Was this project completed? What is Bernhard Kistner doing?
Index of /06_Lit_Archive/14_Books_Tech_Papers/Kistner_Bernard
Index of /06_Lit_Archive/14_Books_Tech_Papers/Kistner_Bernard
Looks like a cross between the Rockport Sirius, Bergmann, and the Air Tangent.
Needs a reduction in horizontal weight.
An overhead magnetic repulsion instead of the counterweight might be doable, but haven't seen it done effectively
Mentioned a milling, lathe machines. You might add a center less grinder to that list.
Regards
David
Needs a reduction in horizontal weight.
An overhead magnetic repulsion instead of the counterweight might be doable, but haven't seen it done effectively
Mentioned a milling, lathe machines. You might add a center less grinder to that list.
Regards
David
... it is only part of a system philosophy - dice45 - Vinyl Asylum
I would like to see pictures of Bernhard Kistner's current tonearm and turntable.
I would like to see pictures of Bernhard Kistner's current tonearm and turntable.
Hello all,
project was never completed. After sketching out several variants of air-borne or low-friction bearing linear trackers, i built an improvised functional prototype (only linear tracking bearing and tonearm wand) to find out how small/big the lateral forces on the stylus actually are.
(Before, I had acquired two Orsonic Side Sorce Checkers and found out that on a pivoted tonearm, a change in lateral bias / antiskating force representing a display change of one needle width on the Side Force Checker's display was clearly audible )
Now, with the linear tracking protype, changes of lateral force caused the Side Force Checker's display needle to travel almost the full scale (air bearing), particularly, if the record is slightly off-center (oscillating display, indicating too high lateral inertia) . On a good pivoted tonearm with antiskating adjusted by ear OTOH, the display oscillations were moderate and the needle was mostly centered, approching expectations. Much better than the air bearing contraption. And on my Shreve-Rabco SL8e (a linear tracker with active position control), the display oscillations were very slight and the needle stood rock solid center, exactly as it should be.
To move a tonearm laterally, work has to be executed.
Work = mass * acceleration * displacement = force * displacement.
On a PASSIVE linear tracker the only force usable for lateral displacement is lateral stylus force. But: Lateral stylus force (if not kept very close to zero) results in a lateral bias on the cantilever suspension -- in other words, the operating point of the suspension is off-center. As a cantilever suspension's force curve is highly progressive, the forces pointing to record center and record edge differ from each other. This leads to clearly audible differences in micro- and macrodynamics between left and right channel. You may like disquieting dynamics and unstable imaging, i however do not.
Before my experiment, i could hardly believe the reservation and lack of enthusiasm towards linear tracking tonearms exhibited on the net. After my experiment, considering my results and keeping in mind that there are only passive linear trackers on the market today (no manufacturer dared to introduce an active linear tracking tonearm after experiences with one product having a poorly working position control reg), I understood the rejection of the concept. Okok, there are fans, too.
Currently, i enjoy my active linear tracker very much, more than any other tonearm i ever owned. And should i ever plan to build another linear tracking tonearm, it would be an active, position-controlled, design (however, I would have to better my buddy David Shreve's fully modded Rabco sonically ... which is a tough call).
To my ear, the absence of lateral forces has a much bigger sonic impact than the reduction of lateral tracking angle error.
Bernhard Kistner
project was never completed. After sketching out several variants of air-borne or low-friction bearing linear trackers, i built an improvised functional prototype (only linear tracking bearing and tonearm wand) to find out how small/big the lateral forces on the stylus actually are.
(Before, I had acquired two Orsonic Side Sorce Checkers and found out that on a pivoted tonearm, a change in lateral bias / antiskating force representing a display change of one needle width on the Side Force Checker's display was clearly audible )
Now, with the linear tracking protype, changes of lateral force caused the Side Force Checker's display needle to travel almost the full scale (air bearing), particularly, if the record is slightly off-center (oscillating display, indicating too high lateral inertia) . On a good pivoted tonearm with antiskating adjusted by ear OTOH, the display oscillations were moderate and the needle was mostly centered, approching expectations. Much better than the air bearing contraption. And on my Shreve-Rabco SL8e (a linear tracker with active position control), the display oscillations were very slight and the needle stood rock solid center, exactly as it should be.
