I didn't use iron filings actually - but it is an excellent idea - I just haven't got round to buying any yet.
I did in fact use my stylus pressure gauge. I measured the tracking force at the point where the magnets are positionesd and found a variation. I then used a very small washer and was able to get it to 'jump' to either side of the magnet positioning. Anyway, the shielding seems to have cured the problem - or reduced it to an extremely low level - no tracking force difference can now be measured.
Anyway, I'm going to re-machine the whole thing on Thursday afternoon from black acrylic.
I'm more concerned with my faulty speaker at the moment. I thought I had sourced a spare mid/bass driver but they have let me down. I'm sending the driver off to a company who may be able to repair it, but they also may not be able to as spares are no longer availiable for Epos ES14's. I really don't want to change my speakers but I might not have much choice. I went to audition potential replacements last week and was very underwhelmed.
i went to buy some more magnets for my MK2 version today and had quite a long chat with the supply company. They tell me that they caan make custom magnets but the mould cost would be in the order of £150 - plus a mimimum order quantity. To be honest, I was surprised the cost was so little. They also had a couple of very large ring magnets with a rod running through them - I couldn't get them to touch even when standing on them.
I did in fact use my stylus pressure gauge. I measured the tracking force at the point where the magnets are positionesd and found a variation. I then used a very small washer and was able to get it to 'jump' to either side of the magnet positioning. Anyway, the shielding seems to have cured the problem - or reduced it to an extremely low level - no tracking force difference can now be measured.
Anyway, I'm going to re-machine the whole thing on Thursday afternoon from black acrylic.
I'm more concerned with my faulty speaker at the moment. I thought I had sourced a spare mid/bass driver but they have let me down. I'm sending the driver off to a company who may be able to repair it, but they also may not be able to as spares are no longer availiable for Epos ES14's. I really don't want to change my speakers but I might not have much choice. I went to audition potential replacements last week and was very underwhelmed.
i went to buy some more magnets for my MK2 version today and had quite a long chat with the supply company. They tell me that they caan make custom magnets but the mould cost would be in the order of £150 - plus a mimimum order quantity. To be honest, I was surprised the cost was so little. They also had a couple of very large ring magnets with a rod running through them - I couldn't get them to touch even when standing on them.
graeme uk said:
Not really sure - no more than £2000 though. There's a shop in sSheffield with a mint second hand pair of Martin Logan's I would like to hear - will arrange a dem next week.
Oh yeah, I also contacted Wilmslow Audio and they should be sending me some info too.
I must come round to hear your speakers.
Whenever you like, although im reduced to using a stanton 500 cart at the moment.
Shure V15VxMR on its way though
Just bought a new cd player too, technics sl p1200, just cost i found one at a good price, i figured it was worth a try.
by the way, if you like mine, the upgraded tweeter is even better. The floor standers have more bass, but as you have a sub you can concentrate elswhere.
I have also heard the acorn ELS kits and there very good, i can put you in touch with there suppler for a demo if you wish, he's blackburn way if i remember right.
Shure V15VxMR on its way though
Just bought a new cd player too, technics sl p1200, just cost i found one at a good price, i figured it was worth a try.
by the way, if you like mine, the upgraded tweeter is even better. The floor standers have more bass, but as you have a sub you can concentrate elswhere.
I have also heard the acorn ELS kits and there very good, i can put you in touch with there suppler for a demo if you wish, he's blackburn way if i remember right.
YNWOAN said:
Sounds like fun! Was the £150 perhaps a quote for ones that would produce that kind of repulsion? I'm guessing you weigh at least 50 or 60kg, which is at least twice what I'd expect most people to go for with platter weight, probably more like four or five times.
Are you sure the tracking guage measurement is fine enough if you're suspending something as sensitive as magnetic pickup directly over the field?
eeka chu said:
I'm afraid I weigh significantly more than 60kg.
I am quite certain that the figure I was quoted was for the cost of manufacturing a custom mould to produce a ring magnet similiar in design to the multiple array I am using at present; I did say most of this in my previous post.
Yes, I'm quite happy that the tracking gauge measurement is fine enough - they are designed to be pretty sensitive you know. in truth it is not possible for the cartridge to sit directly over the field as it exists within the circumference of the record label.
