Hello Sprags
Hello Sprags,
Somewhere I've seen a turntable that operated the way you describe.
I agree with Direct Driver though, that it would be easier to move the tonearm base. When you consider how heavy some platters are, it would require a robust set of tracks and a motor to match to make that work. If you are doing this as a hobby, you can do as you please. But if you have commercial ambitions, you would have to make your own "stationary" tangential tonearm bacause the ones on the market are meant to move.
I have successfully designed and built a tangentially tracking tonearm with a moving base and so have people before me.
Sincerely,
Ralf
Hello Sprags,
Somewhere I've seen a turntable that operated the way you describe.
I agree with Direct Driver though, that it would be easier to move the tonearm base. When you consider how heavy some platters are, it would require a robust set of tracks and a motor to match to make that work. If you are doing this as a hobby, you can do as you please. But if you have commercial ambitions, you would have to make your own "stationary" tangential tonearm bacause the ones on the market are meant to move.
I have successfully designed and built a tangentially tracking tonearm with a moving base and so have people before me.
Sincerely,
Ralf
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Produced in the 1960s (I think), the Transcriptor Transcriber moved the platter-bearing-motor on rails while the tonearm remained still (sort of).
Decades later, Sony made a series of CD transports using the same principle - the platter moved and the optical pickup was immobile (other than the voice-coil focusing mechanism).
If such a design were attempted now, combining a motorized rail system with small phone camera modules and suitable software should make it possible to guide the platter accurately.
Adding an elevator system (and height sensor) to the platter-on-rails would allow the phono cartridge to be bolted to a solid, immobile bridge, completely eliminating the need for a tonearm.
kind regards, jonathan
Decades later, Sony made a series of CD transports using the same principle - the platter moved and the optical pickup was immobile (other than the voice-coil focusing mechanism).
If such a design were attempted now, combining a motorized rail system with small phone camera modules and suitable software should make it possible to guide the platter accurately.
Adding an elevator system (and height sensor) to the platter-on-rails would allow the phono cartridge to be bolted to a solid, immobile bridge, completely eliminating the need for a tonearm.
kind regards, jonathan
Transcriptor Transcriber Turntable
As used in Stanley Kubrick's film A Clock Work Orange in this YouTube video.
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Thank you for reminding me of this analog curiosity. According to Transcriptor's website, the Transcriber was produced between 1977-1981.
You're brilliant, Jonathan! I love far out concepts like that: it makes the brain expand.
I'm glad another designer pays attention to this thread. It's fun!
.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
As used in Stanley Kubrick's film A Clock Work Orange in this YouTube video.
--------------------------------------------------------
Thank you for reminding me of this analog curiosity. According to Transcriptor's website, the Transcriber was produced between 1977-1981.
You're brilliant, Jonathan! I love far out concepts like that: it makes the brain expand.
I'm glad another designer pays attention to this thread. It's fun!
.
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Whether the arm moves or the turntable moves, the same problems exist.
Arms that move on rails do indeed follow the original cutter path perfectly, but that's not the whole story. The entire arm mass (counterweight, pivot housing, arm & pickup) must be moved as well. Since the arm stays perpendicular to a radius, how can its pickup move inward across the record? The answer is, "it can't." The spiral groove pulls the stylus (cantilever) out of position and the mass is dragged by it. This is very bad for the record and stylus, not to mention the sound. "Air-bearings" remove rail friction, but the mass must still be handled.
In theory, motorized versions (which also allow slight non-perpendicular movement) remove the problem.
Some designs sense the error and correct it. In reality, the feedback loop (servo) that does this is slow (that mass, again) and must not be made so accurate that off-center holes continually engage the process (it's audible on good systems).
Others designs "anticipate" the groove spacing and use cams or a (clock-) driven track to position the arm support as the record is played. This is the playback version of what happens in recording, i.e. driving the cutting lathe. The difference is that the lathe is helped by a preview head from the master tape or CD and allows positioning it so the right groove spacing is used to accommodate the modulation level. No such process exists for playback, so all position information must be derived from the groove.
