livemusic, dice,
you talked about wobbling and center of gravity. for those not using a dd there is another force pulling at the platter. if one would use a tape and positioned the upper end just below the CoG end so that if the platter lowers for a defined distance (say 1mm) could the traction of the motor be used to compensate for the downforce of the pickup? i would think of the pickup excercising for on the one side and the motor ajacent to it to compensate. this would mean one would have to measure the tilt one gets from the motor and be able to ajust this to a very fine point.
Hope you got what i meant🙂
you talked about wobbling and center of gravity. for those not using a dd there is another force pulling at the platter. if one would use a tape and positioned the upper end just below the CoG end so that if the platter lowers for a defined distance (say 1mm) could the traction of the motor be used to compensate for the downforce of the pickup? i would think of the pickup excercising for on the one side and the motor ajacent to it to compensate. this would mean one would have to measure the tilt one gets from the motor and be able to ajust this to a very fine point.
Hope you got what i meant🙂
Hi everyone
To my opinion dynamic wobble I mentioned later may be effectively balanced by symmetrical belt arrangement (see the sketch). Belt – platter sufficient friction is essential here. This could be easily achieved by using 1/2" VCR tape. Redpoint reported particularly good results with wide VCR tape – see http://www.nakedresource.com/vinyle...board=general;action=display;num=10267477716. The wide tape is very stiff/not comliant and can balance the tilt moment at the same time it appears, not allowing vibrations to develop.
Is there any specific problem with idler pulley?
Difool,
Putting the belt below bearing pivot point induce the platter tilt in advance due to belt tension. Not good, because CG is already shifted (or stabilizing force is uneven) – the only thing needed to get the wobble started. Things getting worse with low RPM (when the platter only starts spinning): precession magnitude rises because spinning momentum (rotation inertia) is low. Belt centerline being in the same plane with pivot point is a must.
To my opinion dynamic wobble I mentioned later may be effectively balanced by symmetrical belt arrangement (see the sketch). Belt – platter sufficient friction is essential here. This could be easily achieved by using 1/2" VCR tape. Redpoint reported particularly good results with wide VCR tape – see http://www.nakedresource.com/vinyle...board=general;action=display;num=10267477716. The wide tape is very stiff/not comliant and can balance the tilt moment at the same time it appears, not allowing vibrations to develop.
Is there any specific problem with idler pulley?
Difool,
Putting the belt below bearing pivot point induce the platter tilt in advance due to belt tension. Not good, because CG is already shifted (or stabilizing force is uneven) – the only thing needed to get the wobble started. Things getting worse with low RPM (when the platter only starts spinning): precession magnitude rises because spinning momentum (rotation inertia) is low. Belt centerline being in the same plane with pivot point is a must.
Attachments
Umm, seems like a lot of conjecture going on here.
Really, how much is 1 Gram of stylus tracking force going to tilt a very heavy platter ?.
Eric.
Really, how much is 1 Gram of stylus tracking force going to tilt a very heavy platter ?.
Eric.
TT
Livemusic,Bernhard,Havoc et all,
In the context of an airbearing TT system Livemusic's drawing isn't a bad idea.The introduction of a second pulley positioned opposite the pulling force of the motor would effectively null the sideways pull on the floating platter.
Only drawback I see is the introduction of yet another source of noise.
Further musings?
Rgds,
Livemusic,Bernhard,Havoc et all,
In the context of an airbearing TT system Livemusic's drawing isn't a bad idea.The introduction of a second pulley positioned opposite the pulling force of the motor would effectively null the sideways pull on the floating platter.
Only drawback I see is the introduction of yet another source of noise.
Further musings?
Rgds,
what if the stylus movement is not perpendicular but on an arc? like most tonearms?Biggest problem is alignment. Now you have 3 axes that need to be aligned in several directions. Otherwise a valid solution.
If you all don't hear from me for the time coming, don't worry. Or just worry that I will come back 🙂 I had a HD crash this weekend, ruining a registry file. Got it back running without dataloss, but I have to reinstall everything.
If you all don't hear from me for the time coming, don't worry. Or just worry that I will come back 🙂 I had a HD crash this weekend, ruining a registry file. Got it back running without dataloss, but I have to reinstall everything.
