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  »  New  Dynamic viscose stabilization of turntable’s platter...  Will not work...  Analog Playback Forum     14  69771  11-26-2008
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  »  New  How much does it cost to stabilize a turntable speed?..  How much does it cost to stabilize a turntable speed?...  Analog Playback Forum     0  11757  03-13-2010
  »  New  A turntable platter as a turbine?..  A turntable platter as a turbine?...  Analog Playback Forum     0  9339  10-27-2010
02-26-2008 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 450
Joined on 01-07-2006

Post #: 26
Post ID: 6791
Reply to: 6785
Dynamical speed stabilization
 Romy the Cat wrote:

Why should it be so expensive of complex of even simple and cheap $100 turntables already produce speed stability that is order of magnitude more stable that it is imaginable to hear.

Teh caT

isn't that a bit too fast & similar to saying that obtaining an incredibly low THD way below the hearing limit is possible with a cheap $100 transistor amp?
ok, but under which conditions? dynamically, with real life signals and loads?does it relate to the sound in any way?
not that i'd ever try to defend 100$k or whatever mastodonts, and not that i really have much experience with analog, but
let me point out that the force injected by the needle moving through a groove can apparently be quite substantial
(loud passages etc) dynamically slowing down the plate. if i were anywhere close to desing a TT (not in this century for sure)
i'd not underestimate it. heavy plate seems a safe starting point?.


Cheers,
Jarek
02-26-2008 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 27
Post ID: 6794
Reply to: 6787
How to levitate a massive platter?

Very cool question. Without having any rational justification to make any educated guess I would pull idea out of my ass – just because the idea make sense to me.

If I make a massive palter I would go for very tall vertical shaft to minimize the platter’s latitude bearing. As the example might be taken the EMT 927 with a long tail below – I love the idea. However the longer shaft, the more shaft surface the more tension in the shaft - so it should be balanced somehow.  No ball bearing would care >150poinf, unless you want to fix it each two years. So I would use some kind of other methods – air or magnetic. But there is a ketch in it. I still believe that the platter should not be decoupled from the base – I have written about it in the beginning of the thread. A platter should be grounded, not electrically but mechanically and it should have path of mechanically ground. So, if I go for an ultimate solution then I would suspend the platter with air for insane in order the air to care 95% of the platter mass. Then I would have the ball bearing that would care the reminding 5-10 pounds. Sure when the platter is not spinning I should be not lower to the flimsy bottom bearing but somehow maintained in a lifted position.

Rgs, Romy the caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
02-27-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,130
Joined on 10-12-2006

Post #: 28
Post ID: 6795
Reply to: 6794
Errr... doesn't Contimuum do this?
Re, bearing/ground path versus platter mass:  The usual option is to use somewhat less than 150 lb platter ;>Wink, which is the compromise I opted for, for lots of swell reasons, one of which is because a lighter platter still allows for a realistic mechanical bearing/coupling that doesn't drag all that much and still lasts.

However, other factors being equal, I also believe that the heavier platter/lighter bearing is the superior idea.  I'm still leary of air but see no reason that magnets and solinoids could not be employed to do the grunt lifting and holding-off-the-bearing-while-stopped, respectively.  Base bearing could be typical carbide shaft and/or ball on zirconium plate, or similar, as long as it NEVER took full weight or a bump.

Never having played with an actual 150 ib. platter I wonder if it actually benefits from a "ground path" as much as, say, a 35 lb platter.

Now I'm wondering what is the curve for benefit/platter-mass.  I know it's up past Linn, my own Sota Star, etc; but where does it start to trail way off?

Best regards,
Paul S
02-27-2008 Post does not mapped to Knowledge Tree
guy sergeant
United Kingdom
Posts 258
Joined on 08-03-2004

Post #: 29
Post ID: 6797
Reply to: 6795
Platter Mass, How much is enough?
There was a Japanese company called Melco who did some experimentation with platter mass back in the 70's.  I seem to recall that they felt 30Kg was where it stopped making a difference.  The greek ACA president with his flywheel assistance feels its alot more.

http://www.aca.gr/paper37.htm

Personally, I feel DD done properly is an adequate and more elegant solution. The fact that it was accurate enough to cut the records we listen to also suggests this to be the case. 
02-27-2008 Post does not mapped to Knowledge Tree
enjoy_the_music
Strasbourg, France
Posts 12
Joined on 02-21-2007

Post #: 30
Post ID: 6798
Reply to: 6795
Platter becomes plinth.
If the platter was fully levitated then it would essentially become the plinth. Choice of material/s would then be the key issue.