This suggests that designs that change head-angle based on groove position (e.g. Thales, Garrard, van Eps, Wolff, etc.) have an advantage because they can just pivot the arm instead of move the whole mechanism. This is true, within the constraints of non-ideal records (all of them!), except for one thing: any head-angle change brings in a side-thrust (aka "skating"-) force that does everything from cause wear and mistracking to groove-jumping. This is very hard to compensate properly. Some designers have given up on it. Others instead use a compromise approach. The reasoning goes something like this (my apologies to the designers!):
If forced to choose between eliminating either tracking error or side-thrust, they choose the latter. After all, the "best" arms of the past have not had perfect tracking, so maybe a little off is tolerable. Side-thrust, however, is not OK. To that end, they employ no head angle, the arm is longer than usual (some compromises, there), and friction is kept to an absolute minimum; eliminated, if possible. Arm positioning is controlled by moving the pivot/base, etc.
This also has an advantage of sorts with regard to so-called VTA adjusting, which requires minimal effect on playback with pivot-height changing. Such a design can have varying degrees of success depending on its execution, of course.
The perfect arm is impossible. The designers of existing arms all have their own opinions as to what matters more (lowest friction, lowest geometrical error, fewest linkages, et al). They are the ones dedicated to playing the treasure-trove of existing records as well as those still being made (I'm delighted to say!). To them, it is not "obvious" that a linear tracking arm (or any particular design) is the "perfect" solution. Those contributors stating or implying that all other efforts are pointless or mis-directed could do worse than reading this thread instead of jumping in.
Arms that move on rails do indeed follow the original cutter path perfectly, but that's not the whole story. The entire arm mass (counterweight, pivot housing, arm & pickup) must be moved as well. Since the arm stays perpendicular to a radius, how can its pickup move inward across the record? The answer is, "it can't." The spiral groove pulls the stylus (cantilever) out of position and the mass is dragged by it. This is very bad for the record and stylus, not to mention the sound. "Air-bearings" remove rail friction, but the mass must still be handled.
In theory, motorized versions (which also allow slight non-perpendicular movement) remove the problem.
Some designs sense the error and correct it. In reality, the feedback loop (servo) that does this is slow (that mass, again) and must not be made so accurate that off-center holes continually engage the process (it's audible on good systems).
Others designs "anticipate" the groove spacing and use cams or a (clock-) driven track to position the arm support as the record is played. This is the playback version of what happens in recording, i.e. driving the cutting lathe. The difference is that the lathe is helped by a preview head from the master tape or CD and allows positioning it so the right groove spacing is used to accommodate the modulation level. No such process exists for playback, so all position information must be derived from the groove.
This suggests that designs that change head-angle based on groove position (e.g. Thales, Garrard, van Eps, Wolff, etc.) have an advantage because they can just pivot the arm instead of move the whole mechanism. This is true, within the constraints of non-ideal records (all of them!), except for one thing: any head-angle change brings in a side-thrust (aka "skating"-) force that does everything from cause wear and mistracking to groove-jumping. This is very hard to compensate properly. Some designers have given up on it. Others instead use a compromise approach. The reasoning goes something like this (my apologies to the designers!):
If forced to choose between eliminating either tracking error or side-thrust, they choose the latter. After all, the "best" arms of the past have not had perfect tracking, so maybe a little off is tolerable. Side-thrust, however, is not OK. To that end, they employ no head angle, the arm is longer than usual (some compromises, there), and friction is kept to an absolute minimum; eliminated, if possible. Arm positioning is controlled by moving the pivot/base, etc.
This also has an advantage of sorts with regard to so-called VTA adjusting, which requires minimal effect on playback with pivot-height changing. Such a design can have varying degrees of success depending on its execution, of course.
The perfect arm is impossible. The designers of existing arms all have their own opinions as to what matters more (lowest friction, lowest geometrical error, fewest linkages, et al). They are the ones dedicated to playing the treasure-trove of existing records as well as those still being made (I'm delighted to say!). To them, it is not "obvious" that a linear tracking arm (or any particular design) is the "perfect" solution. Those contributors stating or implying that all other efforts are pointless or mis-directed could do worse than reading this thread instead of jumping in.
