both groove walls.

In any event, optimal average AS varies from disc-disc and across the surface, so getting it crudely 'correct' seems the best one can ever do IMO. And not something to worry about, but worth understanding, i think.
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Postby analogaudio » 12 Jun 2010 14:24

The selective left or right channel effect is something that is directly measureable and audible and not a piece of theory. For example when I play the HFN2 disc tone bands at the elevvated levels provided for the purpose, the left channel remains clean while the right channel, alone, breaks up. This is not an opinion or something subjective it is a measureable repeatable fact, the right channel breaks up first and antiskate restores clean tracking to the right channel. I agree with LDs point about things not being very specifically quantifiable but I don't care who wrote what in a dusty manual it is the right channel that experiences loss of trackability and that is what antiskate fixes. There are so many myths in vinyl-land let us not propogate them.

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Postby luckydog » 12 Jun 2010 15:02

Hi analogaudio. If AS is set below average SF, the inner groove wall will be the one that the stylus rides up first, at extreme of modulation. If AS is set above the average SF, then the outer groove wall will be the one the stylus rides up first. Really, it's just a coincidence that this riding motion happens to coincide with pure L or pure R, depending on AS being above or below average skate force.

As to whether inner groove riding corresponds to pure L or pure R distortion, it depends on the absolute phase in which the vertical modulation is recorded. I have not found a definitive answer as to the convention used !
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Postby Paladin » 12 Jun 2010 15:06

I think I’ll stop. I’m making life way too disturbing for a few but very vocal. Again, I set AS and forget about it. I’ll live. And then I move on. Like LD says, the tip is moving around so much that the AS force is just an average, a ballpark number and we are all over the road. But before I go, just one more from the crappy banned book of technical witchcraft that should have been burned with the rest.

“Pretend that the tone arm is a door, and the fulcrum represents the hinges. When applying a force to such a door, it should be obvious that the door will swing clockwise toward the center of the record. In a similar manner, the frictional force tends to force the tone arm inward, causing a greater pressure on the inner wall of the groove as compared to the outer wall. That is why a stylus, which accidentally jumps out of a groove, will skate toward the center of the record.” [I think it should read, ‘if accidentally jumps out of the groove, will skate toward the center.’]
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