When I used to work in robotics research my colleagues began to check out high temperature superconducting (HTS) bearings. They have interesting potential in turntables. Boeing were also looking into the for flywheel/energy conservation duties.

http://www.atz-gmbh.com/Products/HTS_bearing/hts_bearing.html

Obviously it could be a bit OTT but who knows.
02-27-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,130
Joined on 10-12-2006

Post #: 31
Post ID: 6800
Reply to: 6797
Co-equal tasks
Guy, I have used a Technics DD and thought about the lathe/DD connection.  Then I thought about the idea of various transducers, from microphone to cutter, to stylus and speaker, and I wonder if TT/lathe is a similar case, where similar function is not co-equality.

Wouldn't all the mass so far outboard from the motor shaft make for an expensive solution, both in terms of support and speed control, where it seems at first glance to be a case of the tail wagging the dog?  Sure it could be done, but how well, in terms of LP playback, and at what cost?

I'm very suspicious of DSP, or any kind of feedback-type speed control, by the way, if only because it seems superfluous in view of ostensibly simpler solutions.

I think a heavy platter with a small motor and a whimpy belt go a long way toward buffering speed variation in practical playback applications.  How would DD handle it?  Maybe just buy and adapt a lathe?  Shouldn't that do it?

Best regards,
Paul S
02-27-2008 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 32
Post ID: 6801
Reply to: 6797
Vacuum, platters, lathes, and everything elese.

 enjoy_the_music wrote:
Making a vacuum hold down is quite simple, but would it be easier to use a device like the old Audio Technica AT-666? I guess the material used in the latter is not the ultimate. You don't need a great amount of vacuum to hold the record down.

Actually you are incorrect. To make vacuum hold down properly is quite complex. The ay how Audio Technica and Sota did it was simple but it is why it reportedly did not work well. (I used Sota a few times). Micro did it extremely good with real-time sucking. The benefits are arguable though – there are some pluses and some minuses. I feel that the idea of negative curving is much more interning then the vacuum hold down, still even the negative curving have own pain in ass disadvantages.

 N-set wrote:
let me point out that the force injected by the needle moving through a groove can apparently be quite substantial (loud passages etc) dynamically slowing down the plate.

Only with flimsy platters perhaps. With heavy enough platter and with a platter with right damping it should not be the case.

 guy sergeant wrote:
There was a Japanese company called Melco who did some experimentation with platter mass back in the 70's.  I seem to recall that they felt 30Kg was where it stopped making a difference. 

Melco was in bad with Micro and I think Micro came from Melco. Japanese has another company with a ridicules name: it was called “American Sound“, they made TTs even heavier then Micro 8000

 guy sergeant wrote:
The greek ACA president with his flywheel assistance feels its alot more.

http://www.aca.gr/paper37.htm 

Wey good artailsy, I have seen it before but never was able to read it carefully. I hate to read from computer screen and it a site has no printing options then I tend do not read it. From what I was able to glance I might say that if his platter takes 30-60 minutes to stabilize then his design is bogus. Putting, record in, touching the platter, cleaning the record – it is all affect the pressure to the platter and platter should be able to recover it really fast. I hate to think that I need to hard-clean record and then wait 10 min until the platter get cruse speed.  I think all heavy platters should have step-torque controls.

 guy sergeant wrote:
Personally, I feel DD done properly is an adequate and more elegant solution. The fact that it was accurate enough to cut the records we listen to also suggests this to be the case. 