If you look closely, the pivot of the Transcriber arm sits on a "fluid damped jeweled unipivot" and stabilized by a rubber band (!!) so it's not a rigid system and allows for some wiggle room in order for the servo to work. But since the arm is so short the error of angle might be a bit large to be effectively tangential--though the spec says "tracing error: 0.1 degrees." The short arm reminds me of the Revox B790 turntable. The design is quite clever, admittedly.
I wish I can make a living spending all my time pondering on tonearm designs.
I posted my message after not getting a lot of sleep. It was just an idea that popped in my head. My thinking was that virtually any tone arm could be used. The only thought was that there would need to be a way to send location info to the servo motor that's is used for moving the platter transport system. Of course a better tone arm would be a better choice.
Hello Sprags
Hello Sprags,
You must follow your dreams. Just because you reinvented something from the past, is no reason why you couldn't improve upon the idea.
Maybe a swinging arm or a parallelogram could be used to move the platter.
I've always liked the free-standing motors of the Micro-Seiki turntables.
But that would be tricky to achieve with a moving platter.
Sincerely,
Ralf
Hello Sprags,
You must follow your dreams. Just because you reinvented something from the past, is no reason why you couldn't improve upon the idea.
Maybe a swinging arm or a parallelogram could be used to move the platter.
I've always liked the free-standing motors of the Micro-Seiki turntables.
But that would be tricky to achieve with a moving platter.
Sincerely,
Ralf
Hi, Straight Tracker,
It's a pleasure to hear from you. I still have your original Machine Design article in my archives!
I have a friend who refers to Sprags's no-sleep condition as "being hit by dumb-o rays." I can sympathize. The trick, of course, is to not reply to a thread (or write an article) when it happens. I plead guilty to doing so on occasion. In my researches, I've found Edgar Villchur (AR), Ben Bauer (Shure Bros. & CBS Labs) and other legends of hi-fi similarly afflicted, so I can live with it.
The problem that recurs is imagining a different set-up and then mentally putting it through its paces. I can't imagine your arm as well as something I have experience with.
The swapping of a pivoting fixed-offset arm (I call it a PFT) like the SME3009 with a tangential version (I call it an AHT for articulated-head tonearm) is something I would like to try, just as you described. The 3009 is a 12-in design, though. I imagine (!) the extra length might remove the need for anti-skate, but I don't know without constructing such a beast. Consider:
On one hand, Shure's James Kogen did the original testing that established the benefits of anti-skate (article available on Shure's website) but he used the SME3009 in the tests! On the other hand, Shure's emphasis on low mass for proper arm-cartridge resonance should eliminate that arm from consideration. On still another hand (rays of a different kind?) Shure's model 500 cartridge had an extra 3g incorporated in it (for certain commercial reasons). On the final hand (aha! a Martian!) van Eps's armwands were 14 inches long and he claimed he didn't need anti-skate.
Thus, until I build it, I don't know if I'm good-to-go without anti-skate.
(There are other niceties that project would entail, like the diameter of the arm tube. Must it be rigid and unbending, or would bending be OK and actually beneficially upset any standing waves?)
Best wishes!
Andy
It's a pleasure to hear from you. I still have your original Machine Design article in my archives!
I have a friend who refers to Sprags's no-sleep condition as "being hit by dumb-o rays." I can sympathize. The trick, of course, is to not reply to a thread (or write an article) when it happens. I plead guilty to doing so on occasion. In my researches, I've found Edgar Villchur (AR), Ben Bauer (Shure Bros. & CBS Labs) and other legends of hi-fi similarly afflicted, so I can live with it.
The problem that recurs is imagining a different set-up and then mentally putting it through its paces. I can't imagine your arm as well as something I have experience with.
