Modified mechanical anti-skate

Re: Modified mechanical anti-skate

Postby Votan » Tue Mar 12, 2019 11:23 am

Golear wrote:If you are going to do the twisted wire, then you can vary the amount of anti-skate force that the twist brings to the arm (somehow). Perhaps the LEMO socket should be mounted on a rotating assembly if some kind, so that the amount of twist can be varied easily.

I have done it in my previous JMW 12,5 (not having mechanical a/s there), much simpler, as follows: Take out the junction box and turn it upside down. There is a nut in the underside that keeps the female lemo socket fastened to the box. If you lose the nut a bit, you can turn female lemo socket at about 90-120 degrees CCW (looking the junction box overturned), that should give lemo wire a bit more CW preload. Re-fasten the nut. Be careful though, not to stretch too much or short-circuiting the 4 signal wires going from the underside of female lemo socket to RCA sockets of junction box. As a bonus, you avoid a lot more interruptions and new contacts in the signal path of an added rotating assembly, that could downgrade the quality of the very fragile signal of the cart.
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Re: Modified mechanical anti-skate

Postby Golear » Thu Mar 14, 2019 11:33 am

Hi Votan,

Thanks for the info. I have not explored that technique. I'll check it out. (But it will need to be an average across a selection of LPs.)

And as for the LEMO connector, yes, adjusting the socket via the nut sounds like an excellent idea. I'd do that to minimize the twist on the wire (a one-time operation) and then go with the mechanical anti-skate! :-)
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Re: Modified mechanical anti-skate

Postby Votan » Thu Mar 14, 2019 1:16 pm

Hi Golear,
I hope the junction boxes of the new gens JMWs to have the same configuration of nut etc, as in my old JMW 12,5.

Concerning your thoughts on that (minimizing the twist), IMO there is not a twist (preload) of the lemo wire leaving the factory. But it’s its cross knitting (necessary for EMI, RFI rejection because it’s unscreened, as Brf mentioned) that make it a bit stiff. So as the arm is moving inwards spindle wise, it’s the stiff knitting that increasingly resist to that movement creating a/s. So be careful if you turn red dot CCW (looking from above) too much to “pre-relax” it, there is a danger to make it a bit “Skating” in the lead in grooves instead of a/s, then maybe neutral in the center, then a bit a/s in the lead out grooves, but never all the way neutral. Namely, I don’t think that we could ever be able to get totally rid of lemo wire’s stiffness and its influence in a/s (and in azimuth and VTF, as I’ve found in my previous Part I).
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Re: Modified mechanical anti-skate

Postby Golear » Thu Mar 14, 2019 8:28 pm

When I got my 3DR arm, I also got a SoundSmith Zephyr MIMC* cartridge. My dealer handled both lines, and installed them on my turntable. Even though they could have put the cartridge on the arm and sent me on my way, they insisted that I bring the turntable in, so that they could make sure everything worked correctly. Fred's Sound of Music in Portland, Oregon did a great job.

One of the things they insisted on was to use the mechanical anti-skate, as that was what SoundSmith recommended. They made sure that there was minimal twist in the wire. So on my turntable, the LEMO connector fits into the socket without any twisting. I don't think the wire will contribute much of anything as an anti-skate force. If you go with the one-turn twist, then the wire will want to unbend, and this will provide some anti-skate force. But it's very variable - it depends on the orientation of the connector with respect to the wire, the wire itself (Nordost or Discovery), etc. Also the untwisting is going to happen in 3 dimensions, so it's pretty complex and might affect azimuth, too. My wire does not appear to be stiff because of the braid.

The dealer set up the mechanical anti-skate according to VPI guidelines. However, I found that the anti-skate force was less in the inner grooves than in the outer grooves. I could hear it, and see it in the way the loop deformed under tension. That led me to look for a better solution and that led to me starting this discussion. This is not to say that users' set-ups may be wrong. It's possible that the mechanical anti-skate works with some residual anti-skate from the wire and gives good results in the end. But I think in my case, I ran into issues because the dealer did such a good job removing the twist!

