Originally Posted by diyrayk
Mass issues aside, a low compliance cartridge will show less sideways deflection of the cantilever, but that does not mean the problem went away. Even if you no longer see the effects on the cantilever, the sideways forces are still there and rob effective VTF from one groove wall or the other depending on which direction the eccentricity is going.
Ray K
True
Mass issues aside, a low compliance cartridge will show less sideways deflection of the cantilever, but that does not mean the problem went away. Even if you no longer see the effects on the cantilever, the sideways forces are still there and rob effective VTF from one groove wall or the other depending on which direction the eccentricity is going.
Ray K
True
I heard a rumour that you can (suspension allowing) use a little more tracking force with a short LT as there is less inertia in the vertical plane.
Is this true? If so, wouldn't his go some way to keeping the stylus planted centrally in the groove assuming low friction / lightweight sled?
This though goes against the 'heavy sled better' theory I read further back in the thread as that would introduce greater horizontal inertia and the stylus of a low compliance cartridge would be fighting that, and ending up again in the situation described by diyrayk.
For info, I use a DL103, which sounds better in this arm than it has done in any conventional arm I've used.
Is this true? If so, wouldn't his go some way to keeping the stylus planted centrally in the groove assuming low friction / lightweight sled?
This though goes against the 'heavy sled better' theory I read further back in the thread as that would introduce greater horizontal inertia and the stylus of a low compliance cartridge would be fighting that, and ending up again in the situation described by diyrayk.
For info, I use a DL103, which sounds better in this arm than it has done in any conventional arm I've used.
"Mass issues aside, a low compliance cartridge will show less sideways deflection of the cantilever, but that does not mean the problem went away. Even if you no longer see the effects on the cantilever, the sideways forces are still there and rob effective VTF from one groove wall or the other depending on which direction the eccentricity is going."
Hi Ray,
I think that we can agree that the sideways force due to bearing friction will cause the cantilever to be deflected resulting in both a lateral tracking error of the stylus in the groove and a misalignment of the cartridge's generator. Both of these will/can have a negative impact on sound quality.
Using a low compliance cartridge will not eliminate the problem but will reduce it. A cartridge with half the compliance will have half the lateral tracking error/misalignment for the same side force. Similarly reducing bearing friction will reduce the sideways force in the same way, the errors being proportional to the product of the compliance and sideways forces.
Yes the sideways force will result in the VTF being different for the two groove walls. BUT the total VTF, the sum of left and right, will be the same so VTA itself will not be effected. As long as the stylus remains in contact with the groove wall the difference in VTF doesn't matter. If the stylus remains in contact with the groove walls then it will follow exactly the same path which will mean that the relative movement of the coils in the magnetic gap (mc cartridge) will also be the same. The output of the cartridge is only dependant on this movement so there should be no effect on sound quality.
Niffy
Hi Ray,
I think that we can agree that the sideways force due to bearing friction will cause the cantilever to be deflected resulting in both a lateral tracking error of the stylus in the groove and a misalignment of the cartridge's generator. Both of these will/can have a negative impact on sound quality.
Using a low compliance cartridge will not eliminate the problem but will reduce it. A cartridge with half the compliance will have half the lateral tracking error/misalignment for the same side force. Similarly reducing bearing friction will reduce the sideways force in the same way, the errors being proportional to the product of the compliance and sideways forces.
Yes the sideways force will result in the VTF being different for the two groove walls. BUT the total VTF, the sum of left and right, will be the same so VTA itself will not be effected. As long as the stylus remains in contact with the groove wall the difference in VTF doesn't matter. If the stylus remains in contact with the groove walls then it will follow exactly the same path which will mean that the relative movement of the coils in the magnetic gap (mc cartridge) will also be the same. The output of the cartridge is only dependant on this movement so there should be no effect on sound quality.
Niffy
The vertical inertia (effective mass) can be designed to be whatever you want regardless of arm type. There is no reason that a short arm should have a low vertical effective mass.