TT
Hello Havoc,
Guess you're runnin' Windoz NT or 2000?
Installing the command recovery console might have helped.
If you need help on this,I got the expertise I think.
Fully blown Siemens enigeneer you see...
Anyhow you're dead on as usual.
One could align the whole system and isolate both idler pulley and motor form the plinth with lead loaded isolation bases ?
Holding my breath till you'r back online...
Rgds,😉
Hello Havoc,
Guess you're runnin' Windoz NT or 2000?
Installing the command recovery console might have helped.
If you need help on this,I got the expertise I think.
Fully blown Siemens enigeneer you see...
Anyhow you're dead on as usual.
One could align the whole system and isolate both idler pulley and motor form the plinth with lead loaded isolation bases ?
Holding my breath till you'r back online...
Rgds,😉
TT
Havoc,Bernhard and all concerned,
Havoc's expression about the alignment problem is not one to underestimate I think.
This is actually one of the major points why I rejected air-bearing TT's in the first place.No firm reference to earth really.
This is a valid point for air-bearing tonearms as well.Lateral movement is impeded by airpressure and so on.
Only way to go is mass,mass and again mass.Which brings as only solution air-pressure and again air-pressure.
Anyone got a rough idea of the downforce exerted by a 2g loaded cartridge on the tip (a point) of the stylus ?
IMO it's not because a TT design costs an arm and a leg it's half-way decent you know...
Still a lot of things to sort out here.
Personally,I'd rather see a no holds barred pivot design.But then again I'm a plain old school kinda guy.
Rgds,
Havoc,Bernhard and all concerned,
Havoc's expression about the alignment problem is not one to underestimate I think.
This is actually one of the major points why I rejected air-bearing TT's in the first place.No firm reference to earth really.
This is a valid point for air-bearing tonearms as well.Lateral movement is impeded by airpressure and so on.
Only way to go is mass,mass and again mass.Which brings as only solution air-pressure and again air-pressure.
Anyone got a rough idea of the downforce exerted by a 2g loaded cartridge on the tip (a point) of the stylus ?
IMO it's not because a TT design costs an arm and a leg it's half-way decent you know...
Still a lot of things to sort out here.
Personally,I'd rather see a no holds barred pivot design.But then again I'm a plain old school kinda guy.
Rgds,
The force concentrated per square mm at the stylus tip is very high granted. The tipping force on the platter is only 2 grams. Duh
No need necessarily for a snooker ball. If you read my early (first?) post, I was talking about using a very large steel ball as used in ball bearings. They come in sizes larger then you might think. Dice expressed concern about clearance between the ball and socket at the time. I see he has come up with a way to solve this.
There are two air bearing ideas here. The original ball and socket, and the one with the two flat plates. A unipivot would use the ball alone. They were also discussed in various combinations.
There are two air bearing ideas here. The original ball and socket, and the one with the two flat plates. A unipivot would use the ball alone. They were also discussed in various combinations.
test results
Last night I finished my prototype!The design is like the pics I posted before.
It works
Photos will be posted as soon as I have them. (No digital camera).
My findings are very similar to Pete's
I have no suitable motor so I rotated the platter by hand. Clearance around the rim is about 10mm. bottom clearance is adjustable.
Observations:
1) No fluid.
Platter wobbles and doesn't stabilize properly when spinning.
2) 10W40 engine oil.
Bottom clearance is about 2mm. Platter becomes stable very quickly after initial startup wobble. Platter also stops very soon due to high drag. I then changed the clearance to about 6mm. The platter kept on spinning a little a bit longer but still stopped far too quickly.
3) Sunflower cooking oil.
Bottom clearance is about 2mm. Platter again becomes stable very quickly after initial startup wobble. Platter goes on spinning a lot longer than with 10W40. Changed the clearance to 6mm. Again the platter spins longer, though I feel it is not long enough.
4) Water.
Bottom clearance is about 2mm. Platter again becomes stable very quickly after initial startup wobble. Platter goes on spinning for a very long time. Changing the clearance to 6mm didn't make much of a difference in this case.
