Yes I did. But making long, light, stiff and non resonant has always been non-trivial. My inertia comment was because putting all the mass on the end of the stick seems illogical at first esp with the 0.55Hz wobble you have to deal with that the poor little cantilever goes through.
I really would like to experiment with arm making, but other than the biro unipivots and the well tempered clones I don;t think I could do the bearings with enough precision, which means paying someone which means £££. I am sure there are suitable donors out there but its working out which ones.
I really would like to experiment with arm making, but other than the biro unipivots and the well tempered clones I don;t think I could do the bearings with enough precision, which means paying someone which means £££. I am sure there are suitable donors out there but its working out which ones.
Déjà vu 🙂
From my notes (Feb 05, 2011):
"The Very Strange and a Bit Silly Arm (VSBSA)
It all started while I was thinking of an arm that could be as much statically / dynamically balanced relative to it’s fulcrum (pivoting point), as possible.
For this to be achieved, the arm has to be pivoted at a point lying in the middle of it’s length, the masses at both ends to be equal, the forces acting on these masses during record playing to be as equal as possible, so that the dynamic torques (j=M*L^2) that are created, to be in good equilibrium.
To make things simpler, a unipivot arm is the first step.
I think that unipivot arms are easily unbalanced in the transverse direction.
When the cartridge is attached with an offset angle to the arm (or statically worse, when the arm has a “S” or “J” form), side force (skating) is created. The skating force is dynamically varied (as it is also a function of disk groove modulation), therefore it can not be dynamically balanced by the coarse application of the antiskating force. So, a straight unipivot arm with a cartridge fitted on 0 offset angle is the second step.
To further increase the transverse dynamic stability, addition of balanced masses away from the pivot point is required , so an arm with the form of a cross, seems to be the third step.
Next, to make the whole construction stable relative to the single pivot point, the centre of gravity of all the distributed masses has to lie below the pivot point. One way to achieve this, is to raise the pivoting point above the cartridge and counter weight level. Making an arm then with a wide “^” shape is the forth step.
An analysis of the forces and torques shows that it is beneficial to make this “^” sharper (smaller contained angle). This increases the height of the construction, asking for a higher pivoting tower. This, together with the request for (acoustically) uncoupling the base of the pivoting tower from the turntable plinth, begs for alternative pivoting. Instead of having the arm pivoted from beneath, it would be better to have the arm suspended from above at it’s fulcrum. This is the fifth conceptual step."
George
From my notes (Feb 05, 2011):
"The Very Strange and a Bit Silly Arm (VSBSA)
It all started while I was thinking of an arm that could be as much statically / dynamically balanced relative to it’s fulcrum (pivoting point), as possible.
For this to be achieved, the arm has to be pivoted at a point lying in the middle of it’s length, the masses at both ends to be equal, the forces acting on these masses during record playing to be as equal as possible, so that the dynamic torques (j=M*L^2) that are created, to be in good equilibrium.
To make things simpler, a unipivot arm is the first step.
I think that unipivot arms are easily unbalanced in the transverse direction.
When the cartridge is attached with an offset angle to the arm (or statically worse, when the arm has a “S” or “J” form), side force (skating) is created. The skating force is dynamically varied (as it is also a function of disk groove modulation), therefore it can not be dynamically balanced by the coarse application of the antiskating force. So, a straight unipivot arm with a cartridge fitted on 0 offset angle is the second step.
To further increase the transverse dynamic stability, addition of balanced masses away from the pivot point is required , so an arm with the form of a cross, seems to be the third step.
Next, to make the whole construction stable relative to the single pivot point, the centre of gravity of all the distributed masses has to lie below the pivot point. One way to achieve this, is to raise the pivoting point above the cartridge and counter weight level. Making an arm then with a wide “^” shape is the forth step.
An analysis of the forces and torques shows that it is beneficial to make this “^” sharper (smaller contained angle). This increases the height of the construction, asking for a higher pivoting tower. This, together with the request for (acoustically) uncoupling the base of the pivoting tower from the turntable plinth, begs for alternative pivoting. Instead of having the arm pivoted from beneath, it would be better to have the arm suspended from above at it’s fulcrum. This is the fifth conceptual step."
George
so you end up with something like a children's mobile?
This evening my daughter told me about wakefield accelerators. Some groovy stuff happening in labs these days 🙂
This evening my daughter told me about wakefield accelerators. Some groovy stuff happening in labs these days 🙂
I was going to post this last night, but wanted to mull over the claims a bit
Innovative and Creative Nasotec Swing Headshell
Now on first inspection there is a heap of bad going on here. you are adding an extra degree of freedom between headshell and arm effectively decoupling the cart from the arm mass. Their claim to fix tracking errors doesn't stack up. Yes you will get a variable skew due fixed antiskate and variable skating force across the record, but I can't see that being helpful.
But they show videos and pretty graphs showing lower noise and better tracking. I can't see how noise could be reduced but clearly the resonant frequencies will be moved and some damping introduced. I suspect in some conditions it may be beneficial, but not for the reasons they claim. And I'm not going to spend £250 to find out!
Innovative and Creative Nasotec Swing Headshell
Now on first inspection there is a heap of bad going on here. you are adding an extra degree of freedom between headshell and arm effectively decoupling the cart from the arm mass. Their claim to fix tracking errors doesn't stack up. Yes you will get a variable skew due fixed antiskate and variable skating force across the record, but I can't see that being helpful.
But they show videos and pretty graphs showing lower noise and better tracking. I can't see how noise could be reduced but clearly the resonant frequencies will be moved and some damping introduced. I suspect in some conditions it may be beneficial, but not for the reasons they claim. And I'm not going to spend £250 to find out!