To move a tonearm laterally, work has to be executed.
Work = mass * acceleration * displacement = force * displacement.
On a PASSIVE linear tracker the only force usable for lateral displacement is lateral stylus force. But: Lateral stylus force (if not kept very close to zero) results in a lateral bias on the cantilever suspension -- in other words, the operating point of the suspension is off-center. As a cantilever suspension's force curve is highly progressive, the forces pointing to record center and record edge differ from each other. This leads to clearly audible differences in micro- and macrodynamics between left and right channel. You may like disquieting dynamics and unstable imaging, i however do not.
Before my experiment, i could hardly believe the reservation and lack of enthusiasm towards linear tracking tonearms exhibited on the net. After my experiment, considering my results and keeping in mind that there are only passive linear trackers on the market today (no manufacturer dared to introduce an active linear tracking tonearm after experiences with one product having a poorly working position control reg), I understood the rejection of the concept. Okok, there are fans, too.
Currently, i enjoy my active linear tracker very much, more than any other tonearm i ever owned. And should i ever plan to build another linear tracking tonearm, it would be an active, position-controlled, design (however, I would have to better my buddy David Shreve's fully modded Rabco sonically ... which is a tough call).
To my ear, the absence of lateral forces has a much bigger sonic impact than the reduction of lateral tracking angle error.
Bernhard Kistner
dice45,
I am glad to see you posting here. Do you have pictures of your active linear tracker? Do you have pictures of your current diy turntable? If it is possible, I would like to see share your ideas and comments on turntables, tonearms, and cartridges. You can always post on audiokarma, audio asylum, diy audio, vinyl engine and others. You would be helping a lot of audiophiles.
I am glad to see you posting here. Do you have pictures of your active linear tracker? Do you have pictures of your current diy turntable? If it is possible, I would like to see share your ideas and comments on turntables, tonearms, and cartridges. You can always post on audiokarma, audio asylum, diy audio, vinyl engine and others. You would be helping a lot of audiophiles.
2 pictures of Bernhard Kistner's modified Rabco tonearm.
http://www.tnt-audio.com/jpeg/etf2004k.jpg
http://www.theaudioeagle.com/images/schall_rauch_ii/b_k_rabco_tt.jpg
http://www.tnt-audio.com/jpeg/etf2004k.jpg
http://www.theaudioeagle.com/images/schall_rauch_ii/b_k_rabco_tt.jpg
AVWERK,
1st class three-line put-down, compliment, chapeau!!
you could not have been more wrong. The tonearm is structurally like the Kuzma airborne linear tracker marketed in later years with the air fed to the moving part of the tonearm and the rail having a smooth surface w/o holes. A fundamental difference to the Kuzma bearing is that the bearing surface is split into two to address the issue of the bearing stiffness against azimuth-aligned torque coming form the cartridge.
Problem of a circular air bearing is that the curve of pressure distribution along the bearing gap has a belly shape and the pressure at the bearing's end edge is zero -- making the bearing weak and soft where it it supposed to be strong.
Let me rephrase what i pointed out yesterday: considering the fact that a PASSIVE linear tracker has to harvest the force needed to drag its moving mass along from lateral stylus forces only, the intertia of the moving part of the tonearm is always way too high, no matter how lightweight it is. It is a structural flaw which cannot be optimized away.
I took care of the issue as far as possible: I intended to make the bearing tube out of CFK. All milled and turned parts are heavily chambered inside and i would expect the tonearm slider's total weight comparable to that of the Air Tangent. Any air distribution to the bearing tube's nozzles consists of thin walls rings glued to the outer surface (not yet visible on the drawings). Due to the slider tube's manufacturing strategy, it is not perfectly cylindrical at the outer surfaces ... no counterweight on a metal ribbon, see below.
But anyway, this was 12 years ago and I decided to never build it that way.
Unfortunately, not even a classical counterweight can keep TF as constant as i would like it to be; constant force spring mechanisms are complex and space-demanding and tend to be unadjustable.
Rope and weight would be ideal as the TF is kept constant independent of angular excursion.
