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Old 4th November 2004, 03:38 PM   #51
livemusic is offline livemusic  Israel
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Quote:
Friction is NOT larger on the outer groove than on the inner.
Assuming the slider resistance exists, the resulting force vector is not vertical anymore (before the preload applied). See below how the normal to the grooves forces are affected by this.
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Old 4th November 2004, 04:08 PM   #52
fdegrove is offline fdegrove  Europe
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Hi,

Quote:
I'm wondering, if one is going to fiddle with air pumps, if the effort might be better spent on a vacuum platter than a linear tracker.
Unfortunately IME at least these vacuum platters cause more trouble than they're worth.
Obviously the record clamp and platter profile don't match too well in your case which gives a varting impedance as seen by the stylus resulting in chatter fed back to it.

IMO the best playback surface I've ever used was the Goldmund platter mat, a solid metacrylate with a slightly concave profile, combined with their record weight.
This gave an even contact across the entire record surface and was the most neutral sounding combo I ever tried.

Unfortunately, there's almost no info about this gizmo available on the net but it can't be too hard to machine in a workshop.

Quote:
Assuming the slider resistance exists, the resulting force vector is not vertical anymore (before the preload applied).
Once you've overcome the initial slider resistance (AKA stiction) by applying a preloaded force it is no longer required and if left in place it will in effect become the cause of vectorial forces itself.

Cheers,
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Old 4th November 2004, 04:18 PM   #53
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by fdegrove
Hi,



Unfortunately IME at least these vacuum platters cause more trouble than they're worth.
Obviously the record clamp and platter profile don't match too well in your case which gives a varting impedance as seen by the stylus resulting in chatter fed back to it.

IMO the best playback surface I've ever used was the Goldmund platter mat, a solid metacrylate with a slightly concave profile, combined with their record weight.
This gave an even contact across the entire record surface and was the most neutral sounding combo I ever tried.

Unfortunately, there's almost no info about this gizmo available on the net but it can't be too hard to machine in a workshop.

Cheers,
Actually, the clamp works about as well as it could without a concave platter. The effect I mention is subtle, and not always noticable. But it's there. I can see where setting up a vacuum platter would have a number of issues to conquer, but I can't see any other way of effectively clamping the record evenly over its entire surface. I would think that the main problems would result from the pump operating while the platter is spinning, and the bearing/seal issues that entails. If an effective platter to record seal could be developed, such that no active pumping would be required during playback, then it might be feasible.

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Old 5th November 2004, 12:41 AM   #54
fdegrove is offline fdegrove  Europe
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Hi,

Quote:
I would think that the main problems would result from the pump operating while the platter is spinning, and the bearing/seal issues that entails. If an effective platter to record seal could be developed, such that no active pumping would be required during playback, then it might be feasible.
Actually active pumping isn't required during playback provided you can keep the vacuum long enough to play one record side at least.

In most commercial efforts I've seen, a seal is established by using soft rubber lips around the edges of the platter and the use of a valve to keep the air inside the platter/record interface.

However, here's the rub: too high a vacuum and chances are some airpockets in the vinyl will burst open leading to damage and consequently higher surface noise.
Whatever crud is still on the bottom side, be that the platter itself or the unplayed side of the record, is pressed into the soft vinyl surface which in turn will lead to increased surface noise as well...

Too little pressure and the effect is lost entirely, the record won't sit flat on the platter anymore either.
As I toyed with both a Thorens vacuum system and an Audio Technica one as well, I speak from hands on experience.
Needless to say I gave up on the idea and settled for the, to my ears at least, excellent Golmund combo.

Another often forgotten issue with records tightly coupled to the platter via a record puck is that if the spindle is coupled to the bearing housing, it will now also transmit any bearing noise directly to the record itself....

Cheers,
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Old 14th November 2004, 11:39 AM   #55
slowmotion is offline slowmotion  Norway
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Hi all

I haven't read the whole thread
( which I probably should do before I say anything)
but here goes:

Regarding record clamps: I've stopped using them, don't miss them.

Anti skating:
Most of my records do NOT have the spindle hole in the center of the record.
I use a tangential tonearm, and I don't see any need at all for messing with antiskating
on that kind of arm.
Different with a conventional arm, of course.

But the little problem with non-centered records means that antiskating on
tangential tonearms is a waste of time IMHO,
even if there may be a theoretical advantage .

Watching the tonarm from the front when playing records the cantilever never moves sideways even if the record is seriously off center,
if it did there would something seriously wrong, I think.
The arm itself move , of course.

IMHO tangential tonearms may or may not sound better than convention arms,
that's beside the point really. But they are much simpler to set up and adjust,
and they are also simpler to make , I think. No problems with bearings and no antiskating.

YMMV, and all that


cheers
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Old 14th November 2004, 07:45 PM   #56
Jarno is offline Jarno
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Default Congrats

Hello Peterr,

Congratulations on your work! The tone-arm looks great!
I am thinking I should the resume work one mine as well!

Excuse me for being slightly off topic regarding the physics discussion.

Regards,

Jarno.
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Old 14th November 2004, 09:11 PM   #57
harhaug is offline harhaug  Norway
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Quote:
Originally posted by peterr

This I really don't understand
Friction is NOT larger on the outer groove than on the inner.
Friction is INdependent of surface area, speed (except when v = 0), and temperature.
It only depends on the nature of the surfaces in contact and is directly proportional to the normal force. (in this case tracking force)
Just google around a little to see this is true.
So there will not be an inward force resulting from this.
First things first: I like your Ladegaard arm, peterr!

Google is not a good source for facts about friction (nor are freshman physics textbooks): Friction may very well depend on surface area, speed and temperature in a complicated fashion.

For instance, the local temperature depends on the frictional force and speed, since the rate of energy dissipation by friction is W = (friction force) x (speed). This frictional work causes local heating near the contact area, which in turn alters the friction coefficient in a way that depends on the details of the interaction between the two materials.

Furthermore, a large pressure (force/contact area) may alter the properties of one or both of the materials in contact (in this case most likely the vinyl).

So you see, the details of friction is a highly non-trivial area. Fun for the researcher, frustrating for the TT designer!



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Old 20th April 2005, 02:26 PM   #58
seppstefano is offline seppstefano  Italy
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Ciao Livemusic, dice45 and all,
I seem I got what you're saying.

Many thanks for this absolutely interesting thread!




Stefano
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