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Old 24th March 2019, 09:56 AM   #2871
nocdplz is offline nocdplz
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Yes: as said 0.37 mm observed, 0.065 mm calculated with the compliance = 5,6 times more.
Obviously the tip remains steady into the groove, while the arm is pulled by the weight, rotating on the elastomer: where is the problem?
An advice: to do your own calculations according to Niffy, and your own test according to my setup: an hour spent so takes away a lot of doubts, diyer's style.

Now a curiosity: why do you worry about stylus bending? with your active arm absurd weights and excessive frictions of the carriage mean nothing at all (if it works, that's why they make them).
Your bending will vary between the threshold of the servo and 0, and then between the threshold of the servo and 0, and then between the threshold of the servo and 0, and then between ...

ciao carlo

Last edited by nocdplz; 24th March 2019 at 10:02 AM.
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Old 24th March 2019, 07:27 PM   #2872
niffy is offline niffy  England
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I think that test was the static test with 10mN of force. With your 20um/mN cartridge the calculated deflection would be 200um or 0.2mm. Your measurement of the photos showed 0.37mm which is 1.85 times as great. I think the 0.065mm deflection was on the dynamic test and cannot be directly compared to the 0.37mm deflection. I thought your measurement was a bit pessimistic at the time, I thought your photos showed less deflection.
I have a thought on how to measure the static compliance more directly and it doesn't rely on photographs. It should be much more accurate and simple to perform. It will use my stylus force gauge and micrometer. Unfortunately as I was setting up the force gauge ran out of battery. I've ordered a new battery and if it works out will post results. It will definitely be interesting to see how published manufacturer dynamic compliance figures compare to measured static compliance.

Hi Coolerooney,

If you have the entire 20g under the acceleration of gravity you will indeed have about 200mN of down force which would be disastrous for your cartridge. The arm is counterbalanced so only a couple of grams are supported by the stylus. The effective mass is about how much the arm will accelerate due to a force acting on the stylus and how the compliance of the cartridge will interact. It doesn't represent the force acting on the stylus.

Niffy
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Old 24th March 2019, 08:30 PM   #2873
Coolerooney is offline Coolerooney
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But, but......

The arm is balanced within 2 grams of VTF, isn’t the mass that is important, when changing its direction, vertical or lateral? -same as it is required to get the right resonance? F=mxa springs to mind and the effective mass is calculated by taking the F = mxa into account for each main component- right?

According to the earlier quote of Kuzma:

“The effective mass of a tonearm is a figure in grams. It represents the ‘force’ needed on the diamond tip to move the tube at the bearings.”

Probabaly I am mixing things up, but then I am a true Noob ahahahaha

Best,

Coolerooney

Last edited by Coolerooney; 24th March 2019 at 08:40 PM.
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Old 25th March 2019, 04:38 AM   #2874
niffy is offline niffy  England
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Hi Coolerooney,

I originally questioned Frank's statement as it is not well worded making it confusing. I'll forgive Frank as he is a genius and English is not his first language.

His statement is:

“The effective mass of a tonearm is a figure in grams. It represents the ‘force’ needed on the diamond tip to move the tube at the bearings.”

Our good friend Mr Newton says, as you pointed out, that force = mass x acceleration.

From Frank's statement "effective mass" represents "mass" fron Newton's equation.
"'force' needed" represents "force" and
"move the tube at the bearings" represents "acceleration"

"move the tube at the bearings" is ambiguous as it could refer to bearing friction as well as inertia.
The statement does seem to read that the effective mass is a force. It is actually saying that the effective mass needs a force (applied on the stylus) in order to move.

Hope this clears things up.

Niffy
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Old 25th March 2019, 08:38 AM   #2875
nocdplz is offline nocdplz
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Lil Casey MK2 carbon -- the radial rail tonearm

This new arm (see #2758 - #2833) represents an evolution of the first Lil Casey, to which may refer those interested both for the conception #2355 #2383-4, construction #2440 #2469-70 and measurements. #2547 #2574-2605.
Even if the previous arm behaves correctly (carriage effortlessly sliding) and plays pleasantly my records since a couple of months, there remained two weak points to work on: excessive vertical eff. mass - frictions on the parallelogram.
Since the signal is generated simultaneously by both horizontal and vertical movement of the stylus, imho the vert. and hor. effective mass should be quite similar to get a coherent behavior. I know there are completely different opinions and theories, but this is mine.