Now if you substitute the rope by a very thin sheet metal ribbon and let the counterweight go over the full width of the slider and IF-IF-IF you find a region on the circular air bearing cylindrical enough to keep radius (and TF with it) really constant, then you could let this metal ribbon run over this region and maybe the dangling of the counterweight in lateral direction is below the threshold of interference with sonics.
Creating a TF momentum by a rope pulling from a vertical pulley face and pulled down by a weight independently of the tonearm wand will need deflecting the rope/thread by pulleys and those pulley's bearing torques then add to the vertical gymbal's bearing torque. As vertical bearing torques must be minimized as far as even possible (or the treble resolution goes down the toilet), this is a no-go to me.
To me, it is adjustable counterweight on a beam, for simplicity's sake and aforementioned reasons.
Regards,
Bernhard
1st class three-line put-down, compliment, chapeau!!
you could not have been more wrong. The tonearm is structurally like the Kuzma airborne linear tracker marketed in later years with the air fed to the moving part of the tonearm and the rail having a smooth surface w/o holes. A fundamental difference to the Kuzma bearing is that the bearing surface is split into two to address the issue of the bearing stiffness against azimuth-aligned torque coming form the cartridge.
Problem of a circular air bearing is that the curve of pressure distribution along the bearing gap has a belly shape and the pressure at the bearing's end edge is zero -- making the bearing weak and soft where it it supposed to be strong.
How do you know? Opinion or can you express it in numbers?
Let me rephrase what i pointed out yesterday: considering the fact that a PASSIVE linear tracker has to harvest the force needed to drag its moving mass along from lateral stylus forces only, the intertia of the moving part of the tonearm is always way too high, no matter how lightweight it is. It is a structural flaw which cannot be optimized away.
I took care of the issue as far as possible: I intended to make the bearing tube out of CFK. All milled and turned parts are heavily chambered inside and i would expect the tonearm slider's total weight comparable to that of the Air Tangent. Any air distribution to the bearing tube's nozzles consists of thin walls rings glued to the outer surface (not yet visible on the drawings). Due to the slider tube's manufacturing strategy, it is not perfectly cylindrical at the outer surfaces ... no counterweight on a metal ribbon, see below.
But anyway, this was 12 years ago and I decided to never build it that way.
No, it is not doable (did I really say that ? ... doesn't sound like me ... and to be honest I mused about the idea myself). Tracking force should be finally adjusted by ear, desirably to a resolution of 0.01gram(force), to find the really sweeet spot (where e.g. the tone colours of a violoncello stay plausible independent of the 'cello's pitch or volume ). To retain that sweeet spot, tracking force has be kept as constant as possible even when tracking record warps or pressing bubbles. Magnetic repulsion OTOH is highly non-linear and resulting angular excursions of the tonearm wand will influence tracking force to considerable extent. The demand for constant TF will conflict with the magnetic repulsion's non-linearity; it is a structural flaw. I would not like to listen to it.
Unfortunately, not even a classical counterweight can keep TF as constant as i would like it to be; constant force spring mechanisms are complex and space-demanding and tend to be unadjustable.
Rope and weight would be ideal as the TF is kept constant independent of angular excursion.
Now if you substitute the rope by a very thin sheet metal ribbon and let the counterweight go over the full width of the slider and IF-IF-IF you find a region on the circular air bearing cylindrical enough to keep radius (and TF with it) really constant, then you could let this metal ribbon run over this region and maybe the dangling of the counterweight in lateral direction is below the threshold of interference with sonics.
Creating a TF momentum by a rope pulling from a vertical pulley face and pulled down by a weight independently of the tonearm wand will need deflecting the rope/thread by pulleys and those pulley's bearing torques then add to the vertical gymbal's bearing torque. As vertical bearing torques must be minimized as far as even possible (or the treble resolution goes down the toilet), this is a no-go to me.
To me, it is adjustable counterweight on a beam, for simplicity's sake and aforementioned reasons.
Regards,
Bernhard
.... stopped posting long ago, on any forum
Dear audiostar,
I have come to the insight that the internet in general and forums in partricular is an anarchistic structure. To me, it is an uncomfortable place.