I think it is incorrect rational. I am not proposing that DD idea are bad or good I just say that juts because some companies in past make DD cutting lathes then it proves absolutely nothing and should not be a reason for imitation juts “because it was cut on TT lathe”.  It is not to mention that all earlier cutting lathes were belt driver and then, for the sake of economy/space some of them went to DD. BTW, none of the c used heavy platters. I am sure if someone would case to make the cutting lathes today, with contemporary high level of demands and with the same amount of appreciation as it was done 60 years back then the today’s lathes would be much  more capable then the best  Georg Neumann’s lathes…

Rgs, Romy the caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
02-27-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,130
Joined on 10-12-2006

Post #: 33
Post ID: 6802
Reply to: 6801
In lieu of the vacuum, what? (and a sneaky clamp reference)
Yes, the varying profiles of disc faces present another issue, all right.  But is this to say that a typical loose arrangement gives superior sonics during real world playback?  After all, the profile/slope must still be reckoned with.  Futzing around, tapping a loose disc with a straightened out paper clip while the stylus rests on the disc is not a pure "scientific" test, of course; but if nothing else the wild variation in the sound from loose discs is troubling.  Now, I think I hear this stuff when my vacuum is not properly engaged.  In any case, I obviously buy into the aural benefits of vacuum HD, even at the rather primitive level of implementation that my TT offers, although the Sota does not just suck down then shut off like the AT, but it continues sucking enough to keep the established vacuum constant; it just takes far less work from the pump once the initial purge is done, and there is a servo that handles this.

Though a long-time "vacuum guy" I feel no need to beat the gong for it.  Still, I have for some time wondered that otherwise-better TTs do not offer the vacuum option.  It just seems like something worth doing if you're going that far out to begin with.  With all the ancillary technology, it still seems like disc/platter interface gets brushed under the rug, especially when "manufacturers" go to great lengths to tout platter composition as it relates to vinyl and/or they offer clamps.  I also happen to use a fancy clamp; but I would not bother if I did not already have a +/- effective disc/platter connection.  I certainly do not see clamps as any kind of solution for warped disces.  For that matter, vacuum at the level I use it is not a solution for warped discs.  While it miight make a warped disc playable, vacuum might or might not make a warped disc flat enough to do the interface job I want from it.  I get the best results from discs that are reasonably flat to begin with.  Also, the clamp is mostly a sink, and I would never recommend the use of a clamp across the board, as I have seen/heard plenty of cases where a clamp made things way worse in short order.

Best regards,
Paul S
02-29-2008 Post does not mapped to Knowledge Tree
mats
Chicago
Posts 76
Joined on 09-18-2005

Post #: 34
Post ID: 6819
Reply to: 6801
DD again
Romy wrote:


"
 N-set wrote:
let me point out that the force injected by the needle moving through a groove can apparently be quite substantial (loud passages etc) dynamically slowing down the plate.

Only with flimsy platters perhaps. With heavy enough platter and with a platter with right damping it should not be the case."


It should not be the case one would think, but perhaps it is.  What after all accounts for the congestion one so often encounters with large scale, content rich orchestral recordings.  (Why do so many audiophiles play simple pop and jazz music, and why do classical lovers often go all digital?)  Well, a friend of mine suggested that not even his Verdier could maintain speed through complex passages, and that this was the main cause for congested sound.   He preferred a simple Technics SL1200 for speed stability.  The SL1200 has its own issues, (some of which I have adressed; battery power, cooler running),  but my personal  experience is that  the Technics offer  better  performance of complex music than the TT's I have had, A Well Tempered, a Linn and a Townshend.   No personal experience with heavy platters as you can see.  Still this is a subject I feel worthy of further discussion.  Who has had a DD and a heavy platter table side by side for comparison?

Mats
03-01-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,130
Joined on 10-12-2006

Post #: 35
Post ID: 6821
Reply to: 6819
Not that heavy
Mats, I am not so sure about where this may be headed, because the last thing I want to do is start an AA style pissing contest or suggest that any given product or design is the one to have, mainly because I just don't believe that any product simply plugged into a system is going to make a positive contribution.  So please consider my remarks as abstract and related to the technological ramifications of each design rather than brand or genre loyalty, which I certainly lack, anyway.  Since I know these threads can get heated from here out, please feel welcome to make me wrong, and I'll thank you and move on.  I don't remember you ever introducing isolated stats or theories or dragging in witnesses as proof of anything, and I hope no one else will do this either, because where would that get us?