If you increase tracking force you will change the vertical tracking angle introducing an error. Increasing tracking force can be useful if you are suffering tracking problems due to excessive bearing friction. It is much better to sort out the bearings problems than increasing tracking force.
Increasing carriage mass will increase its inertia and result in the cartridge body moving less due to groove modulation, a good thing. Increasing cartridge mass will also cause bearing friction to increase. This will result in greater lateral tracking error, a bad thing. The ideal carriage mass will be a compromise between the two.
Your cartridge is very low compliance so would be more suited to a heavier carriage.
Niffy
When I was a kid we had a portable record player that had a Voice of Music changer just like this one:
YouTube
Is this the reference standard we are trying to beat? You ask if all we need to do is increase VTF to keep the stylus “planted in the groove”. You assume low friction but the practical evidence from the posted comments in this thread shows that low friction/stiction is exceedingly difficult to achieve in a passive LT. In the extreme, my old VoM changer meets all the criteria of your argument in that it has a low enough compliance cartridge and tracks at high enough VTF (6-8 grams). To my recollection, I never observed any cantilever deflection, so it must have had very low friction/stiction, Right?
BTW, the higher VTF rumor is not a rumor. The concept was put forth by Ed Villchur in the 60’s. When he came out with the AR turntable he was asked why it didn’t have an anti-skate device. He responded that all you need to do is use a “little more tracking force”. Unbalanced groove wall pressure from bearing friction/stiction in a passive LT is no more benign than unbalanced groove wall pressure from skating in an offset pivot arm, even one that has no bearing friction/stiction. I know skating is another can of worms and is off-topic in a LT thread but side forces are side forces, and less is more.
Ray K
After careful contemplation, I have concluded that my ideas for linear tracking are at a stalemate with the key players on this thread. It is evident that passive linear followers have a higher threshold point for what is acceptable horizontal friction/stiction and cantilever side-thrust than I do. To me, no amount is acceptable. We have different approaches for achieving a LT design. I favor active servo control. My philosophy is: take a traditional tonearm design, eliminate the offset angle to remove skating side-thrust, and then use a servo to move the pivot end so as to maintain tangency. The key advantage of my approach is that the side-thrust a cantilever sees from pivot bearing friction/stiction becomes almost non-existent due to the mechanical advantage of the tonearm length acting as a lever. Cantilever side-thrust from conventional pivoted arm bearing friction/stiction has long been a non-issue. The huge numbers of commercial pivoted arms that have passed the vanishingly low horizontal bearing friction/stiction milestone have become the norm, be they unipivot, gimbal, or even a diy ball point pen tip bearing like diyaudio’s own Nanook 219. It is very easy to manufacture or diy a conventional arm bearing in which friction/stiction is not an issue. While servos have the downside of added complexity, I have diy’d my own servo controls, shared the details on another diyaudio thread and demonstrated that my servo design functions without any start/stop friction/stiction issues of the carriage.
The OP didn’t say anything about excluding active linear tonearms on this thread, but I guess it was implied, judging by the anti-servo undertone in comments posted. One post in particular that really hit home said servo arms are not linear at all, made me feel unwelcome, and that my presence in this thread is illegitimate. With that, I am not allocating any more interest or time on this thread. I have my own ideas and theories about what makes LT arms sound special but I’m going to present them elsewhere, not here.
Ray K
The OP didn’t say anything about excluding active linear tonearms on this thread, but I guess it was implied, judging by the anti-servo undertone in comments posted. One post in particular that really hit home said servo arms are not linear at all, made me feel unwelcome, and that my presence in this thread is illegitimate. With that, I am not allocating any more interest or time on this thread. I have my own ideas and theories about what makes LT arms sound special but I’m going to present them elsewhere, not here.
Ray K
Hi Ray,
Here is a thought....... Use a servo to move a fixed rigid arm, then pop a very short arm on the end that has vertical and horizontal pivots. Kind of like the DV 507. This should work but will need horizontal damping to get the bass response of a rail arm.