My post 2 months ago was about the 1st posting on any forum since i left diyAudio.com more than 10 years ago. During my stay @ diyAudio.com (as contributing member as well as as moderator), i had to learn that few members contribute knowledge.
In my post 2 months ago, i said that i have abandoned designing passive linear trackers; has been quite some years since i did. I did it for described reason and when discussing my insights in private with people interested in tonearms, i basically ran into either of two prototypical opinions (very strong opinions, quasi-religious true-believer opinions):
Let me give you an example: i observed that very few people know what to listen for when adjusting VTA. It is ignored that VTA adjustment deals with ambulant if not transient events: an opera singer hitting that hight note at full volume or a double bass plucked and you have to decide if the low or high frequency component of that sound arrives at you first and how much substance and depth the low sound has, Needed adjustment precision is at 0.02mm of tonearm pivot height at a tonearm length of 230mm. And if you tinker and then listen and then tinker and then listen, you may find the sweet spot where the plucked bass note hits you as a whole or where imaging-wise, the opera singer's mouth size stays constant independent of pitch and volume (BTW, this a THD-minimizing strategy).
But instead of having interesting learning experiences about what else to possibly listen for VTA adjustment or how to realize the needed precision on a tonearm of choice, I find myself dragged into discussions whether VTA adjustment has any worth or, worse, into discussions about secondary warplaces like how fervently needed remote-controlled VTA-adjustment-on-the-fly is.
Just see above: VTA events are almost transient and if the adjuster adjusts on-the-fly, he will find himself on a wild goose chase, never coming close to the sweet spot. And finally join the ignorant crowd fervently claiming that VTA makes no difference.
To be honest, I find it fruitless to be part of such discussions.
What I want to read: how do others optimize their stuff. Strategy, circuits, components, what to listen for.
What I do NOT want to read: extended reasoning why something cannot work. I have no use for nay-sayers or spoil-sports. But forums are full of them. No wonder I stopped posting.
--------------
Greets,
Bernhard
-------------
P.S.
Last week, i visited an audio buddy, a wealthy guy who travels a lot and gets to try out many things. We discussed tonearms and he enthusingly told me about a pivoted tonearm (a Reid if i remember correctly) where you can adjust about anything on-the-fly and he reported how amazingly everything sonically changed when one of the adjustment screws was turned. I then asked him whether he got anywhere in improving the overall sonics of the arm. He admitted he got lost. I then inquired about VTA-adjustment and what he heard and how this particularly improved. He muttered something about changes not always being improvements and then i told him what i described in the example above: what to listen for and required resolution being better than 0.02mm in pivot height. Answer: an unbelieving face expression . Had been an entertaining wild goose chase for him.
Dear audiostar,
I have come to the insight that the internet in general and forums in partricular is an anarchistic structure. To me, it is an uncomfortable place.
My post 2 months ago was about the 1st posting on any forum since i left diyAudio.com more than 10 years ago. During my stay @ diyAudio.com (as contributing member as well as as moderator), i had to learn that few members contribute knowledge.
In my post 2 months ago, i said that i have abandoned designing passive linear trackers; has been quite some years since i did. I did it for described reason and when discussing my insights in private with people interested in tonearms, i basically ran into either of two prototypical opinions (very strong opinions, quasi-religious true-believer opinions):
- linear trackers cannot work and are a waste of time and effort
- linear trackers are the only possible solution to the task and do everything right
Let me give you an example: i observed that very few people know what to listen for when adjusting VTA. It is ignored that VTA adjustment deals with ambulant if not transient events: an opera singer hitting that hight note at full volume or a double bass plucked and you have to decide if the low or high frequency component of that sound arrives at you first and how much substance and depth the low sound has, Needed adjustment precision is at 0.02mm of tonearm pivot height at a tonearm length of 230mm. And if you tinker and then listen and then tinker and then listen, you may find the sweet spot where the plucked bass note hits you as a whole or where imaging-wise, the opera singer's mouth size stays constant independent of pitch and volume (BTW, this a THD-minimizing strategy).