OK, I said that.  So, I had an old SP10, which I simply did not care for.  It just never sounded right to me either in terms of noise via playback or the speed - in terms of music -  despite the fact that the built-in strobe looked great.  So, naturally, I wound up with an SP12 and, naturally, it was not much better in terms of speed but way worse in terms of noise via playback.  FWIW, I had the same issues with a Dennon I played with, and also a friend's friend's Kenwood; they all had the same problems.   You must have had a reason or reasons to go to batteries.  I never tried that, but the "perfect" speed control I was getting sounded more like original CD to me, and I never could solve the breakthrough issues, either, despite exotic coatings under the platter, isolation measures, etc.

And that's where the Sota Star (vacuum) came in.  To the point, I am NOT saying the Sota Star is a world beater, but - once set up properly - in terms of sound via playback it is in another class altogether where it matters to me, simply more musically coherent and a lot less noise via playback.  While I would not say that speed is my old Sota's strong point, it's problems are yet more tolerable to me.  Also, I imagine I could improve it significantly by replacing the 20 year old drive motor.  I'll tell all if I ever get around to it.

If I were designing from scratch I would try to find my bearing and levitation components first, then make the platter as heavy as I could given the beaings/suspension.  I'm guessing around 25-35 kilos. Then I would find the drive system, meaning a no-larger-than-necessary AC motor, minimal analog regulation and a suiltable whimpy belt.  Then I'd do primitive and reliable vacuum, having allowed for it as I went along. 

If nothing else, DD seems to work against a heavy platter, and runout becomes so damned critical, in practical terms.  Also, and also critical to me, DD seems to preclude the vacuum, because why would you couple the disc to the motor?   Lastly, what about the "perfect speed control", anyway?   How come that never seemed to work in the first place, at least in terms of sonics?

Basically, I don't understand why anyone would put a great deal into solving DD problems when it appears to me that relatively cheap, simple technology is already available to do the job more effectively, based on my own experience, anyway.

Best regards,
Paul S
03-01-2008 Post does not mapped to Knowledge Tree
mats
Chicago
Posts 76
Joined on 09-18-2005

Post #: 36
Post ID: 6825
Reply to: 6821
Is it a drag?
Nice to read your thoughts on this subject Paul.  My interest at this point is to explore the issue of speed stability in the face of complex music, and its possible effect on congested sound.  Is there a relationship?  I suspect there is.

My experience is that none of the light platter belt drives that I have had were able to perform well.  My current DD however, is doing better at negotiating complex passages.  Now, you who have heavy platter belt drive tables, do you not have issues with congestion due to speed irregularities?  To make it even trickier, if you have trouble resolving complex passages, how do you know if it is the turntable or the recording?

That there are other issues with DD tables that may prevent acceptable musical performance I do not doubt.  My initial modifications with batteries, decoupling and lowered power consumptioin have been helpful.  The platter should likely be even lighter and made of wood.

Take care,

Mats.
03-01-2008 Post does not mapped to Knowledge Tree
enjoy_the_music
Strasbourg, France
Posts 12
Joined on 02-21-2007

Post #: 37
Post ID: 6826
Reply to: 6784
Forces in the groove
Just a quick question.

There has been mention of the forces in the groove during play. Out of interest how strong are these forces?

03-02-2008 Post does not mapped to Knowledge Tree
hagtech


Hawaii
Posts 117
Joined on 02-13-2006

Post #: 38
Post ID: 6827
Reply to: 6826
Lathe as reference
So why wouldn't you just copy what was done with most cutting lathes?  Seems to me that stylus drag would be roughly the same (geometrically) for both cutting  and playback.  Thus, the cutting lathe slows down in response to large orchestral passages.  Would you not want the same effect during playback, thus cancelling out a velocity error?  I would think a cutting lathe makes for perhaps the best playback.

jh
03-02-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,130
Joined on 10-12-2006

Post #: 39
Post ID: 6828
Reply to: 6825
Finding the message
Sure, I believe there is a speed/congestion relationship, but I do not think it is singular, and furthermore I think there is more to the speed issue "itself" than meets the eye, if you get what I mean.