I agree nothing is 100%, and the wire may be adding/taking away something. There is the Wally Skater, which can measure the anti-skate across the whole path. But in my case, I can see just by looking at the loop that there's minimal anti-skate in the outer grooves, which rises via a cosine function to a max near the innermost grooves, then drops slightly from max at the very end of the music (90%, I think). It's not perfect, but don't hear any ill effects.
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Re: Modified mechanical anti-skate

Postby Votan » Fri Mar 15, 2019 9:28 am

Golear wrote:One of the things they insisted on was to use the mechanical anti-skate, as that was what SoundSmith recommended. They made sure that there was minimal twist in the wire. So on my turntable, the LEMO connector fits into the socket without any twisting. I don't think the wire will contribute much of anything as an anti-skate force.
Also the untwisting is going to happen in 3 dimensions, so it's pretty complex and might affect azimuth, too. My wire does not appear to be stiff because of the braid.

As you can see in attached video of mine, even with no preloaded lemo wire, it creates a considerable a/s force when arm sails on the platter, pushing it to return to its arm rest, neither too fast, but nor too slow (https://youtu.be/xNbstN7GhZQ). As well, it has a (minimal) influence in VTF and azimuth as I have described in PART I “A/s with lemo wire only” of my previous post.
Maybe a CCW minimal turn (< 90 degrees) with the "nut" technique could degrease a bit that inevitable a/s from lemo wire. You can decide for your best adjustment, each time balancing the tonearm floating in horizontal. If you do that please let us know your findings.

Golear wrote:The dealer set up the mechanical anti-skate according to VPI guidelines. However, I found that the anti-skate force was less in the inner grooves than in the outer grooves. I could hear it, and see it in the way the loop deformed under tension. That led me to look for a better solution and that led to me starting this discussion.
I agree nothing is 100%, and the wire may be adding/taking away something. There is the Wally Skater, which can measure the anti-skate across the whole path. But in my case, I can see just by looking at the loop that there's minimal anti-skate in the outer grooves, which rises via a cosine function to a max near the innermost grooves, then drops slightly from max at the very end of the music (90%, I think). It's not perfect, but don't hear any ill effects.

Being already in the phase of experimenting with the addition of mechanical a/s in my 10”-3DR, your findings (which I have no reason to doubt) intrigued me a lot, so (not processing Wally Skater) I think it’s time to refresh the maths in mechanics to calculate the exact torque been created from VPI’s mechanical a/s all the way from lead in grooves till the lead out grooves. Coming soon…
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Re: Modified mechanical anti-skate

Postby Golear » Fri Mar 15, 2019 11:14 am

I see what you mean about the wire - I stand corrected. Even when there's minimal twist, the wire has stiffness and when it is held in a half-loop, it wants to straighten out. This will move the arm away from the spindle. We all run into this when cueing the arm. But as far as anti-skate is concerned, this is not a bad thing. The anti-skate force from the mechanical anti-skate will be additional to this. (Good of you to post the video.)

Is this a constant force, or is it something that will start low for the outer grooves and increase for the inner grooves?

The force will depend on the type of wire, room temperature and how old the wire is - may be an old wire will develop some memory and want to straighten out less. The twist adds complexity. The wire will want to untwist as well as straighten out. There will be more force.

The force from the wire can be a major issue with an air-bearing, linear tracking arm like the AirTangent. They have a long wire, that follows a helical path to the junction box.