Bass response on my arm is phenomenal even with the issue I have yet to fix. Better than any pivoting arm I have heard in my 40 years. This is due to the damping in the horizontal plane holding the cartridge still, albeit mine is over damped and struggles on off centre pressings. I have dismantled it and found a couple of issues.
I am reading these threads and come across lil Casey, what is it please? - also floating headshell?
Hmmm... I don't think I stated any of that. Most of it was phrased as questions as I am still at the low end of the learning curve in terms of the physics of this kind of arm, but thanks for the reply.
WRT a servo LT, I would love to see that! I imagine that the hysteresis between the sensing and movement would have to be super small or you'd end up with constant l-r side pressure on the stylus, or LT error if there was some float.
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(...) One post in particular that really hit home said servo arms are not linear at all, made me feel unwelcome, and that my presence in this thread is illegitimate. With that, I am not allocating any more interest or time on this thread. I have my own ideas and theories about what makes LT arms sound special but I’m going to present them elsewhere, not here. (Ray K)
Hi Ray,
I would like to ask you, on a personal level, not to do it; to continue contributing to the this thread with your knowledge, ideas and criticisms, in the interest of the evolution of the linear trackers, and therefore of all of us.
A voice out of the chorus is essential, because we all tend to fall in love with what we do, only seeking confirmations of what we are convinced of, sometimes even wrongly: instead it's much easier to learn from criticism and errors than from superficial applause. Of course if one is willing to confront other people's ideas - opinions.
As known, I am also critical of the linear ones, which with their negative lever seem to me a mechanical paradox, but also a challenge to be accepted, as there are (few) excellent solutions around to be understood, and possibly improved. And maybe new solutions "out of the box" still to find.
But I am also critical of the active ones: due those few that I have had the opportunity to listen and examine long ago, and the way they were advertised, but above all for a matter of "fair play": it seems to me like trying to win a bike race with a motorcycle. No technical reason, just a matter of taste
ciao carlo
Sorry again if my post bothered you - As explained, that video showed clearly the good visible behavior of a pivoted arm on a linear mobile active basis - therefore definable as a hybrid, not literally a linear tracker. Never said that all servo-arms are not true linear, since the vast majority are exactly that way: but not that one of the video.
Hi Ray,
I would like to ask you, on a personal level, not to do it; to continue contributing to the this thread with your knowledge, ideas and criticisms, in the interest of the evolution of the linear trackers, and therefore of all of us.
A voice out of the chorus is essential, because we all tend to fall in love with what we do, only seeking confirmations of what we are convinced of, sometimes even wrongly: instead it's much easier to learn from criticism and errors than from superficial applause. Of course if one is willing to confront other people's ideas - opinions.
As known, I am also critical of the linear ones, which with their negative lever seem to me a mechanical paradox, but also a challenge to be accepted, as there are (few) excellent solutions around to be understood, and possibly improved. And maybe new solutions "out of the box" still to find.
But I am also critical of the active ones: due those few that I have had the opportunity to listen and examine long ago, and the way they were advertised, but above all for a matter of "fair play": it seems to me like trying to win a bike race with a motorcycle. No technical reason, just a matter of taste
ciao carlo
Sorry again if my post bothered you - As explained, that video showed clearly the good visible behavior of a pivoted arm on a linear mobile active basis - therefore definable as a hybrid, not literally a linear tracker. Never said that all servo-arms are not true linear, since the vast majority are exactly that way: but not that one of the video.
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Good morning gents, becoming more intrigued with the idea of a simple LTA, is there something in this concept or other maglev, very low friction, probably has damping possibilities and side force all built in? couldn't make the link copy but search on below
True Magnetic Levitation - No Power Required
YouTube · 68,000+ views · 17/02/2019 · by lasersaber
True Magnetic Levitation - No Power Required
YouTube · 68,000+ views · 17/02/2019 · by lasersaber
If you look at the video , you can see the main problem with the magnetic levitation: It is like a spring, and that is not what is disirerbly in a tonearm bearing. It should be as solid as possible. One of the things that is difficult in such a bearing: It should be completely solid and with no friction. Very hard to obtain
. My 25cIf you look at the video , you can see the main problem with the magnetic levitation: It is like a spring, and that is not what is disirerbly in a tonearm bearing. It should be as solid as possible. One of the things that is difficult in such a bearing: It should be completely solid and with no friction. Very hard to obtain
Understood thanks, so is the pin bearing/wheel or ball bearing either running on a hard rod/tube the current best thought? - and what format/how many?