General findings:
Although I made all surfaces reasonably smooth I noticed quite a bit of ripple in the fluid ( especially water) Around the platter you could see a pattern of very small ( perhaps 0.5mm high, 15mm wide) waves.
The amount of fluid didn't seem to make much difference. As long as the gap between the bottom and the plinth was filled.
Stabilization of the platter is more or less independent of fluid viscosity. But it is dependent of rotational speed. When the platter slows down there comes a moment it begins to wobble again. We will have to make sure that this happens well below 33 rpm.
It is messy. Once everything is in place I think it will be allright, but before that it is very difficult to keep the oil from places you don't want it to go. In a final design I think the fluid must be kept under the platter and out of sight and touch.
And now?
I have made my model in such a way that I can actually use it. So when I get the motor I will do so and see how it sounds. After all that's what it is all about, right? I can only compare it to is my Thorens td125 mk2 though.
Areas I feel could be further explored are first of all the size of the bottom area in contact with the fluid. In this model that area is the size of the platter. I guess that if you reduce this you also reduce drag a lot without, I hope, reducing the stabilizion forces to the same degree. Secondly I like to know what happens if you change the size of the opening around the platter, but I suspect this will have very little influence as long as the bottom area is so much larger.
Last night I finished my prototype!The design is like the pics I posted before.
It works
Photos will be posted as soon as I have them. (No digital camera).
My findings are very similar to Pete's
I have no suitable motor so I rotated the platter by hand. Clearance around the rim is about 10mm. bottom clearance is adjustable.
Observations:
1) No fluid.
Platter wobbles and doesn't stabilize properly when spinning.
2) 10W40 engine oil.
Bottom clearance is about 2mm. Platter becomes stable very quickly after initial startup wobble. Platter also stops very soon due to high drag. I then changed the clearance to about 6mm. The platter kept on spinning a little a bit longer but still stopped far too quickly.
3) Sunflower cooking oil.
Bottom clearance is about 2mm. Platter again becomes stable very quickly after initial startup wobble. Platter goes on spinning a lot longer than with 10W40. Changed the clearance to 6mm. Again the platter spins longer, though I feel it is not long enough.
4) Water.
Bottom clearance is about 2mm. Platter again becomes stable very quickly after initial startup wobble. Platter goes on spinning for a very long time. Changing the clearance to 6mm didn't make much of a difference in this case.
General findings:
Although I made all surfaces reasonably smooth I noticed quite a bit of ripple in the fluid ( especially water) Around the platter you could see a pattern of very small ( perhaps 0.5mm high, 15mm wide) waves.
The amount of fluid didn't seem to make much difference. As long as the gap between the bottom and the plinth was filled.
Stabilization of the platter is more or less independent of fluid viscosity. But it is dependent of rotational speed. When the platter slows down there comes a moment it begins to wobble again. We will have to make sure that this happens well below 33 rpm.
It is messy. Once everything is in place I think it will be allright, but before that it is very difficult to keep the oil from places you don't want it to go. In a final design I think the fluid must be kept under the platter and out of sight and touch.
And now?
I have made my model in such a way that I can actually use it. So when I get the motor I will do so and see how it sounds. After all that's what it is all about, right? I can only compare it to is my Thorens td125 mk2 though.
Areas I feel could be further explored are first of all the size of the bottom area in contact with the fluid. In this model that area is the size of the platter. I guess that if you reduce this you also reduce drag a lot without, I hope, reducing the stabilizion forces to the same degree. Secondly I like to know what happens if you change the size of the opening around the platter, but I suspect this will have very little influence as long as the bottom area is so much larger.
Peterr,
i am home. Tututut!
Good work!
I would go with demineralized water and keep the bottom gap small.
And see that you get as much drag as you still feel comfortable with: steady base load, dynamically changing load as small as possible = good speed stability.
Oh yes, think about a mess-free design. 🙂
i am home. Tututut!
Good work!
I would go with demineralized water and keep the bottom gap small.
And see that you get as much drag as you still feel comfortable with: steady base load, dynamically changing load as small as possible = good speed stability.
Oh yes, think about a mess-free design. 🙂
Peterr
Congratulations!!