In order to improve those aspects I've used a carbon fiber tube to halve the moving masses and pen tip bearings to reduce parallelogram frictions, obtaining a simple compact arm with the same comfort of use of the previous one (rotatable and leveling base, lifter) and -hopefully- better performances on warps.
The arm is just ended, but from the first tests the movements seem OK: the carriage sliding is just a bit worse, while the vertical articulation (the main goal of this design) is greatly improved.
The construction needs just a (small) circular saw and pillar drill, but can not be called trivial - skill, templates and a lot of care are necessary, especially for the geometry of the parallelogram.
Photos and construction drawings as attachment


carlo
Niffy, I am curious to know your method of measurement, certainly less naive than mine: and given that the variations with respect to the calculation were significant but not huge (in the second answer, reading the old post in a hurry I kept the wrong data ) certainly the problem deserves to be better examined
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File Type: jpg L CASEY MK2 IMG.jpg (352.7 KB, 155 views)
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Old 25th March 2019, 02:08 PM   #2876
niffy is offline niffy  England
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Hi Carlo,

As always I am thoroughly impressed with the fit and finish of your work. Lil Casey mk2 looks amazing. Hope the sonics match the visuals.

I have heard many people say that vertical and horizontal effective masses should be the same. It is one of the main criticisms leveled at linear tracking arms, that the vertical and horizontal masses are different. Although I have heard it stated that they should be the same I have never heard a cogent reason for this to be the case. I have solid reasons why it is better for them to be different. Could you please expand on your reasoning for them to be the same.

If you don't mind I'll wait for the new batteries for my stylus force gauge to turn up. Then I can post pictures and a description of the test as well as any results.

Niffy
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Old 25th March 2019, 07:23 PM   #2877
super10018 is offline super10018  United States
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Hi Niffy,

I am not 100% sure why vertical and lateral masses should be same either. I assume the resistance of the damping rubber which holds cantilever is same in every directions, i.e. 360 degree. So, the difference in vertical and lateral masses may cause difference in output. However, I can be wrong.

Jim
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Old 26th March 2019, 05:38 AM   #2878
niffy is offline niffy  England
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In a way the different masses do cause a difference in output. The higher mass will stop the cartridge body from moving as much. The output signal generated by the cartridge body's movement is an unwanted distortion, reducing it is a good thing. This is more down to the compliance being lower relative to the mass. The use of a higher mass will result in the damping ratio being reduced which is to be expected as the same amount of damping is being used on a greater mass. This mainly effects the arm/cartridge at resonance.

Niffy
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Old 26th March 2019, 09:26 AM   #2879
nocdplz is offline nocdplz
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Vertical & horizontal mass
Not much more than what said in those two words. Seems so complex to model that is easier to have opinions than reasons
Here some points
1 - If the stylus was alone in the world we would get a pure signal: everything around it, from the cartridge body, introduces complex resonances that go to compose (sum or difference) the signal itself. Every part of the system influences each other
2 - There are no separate horizontal or vertical movements of the stylus, only complex movements in a cone whose vertex is a point inside the elastomer, shifting with resonance feedbacks
3 - The elastomer is a cylinder of homogeneous material (not a prism with different sides) that reacts with its compliance to the movements of the stylus - the only inhomogeneity is the inclination induced by the VTF, with respect to which the manufacturer positions the generator.

From this the simple conviction that it is not worthwhile to complicate my life by introducing unpredictable inconsistencies: on pivoted ones matching the axes of rotation, aligned with the stylus tip, here trying to get masses similar to those for which are designed the cartridges (there is only one effective mass for the calculation, not two).
Experience tells me that decoupled tonearms, with their mechanical discontinuity, sound very different from each other (better? worse? i don't care at all) and this makes me so suspicious to avoid them as much as i can.
Of course these are only my impressions, meaning nothing more than others: only trying not to confuse the role of the effective mass with the absorption of resonances due to the impedance (and mass of course) of the material.

carlo
Knowing the sophistication and precision of your constructions, your appreciation was greatly appreciated - thx Niffy
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Old 26th March 2019, 04:56 PM   #2880
Coolerooney is offline Coolerooney
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Quote:
Originally Posted by niffy View Post
Hi Coolerooney,

I
The statement does seem to read that the effective mass is a force. It is actually saying that the effective mass needs a force (applied on the stylus) in order to move.

Hope this clears things up.

Niffy
Hmm, not really.....

Tried to apply the F=mxa to an hypothethical arm- taking a page of your post 2599+some Kuzma sauce

Length 20 cm, weight eff 20 grams- no bearing friction
Gives an F of 0,004 Newton (0,2x0,02) multiplied with a cartridge compliance of 22 mu/mN would give a deflection of the cantilever of 0,088 mm, or 88 microns- this seems a reasonable number- any bearing friction would be additional-potentially pushing it to 0,1-0,2 mm

Food for thought:does a normal pivot arm do a better job than TT’s in keeping the cantilever/stylus at right angles vs the groove, due to the ability to use antiskating??

Best,

Coolerooney

Last edited by Coolerooney; 26th March 2019 at 05:04 PM.
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