Birch birth?
After all the math and alphabet soup, that's also the conclusion I drew: yes, there's skating force but not enough to affect actual usage or to necessitate an anti-skating device, at least in the 6B arm. If one were to install anti-skating, it would be easier and more linear to employ. A Birch style arm certainly has much less skating force than conventional overhung pivot arm and perhaps it's enough to spawn a new era of the genre. Now, if bearing friction (and mass) continues to be reduced, will skating force affect cantilever deflection? I don't know. I look forward to your listening test.... and perhaps another version of 6B or 6C, etc...
People seem to complain a Birch arm has too many bearings. I want to point out that you are really adding ONE extra horizontal bearing that holds majority of the mass, the rest of the bearings are part of the guiding mechanism that's negligibly low mass and low friction. Just think of the Dynavector arm with an extra horizontal pivot.
After all the math and alphabet soup, that's also the conclusion I drew: yes, there's skating force but not enough to affect actual usage or to necessitate an anti-skating device, at least in the 6B arm. If one were to install anti-skating, it would be easier and more linear to employ. A Birch style arm certainly has much less skating force than conventional overhung pivot arm and perhaps it's enough to spawn a new era of the genre. Now, if bearing friction (and mass) continues to be reduced, will skating force affect cantilever deflection? I don't know. I look forward to your listening test.... and perhaps another version of 6B or 6C, etc...
People seem to complain a Birch arm has too many bearings. I want to point out that you are really adding ONE extra horizontal bearing that holds majority of the mass, the rest of the bearings are part of the guiding mechanism that's negligibly low mass and low friction. Just think of the Dynavector arm with an extra horizontal pivot.
Skate force is as real as in a traditional arm which has mass and friction.
Yous usage of physical concepts is a little weird. A force cannot be dampened, mass cannot be heavy and you cannot reduce inertia with a silicone trough.
Hi super10018,
is it possible to print the wand "around" the carbon fiber tube?
sincerely,
Ralf
I have not been following the Tuthill/Reed 5A pivot configuration. My considerations are usually based on a perfect tangential tracking geometry which takes the pivot arrangement out of the picture. That way, the conclusions should be applicable to all passive tangential tracking tonearms regardless of the physical length or pivot configuration.
Previously my skating torque calculations for tangential tracking tonearms with various pivoting configurations, have consistently arrived at the same formula, sometimes via tedious resolving of pivot forces induced by stylus drag. The identification of the instantaneous centre of rotation (IC) now makes the reason for this obvious.
In the attached diagram, the tangential stylus drag vector (bold orange) generates a clockwise torque of the tonearm about the IC, proportional to the radial distance from stylus to spindle. This is independent of the pivoting configuration. The skating torque is present regardless of the pivot arrangements.
For a nominal outer groove radius b = 14.605 cm and inner groove radius a = 5.75 cm, the skating torque decreases linearly from 100% to 39.37%.
Attachments
The ball point pen pivot is beyond my expectation. I am so confident that I even added more weight in the arm wand as I mentioned above in spite of my 6B is on heavy side already.
With my limited knowledge in 3D printing, I would say no. You can't.
Rotary 3D Printing | H-Series Machine
3D-Rotoprinter: What Is It? | All3DP
Not a very mature technology.
3D-Rotoprinter: What Is It? | All3DP
Not a very mature technology.
Based on #234, the lateral effective mass is much bigger than that of a comparable trad. tonearm. So the lateral resonant frequency cannot be the same as or close to vertical resonant frequency.
My expectation is based on my experience of building air-bearing linear arm. For linear arms, some people criticized that the lateral effective mass of a linear arm is not the same as its vertical effective mass. However, I don’t dispute the such statement, in stead I tested the resonant frequencies of my air-bearing arms because all I care about is the resonant frequencies. My air-bearing arm has 98 grams lateral effective mass. The lateral resonant frequency and vertical resonant frequency are the same for my air-bearing arm, 5 Hz. If the resonant frequencies are the same, I don’t see the reason to worry about the difference of effective masses.
For Birch style arms, such as my 6B, I don’t want to argue if its resonant frequencies are the same or close without measuring it in reality. It is merely my expectation. An expectation can be correct or wrong.
It is the same situation here for my 6B arm. All the calculations and simulations point out that my 6B does skate. But in the meantime, my 6B proudly refuses to skate. I don’t dispute that the skating force does EXIST in my 6B. But I dispute the statement that my 6B skates. If there is a conflict between theory and reality, you need to go back to check if your theory is correct, or if your assumptions represent the reality correctly. You can’t force to change the narrative about reality because your calculation and simulation indicate other wise.
Last edited:
That is very interesting. But I don't know how strong is the joint between the printing filament and carbon fiber tube. In stead, I think continue carbon fiber printing can be very promising.
Last edited:
Hi super10018.
I have been checking the passive tangential tracking geometry as the physical length is varied. To be clear, I am referring to a tangential tracking geometry, not an approximate one. As the Thales circle diameter increases there will be a penalty due to increased moment of inertia. With increased length also comes increased positional sensitivity. Any small errors in the rear pivots are amplified at the stylus.