But instead of having interesting learning experiences about what else to possibly listen for VTA adjustment or how to realize the needed precision on a tonearm of choice, I find myself dragged into discussions whether VTA adjustment has any worth or, worse, into discussions about secondary warplaces like how fervently needed remote-controlled VTA-adjustment-on-the-fly is.
Just see above: VTA events are almost transient and if the adjuster adjusts on-the-fly, he will find himself on a wild goose chase, never coming close to the sweet spot. And finally join the ignorant crowd fervently claiming that VTA makes no difference.
To be honest, I find it fruitless to be part of such discussions.
What I want to read: how do others optimize their stuff. Strategy, circuits, components, what to listen for.
What I do NOT want to read: extended reasoning why something cannot work. I have no use for nay-sayers or spoil-sports. But forums are full of them. No wonder I stopped posting.
--------------
Greets,
Bernhard
-------------
P.S.
Last week, i visited an audio buddy, a wealthy guy who travels a lot and gets to try out many things. We discussed tonearms and he enthusingly told me about a pivoted tonearm (a Reid if i remember correctly) where you can adjust about anything on-the-fly and he reported how amazingly everything sonically changed when one of the adjustment screws was turned. I then asked him whether he got anywhere in improving the overall sonics of the arm. He admitted he got lost. I then inquired about VTA-adjustment and what he heard and how this particularly improved. He muttered something about changes not always being improvements and then i told him what i described in the example above: what to listen for and required resolution being better than 0.02mm in pivot height. Answer:
an unbelieving face expression . Had been an entertaining wild goose chase for him.dice45,
Haters are going to hate and lovers are going to love. So when I posted on a certain forum about a dac that I wanted guys to know, all I got was hate. I got rude, abrasive, and sarcastic comments. A total turnoff. It seems that a forum brings out the worst in people. But you have to know that sticks and stones may break my bones but words cannot hurt me. I don't let it bother me.
Man is a social animal not a recluse. Hi Fi is about sharing. It is fun to invite your friends over for a listen. And you to listen to your friend's Hi Fi. You got a great Hi Fi project of course you want to post it on the forum. You want people to know what you have created. Yeah, some people are to going to say ugly things about your projects and ideas about what Hi Fi should be. Ignore the hate. But what if they are right! You can never stop learning. You can't stay in your house forever and not interact with others. Man has a need to communicate. When you feed a dog, he may bite your hand. When you post in a forum somebody is going to bite your hand. So be it, that is life. Do not run away from it. I f you love Hi Fi and you know more about it than I then you got to post about Hi FI. See you around here Bernhard.
Haters are going to hate and lovers are going to love. So when I posted on a certain forum about a dac that I wanted guys to know, all I got was hate. I got rude, abrasive, and sarcastic comments. A total turnoff. It seems that a forum brings out the worst in people. But you have to know that sticks and stones may break my bones but words cannot hurt me. I don't let it bother me.
Man is a social animal not a recluse. Hi Fi is about sharing. It is fun to invite your friends over for a listen. And you to listen to your friend's Hi Fi. You got a great Hi Fi project of course you want to post it on the forum. You want people to know what you have created. Yeah, some people are to going to say ugly things about your projects and ideas about what Hi Fi should be. Ignore the hate. But what if they are right! You can never stop learning. You can't stay in your house forever and not interact with others. Man has a need to communicate. When you feed a dog, he may bite your hand. When you post in a forum somebody is going to bite your hand. So be it, that is life. Do not run away from it. I f you love Hi Fi and you know more about it than I then you got to post about Hi FI. See you around here Bernhard.
In your experiment, there is no damping. How about adding damping? Is the result still same? In my experiment, a pivot arm without anti-skating force displays greater skating force (a force toward to center of the record) than a air bearing linear tracking arm although lateral stylus force is the only force to move the heavy mass, i.e. air bearing.
I would love to see your active linear tracking arm. Do you mind posting your active arm here?
Last edited:
The matter of force on the stylus was one of the reasons for the design of our passive linear tracker (see my thread on DIY tonearms) The vertical elements exert a force downwards which pushes the cartridge across the record. The balance weight counteracts as much of the force as we choose. The whole thing is extremely free moving and you can see that the stylus stays dead centred whilst playing.