Different subject as i read and learn, the outside of the groove has to move the carriage to centre unless there is a bias mechanism, what is current best practice?
I guess there are different opinions on what is best. The L'il Caesy is a special case, where the main feature is that there is no pivot in the horizontal plane ( well there is actually a very small one, but 90 deg. to the groove, not mentioned by anyone. This does not give an angel error, but rather a displacement error) so the cartridge moves directly up and down without any angel error to the platter surface. Carlo will be the better to explain, as he is the inventor.
Ray, in the short time i have explored various topics on this forum, since lock down i have found or read of many people offering sincere advice to newbies like me and its appreciated and valuable, equally in my short experience I have seen the occasional comments that could cause unease, misunderstanding or more with others, but its difficult posting, its not like being face to face when you can see if you're in the middle of offending someone, when one is posting the whole script goes out in one, and you can go on digging unintentionally.
I have valued what i have read from you and others and i hope you all go on contributing, i for one, am grateful
Best
Mike
I agree completely with Mike, therefor this disclaimer:
My native tongue is not English and I have no intention to upset people or make hostile statements. All I want is to contribute to a very interesting pursue of the holy grail in TT arms.
I, as Ray, have been a little puzzled over the reaction to servo assistance as being almost a form for heresy. But I was also surprised that you , Ray , commented that the servo aid I suggested would have the drawbacks of both a conventional servo arm (read pivot arm with a servo) and a linear passive arm.
I think that my suggestion actually solves problems in both systems. A pivoted servo arm has to have a relatively long arm tube to work (very short arm would cause a big angel error before the servo could correct) and a long arm tube is IMHO undesirable.
At the same time I think that the stiction/friction problem in passive LT arms could be reduced pretty much , as it will be far easier to reduce stiction/friction in a rail that is only few mm long as opposed to 100 mm and the hole moving mass could also be reduced. Furthermore the distance to a solid mechanical ground (the servo sledge, which can be made very heavy, so even if it rides on traditional ballrace bearings, the chatter in those can not be provoked by the very small energy from the cartridge).
And the movement of the sledge , relatively to the cartridge, is not affecting the cartridge, if the friction is small enough. The cartridge cannot feel the movement of the sledge, if there is no friction. Of course the servo system should be made in a way so it is not making abrupt movements of the sledge, but that is an almost trivial proble to solve in a feedback system.
I like the thought that this suggestion is NOT an error-correction system.
It is essential the same as the arm Ralf described, with his "floating headshell", but he has the long armtube , because he chose to make the lateral bearing a pivot bearing (and actually there is a timing problem in that design, as the tangent the cartridge is moving on is actually moving itself!)
Ralf's arm is not an error correction system either.
Another benefit in servo arms is that there is (well almost) no problems with tonearm wires (drag , big loops that picks up hum, and long very small diameter).
These are my reason to investigate if there actually are benefits in some sort of servo assistance to a Linear Tracker.
My native tongue is not English and I have no intention to upset people or make hostile statements. All I want is to contribute to a very interesting pursue of the holy grail in TT arms.
I, as Ray, have been a little puzzled over the reaction to servo assistance as being almost a form for heresy. But I was also surprised that you , Ray , commented that the servo aid I suggested would have the drawbacks of both a conventional servo arm (read pivot arm with a servo) and a linear passive arm.
I think that my suggestion actually solves problems in both systems. A pivoted servo arm has to have a relatively long arm tube to work (very short arm would cause a big angel error before the servo could correct) and a long arm tube is IMHO undesirable.