In the end, I believe in using one's ears to make the final judgement. If you hear an improvement, then go with it.
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Re: Modified mechanical anti-skate

Postby Brf » Fri Mar 15, 2019 11:57 am

In an attempt to remove the influence of the tonearm wire on the tonearm's free movement, I remember not too long ago users and some manufactures replacing their internal tonearm wire with silk insulated ultra fine wire. Although the wire was very supple, it was prone to RFI/EMI and extremely delicate.
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Re: Modified mechanical anti-skate

Postby Mr_Putty » Fri Mar 15, 2019 3:22 pm

Votan,
Your video looks good to me, a/s based on wire twist is in the ball park. What it doesn’t show is how little a/s force is on the arm near the outer record groove. That’s ok, we just need to remember that in the video the force on the arm is decreasing as the arm nears the outer grooves while at the same time the arm is still accelerating at a reduced rate. Another video showing the arm at rest over the outer grooves might make this more obvious. I like my a/s force to be barely noticeable at the outer groove and increase at a constant rate as the arm moves toward the inner grooves. That’s a generalization based on what the wire seems to be doing. It sounds right on most of the grooves to me. Ideally it probably should increase in a modified logarithmic manner because musical density on average is not linear across the record as it plays from start to finish. That leads me to the mechanical a/s that I am not convinced is the best design. But, my experience with it is limited. I support the idea that it can be used to increase a/s if used carefully with wire twist. That seems to be the only option available for the current state of the art turntables. (Thanks for posting the video). My current setup uses only relaxed-wire twist for a/s. Also, I am using the mechanical a/s device to counterbalance the azimuth twisting force on the tonearm caused by the wire as the arm nears the inner grooves. This is possible by relocating the a/s line from near the counterweight to the top of the arm, just behind or on top of the pivot spike location. In theory this should work with any unipivot arm both with and without the 2nd pivot. I have only tried it with the 2nd pivot and it does work.
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Re: Modified mechanical anti-skate

Postby Votan » Fri Mar 15, 2019 4:21 pm

Mr-Putty,
Thanks for your response and for your comments. I’ll take care to make a video with the lemo wire’s attraction when the arm is starting from the lead in grooves, in one of my next posts. For the time being here’s a video (https://youtu.be/IFFXHtrl60o) of a/s attraction via both lemo wire plus mechanical a/s with 4 donuts in the outer area of the lower pole.
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Re: Modified mechanical anti-skate

Postby Votan » Fri Mar 15, 2019 5:05 pm

Golear wrote:The dealer set up the mechanical anti-skate according to VPI guidelines. However, I found that the anti-skate force was less in the inner grooves than in the outer grooves. I could hear it, and see it in the way the loop deformed under tension. That led me to look for a better solution and that led to me starting this discussion. This is not to say that users' set-ups may be wrong. It's possible that the mechanical anti-skate works with some residual anti-skate from the wire and gives good results in the end. But I think in my case, I ran into issues because the dealer did such a good job removing the twist!

I agree nothing is 100%, and the wire may be adding/taking away something. There is the Wally Skater, which can measure the anti-skate across the whole path. But in my case, I can see just by looking at the loop that there's minimal anti-skate in the outer grooves, which rises via a cosine function to a max near the innermost grooves, then drops slightly from max at the very end of the music (90%, I think). It's not perfect, but don't hear any ill effects.


Golear finally is right in his findings! Namely:
In order to ad mechanical a/s in my JMW 3DR-10’’ tonearm, I decided to ponder a bit its behavior, namely doing the math to calculate the way it increases the a/s torque during arm’s moving inwards, comparing 2 alternative weighting of the lower pole, one with 4 rubber donuts, the other with the 4 rubber donuts and 1 brass washer. The whole calculus procedure is listed in the end of the post (in between {}), not to bother those who are interested exclusively for the results, listed below in the Table 1, with reference to the sketch below, as well as to the following symbolisms and explanations:
VPI Anti-skating mechanism.jpg
VPI Anti-skating mechanism.jpg (42.72 KiB) Viewed 263 times