At this point all I can say is that the belt/heavy combo I am using simply beats the DD's I've tried for getting the music from the LP, including complex music, and this is a big part of why I prefer LPs to CD for all types of music, including classical, given good electricity.  How else to say it?  The belt drive/heavy platter just seems more "steady" and neutral in musical terms to me; it is less of a factor, less "jittery" and less of a "participant" than light and/or DD 'tables I've tried.  What does that say about speed, per se?  I'm not exactly sure.  But I don't want a definition of speed stability that costs me my music, that's for sure, eg, It's accurate to .00001%, but it sounds like crap.  No, thanks.

TT or recording?  I use the best sound I can get as a reference for what is possible.  If I can EVER get great sound from a complex, overcut disc, then the both the TT and the recording are doing something right.  Now, what TT does it best?

There are so many issues to consider, though, even with respect to speed alone.  At this point it is easier for me to figure out how to get the most music from the belt/heavy platter, and I have laid out my thinking.  But my mind is not closed.  As soon as I hear someone do better with DD, I'll try it again.  At this point, give me a massive flywheel over a servo motor and a light platter, since steady beats "nimble" where music via TT is concerned, according to my experience. 

Best regards,
Paul S
03-02-2008 Post does not mapped to Knowledge Tree
coops
London, United Kingdom
Posts 115
Joined on 02-16-2007

Post #: 40
Post ID: 6829
Reply to: 6828
Dd tt's
Paul which direct drives have ou tried?
03-02-2008 Post does not mapped to Knowledge Tree
guy sergeant
United Kingdom
Posts 258
Joined on 08-03-2004

Post #: 41
Post ID: 6830
Reply to: 6828
DD progress
Certainly it took Technics a while to sort out the motor control systems in their serious DD machines. The earlier SP10 Mk1 is not a good example. On the Mk2 they seem to have got it right. Even with that there are other issues like the mat & plinth used with it that will affect the end result. There does seem to be a relationship between the weight of platter controlled and the mechanism employed to control it. You'd change that relationship at your peril. The SP10Mk3 was their ultimate statement, a heavier platter and a far more powerful motor although I've yet to hear what difference the system brings alongside a Mk2.

Paul, I find your observations regarding the speed constancy of a belt driven suspended 'heavy' design very much at odds with my own experience. They seldom remove the impression that something cyclical is happenening or instill a feeling of real security & sure footedness. Not that speed constancy is the be all and end all. A CD player will always have that but may fail to satisfy in many other areas.

I'm keen to hear the latest modern take on DD made by GP Audio (Monaco).  Michael Fremer was sniffy about it so it could be interesting!
03-02-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,130
Joined on 10-12-2006

Post #: 42
Post ID: 6831
Reply to: 6829
Not so much a contest, as I see/hear it
Coops, do you have any personal observations or ideas about the ultimate TT, or are you already invested and just checking my credentials?  I would like to know your thoughts, too, based on your own personal listening habits, preferences and evaluations.

FWIW, I was using a modified Rek-O-Kut "transcription" TT when I bought a new Technics 1200, and before I even got that set up I got a chance to get a used 1-box SP10  at a great price.  I fancied it would be a step up in terms of sonics, based on Gordon Holt's opinions at the time, so I over extended myself to get it.  I wound up thinking that both DDs had similar issues that emerged with all sorts of music, and both had what I could only perceive as "speed issues" that annoyed me with all music apart from bog-standard rock and roll played during gatherings.  I know about the great specs, and that's why I bought the DDs, but I just could not shake the sense of something "jittery" turning the platters, which is perhaps similar to but at the same time different from the little ARs, Regas, etc.  And ironically, the old Rek-O-Kut seemed better in this regard.  I finally unloaded the 10 and kept the 1200, which I continued to play with for several years.  In the meantime I took every chance to try everything else, including a fancy Denon DD and, as I recall, a Kenwood DD, anything also touted by JGH at the time.  I have incidentally and forgettably heard other Japanese DDs along the way.  Because this happened years ago I am putting my previous experience into perspective/context of my present day experience and understanding, again FWIW.  The Sota Star vacuum was the first real breakthrough for me on the TT front, its own problems notwithstanding, and I have not progressed passed optimizing that TT so far, although I can presently imagine better TT performance and I am getting some workable ideas about implementing them.  And those ideas do not include DD.

