Wow, super stuff. Congrats on your ingenuity. 
I've got a couple of magnet ideas on the drawing board too, but the idea suspending my platter was causing me sleepless designing nights due to the fact my TT motor is a direct-drive. (Paradoxically a type of design which would benefit the most, but with the magnetics of the motor being so close... <gulp!>
)
I've got a couple of magnet ideas on the drawing board too, but the idea suspending my platter was causing me sleepless designing nights due to the fact my TT motor is a direct-drive. (Paradoxically a type of design which would benefit the most, but with the magnetics of the motor being so close... <gulp!>
)
Vinyl-Addict said:
sorry, I didn't explain myself very well. You are quite correct there is potentially a cogging issue with using individual magnets; that is why I chose to use many small magnets. I cannot detect any cogging now even at very slow speed and very low load. It is possible that using an uneven number of magnets for the top and bottom elements of the bearing would reduce this effect even further as it when be impossible for the poles to line up and any time. The outer diameter of the ring is not much of an issue. It is possible that a larger ring aids stability but the main reason I chose the size I did was purely practical. i needed 80 magnets to provide sufficient 'lift' and that dictated the bearing diameter. I don't see a problem with using a single ring magnet as you suggest if they provide sufficient force.
sq225917 said:
No, the platter does not vary in height at all during rotation. However, I too would be very interested in measuring any variation if you have access to very accurate measuring equipment. I am happy that cogging is not an issue in this particular implementation unless proved other wise.
I do indeed have access to both a CNC router and a CNC milling machine. The router was used for both the platter mat and the main bearing - lucky me
sq225917 said:
I would be interested in the epoxy/mineral material you describe. However, I am less inclined to use it for the subchasis. The aim with this component was to achieve the greates siffness to mass ratio possible; this aim would be somewhat defeated if I then added a load of mass
- sounds very interesting though.
graeme uk said:
Umm, I'm not sure, I'm getting all confused by people having one user name, then a different real name, and yet another e-mail name. I have received and responded to one e-mail about coming round to my house - if this wasn't to you then I haven't rec'd your e-mail - but you are welcome to come round.
Just seen your e-mail and will repond now - cheers matey
I think it would be great if we could get together.
sq225917 said:
The stuff I used is manufactured for use in the aerospace industry. It consists of twin skins of carbon fibre laminate bonded to an internal structure of honeycomb paper. It is a version of the material used by Pink Trianhel but they used the aluminium bersion which uses aluminium skins and honeycomb. I have used two 12 mm layers bonded together for my suchasis.
I look forward to hearing all about it when we meet up though
Does that mean our other sheffield member wants to meet too?
I dont mind whose house/system we use, whatever works out easiest, but we'll arange via email and leave this thread to its intended purpose.
P.S. im not sure what e.mail address is registered with this site. The e.mail im using now is whtf812@aol.com
If you replied to a different address i wont get it.
I dont mind whose house/system we use, whatever works out easiest, but we'll arange via email and leave this thread to its intended purpose.
P.S. im not sure what e.mail address is registered with this site. The e.mail im using now is whtf812@aol.com
If you replied to a different address i wont get it.
Graeme , yes a meet does seem in order. I have e-mailed you so...I look forward to hearing from you
With regard to using my bearing to suspend a direct drive platter I think it would still be possible. I'm not that familiar with direct drive so will give it an investigate.
With regard to idler wheels, it may also be possible. However, I feel it very much depends on the specific implementation of the drive system.
With regard to using my bearing to suspend a direct drive platter I think it would still be possible. I'm not that familiar with direct drive so will give it an investigate.
With regard to idler wheels, it may also be possible. However, I feel it very much depends on the specific implementation of the drive system.
re and idler driver set up,if it's a rim drive then the contact would be in the same axis as the bearing sleeve, not such a bad thing.
if it was a platter drive, Garrard, most Lencos then the contact would be in the verticle axis which would introduce contact along the floating axis,maybe not so good as the primary load of the wheel to the platter would interrupt the magnetic bearings.
if it was a platter drive, Garrard, most Lencos then the contact would be in the verticle axis which would introduce contact along the floating axis,maybe not so good as the primary load of the wheel to the platter would interrupt the magnetic bearings.