So, I reckon passive linear trackers can work. Our does nicely
So, I reckon passive linear trackers can work. Our does nicely
lateral force experiment
Hello all,
no, there was no damping in my experiment, but the bearing gap was SUPER tight (4µm) so possible overshoot amplitude was very limited. I cannot say how it would have worked with added damping as the result was utterly disappointing to me and i ripped it apart after the test without even documenting it, having no digicam available at that time.
Just let me add that i took care that the air bearing was really level, measured with a precision bubble level gauge (resolution 0.01mm/m per scale division), so no lateral force component from the air bearing trying to run downhill.
Damping: <tale-telling mode on>
Back when i was at the university, i earned money by adjusting tonearms/cartridges by ear. Many. From that experience, I have learned to distrust tonearm-cartridge combinations which need damping, even if it is only lateral. Sounded dull and lifeless in allmost all cases. (In)famous exception: the Elite Rock with its curved damping trough in front of the headshell path. Any tonearm on it sounded decent. Not good, no high resolution, but decent. Later, on a buddy's Elite Rock i tried out an SAEC arm and some Jelco-lookalike arm; both arms had damaged gymbal bearings. They too sounded decent. Obviously the damping was masking untoward and nasty things. So: i do not want to spoil your fun, use damping as much as you enjoy. But for me: No, thank you. if it turns out i need tonearm damping, i wonder what is wrong in the match. Or in one of the components.
<tale-telling mode off>
A pivoted arm without skating compensation has higher lateral forces, this is out of question. But the lateral forces on the air bearing rig's stylus/cantilever was still about 5 times higher that those on a pivoted arm with skating compensation perfectly adjusted by ear. And that was on a record with a perfectly centered groove pattern. With an off-center record, lateral forces got out of hand.
Considering the effort/cost/hassle entailed with an airborne tonearm, static and dynamic lateral stylus forces are still too high. The main to get the lateral stylus forces as close to zero as possible is only partially met. Under perfect boundary conditions.
I have to agree that with an air bearing, the forces to get the slider assemby into motion i.e. to break the bearing loose from rest are practically zero. However, there still is work to be done to translate the slider laterally, and as the groove pitch in on LP is constantly varying, there are accelerating and decelerating forces which definitely are small but not zero. On off-center records, accelerating and decelerating forces are not small at all. What makes the latter more spicy: about 1/3 of my records are off-center and usually A-side's and B-side's excentricity differ (Think about the record press' hinge having play).
On my Shreve-Rabco, lateral stylus forces (and bearing torque) are close to zero, far more that with any other tonearm i had the occasion to try out. This arm lets the cartridge project an undistorted holographic
(acoustic) image into my listening room.
For my own design, I have settled on a classical linear tracking layout with the rail following a straight line at about 190mm distance from the platter spindle center, positioned behind the platter, not right beneath it. That means the arm assembly has to be translated over 135mm for a shellac record. A lot of work to do. I decided to let a servo motor do that work.
For a pivoted tangential tracking tonearm the needed excursion is rather ar 35mm, be it on a rotating subarm on on a linear sled -> less work needed. Would i try my hand at designing such an arm, rather that following Frank Schröder's LT path, I would go with StraightTracker's layout as he uses a servo motor to do the work 
.
Currenty i do not want to post much about my linear tracker as my design is a construction site all over. I abandoned a dual pivot bearing for the vertical movement due to lacking geometric/angular precision and went back to ball bearings. And I abandoned the rail's linear guide due to play / lacking mechanical precision, opted for a miniature linear ball bearing. And, i ran out of space for my tonearm lift and had to increase the tonearm wand lenght (which has impact on many components). And i want to get many subassemblies simpler than they are today to get the manufacturing effort down.
I have a few requirements which add to the challenge:
* tonearm assembly has to swappable in a minute in order to choose the cartridge suiting the needs: shellac records, pre1956 vinyl, mono, opera, different music etc.
* all geometry parameters have to be independently adjustable, measurable, reproducable. With adequate resolution. With ease, to lower the pain threshold.
* Interfaces between cartridge, tonearm wand and gymbal assy are precisely specified: seeking out a tonearm wand with its sonic footprint matching the cartridge is feasible and one can skip going thru the complete adjustment-by-ear procedure again.
