First impression of the Dual Pivot Kit

Re: First impression of the Dual Pivot Kit

Postby Brf » Tue Dec 04, 2018 11:53 am

Votan, welcome to the VPI forum and we look forward to your continued participation.

Please allow me to make an observations.

The cartridge is held in an offset headshell, therefore, using the arm tube as the longitudinal axis to create a constrained pivot in the vertical plane would create the torque in which you describe in point #4 and further in you analysis. Since the cartridge is not in line with the arm tube, the optimal position of the dual pivot would be behind the side azimuth weight to allow for the cartridge to move in the same vertical plane and the constrained dual pivot thereby eliminating any rotational torque.

If you look at a fixed bearing tonearm, you will notice that the bearing assembly has a yoke offset equal to the headshell offset.
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Re: First impression of the Dual Pivot Kit

Postby Votan » Tue Dec 04, 2018 12:19 pm

suntea wrote:Very interesting. Is there a way to actually measure what you state in paragraph 4?


Yes, but a bit approximately!( I stress that my analysis is theoretical because I have not tried Dual Pivot in my JMW, due to the above reservations).
Firstly you set up very precisely tonearm in the recommended VTF, having:
1. The Pivot No 2 (Dual Pivot) on the arm’s cup, (behind the left side azimuth weight), BUT NOT IN TOUCH yet with its sliding plate, as well
2. Your stylus sitting on the very precise electronic scale, taking extremely care the VTA in this position to be as precise as possible (the arm parallel to the platter).
3. The Azimuth to lean very slightly towards the left side of arm as we look it from the front.
4. Keep a precise note for what you read in the electronic scale, say VTF1.
Then, without to remove the stylus, you screw the Pivot No 2 (VERY SMOUTHLY AND VERY CAREFULLY, otherwise you start searching for a new cartridge, this is the most dangerous point in adjusting Dual Pivot) until it touches its sliding plate. You screw it until the Azimuth to be precisely parallel to the platter.
Then you read again the electronic scale, say VTF2. Been everything else equal, normally it should be slightly higher than VTF1 if everything is correct and precise.
The (unwanted) torque that dual pivot presses the cantilever is (VTF2-VTF1)*Lc, where Lc the distance of the stylus to Pivot No 1.
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Re: First impression of the Dual Pivot Kit

Postby Brf » Tue Dec 04, 2018 1:05 pm

Votan wrote:4. Keep a precise note for what you read in the electronic scale, say VTF1.
Then, without to remove the stylus, you screw the Pivot No 2 (VERY SMOUTHLY AND VERY CAREFULLY, otherwise you start searching for a new cartridge, this is the most dangerous point in adjusting Dual Pivot) until it touches its sliding plate. You screw it until the Azimuth to be precisely parallel to the platter.
Then you read again the electronic scale, say VTF2. Been everything else equal, normally it should be slightly higher than VTF1 if everything is correct and precise.
The (unwanted) torque that dual pivot presses the cantilever is (VTF2-VTF1)*Lc, where Lc the distance of the stylus to Pivot No 1.


Sorry, I cannot endorse any dual pivot adjustment in which the cartridge is not secured in the arm holder. Yes, it is more tedious and will take more time, but you will not risk damage to your cartridge.
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Re: First impression of the Dual Pivot Kit

Postby Golear » Tue Dec 04, 2018 2:47 pm

Hi Votan

I think you have to take the offset into account, and think about the forces that are on the stylus as it plays in the groove. What you wrote would be valid for an arm that does not have an offset - like a linear tracking arm. I think that you have to resolve forces along the axis of the cantilever, not along the axis of the arm tube. So you can't do a direct measurement. You should find that, when the second pivot is located according to the diagram posted by Brf, VTF2 and VTF1 will be equal.

(Just had second thoughts on the above. It might not be that simple but rather than try and do the math or make measurements, and figure out the proof, I'd rather just use my ears. If the second pivot improves the sound, then have at it. If it doesn't, then don't use it.)
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Re: First impression of the Dual Pivot Kit

Postby Votan » Tue Dec 04, 2018 4:43 pm

Brf wrote:Sorry, I cannot endorse any dual pivot adjustment in which the cartridge is not secured in the arm holder. Yes, it is more tedious and will take more time, but you will not risk damage to your cartridge.