So, what are you using, Coops, and why? 

Best regards,
Paul S
03-02-2008 Post does not mapped to Knowledge Tree
hagtech


Hawaii
Posts 117
Joined on 02-13-2006

Post #: 43
Post ID: 6832
Reply to: 6830
Feedback Loops
I believe a lot of the issues with earlier DD tables was that they were all servo controlled.  That is, a feedback loop kept the average velocity constant.  As a musical passage of complexity would slow the platter, the loop would respond with more motor torque and speed it back up.  Hence, the platter speed was always chasing its tail.  So you didn't have a passive reaction to stylus drag, but a reactive one, adding a new pitch signature.  Speed up, slow down, etc.  Always chasing.  And it depended a lot on the natural frequency response of the feedback loop.  Heavier platters required a slower loop.

DD itself might be ok, if not servo'ed.  I am curious as to what the changes were that made the later Technics sonically improved.

jh
03-02-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,130
Joined on 10-12-2006

Post #: 44
Post ID: 6833
Reply to: 6830
The newer/better DD
Guy, that is a VERY interesting observation about your sense that belt drive speed is "cyclical".  I agree that belt/heavy problems are more "long term" versus DD "short term".  So in this sense I suppose it's pick your poison.  I wonder if the big Versa Dynamics I heard would have eventually showed the same belt/heavy problems, if it had stayed operational longer. 

But speed is not the end-all for me, and the belt/heavy allows me get the disc coupled down to a heavy platter for remarkable benefits that I have never heard from DD.  And, again, I am much more at ease as a listener with belt/heavy "long term" shortcomings, which, as I have noted, come across to me as greater stability and coherence versus DD "jittery", which has for me a rather digital vagueness with respect to time.

BTW, I did add damping to the platters on my Technics DDs, and even though I got reduced sonic breakthough it just made the speed problems worse, so I certainly agree with your remarks about platter changes.

Best regards,
Paul S
03-02-2008 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 45
Post ID: 6835
Reply to: 6833
I share your prejudges.

I am with you with you anti-servo prejudgeses. The moment from motor, regardless if it is strong or now weak, should be constant. At the very moment when the moment changes it’s value the platter performs a microscopic “move” in it’s bearing. So the forcing moment and the force of slipping in belt or on a roll should be very constant – juts stabilize the voltage and let it to spin as is.

BTW, I very much like how Micro did it this big TT. They have a moron run for a first few seconds in servo mode, just enough to push the platter from stationary position then the servo was shut and the motor/platter tandem are spinning linearly.

Somebody have asked in this thread - where is the necessary limit of stability and compare the low numbers of platter stability with low number of distortions. I do not think that it is a correct comprising. Anyhow, I feel that the stability of platter should be low-enough in order a listener juts not to hear tone variation. It should not be better…

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
03-13-2008 Post does not mapped to Knowledge Tree
enjoy_the_music
Strasbourg, France
Posts 12
Joined on 02-21-2007

Post #: 46
Post ID: 6901
Reply to: 6835
Versa Dynamics 2.3
Hi Romy

I was recently offered two of these turntables...apparently in full working order with all the 'expensive' upgrades.

PaulS tells me they are a real pain!

Do you have experiences with them?

Thanks

Richard
03-17-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,130
Joined on 10-12-2006

Post #: 47
Post ID: 6929
Reply to: 6901
Stirring the water (keeping it murky)

Not one to fix too firmly on a given implementation, I rdecided to futz around with my vacuum holddown this weekend.