But much more important: i do not post unfinished work. Made that mistake in the past, won't repeat it. If i have something ready and real pictures of it, not fancy CAD pixes, i may decide to post it.
Hello all,
no, there was no damping in my experiment, but the bearing gap was SUPER tight (4µm) so possible overshoot amplitude was very limited. I cannot say how it would have worked with added damping as the result was utterly disappointing to me and i ripped it apart after the test without even documenting it, having no digicam available at that time.
Just let me add that i took care that the air bearing was really level, measured with a precision bubble level gauge (resolution 0.01mm/m per scale division), so no lateral force component from the air bearing trying to run downhill.
Damping: <tale-telling mode on>
Back when i was at the university, i earned money by adjusting tonearms/cartridges by ear. Many. From that experience, I have learned to distrust tonearm-cartridge combinations which need damping, even if it is only lateral. Sounded dull and lifeless in allmost all cases. (In)famous exception: the Elite Rock with its curved damping trough in front of the headshell path. Any tonearm on it sounded decent. Not good, no high resolution, but decent. Later, on a buddy's Elite Rock i tried out an SAEC arm and some Jelco-lookalike arm; both arms had damaged gymbal bearings. They too sounded decent. Obviously the damping was masking untoward and nasty things. So: i do not want to spoil your fun, use damping as much as you enjoy. But for me: No, thank you. if it turns out i need tonearm damping, i wonder what is wrong in the match. Or in one of the components.
<tale-telling mode off>
A pivoted arm without skating compensation has higher lateral forces, this is out of question. But the lateral forces on the air bearing rig's stylus/cantilever was still about 5 times higher that those on a pivoted arm with skating compensation perfectly adjusted by ear. And that was on a record with a perfectly centered groove pattern. With an off-center record, lateral forces got out of hand.
Considering the effort/cost/hassle entailed with an airborne tonearm, static and dynamic lateral stylus forces are still too high. The main to get the lateral stylus forces as close to zero as possible is only partially met. Under perfect boundary conditions.
I have to agree that with an air bearing, the forces to get the slider assemby into motion i.e. to break the bearing loose from rest are practically zero. However, there still is work to be done to translate the slider laterally, and as the groove pitch in on LP is constantly varying, there are accelerating and decelerating forces which definitely are small but not zero. On off-center records, accelerating and decelerating forces are not small at all. What makes the latter more spicy: about 1/3 of my records are off-center and usually A-side's and B-side's excentricity differ (Think about the record press' hinge having play).
On my Shreve-Rabco, lateral stylus forces (and bearing torque) are close to zero, far more that with any other tonearm i had the occasion to try out. This arm lets the cartridge project an undistorted holographic
(acoustic) image into my listening room.
For my own design, I have settled on a classical linear tracking layout with the rail following a straight line at about 190mm distance from the platter spindle center, positioned behind the platter, not right beneath it. That means the arm assembly has to be translated over 135mm for a shellac record. A lot of work to do. I decided to let a servo motor do that work.
For a pivoted tangential tracking tonearm the needed excursion is rather ar 35mm, be it on a rotating subarm on on a linear sled -> less work needed. Would i try my hand at designing such an arm, rather that following Frank Schröder's LT path, I would go with StraightTracker's layout as he uses a servo motor to do the work
.Currenty i do not want to post much about my linear tracker as my design is a construction site all over. I abandoned a dual pivot bearing for the vertical movement due to lacking geometric/angular precision and went back to ball bearings. And I abandoned the rail's linear guide due to play / lacking mechanical precision, opted for a miniature linear ball bearing. And, i ran out of space for my tonearm lift and had to increase the tonearm wand lenght (which has impact on many components). And i want to get many subassemblies simpler than they are today to get the manufacturing effort down.
I have a few requirements which add to the challenge:
* tonearm assembly has to swappable in a minute in order to choose the cartridge suiting the needs: shellac records, pre1956 vinyl, mono, opera, different music etc.
* all geometry parameters have to be independently adjustable, measurable, reproducable. With adequate resolution. With ease, to lower the pain threshold.