Hmmm, interesting stuff.
I expect a solid ring magnet would be better for this but they can get pretty darn expensive and are, as has already been said, tricky to find.
I don't think you'd want to do away with the radial bearing and replace it with a magnetic one. Firstly you have the pull from the belt, which will mean that your platter inevitably ends up sitting off centre in the magnetic field in a form of 'dip' where the magnetic repulsion and belts pull are in equilibrium. Secondly, you're asking for problems with the platter moving on the horizontal plane, which would make it harder for the arm to track and introduce distortion. Some of the horizontal component of the field ends up being absorbed by the squishyness of the horizontal magnetic suspension - the same as it would in the play of a poor radial bearing, an ideal bearing has 0 tolerance of coarse.
I've spent a lot of time wondering about what the ultimate way to suspend a platter might look like. And I've seen something pretty close on the net.
The platter used regular thrust and radial bearings (I think, and by regular I mean, expensive ceramic bearings... but normal in the contact sense; ceramic obviously less of a problem with the magnets involved) and magnets to offset the weight of the platter. That's important if your platter weighs 30kg, because the weight will mean accelerated wear and increased noise generation / transmission. Using magnets, the design took most of the platter weight off the bearings, reducing those problems.
So then you wonder why bother with the regular bearings at all. Back to the first bit. They'll provide much, much higher rigidity than the magnetic fields, allowing for better tracking. If the platter is completely floating in the vertical direction, some of the force produced as the stylus goes over a vertical component in the groove will be bypassed by the squishyness of the vertical support provided by the magnetics. Hence, how a contact thrust bearing backing up the magnetic bearing might help.
More thoughts....
You could build a magnetic bearing with copper coils or something probably. Might be worth some investigation. A big, flat, multiturn coil should be able to levitate a heavy platter with not a lot of current. Stealing from Valvitude's CD idea for his tesla turbine, you could use two CD's separated by their moulded spacers as a former for a flat coil.
You only need a fraction of a mm for clearance, as the platter doesn't have much vertical force on it. Magnetic fields decay exponentially with distance, and that means the force they produce does as well. So separation distance is expensive, and large values not needed in such an application, making large separations even more of a money burn when magnets aren't cheap
Although the magnetic field might not visibly pull the cartridge down, it does worry me that a magnetic bearing is potentially bathing it in a DC field. The only AC noise with a big, two solid ring magnet layout will be due to grain errors in the magnets. With individual magnets, there will be some AC component as the individual magnets spin past the cartridge.
You could shield the cartridge from the field with strategically placed iron / cobalt / mumetal sheet. I'd recommend waving a cheapo hall sensor over the platter, above the magnetic ring, as it spins, and that way you can see what's actually going on magnetically. Failing a hall sensor, an ultra nasty guitar pickup. Failing the guitar pickup, a coil of wire with a steel bolt through it.
Any change in the DC magnetic field over the cartridge will equate to a magnetic bias. Obviously, it might be so tiny you can't even hear it, but being the people audiophiles are, it's always interesting to consider if something could be improved even further still.
The alternative to a magnetic bearing is an air bearing, but then you're going down the pumps road obviously. Valvitude has an interesting TT thread with mention of a tesla turbine in it. That might a nice, quiet way of levitating a platter.
To test for floating errors on the platter, you'd want to get hold of test record with a flat groove and watch the cartridge output for changes. Changes will, of coarse, include errors in the test track depth and errors in the angle the record makes with the platter surface. You could use a cheap cartridge dragging over the platter surface, with the tonearm locked in place, to test for errors but you'll get a whole load of nosie if the surface isn't smooth, and the cartridge will probably die soon after. Maybe you could put some kind of bearing between the stylus and surface such that the stylus doesn't make direct contact with something moving; effectively turning the tonearm into the arm of a balance, upside down. The only other idea I can think of immediately is to electrically contact the platter with a bent bit of wire than use a second contact above the platter, very close to the surface, and watch for contact / breaks. The second contact could be attatch to a micrometre to allow for very fine adjustment.
The only reasons for the platter to have vertical errors would be;
the vertical 'errors' in the groove (music) pushing it up and down
vertical errors in the turning of the platter
the cogging effect of the magnets
Maybe you could go insane and add an extra ring around the top edge of the disc, pushing it downwards, for even more vertical rigidity.