The power was not very good, but I was none the less able to determine conclusively that [within the context of my rig] although the sound certainly benefits from the vacuum (as opposed to no vacuum), there is such a thing as too much vacuum suction, which, past a critical point, begins to vacuum away ambience, where it would otherwise be part of the program, and likewise bass harmonics suffer when I overdo the vacuum.

I do not conclude from this that a lesser LP-to-platter coupling is better, because I am not certain if the coupling is wholly directly proportional to the vacuum, or perhaps there are other factors at work having to do with reflections, or new transmission paths, or vacuum leaks, or whatever.  Certainly this phenomenon could be peculiar to my TT - as opposed to all vacuum HD rigs - but even if this is the case I find it interesting.

Anyway, just in the interest of science (in its humorous guise).

I was also thinking some more about speed control and wondering about the "perfect platter bearing", whether it would indeed be friction free or perhaps it should acyually have a certain controlled viscocity/drag, in order to offset motor stepping?  I wonder if in practical terms a quite heavy platter with no perceptable drag would overcome motor cogging and related belt response?  In the case of less-than-very-heavy platters I suspect that some sort of damped "drag" might be a good thing, and perhaps best applied at the spindle as "oil", maybe multi-viscocity oil.

Lastly, if a "fully-levitated platter" is already 100 lbs. of - say - lead, then why should it have a "ground"?  Why not just let it serve as a sink all by itself?

Paul S

03-17-2008 Post does not mapped to Knowledge Tree
hagtech


Hawaii
Posts 117
Joined on 02-13-2006

Post #: 48
Post ID: 6930
Reply to: 6929
Thicker Oil
Paul, I think that is a very good observation.  Seems to me that a really thick grease or oil in a large bearing would offer enough friction such that the motor was always biased into an active positive torque region.  Such would be the equivalent of biasing heavier into class A, as opposed to class AB in a frictionless system.  I think of the motor/belt/platter/stylus as an analog to a single-ended output stage.  The motor can pull or coast, resulting in a non-linear system.  If in a servo loop, it speeds up faster than it can slow down.  I think oil friction might be a good solution to biasing a motor into a more linear operating region.  They key is to minimize the noise of the friction.  It must be as constant as possible.

jh
03-17-2008 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 49
Post ID: 6931
Reply to: 6929
Actually another idea came to me…
I did not think about it in details – juts a brainstorming idea. Pretend you have 100 pounds 12 inch metal platter spinning 33 RPM. The platter has only two problems – suspension and horizontal bearing. The horizontal bearing is regular via a long cylinder but it has a kink about with I will mention later. The bottom of the cylinder via non-decupling gears attached to another 100 pounds cylinder but this bottom cylinder spins, I would say, 500-700 RPM. The bottom cylinder has a slight triangle curve and sits on the cushion of oil. Because the curves and high speed the bottom cylinder slightly rises and floats exploiting the skin effect. The high speed of the bottom cylinder creates a centrifuge effect that maintains the vertical axis, unloading tension from the horizontal bearing. I think it might work…


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
03-17-2008 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,130
Joined on 10-12-2006

Post #: 50
Post ID: 6932
Reply to: 6931
Fluid viscocity/tension
When I was a kid we had a "Fluid Drive" Dodge that used oil rather than gears or friction plates as a torque converter.  But I suspect fluid viscocity and film strength would need to be kept very consistent for the sort of speed accuracy one needs for a TT.  As far as I know, viscocity is always +/- affected by temperature and load conditions, even multi-vis, and if this is true then there would have to be an effective way or ways to counter this in the "drive/float" TT application.

I think both lower speeds and tighter tolerances help the viscous platter bearing scenario, along with the fact that there is the drive motor, too, and the oil is merely offering resistance there.  But in either case it might help to use some sort of sensor controlled heater.

Of course we aren't crunching fluid mechanics numbers, but I wonder, practically speaking, about the potential accuracy available from fluid drive in the home (as opposed to the lab).  If do-able, fluid drive would likely cure cogging or read-and-react type effects.  This might even allow the "transparent use of a speed servo to control the fluid driver. I am not sure about moving fluids as high/low pass filters, but fluid in motion might be different than "static" fluid in these terms.

Paul S
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