At the same time I think that the stiction/friction problem in passive LT arms could be reduced pretty much , as it will be far easier to reduce stiction/friction in a rail that is only few mm long as opposed to 100 mm and the hole moving mass could also be reduced. Furthermore the distance to a solid mechanical ground (the servo sledge, which can be made very heavy, so even if it rides on traditional ballrace bearings, the chatter in those can not be provoked by the very small energy from the cartridge).
And the movement of the sledge , relatively to the cartridge, is not affecting the cartridge, if the friction is small enough. The cartridge cannot feel the movement of the sledge, if there is no friction. Of course the servo system should be made in a way so it is not making abrupt movements of the sledge, but that is an almost trivial proble to solve in a feedback system.
I like the thought that this suggestion is NOT an error-correction system.
It is essential the same as the arm Ralf described, with his "floating headshell", but he has the long armtube , because he chose to make the lateral bearing a pivot bearing (and actually there is a timing problem in that design, as the tangent the cartridge is moving on is actually moving itself!)
Ralf's arm is not an error correction system either.
Another benefit in servo arms is that there is (well almost) no problems with tonearm wires (drag , big loops that picks up hum, and long very small diameter).
These are my reason to investigate if there actually are benefits in some sort of servo assistance to a Linear Tracker.
An advantage of servo control
These are just my thoughts and I do not want to cause anyone offensive. I always like to explain my thinking to avoid this.
Most designers who pursue the servo control of a tonearm seems to do so in order to minimise lateral tracking error and cartridge generator misalignment (bending).
The main advantage of using a linear arm is to maximise arm rigidity in order to minimise colouration. This is done by keeping the arm short. The maximising of arm rigidity has a MUCH greater positive effect on sound quality than reducing lateral tracking error. Ideally a servo controlled arm will still be a short arm.
It is possible to get lateral tracking error and bending down to very low levels, one or two tenths of a degree, using a passive linear tracking arm. Both Jim's and my arms show such low levels of lateral tracking errors that even under high magnification it is very difficult to see.
It also needs to be recognised that the specifications for most cartridges have the stylus aligned to the cantilever to within +/-2°. It is probably the case that the coils will not be aligned to a greater accuracy than this either. Even if this is set within a 3 sigma quantity control range the average cartridge would likely still have the stylus misaligned by around 0.8°. Even the best of us is probably not able to align their cartridge to within 0.5°. If you rotate a cartridge so that the mounting screws move by just 11 microns you will get a 0.1° change in LTA. When compared to the likely 1°+ of alignment error that most of us are living with unawares the 0.1-0.2° introduced by the arm becomes much less significant.
There will be two main types of servo control systems, reactive and proactive.
A reactive system senses that the arm has gone out of alignment and then corrects itself. The amount that the arm goes out of alignment will depend on the sensitivity of the system. With a short arm this could easily be in the 0.1°+ range. A long arm will reduce this but of course you will loose all the advantages of a short arm, not a good trade off. With a reactive system you will still have to be mindful of effective mass as the inertia of the arm is still seen by the cartridge. You will have the advantage that the mechanical grounding can be made very positive. The big question is "does the added complexity take more than the servo gives?". In my opinion it probably does which is why I went passive.
A proactive system is a completely different kettle of fish. A proactive system reads the groove in front of the stylus using a completely independent sensor and moves the arm accordingly. This type of system should be able to reduce tracking errors even further than that achievable with either the passive or reactive systems. As these 0.1-0.2° errors are almost certainly inaudible by themselves (especially considering the previously mentioned alignment issues) this advantage of the proactive system is probably moot.
HOWEVER...
If the proactive approach is used for both the vertical and lateral motion of the arm the effective mass of that arm no longer needs to be kept low. The cartridge can be mounted directly to a high mass block that is in turn coupled via the servo system to the arms support structure. The high mass will hold the cartridge body much more stably allowing much less movement, a 30-40dB improvement with no resonant peeks in the audio band should be attainable. You will no longer be needing to tune the arm to the cartridge with effective mass. This means that the arm will be suitable for any compliance cartridge.
The ability to increase the mass of the arm would likely outweigh the disadvantages of increasing complexity.