On the converse, as the tonearm length decreases, so will the Thales circle diameter and the positional sensitivity decreases. Taking into account the inertial benefit, there is an advantage to choosing the shortest convenient length to achieve a vernier type of effect due to the pivoting structure. There is a practical limit to how short because the stylus has to reach the inner groove.
I anticipate that there will be arguments that higher sensitivity is good … smaller pivot motions to achieve stylus position.
I don’t agree if accuracy is the target. There are consequences to high gain.
I have settled on a compromise of total length equal to the Thales circle diameter as in my diagram #206. A consequence of shorter tonearms is that depending on the configuration, the pivoting structure may overhang the LP surface. I am not bothered by this, but some implementations might be affected. Your tonearms seem quite compact though, so my analysis
may not accurately reflect the approximately tangential geometry.
As Straight Tracker (#217) has pointed out, we mostly are obsessive about perfection in this thread. I accept that badge and restrict my investigations to exclusively what I consider to be perfect passive tangential tracking geometry. For me, discussions of approximate tangential geometry quickly gets bogged down in the minutiae of the particular implementation.
Regards
Bon
Bon,
If I understand it correctly, the arm you are talking about in #245 is on paper only. It is not doable because I don't see a guiding mechanism. For a Birch style arm, there are at least two links as my 6B. So, it is hard to discuss the pros and cons of the arm which is not doable. Once you have a geometry and it can be implemented, I will be glad to express my opinions.
Jim
If I understand it correctly, the arm you are talking about in #245 is on paper only. It is not doable because I don't see a guiding mechanism. For a Birch style arm, there are at least two links as my 6B. So, it is hard to discuss the pros and cons of the arm which is not doable. Once you have a geometry and it can be implemented, I will be glad to express my opinions.
Jim
Additional comments about resonant frequency.
Let's assume that the lateral resonant frequency and vertical resonant frequency are different for my 6B tonearm. Its lateral resonant frequency is 1 Hz and its vertical resonant frequency is 15 Hz. It is a big difference from 1 Hz to 15 Hz. I still don't see any problem whatsoever as long as both of the frequencies are under 20 Hz, ideally under 15 Hz.
Thanks for trying. I think the paper piece on headshell should also work; to see bearing friction while we wait for more precise measurements. Also same with LD surface to see if tonearm is skating or not. If anyone has PLT tonearm and LD disk can post video. (With cheap cartridge so as not to damage it, even one with broken stylus should work). Naturally the actual record will have more skating than LD disc. The Kogen article which shows simple skating identifying device should also give reasonable judgement. Very easy to make. In that device moving the device's pivot further away from the headshell would give more errorfree output.
regards.
regards.
In the case of my 6B, the most accuracy way to see if the arm is balanced horizontally is to suspend the arm in the air and to see if the arm moves to side. If not, my tonearm is balanced. I have done that.
The finish of surface won't alter the outcome of skating test. However, I still gave it a try with a piece of plastic. The surface finish of the plastic piece is very close to the surface finish of a LD disk. There is no difference whatsoever.
There are many factors to cause skating. But the dominant factor is the geometry of a tonearm. The purpose of the skating test here is to see if the arm skates due to its geometry. Therefore, I may not need the device used by Kogen. In fact, a blank disc is even better because I can separate other factors and concentrate on the dominant factor.
The finish of surface won't alter the outcome of skating test. However, I still gave it a try with a piece of plastic. The surface finish of the plastic piece is very close to the surface finish of a LD disk. There is no difference whatsoever.
There are many factors to cause skating. But the dominant factor is the geometry of a tonearm. The purpose of the skating test here is to see if the arm skates due to its geometry. Therefore, I may not need the device used by Kogen. In fact, a blank disc is even better because I can separate other factors and concentrate on the dominant factor.
I finally had a listen to my 6B.
The cartridge I used is Ortofon A90, a medium compliance one. I was very impressed by the bass performance of 6B tonearm. A90 is not a bass-heavy cartridge, but on the 6B, its bass is fully competent with the same cartridge on my air-bearing tonearm. I feel it may be slightly better than it on my air-bearing tonearm. High frequency and mid-range sound natural and smooth although the detail can be improved. However, A90 is not a very detailed cartridge. All Ortofon cartridges are kind of “boring” without special sonic characteristics except their top-of-the-line, Anna. Natural sounding is the outcome of lacking tracking errors and skating.
The background is quiet. It is far better than regular pivot arms. It further got improved once I added silicone fluid. I used 40 CST silicone fluid. Please see the photo. I understand that silicone fluid mainly damps the peak of the resonant frequency. It also reduces inertia and other unwanted movements so the background seems to get quieter once I added silicone fluid. But my air-bearing tonearm is still the king of the darkness.
I made a template to align the cartridge. Please see the photo. It is very easy to align the cartridge on my 6B.