* Interfaces between cartridge, tonearm wand and gymbal assy are precisely specified: seeking out a tonearm wand with its sonic footprint matching the cartridge is feasible and one can skip going thru the complete adjustment-by-ear procedure again.
But much more important: i do not post unfinished work. Made that mistake in the past, won't repeat it. If i have something ready and real pictures of it, not fancy CAD pixes, i may decide to post it.
I came to a similar conclusion about the absence of lateral forces in active position controlled linear tracker designs 39 years ago. I authored a viscous damped unipivot diy retrofit of the Rabco SL8E in the 3/76 issue of “The Audio Amateur” magazine, now no longer published. I serendipitously meandered into that project while trying to get an original ADC-XLM (the mega high compliance version) mounted in a Decca International arm to track through a cymbal crash of ‘The Perfect Song’, Lincoln Mayorga & Distinguished Colleagues Volume 3 Sheffield SL5/SL6 Side 1, without skipping. No matter what combination of VTF and anti-skate I tried, it would not play through that spot without literally jumping the groove. When installed in my modded SL8E, it not only negotiated that cut without skipping, it SAILED through effortlessly, clean and crisp at the XLM’s specified 0.6g VTF. I observed that the modded arm exhibited exceptional stability in negotiating dynamic disturbances, such as pinch warps, footfalls, etc. It is basically the same design concept as the Decca International with somewhat lower but comparable mass, so the dramatic difference in performance would be attributable to something other than the usual mass/compliance issues.
I’ve concluded over the years that the main advantage of what I call true ‘linear’ trackers (which are a special sub-category of ‘tangential’ trackers that include multiple linkage types) is that the drag force vector on the stylus is in the same plane as the pivot. With conventional offset pivoted arms the drag force vector does not line up with the pivot, and acts on some moment arm (a consequence of the offset angle) which resolves into a skating force component. Papers published in the JAES (how many posters ever bother to read and study any of those?) have shown that stylus drag, and consequently skating force, varies with groove modulation. Thus, groove modulation transients can introduce horizontal dynamic forces and instability in conventional offset pivoted arms, whereas true ‘linear’ trackers are inherently less susceptible to dynamic variations in stylus drag.
True ‘linear’ trackers can be passive mechanical/air bearing, or active (servo-driven). I’ve seen a lot of anti-servo sentiment displayed on several audio websites. I’ve encountered blowback after posting key points in favor of servo linear trackers. Most readers automatically assumed I was talking about passive designs. I don’t understand the anti-servo sentiment, because I have found that making an active servo function properly is FAR easier than dealing with anti-skating issues. My original SL8E mod has undergone 2 significant improvements in the intervening years. First, it now has a 2 stage cueing linkage that limits the cueing height to about ¼ inch. Second, and most beneficial, an optoelectronic circuit that drives the carriage motor continuously in a variable speed mode, eliminating the troublesome OEM cat whisker contact on/off control. I have enjoyed using my modified arm for all these years as I read post after post of user frustrations with anti-skate settings, Lofgren/Baerwald/Beethoven alignment wars, sticky bearings, noisy air pumps, and causes of end-of-record IGD.
I am very much looking forward to see your new linear tracker!
I just bought a Rabco SL-8E off ebay and start to study its documents over the internet. I don’t have actual arm yet. But I looked the mechanism of the arm. Its construction isn’t dated. Its transit mechanism, its sensor system and its bearing are all needed to be updated. So, my question is why I need an original arm at first place and why I don’t build a complete new one.
Here is the seller's description:
Rabco tonearm off of a Thorens TD 124. No rust or corrosion. Just out of storage by original owner. Item was functional and battery removed prior to storage 20+ years ago.
I tried it tonight after a few minutes still powers up raises and lowers and appears to track slowly in one direction down the chain/ track. Needs to be serviced. I don't have a cartridge to test it fully.
Here is the seller's description:
Rabco tonearm off of a Thorens TD 124. No rust or corrosion. Just out of storage by original owner. Item was functional and battery removed prior to storage 20+ years ago.
I tried it tonight after a few minutes still powers up raises and lowers and appears to track slowly in one direction down the chain/ track. Needs to be serviced. I don't have a cartridge to test it fully.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.