Golear wrote:Hi Votan
I think you have to take the offset into account, and think about the forces that are on the stylus as it plays in the groove. What you wrote would be valid for an arm that does not have an offset - like a linear tracking arm. I think that you have to resolve forces along the axis of the cantilever, not along the axis of the arm tube. So you can't do a direct measurement. You should find that, when the second pivot is located according to the diagram posted by Brf, VTF2 and VTF1 will be equal.


Brf wrote:Votan, welcome to the VPI forum and we look forward to your continued participation.
Please allow me to make an observations.
The cartridge is held in an offset headshell, therefore, using the arm tube as the longitudinal axis to create a constrained pivot in the vertical plane would create the torque in which you describe in point #4 and further in you analysis. Since the cartridge is not in line with the arm tube, the optimal position of the dual pivot would be behind the side azimuth weight to allow for the cartridge to move in the same vertical plane and the constrained dual pivot thereby eliminating any rotational torque.

If you look at a fixed bearing tonearm, you will notice that the bearing assembly has a yoke offset equal to the headshell offset.
[/quote]

Dear BRF, Golear at all, thanks a lot for the welcome! I’ll be glad to share experiences, as well to exchange opinions and participate in goodwill debates in the Forum.
I am not sure what you mean for the offset of the bearing assembly of bearing tonearms, because in the attached picture is vertical to the tonearm's axle.
Conqueror-Tonearms-top1.png
Conqueror-Tonearms-top1.png (36.64 KiB) Viewed 146 times


I am afraid though that this way we should go to very extensive theoretical analyzes that go far beyond the purpose of the forum. The only thing I would like to point out in closing this, is that the transversal torque which keeps Dual pivot in touch to its sliding plate and charges it, is the one that is created from the eccentric central counterweight. This torque has as axle the arms axle, not the cantilever’s imaginable axle. So statically (at least) Dual Pivot creates torque to the stylus, thus VTF2 should be a bit greater than VTF1 which makes set up with Dual Pivot an extremely tedious and adventurous task.

And of course Brf, No one should endorse any dual pivot adjustment in which the cartridge is not secured in the arm holder. It was a theoretical description on how one can measure the described in my analysis torque, something that in real life no one should do ever! But (theoretically) if you adjust the Dual Pivot to be in touch to its sliding plate when the arm-cartridge are secured in the arm holder (which means that the arm is not parallel to the platter, leaning backwards), then, when you shall put the stylus on the groove, the Dual Pivot would be in the air! Which means that you enter in the twilight zone in adjusting countless times VTF>VTA>Azimuth>DUAL PIVOT>VTF>VTA>Azimuth>Dual Pivot>>>>>>>>>>>>>, in that circular path to hell!
The whole point of my post is that life is too short to be tempted to aftermarket modify a delicate unipivot arm to a 2 (or 3, or 4) Point pivot! And to be forced to go to the very tedious, tiring, irritating, dangerous (for the stylus, as well for your mental balance) procedure, which upset the original geometry and potentially degrade the sonic quality of an already very good and time-tested tonearm.
Which, to my philosophy means that: If you like gimbaled go factory gimbaled (there are a lot of excelled ones), if you like Unipivots stay to a lot of excellent factory ones, if you like more pivots go to Kuzma 4Point or to mixed technologies like Reed.
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Re: First impression of the Dual Pivot Kit

Postby Votan » Tue Dec 04, 2018 5:04 pm

Golear wrote:Just had second thoughts on the above. It might not be that simple but rather than try and do the math or make measurements, and figure out the proof, I'd rather just use my ears. If the second pivot improves the sound, then have at it. If it doesn't, then don't use it.

I agree with all my heart! This is the epitome of Hi End.....
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Re: First impression of the Dual Pivot Kit

Postby Golear » Tue Dec 04, 2018 8:36 pm

Hi Votan

If you look at an SME tonearm, you'll see the vertical bearing mounted at an angle to the arm tube. Is this better/worse than what is done on the Conqueror arm? Given the degree of motion (very little) and the speed of motion (very slow), I can't imagine this making the slightest difference.