I'm obviously not trying to say any of this matters and it could all be completely uncalled for.... i'm just thinking aloud in case you find anything interesting to try!
Short of doing all this stuff, I think I'd go for some AAA taper bearing from someone like National Precision. But getting hold of one cheaply would be a mission
You UK guys aware of the UK DIY Audio meet?
I expect a solid ring magnet would be better for this but they can get pretty darn expensive and are, as has already been said, tricky to find.
I don't think you'd want to do away with the radial bearing and replace it with a magnetic one. Firstly you have the pull from the belt, which will mean that your platter inevitably ends up sitting off centre in the magnetic field in a form of 'dip' where the magnetic repulsion and belts pull are in equilibrium. Secondly, you're asking for problems with the platter moving on the horizontal plane, which would make it harder for the arm to track and introduce distortion. Some of the horizontal component of the field ends up being absorbed by the squishyness of the horizontal magnetic suspension - the same as it would in the play of a poor radial bearing, an ideal bearing has 0 tolerance of coarse.
I've spent a lot of time wondering about what the ultimate way to suspend a platter might look like. And I've seen something pretty close on the net.
The platter used regular thrust and radial bearings (I think, and by regular I mean, expensive ceramic bearings... but normal in the contact sense; ceramic obviously less of a problem with the magnets involved) and magnets to offset the weight of the platter. That's important if your platter weighs 30kg, because the weight will mean accelerated wear and increased noise generation / transmission. Using magnets, the design took most of the platter weight off the bearings, reducing those problems.
So then you wonder why bother with the regular bearings at all. Back to the first bit. They'll provide much, much higher rigidity than the magnetic fields, allowing for better tracking. If the platter is completely floating in the vertical direction, some of the force produced as the stylus goes over a vertical component in the groove will be bypassed by the squishyness of the vertical support provided by the magnetics. Hence, how a contact thrust bearing backing up the magnetic bearing might help.
More thoughts....
You could build a magnetic bearing with copper coils or something probably. Might be worth some investigation. A big, flat, multiturn coil should be able to levitate a heavy platter with not a lot of current. Stealing from Valvitude's CD idea for his tesla turbine, you could use two CD's separated by their moulded spacers as a former for a flat coil.
You only need a fraction of a mm for clearance, as the platter doesn't have much vertical force on it. Magnetic fields decay exponentially with distance, and that means the force they produce does as well. So separation distance is expensive, and large values not needed in such an application, making large separations even more of a money burn when magnets aren't cheap
Although the magnetic field might not visibly pull the cartridge down, it does worry me that a magnetic bearing is potentially bathing it in a DC field. The only AC noise with a big, two solid ring magnet layout will be due to grain errors in the magnets. With individual magnets, there will be some AC component as the individual magnets spin past the cartridge.
You could shield the cartridge from the field with strategically placed iron / cobalt / mumetal sheet. I'd recommend waving a cheapo hall sensor over the platter, above the magnetic ring, as it spins, and that way you can see what's actually going on magnetically. Failing a hall sensor, an ultra nasty guitar pickup. Failing the guitar pickup, a coil of wire with a steel bolt through it.
Any change in the DC magnetic field over the cartridge will equate to a magnetic bias. Obviously, it might be so tiny you can't even hear it, but being the people audiophiles are, it's always interesting to consider if something could be improved even further still.
The alternative to a magnetic bearing is an air bearing, but then you're going down the pumps road obviously. Valvitude has an interesting TT thread with mention of a tesla turbine in it. That might a nice, quiet way of levitating a platter.
To test for floating errors on the platter, you'd want to get hold of test record with a flat groove and watch the cartridge output for changes. Changes will, of coarse, include errors in the test track depth and errors in the angle the record makes with the platter surface. You could use a cheap cartridge dragging over the platter surface, with the tonearm locked in place, to test for errors but you'll get a whole load of nosie if the surface isn't smooth, and the cartridge will probably die soon after. Maybe you could put some kind of bearing between the stylus and surface such that the stylus doesn't make direct contact with something moving; effectively turning the tonearm into the arm of a balance, upside down. The only other idea I can think of immediately is to electrically contact the platter with a bent bit of wire than use a second contact above the platter, very close to the surface, and watch for contact / breaks. The second contact could be attatch to a micrometre to allow for very fine adjustment.