Someone actually doing stuff is always so impressive!!!
so here's a smily party for you!
🙂 😎 😀
Well, your fluid bath combined with the high unipivit idea seems to be a winner. Different then all of our original ideas, but a successful synthesis of most of them. I guess the next issue is whether it is actually a good turntable for playing music. 😉
I'm tempted to try my original concept- the 2" ball air bearing unipivot with your fluid damping. Using water as a fluid might be a lot of hassle with evaporation. A possible solution to the mess problem is to have a fin that extends from the platter to cover the crack between the platter and plinth.
One of the apealing things about oil is that it is available in so many viscosities, but this doesn't seem so necessary.
Here's an idea: use distilled water but with a resovior bottle upside down in the plinth with a tube that ends at the height we want the water at. Very similar to the water bottles for rat and hamster cages! this would ensure that the level is constant.
If this thread is ever divided, I think it would be better to split it into "Highest end turntable" and "great high end turntable for the money" rather than functionally (motor, plinth, etc)
Too many splits takes away life I think. Some topics such as the motor might be applicable to both, such as the motor maybe.
Again: way to go!!
MArk
Congratulations!!
Someone actually doing stuff is always so impressive!!!
so here's a smily party for you!
🙂 😎 😀
Well, your fluid bath combined with the high unipivit idea seems to be a winner. Different then all of our original ideas, but a successful synthesis of most of them. I guess the next issue is whether it is actually a good turntable for playing music. 😉
I'm tempted to try my original concept- the 2" ball air bearing unipivot with your fluid damping. Using water as a fluid might be a lot of hassle with evaporation. A possible solution to the mess problem is to have a fin that extends from the platter to cover the crack between the platter and plinth.
One of the apealing things about oil is that it is available in so many viscosities, but this doesn't seem so necessary.
Here's an idea: use distilled water but with a resovior bottle upside down in the plinth with a tube that ends at the height we want the water at. Very similar to the water bottles for rat and hamster cages! this would ensure that the level is constant.
If this thread is ever divided, I think it would be better to split it into "Highest end turntable" and "great high end turntable for the money" rather than functionally (motor, plinth, etc)
Too many splits takes away life I think. Some topics such as the motor might be applicable to both, such as the motor maybe.
Again: way to go!!
MArk
Peterr
Well done!
1.Important finding: quick stabilization – really encouraging. What is the platter weight? Small bottom gap: good point,- dynamic wedge effect.
2.Try to set the pivot point close to center of mass (now the pivot is above CM, I guess?) – that’s why the platter wobbles without fluid (gyro precession).
3.You right – the less the platter submerged diameter, the better for fluid laminar flow. So more viscous fluid does. But: actually stabilizing force is proportional to square of radius (volume increment) and fluid density. Anyway, it is highly desirable to keep the flow laminar – no ripples, no waves, no vibrations. The constant drag is not such a bad thing.
Congrat
Michael
Well done!
1.Important finding: quick stabilization – really encouraging. What is the platter weight? Small bottom gap: good point,- dynamic wedge effect.
2.Try to set the pivot point close to center of mass (now the pivot is above CM, I guess?) – that’s why the platter wobbles without fluid (gyro precession).
3.You right – the less the platter submerged diameter, the better for fluid laminar flow. So more viscous fluid does. But: actually stabilizing force is proportional to square of radius (volume increment) and fluid density. Anyway, it is highly desirable to keep the flow laminar – no ripples, no waves, no vibrations. The constant drag is not such a bad thing.
Congrat
Michael
thank you all 
What is the platter weight? 9.3kg
I think the best fluid will be some sort of very runny oil (viscosity about the same as water) as water evaporates too fast. Haven't done research into this though. So if anybody has any suggestions....
Otherwise the hamsterbottlemay be a good solution.
The
Peterr
That new avatar is wild. On 1st glance it looks like something from Alien the movie. A closer look it looks like someone's supper. On 3rd look i'm back with Aliens.
dave
That new avatar is wild. On 1st glance it looks like something from Alien the movie. A closer look it looks like someone's supper. On 3rd look i'm back with Aliens.
dave
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