Using a servo to decrease lateral errors is probably not going to bring any positive sonic changes. Using a servo to increase effective mass probably will.
Niffy
These are just my thoughts and I do not want to cause anyone offensive. I always like to explain my thinking to avoid this.
Most designers who pursue the servo control of a tonearm seems to do so in order to minimise lateral tracking error and cartridge generator misalignment (bending).
The main advantage of using a linear arm is to maximise arm rigidity in order to minimise colouration. This is done by keeping the arm short. The maximising of arm rigidity has a MUCH greater positive effect on sound quality than reducing lateral tracking error. Ideally a servo controlled arm will still be a short arm.
It is possible to get lateral tracking error and bending down to very low levels, one or two tenths of a degree, using a passive linear tracking arm. Both Jim's and my arms show such low levels of lateral tracking errors that even under high magnification it is very difficult to see.
It also needs to be recognised that the specifications for most cartridges have the stylus aligned to the cantilever to within +/-2°. It is probably the case that the coils will not be aligned to a greater accuracy than this either. Even if this is set within a 3 sigma quantity control range the average cartridge would likely still have the stylus misaligned by around 0.8°. Even the best of us is probably not able to align their cartridge to within 0.5°. If you rotate a cartridge so that the mounting screws move by just 11 microns you will get a 0.1° change in LTA. When compared to the likely 1°+ of alignment error that most of us are living with unawares the 0.1-0.2° introduced by the arm becomes much less significant.
There will be two main types of servo control systems, reactive and proactive.
A reactive system senses that the arm has gone out of alignment and then corrects itself. The amount that the arm goes out of alignment will depend on the sensitivity of the system. With a short arm this could easily be in the 0.1°+ range. A long arm will reduce this but of course you will loose all the advantages of a short arm, not a good trade off. With a reactive system you will still have to be mindful of effective mass as the inertia of the arm is still seen by the cartridge. You will have the advantage that the mechanical grounding can be made very positive. The big question is "does the added complexity take more than the servo gives?". In my opinion it probably does which is why I went passive.
A proactive system is a completely different kettle of fish. A proactive system reads the groove in front of the stylus using a completely independent sensor and moves the arm accordingly. This type of system should be able to reduce tracking errors even further than that achievable with either the passive or reactive systems. As these 0.1-0.2° errors are almost certainly inaudible by themselves (especially considering the previously mentioned alignment issues) this advantage of the proactive system is probably moot.
HOWEVER...
If the proactive approach is used for both the vertical and lateral motion of the arm the effective mass of that arm no longer needs to be kept low. The cartridge can be mounted directly to a high mass block that is in turn coupled via the servo system to the arms support structure. The high mass will hold the cartridge body much more stably allowing much less movement, a 30-40dB improvement with no resonant peeks in the audio band should be attainable. You will no longer be needing to tune the arm to the cartridge with effective mass. This means that the arm will be suitable for any compliance cartridge.
The ability to increase the mass of the arm would likely outweigh the disadvantages of increasing complexity.
Using a servo to decrease lateral errors is probably not going to bring any positive sonic changes. Using a servo to increase effective mass probably will.
Niffy
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Here is a guy who DIYed a servo linear
DIY Turntable | sandiegoturntableinstitution
Here is another on where the goal was to make the best linear tonearm possible, in the text one of the issues to solve was noise of the linear motor under certain conditions was measurable. I think this would be the most difficult part to get right, isolating the mecanical noise of the motor from the tonearm.
I know with my LTA when the carriage is raised and moved back to park it is audible through the speakers.
DIY Turntable | sandiegoturntableinstitution
DIY Turntable | sandiegoturntableinstitution
Here is another on where the goal was to make the best linear tonearm possible, in the text one of the issues to solve was noise of the linear motor under certain conditions was measurable. I think this would be the most difficult part to get right, isolating the mecanical noise of the motor from the tonearm.
I know with my LTA when the carriage is raised and moved back to park it is audible through the speakers.
DIY Turntable | sandiegoturntableinstitution
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