The only reasons for the platter to have vertical errors would be;
the vertical 'errors' in the groove (music) pushing it up and down
vertical errors in the turning of the platter
the cogging effect of the magnets
Maybe you could go insane and add an extra ring around the top edge of the disc, pushing it downwards, for even more vertical rigidity.
I'm obviously not trying to say any of this matters and it could all be completely uncalled for.... i'm just thinking aloud in case you find anything interesting to try!
Short of doing all this stuff, I think I'd go for some AAA taper bearing from someone like National Precision. But getting hold of one cheaply would be a mission
You UK guys aware of the UK DIY Audio meet?
Bismuth has been mentioned as a good shielding material. Here is a source in the US for ring magnets.
http://www.unitednuclear.com/magnets.htm
http://www.unitednuclear.com/magnets.htm
The problem with using a ring magnet is that the magnetic force cannot be modified. By using a large number of smaller magnets it is relatively easy to adjust the forces by increasing or decreasing the number of magnets.
I agree that one does not want to do away with the radial bearing - partly for the reasons you give - but also because I doubt that it is possible to do so, as posted earlier.
I am not convinced that rigidity is essential, or even necessarily, desirable, in the vertical plane. The magnetic field is 'squeezed' very tight in my system already.
I am happy that there is no cogging, even at speeds considerably lower than 33rpm if a large number of small magnets are used.
The magnetic bearing sits within the circumference of the label area of the platter so the cartridge does not pass over the magnets at any time.
An electro magnet would have to have a very even and continuously stable field generated.
Air bearings can also suffer from uneven pressure fluctuations and must be a continual loss system (in my opinion).
The whole stability - in terms of flutter - issue is a 'red herring' in my view and is easily avoided with accurate manufacture. Absolutely no 'wavering' in the platter can be seen.
I agree that one does not want to do away with the radial bearing - partly for the reasons you give - but also because I doubt that it is possible to do so, as posted earlier.
I am not convinced that rigidity is essential, or even necessarily, desirable, in the vertical plane. The magnetic field is 'squeezed' very tight in my system already.
I am happy that there is no cogging, even at speeds considerably lower than 33rpm if a large number of small magnets are used.
The magnetic bearing sits within the circumference of the label area of the platter so the cartridge does not pass over the magnets at any time.
An electro magnet would have to have a very even and continuously stable field generated.
Air bearings can also suffer from uneven pressure fluctuations and must be a continual loss system (in my opinion).
The whole stability - in terms of flutter - issue is a 'red herring' in my view and is easily avoided with accurate manufacture. Absolutely no 'wavering' in the platter can be seen.
YNWOAN said:
Yes, but it has been calculated that the smallest groove variation on an LP is the same size as the wavelength of light- are you THAT sure that there is no movement? Can you even see the vibrations of your stylus? Just a thought.
I was thinking about this today, and I agree with eeka chu that a rigid bearing providing the location for the platter, with (permanent) magnets taking 99% of the weight is the way to go. Although with the electromagnet the thrust plate would take a hell of a beating when the magnet is off, especially if there was a power cut while listening to your 78s.
This could even let you use a Rega planar or Linn/Thorens bearing on a table with a 50kg platter- they are good, readily available bearings, but can only really take 1 or 2 kg without damage.
I can see that a floating platter seems nice from a vibrations point, but a suspended plinth should take care of those. Also, the radial bearing will transmit vibrations anyway.
I did read somewhere (the huge 'Let's make a DIYAudio TT' thread?) that having a suspended platter (e.g. magnetic or air bearing) on a suspended plinth would cause all sorts of horrible vibrations all over the place, with each element vibrating at it's own resonant frequency.
James
Your easiest source of ring magnets, are blown ( or new ) bass or PA loudspeakers. The description of the "Platine Verdier" published in l'Audiophile in the late 80's, called for large loudspeaker mag's encased in turned polepieces to increase the field strength.
I started this project many years ago, but it came to a halt when I could not find suitable magnets without buying new and expensive speaker units - as I live in rather rural areas, my sources of "interesting scrap and junk" are quite limited.