- Calculations do not take into account (it’s not possible) the extra a/s torque created from lemo wire.
- No Dual Pivot for the time being
Φ: The each time angle of the lower pole relative to the vertical.
T1: The total torque created from both (upper and lower) bare poles (without any donuts on them).
T2: The additional (to T1) torque created from all 4 donuts placed in such a way that the center of gravity of this quadruple is suspended in point F of the lower pole, supposed to be approx. in a 3/4L distance from the pivot.
T’2: The alternative additional (to T1) torque created from all 4 donuts plus 1 brass washer placed as above mentioned.
Ttot: The total Torque creating from the whole VPI mechanical a/s (wearing only 4 donuts) in relation to each time angle Φ.
T’tot: The total Torque creating from the whole VPI mechanical a/s (wearing 4 donuts plus 1 brass washer) in relation to each time angle Φ.
Table 1. Anti-skating in relation to angle Φ.jpg
Table 1. Anti-skating in relation to angle Φ.jpg (59.42 KiB) Viewed 263 times

Conclusions (of mine): Table 1 tells us that with 4 rubber donuts in the lower pole, torque is increasing from Φ=0° up to 60° plus (~63°), but from this point up it starts to degrease! Is this too bad? Maybe not, because if we take into account the lemo wire’s additional a/s torque as well, which supposedly is continuously increasing, then the total sum could be finally (but not so linear) increasing up to 75°. This is adequate I think, because if we start with the lower pole at Φ=5° in the lead in grooves, then most records have their lead out grooves way before lower pole reaches Φ=75°. But if you start with the lower pole at (say) Φ=15° in the lead in grooves, then there should be the problems that Golear detected in his setup, which isn't a good thing at all.
If in the 4 rubber donuts we add 1 brass washer, we can go up to Φ=75° increasingly, so here normaly no problem. But making preliminary tests for a/s in my 3DR-10’’, I found (via “By Eye” and “By Ear” techniques) this 4 rubber donuts plus the 1 brass washer version a bit too much for a/s.

{Calculations:
Let it be (see the above attached sketch):
L: the total length of each one pole, reaching till the pivot of a/s hub.
B1: the weight of each one pole, suspended in L/2 distance of the pivot (middle of the L length where the center of its gravity is), in point D in the upper pole, in point E for the lower pole.
B2: The total weight of (say) 4 rubber donuts (because those are the total that VPI provides), the center of gravity of this quadruple suspended in point F of the lower pole, supposed to be approx. in a 3/4L distance from the pivot.
B’2: As B2 but adding 1 brass washer to the already existing 4 donuts.
b and a: The distance of points D and E respectively from the vertical passing through the pivot (This is the lever arms of the torque creating respectively from the upper and the lower arms).
c: The distance of point F from the vertical passing through the pivot (This is the lever arm of the torque creating from all 4 donuts in the lower arm).

According to the attached sketch there should be:
DO=L/2, EO=L/2, FO=3L/4, a=(EO)xsinΦ= sinΦxL/2, b=(DO)xcosΦ=cosΦxL/2
T1=B1xb+B1xa=B1x(b+a), =>T1=B1x(cosΦ+sinΦ)x(L/2),
T2= B2xc, =>T2=B2xsinΦx(3L/4)
T’2=B’2xc, =>T’2=B’2xsinΦx(3L/4)

For each cylindrical pole we measure: L=20mm (till the pivot), d=3,44 mm, so Vpole=(πd*2/4)xL=185,8 mm*3
Density of each steel pole is Dpole=7.530 Kg/m*3=7,53x10*(-3) gr/mm*3
Thus B1=VpolexDpole= 185,8x7,53x10-3=>B1=1,4gr
The weight of each rubber donut is Bdonut=0,12gr, so B2=4xBdonut=>B2=0,48gr
The weight of a brass washer is Bwasher=0,82gr, So B’2=B2+Bwasher=>B’2=1,30gr
Thus, T1=1,4x(20/2)x(cosΦ+sinΦ)=>T1=14x(cosΦ+sinΦ), [gr.mm]
T2=0,48x(3x20/4)xsinΦ =>T2=7,2xsinΦ, [gr.mm]
T’2=1,30x(3x20/4)xsinΦ =>T’2=19,5xsinΦ, [gr.mm]
So: Ttot= 14x(cosΦ+sinΦ)+7,20xsinΦ, [gr.mm], as well as
T’tot=14x(cosΦ+sinΦ)+ 19,5xsinΦ, [gr.mm] }
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