Better alignment = lower stylus-groove friction = lower surface noise ? Eliminating imbalance of forces between inner/outer groove walls raises threshsold at which friction causes momentary mistracking ? I know, I'm getting boring, but it does explain such otherwise odd observations very well.....in fact I would predict it ! It auto-aligns, at least as to tracking angle, based on minimal and balanced friction.
I also think the headshell pivot idea should work well, assuming other problems, such as persuading LF mechanics to work, can be solved.
LD
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OK I'm being dense then. The skating force is acting on the stylus, the anti-skate on the arm and with a joint in the middle. How is that going to auto-align the tracking angle?
And I finally remembered why I had seen the 'pivoted linear tracker'. https://www.youtube.com/watch?v=QYqcQl5pLgU the Shroeder LT. At $9000 not for mortals and I'm not clear how the double pivot actually achieves it's magic without causing other problems, but sure if you spent $9000 you wouldn't tell people you had bought a pup!
Just nit-picking but 'anti-skate' required is also independent of arm length.
All the common bent arm design eqns. resolve to a given linear offset.
ie a 12" arm has the same linear offset as a 9" one designed to the same eqns. so the 'anti-skate' required is the same.
This has been known (though not well known) since the late 60s when loadsa clever folk tried to achieve low 'tracking error' .. including articles in Gramaphone, HFN, Audio etc. But all the articles started off with loadsa maths which put people off analysing to the simple conclusion.
The Queen's english
Hi billshurv,
As I am always eager to increase my english vocabulary, would you please explain the quoted phrase.
Sincerely,
Ralf
Hi billshurv,
As I am always eager to increase my english vocabulary, would you please explain the quoted phrase.
Sincerely,
Ralf
For you it would be 'bought a lemon'.
From an etymological perspective comes from the same root as 'pig in a poke', or as they say in France 'Chat en poche'. You think you are buying a nice fat piglet but when you open the bag there is a dog/puppy in it.
From an etymological perspective comes from the same root as 'pig in a poke', or as they say in France 'Chat en poche'. You think you are buying a nice fat piglet but when you open the bag there is a dog/puppy in it.
Appols, it took a few days of switching between 'it works' and 'it doesn't work' before settling on that I just can't decide so appreciate help to put me out of misery !
The arrangement is a pivoting cartridge and a pair of springs that apply restoring torque to a nominal optimal alignment. Friction force is always exactly tangential to the groove spindle radius on long term average. Friction force is minimum at optimal alignment, but otherwise increases rapidly with error angle in either direction.
What happens during playback as to alignment ? What happens if the springs are removed ?
Help, I have a block on this ?!
LD
well I guess it depends what the magnitude of friction force vs skating force is. anything being dragged will tend to a straight line, which is lucky when towing a trailer, so the pivot will normally be in a straight line. And that is where I am stuck as to which force would dominate and could the additional friction of misalignment twist the headshell against the springs and the general drag of rotation!
BTW: you have mail.
BTW: you have mail.
I don't understand the reason for twisting the headshell of a linear tracker, like on this video:
https://youtu.be/Kfp8KtanP8w
https://youtu.be/Kfp8KtanP8w
I find it interesting. Really a pivoting headshell with a restoring torque spring is very similar to a normal cartridge suspension, where the cantilever has a free pivot point held in position by a restoring spring.
Putting aside pivoting headshells for a moment, the normal cantilever has a free pivot within a cartridge suspension. In normal playback of a silent groove, there must be a balance of torques about the cartridge suspension pivot: a skate force applied at the tonearm pivot at a distance of a tonearm's length, and a restoring torque provided by the cartridge suspension spring due to deflection of the stylus from nominal position.
We roughly know cartridge suspension spring constant from suspension compliance, let's say 0.05mN/µm. So for a stylus say 7mm long, and for a typical stylus deflection (due to skate force) of 1mm, force on the stylus is approx 5 mN or 0.5gf (skate force), and torque about the cart suspension pivot is about 0.07 kg/m for both the cantilever and tonearm equally.
But the cantilever pivot is not self-aligning, because no matter what sense any error in tracking alignment has, + or -, defelection of the cantilever is always in the same direction, long term, in response to friction, and skate force.
For this reason, I now doubt the free pivoting headshell with restoring spring can self-align.
LD
Putting aside pivoting headshells for a moment, the normal cantilever has a free pivot within a cartridge suspension. In normal playback of a silent groove, there must be a balance of torques about the cartridge suspension pivot: a skate force applied at the tonearm pivot at a distance of a tonearm's length, and a restoring torque provided by the cartridge suspension spring due to deflection of the stylus from nominal position.
We roughly know cartridge suspension spring constant from suspension compliance, let's say 0.05mN/µm. So for a stylus say 7mm long, and for a typical stylus deflection (due to skate force) of 1mm, force on the stylus is approx 5 mN or 0.5gf (skate force), and torque about the cart suspension pivot is about 0.07 kg/m for both the cantilever and tonearm equally.
But the cantilever pivot is not self-aligning, because no matter what sense any error in tracking alignment has, + or -, defelection of the cantilever is always in the same direction, long term, in response to friction, and skate force.
For this reason, I now doubt the free pivoting headshell with restoring spring can self-align.
LD
Given a very soft set of springs in the shell, the cantilever will deflect less as it would with stronger springs or no springs at all.
But less deflection is not at all the same as self aligning.
The shell would at least need to have some damping mechanism with a sub-audio corner frequency, if not it will reduce the output voltage coming from the cart at lower audio frequencies.
I agree, this flexible shell with or without damping does not seem to be a solution for whatever thinkable problem.
Hans