I also found that horizontal balance is very important to the sound as well. It is probably never enough to emphasize how important it is for Birch style arms. Horizontal balance is critical to eliminate side forces. The horizontal balance must be achieved across the surface of the record to have an open and balanced sound. When I adjust the balance, I am not compensating or canceling a side force. I am getting close to the perfect leveling for a particular arm. An effective and easy operating level adjusting mechanism is a must for all Birch-style arms.
Here are two videos to show the stylus movement. These videos may not mean too much since there is very little eccentricity.
stylus movements 1 - YouTube
stylus movements 2 - YouTube
This video shows you there is no distortion at the end of the groove.
inner groove - YouTube
The journal to build my 6B is a learning process for me. First, I learned a lot about Birch-style geometry. Secondly, it was a surprise to me that the tonearm doesn’t skate. This alone enforces my confidence about PT arm greatly. Last, it helps me to realize how important horizontal balance is for Birch stylus arms. The total cost of my 6B is about $400. It is worth the money spent to achieve such sonic performance. It is funny to me that people are still trying to eyeball two null points, and all they get are inner groove and skating distortions.
I may do more tests in the future.
The cartridge I used is Ortofon A90, a medium compliance one. I was very impressed by the bass performance of 6B tonearm. A90 is not a bass-heavy cartridge, but on the 6B, its bass is fully competent with the same cartridge on my air-bearing tonearm. I feel it may be slightly better than it on my air-bearing tonearm. High frequency and mid-range sound natural and smooth although the detail can be improved. However, A90 is not a very detailed cartridge. All Ortofon cartridges are kind of “boring” without special sonic characteristics except their top-of-the-line, Anna. Natural sounding is the outcome of lacking tracking errors and skating.
The background is quiet. It is far better than regular pivot arms. It further got improved once I added silicone fluid. I used 40 CST silicone fluid. Please see the photo. I understand that silicone fluid mainly damps the peak of the resonant frequency. It also reduces inertia and other unwanted movements so the background seems to get quieter once I added silicone fluid. But my air-bearing tonearm is still the king of the darkness.
I made a template to align the cartridge. Please see the photo. It is very easy to align the cartridge on my 6B.
I also found that horizontal balance is very important to the sound as well. It is probably never enough to emphasize how important it is for Birch style arms. Horizontal balance is critical to eliminate side forces. The horizontal balance must be achieved across the surface of the record to have an open and balanced sound. When I adjust the balance, I am not compensating or canceling a side force. I am getting close to the perfect leveling for a particular arm. An effective and easy operating level adjusting mechanism is a must for all Birch-style arms.
Here are two videos to show the stylus movement. These videos may not mean too much since there is very little eccentricity.
stylus movements 1 - YouTube
stylus movements 2 - YouTube
This video shows you there is no distortion at the end of the groove.
inner groove - YouTube
The journal to build my 6B is a learning process for me. First, I learned a lot about Birch-style geometry. Secondly, it was a surprise to me that the tonearm doesn’t skate. This alone enforces my confidence about PT arm greatly. Last, it helps me to realize how important horizontal balance is for Birch stylus arms. The total cost of my 6B is about $400. It is worth the money spent to achieve such sonic performance. It is funny to me that people are still trying to eyeball two null points, and all they get are inner groove and skating distortions.
I may do more tests in the future.
Attachments
Last edited:
Thanks for building the PLT and sharing. I enjoyed the build process/reading/comments. Thanks for listening impression too. 
----------------------------------------------
Parallel alignment with platter :
I am not posting with confidence but I thought with multiple bearings the horizontal balance would need to be looked at differently as resistance would be greater. Secondly we have three plane to balance. The tonearm base + the linkeages which move horizontally + tonearm which moves horizontally. So if the base is perfectly balanced and tonearm is also balanced the linkages assembly if not perfectly horizontal/balanced (And which will be difficult to adjust with bubble level) would probably give a little different balance at different positions.
----------------------------------------------
Friction :
It is natural that the horizontal friction would be more than typical tonearm. But it would be nice to compare. I suppose 2wice tonearm will have comparatively less friction. If both designs does not have much friction and effective mass within limit compared to the friction it posses, what we would have is a very very well made tonearm.
Regards
----------------------------------------------
Parallel alignment with platter :
I am not posting with confidence but I thought with multiple bearings the horizontal balance would need to be looked at differently as resistance would be greater. Secondly we have three plane to balance. The tonearm base + the linkeages which move horizontally + tonearm which moves horizontally. So if the base is perfectly balanced and tonearm is also balanced the linkages assembly if not perfectly horizontal/balanced (And which will be difficult to adjust with bubble level) would probably give a little different balance at different positions.
----------------------------------------------
Friction :
It is natural that the horizontal friction would be more than typical tonearm. But it would be nice to compare. I suppose 2wice tonearm will have comparatively less friction. If both designs does not have much friction and effective mass within limit compared to the friction it posses, what we would have is a very very well made tonearm.
Regards