When it comes to the Dual Pivot, here's an idea on set-up:

1. Install the SoundSmith CounterIntuitive and Dual Pivot.
2. Set VTA then set VTF. Repeat as necessary.
3. Rotate the CounterIntuitive slightly in a clockwise direction, until the stylus wants to point away from the spindle.
4. Set the azimuth, using the Dual Pivot.
5. Align cartridge.

You're all set. You can vary the force on the Dual Pivot by rotating the CounterIntuitive. The VTF will not be affected if all you only rotate the CounterIntuitive. (The force on the Dual Pivot may act as an anti-skate.)
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Re: First impression of the Dual Pivot Kit

Postby Brf » Tue Dec 04, 2018 8:42 pm

A cartridge that is offset from the main pivot will exhibit azimuth changes in the vertical plane (i.e. warped records) if there is not a corresponding offset in the tone arm’s bearing assembly – this fact is not in dispute and is based on the principles of geometry.

The image that you posted is that of an Origin Live tone arm in which the designer made a conscious and deliberate decision not to offset the bearings as a design compromise to favor frictional bearing tolerance over slight azimuth errors in the vertical plane.

If you google fixed bearing tone arms, it will yield many example of tone arms with offset main bearings i.e. SME, Rega, Jelco, Reed, Kuzma, SAT, etc.

In addition, I am not sure how torque is transferred to the cantilever with the addition of a second pivot, as free rotation is now restricted (constrained) along the longitudinal axis (azimuth) but retains free rotation in both the perpendicular and lateral axis.

In any event, I would urge you to try a dual pivot yourself.
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Re: First impression of the Dual Pivot Kit

Postby VinBob » Wed Dec 05, 2018 12:02 am

Any chance of someone kindly posting a video on how to perform the Dual Pivot setup as a gift for the holidays so I can do mine?! ;) :lol:

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Re: First impression of the Dual Pivot Kit

Postby Mr_Putty » Wed Dec 05, 2018 12:46 am

Here’s my setup procedure for the second pivot. It’s not that complicated but it’s a “roadmap”. I use the standard 3D arm with side weights, counterweight and gentile loop in the tonearm wire, and antiskate weights. This is easier if you have some previous listening experience that you used to determined the best VTA, azimuth and stylus force. Find you stylus guard and use it whenever you can, see below.
1. Set the cartridge on a record. Place the aluminum cartridge setup rod on the head shell with azimuth previously set as desired. (Carefully note rod angle if not parallel to the record. This WILL be used later.)
2. Put stylus guard ON.
3. Examine new pivot for QC and fit to arm placement BEFORE installing. Use Allen wrench to check effort needed to adjust both pivot screws. If excessive turn wrench in and out until acceptable.
4. Remove wiring from the lemo connector, and arm and install the new pivot on arm (only moderate pressure is needed). Put some CA on the lower contact point with the arm. Use kicker or wait 24 hours (latter recommended to be safe). Install base plate following instructions. Screw both arm side weights all the way in.
5. With stylus guard ON remount the arm. Use the same record or spacer as before.
6. Set the azimuth as measured before with the alignment rod, by turning the pivot screw being careful not to dislodge the pivots arm mounting. I used a backup when possible. This is not easy and is why you need to check the force needed to adjust the pivot point. If it pops off you know what to do.
7. Reconnect the wiring. Using the side weight opposite the pivot, unscrew it until the pivot barely touches down in mid record. Then screw it clockwise about a half turn for a starting point. Check for contact at various points on the record with stylus guard ON if possible. IMO, The antiskate effect of the wire loop will affect the downward pivot force at different points on a record. I prefer no anti skate mid record based only on the wire twist as a reference. I do use some antiskate weights as well.
Almost done! You can scratch the pivot plate while setting the proper downward force, so I recommend a light dusting of the plate with microfine PTFE powder. It works well for me. I occasionally apply it with a soft artist brush.
8. Recheck the VTF and cart alignment and adjust if necessary. Now the fun!

If the pivot force is too light you will hear an occasional “rattling” in the sound. If it’s too heavy it will just sound bad. I know BRF has a recommended force based on stylus pressure, but so far I don’t find that much precision necessary. And as I mentioned, at least for my wiring, the pivot pressure will vary at different points on the record. IMO, It is this azimuth affected situation that is one of several compromises a unipivot arm has to deal with. And the second pivot does a very good job of removing at least this from ideal playback.
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