The swapping of a pivoting fixed-offset arm (I call it a PFT) like the SME3009 with a tangential version (I call it an AHT for articulated-head tonearm) is something I would like to try, just as you described. The 3009 is a 12-in design, though. I imagine (!) the extra length might remove the need for anti-skate, but I don't know without constructing such a beast. Consider:
On one hand, Shure's James Kogen did the original testing that established the benefits of anti-skate (article available on Shure's website) but he used the SME3009 in the tests! On the other hand, Shure's emphasis on low mass for proper arm-cartridge resonance should eliminate that arm from consideration. On still another hand (rays of a different kind?) Shure's model 500 cartridge had an extra 3g incorporated in it (for certain commercial reasons). On the final hand (aha! a Martian!) van Eps's armwands were 14 inches long and he claimed he didn't need anti-skate.
Thus, until I build it, I don't know if I'm good-to-go without anti-skate.
(There are other niceties that project would entail, like the diameter of the arm tube. Must it be rigid and unbending, or would bending be OK and actually beneficially upset any standing waves?)
Best wishes!
Andy
The effective length of the SME 3009 is 9 inches. Whereas the 3012 is a 12 inch arm, hence the model number. I know because I owned both before. Perhaps you were referring to the 3012?
Hi, DD
Ignore the previous reply. I edited and re-edited it and it didn't take. I hope this time it will.
In essence:
1) Thanks for the correction, and for going easy on me. I blame it on dumb-o rays.
2) In Kogen's article, he refers to all of the info on his Figs 6-9 as being taken with the 12-in. SME3009 with an overhang of 0.6 in. (His bad).
3) This doesn't acquit me, of course. I was so distracted by the image of a 12-in arm and a high-compliance Shure pickup that I lost focus.
4) Anti-skate can enable low-compliance pickups to halve their VTF, but it might be unnecessary for high-compliance pickups if the arm were indeed 12in. instead of the usual 9.
5) This notion is different from the usual. That is, longer arms are thought of as lowering tracking error, not as also lowering the anti-skate force required. Yes, the two are frequently stated to be linked, but that's not true in general.
6) In my imagination (!), I picture a high-compliance pickup as not needing a lot of anti-skate at the outer grooves, and at the inner grooves, not needing any at all if the arm is an AHT whose offset angle has been continually decreasing. This would be even more true if the arm were longer and I could solve the moving-mass issues.
Again, thanks for the correction, and I will keep my fingers crossed as I hit "Submit Reply!"
Andy
Ignore the previous reply. I edited and re-edited it and it didn't take. I hope this time it will.
In essence:
1) Thanks for the correction, and for going easy on me. I blame it on dumb-o rays.
2) In Kogen's article, he refers to all of the info on his Figs 6-9 as being taken with the 12-in. SME3009 with an overhang of 0.6 in. (His bad).
3) This doesn't acquit me, of course. I was so distracted by the image of a 12-in arm and a high-compliance Shure pickup that I lost focus.
4) Anti-skate can enable low-compliance pickups to halve their VTF, but it might be unnecessary for high-compliance pickups if the arm were indeed 12in. instead of the usual 9.
5) This notion is different from the usual. That is, longer arms are thought of as lowering tracking error, not as also lowering the anti-skate force required. Yes, the two are frequently stated to be linked, but that's not true in general.
6) In my imagination (!), I picture a high-compliance pickup as not needing a lot of anti-skate at the outer grooves, and at the inner grooves, not needing any at all if the arm is an AHT whose offset angle has been continually decreasing. This would be even more true if the arm were longer and I could solve the moving-mass issues.
Again, thanks for the correction, and I will keep my fingers crossed as I hit "Submit Reply!"
Andy
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So I'm assuming that your friend has never thought outside the box which makes me think your friend really hasn't come up with any new ideas.
Some people seem to enjoy going through life without attempting to come up with something new. Most of the people I know that are like that are accountants or government clerical workers.
All opinions and ideas are welcome in this thread, particularly outside of the box kind. This thread itself took some ridicules in the beginning and still does but it has grown into one of the most visited threads in the analog category. Either I'm doing something right or is a laughingstock. Either way, I don't care. Audio is a hobby so let's have fun, guys!
Considering that someone else following this thread said they thought someone else also thought of and possibly attempted to develop the concept I thought of to me validates that idea is not so ridiculous or improbable. The poster that attempted to insult me perhaps is incapable of thinking. Is that guy that made that statement a light bulb installer?