If your platter is of reasonable weight, this could be fairly easy. .the Verdier platter I started was over 10 kg's....
EDIT: the bearing for the Verdier, was essentially a combination of the magnet cushion and an inverted bearing, as the platter was also resting on a steel ball on the top of the steel shaft, to take a minor part of the load. Personnally, I think the idea of no true radial bearing is totally futile, given our demands for platter stability.
I started this project many years ago, but it came to a halt when I could not find suitable magnets without buying new and expensive speaker units - as I live in rather rural areas, my sources of "interesting scrap and junk" are quite limited.
If your platter is of reasonable weight, this could be fairly easy. .the Verdier platter I started was over 10 kg's....
EDIT: the bearing for the Verdier, was essentially a combination of the magnet cushion and an inverted bearing, as the platter was also resting on a steel ball on the top of the steel shaft, to take a minor part of the load. Personnally, I think the idea of no true radial bearing is totally futile, given our demands for platter stability.
jrevillug said:
Yes, but it has been calculated that the smallest groove variation on an LP is the same size as the wavelength of light- are you THAT sure that there is no movement? Can you even see the vibrations of your stylus? Just a thought.
I was thinking about this today, and I agree with eeka chu that a rigid bearing providing the location for the platter, with (permanent) magnets taking 99% of the weight is the way to go. Although with the electromagnet the thrust plate would take a hell of a beating when the magnet is off, especially if there was a power cut while listening to your 78s.
This could even let you use a Rega planar or Linn/Thorens bearing on a table with a 50kg platter- they are good, readily available bearings, but can only really take 1 or 2 kg without damage.
I can see that a floating platter seems nice from a vibrations point, but a suspended plinth should take care of those. Also, the radial bearing will transmit vibrations anyway.
I did read somewhere (the huge 'Let's make a DIYAudio TT' thread?) that having a suspended platter (e.g. magnetic or air bearing) on a suspended plinth would cause all sorts of horrible vibrations all over the place, with each element vibrating at it's own resonant frequency.
James
James,
Obviously, I am unable to see the specific movement of the stylus but luckily it is attached to the rest of my Hi-Fi and my ears tell me that a significant improvement in all areas has been achieved. I wonder what specific mechanism you think is likely to cause erroneous signal to enter the cartridge. A suddenly applied force in the nature of pounds would be required to compress the bearing further and this assumes the decks suspension system does not deflect first (which obviously it will). Also, although information is contained in the vertical plane the majority is in the horizontal - the left and right walls of the groove.
I do not agree that taking most of the weight off the platter is the ideal solution - two surfaces scraping together are still scraping (even under a lesser load), though I do agree that it is much better - I may well have a bit more of an experiment along this line.
I do not see the bearing as being in any way a replacement for suspension as it is in fact very stiff and offers very little 'bounce'. I should add that I am not a great fan of very high mass platters or of suspension less decks.
As far as the 'horrible vibrations' issue, I believe this to largely be nonsense. If an element of the structure is going to 'ring' or worse vibrate at its natural resonant frequency it will do whether you are using a point bearing or not. The mechanical damping afforded by a ball and thrust pad is minimal at best. To make 'each element' vibrate at its own resonant frequency would require an energy input level significantly beyond that existing in a turntable in my opinion. Obviously vibration exists and must be channelled or damped but this in no way means that the natural resonant frequency of anything will necessarily be excited.
jrevillug said:
I was thinking about this today, and I agree with eeka chu that a rigid bearing providing the location for the platter, with (permanent) magnets taking 99% of the weight is the way to go. Although with the electromagnet the thrust plate would take a hell of a beating when the magnet is off, especially if there was a power cut while listening to your 78s.
I'm still debating trying out the 99% method myself. I hadn't really thought about completely suspending the bearing because I was concerned about controlling vertical motion during playback. I see now that YNWOAN seems to have achieved this and congrats to him for accomplishing that.
My only concern with his design is the possibility of cogging with multiple magnets eventhough they are equally spaced and defined on a precise circular pattern. I think YNWOAN brought up a good way around possible cogging by using an unequal number of magnets on one surface. BTW YNWOAN, I am not implying that your design suffers from cogging, just concerned that I may not be so "lucky".
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