Ok, I've just spent seven long hours, with no break or lunch, making the Mk2 version of my magnetic bearing. Technically, it's an improvement in accuracy, ballance and shielding but what a pain to make - even with a full workshop and CNC machinery. I've taken a couple of pics and will post them tomorrow if anybody is interested. I've just finished installing it and it seems to be an improvement . However, the MK1 worked fine, if I'm honest, and I can't help but wonder if it really needed to be 'improved'- anyway, it has been now so that's that.
Going for a shave and a wash now before I go out
Going for a shave and a wash now before I go out
OK, here are the pics; I've taken them showing the new part (black) with the equivalent MK1 part (white):
The lower part of the bearing that sits on the sub-chasis surrounding the main bearing. Now has slightly tighter tolerances and is lower in profile.
The upper part of the bearing that sits in the inner platter. Now incorporates a large shielding disc and is constructed in such a manner as to create a gap between the magnets and the shielding and between the shielding and the under side of the platter. Toleranxes of this component are also improved.
The lower part of the bearing in place on the sub-chasis.
The upper part of the bearing fitted to the inner platter (the radial ring pattern seen is a reflection of the flash from the oil on the shaft of the main bearing).
I've done some experimentation to make sure the stray magnetic field has been elimenated and all seems well. However I have a 'cunning plan' that should test it a bit better - will see tomorrow.
I've had a few more thoughts on materials and manufacturing methods; as a ressult it is likely I will do a MK3 version in a week or so. I think I will probably use HIPS instead of Acrylic and the specific construction and manufacture method will be steamlined; the form will be the same (at the moment).
On a different note(sic) the speaker top cone things are made by Totem and called Beak's (not Audio Physics as I stated earlier).
I've also been having a lot of turntable (and speaker) design thoughts. i think most of the turntable is clear in my head now. I've got a lot of CAD to do though before I can start any manufacture - and I may have to make speakers my priority, I really fancy building some. I've built lots of spaekers in the past as projects with my students (some used some nice ideas and materials) but I could do some really nice ones aiming for SOTA - carbon fibre laminate cabinet, CNC machined baffles etc.
An externally hosted image should be here but it was not working when we last tested it.
The lower part of the bearing that sits on the sub-chasis surrounding the main bearing. Now has slightly tighter tolerances and is lower in profile.
An externally hosted image should be here but it was not working when we last tested it.
The upper part of the bearing that sits in the inner platter. Now incorporates a large shielding disc and is constructed in such a manner as to create a gap between the magnets and the shielding and between the shielding and the under side of the platter. Toleranxes of this component are also improved.
An externally hosted image should be here but it was not working when we last tested it.
The lower part of the bearing in place on the sub-chasis.
An externally hosted image should be here but it was not working when we last tested it.
The upper part of the bearing fitted to the inner platter (the radial ring pattern seen is a reflection of the flash from the oil on the shaft of the main bearing).
I've done some experimentation to make sure the stray magnetic field has been elimenated and all seems well. However I have a 'cunning plan' that should test it a bit better - will see tomorrow
.I've had a few more thoughts on materials and manufacturing methods; as a ressult it is likely I will do a MK3 version in a week or so. I think I will probably use HIPS instead of Acrylic and the specific construction and manufacture method will be steamlined; the form will be the same (at the moment).
On a different note(sic) the speaker top cone things are made by Totem and called Beak's (not Audio Physics as I stated earlier).
I've also been having a lot of turntable (and speaker) design thoughts. i think most of the turntable is clear in my head now. I've got a lot of CAD to do though before I can start any manufacture - and I may have to make speakers my priority, I really fancy building some. I've built lots of spaekers in the past as projects with my students (some used some nice ideas and materials) but I could do some really nice ones aiming for SOTA - carbon fibre laminate cabinet, CNC machined baffles etc.
Well, I did a whole lot of messing about and measuring today to discover problems (if they exist). I tried to get an idea of the residual magnetic field produced but with no clear result. There is definately still a field present but it is very low in level and I can't get my cartridge (Linn Troika) to 'see it'. I rooted out another stylus ballance of mine - this one was made by michell engineering and uses a unipivot in a saphire cup as its pivot so is very, very sensitive to movement (but a major pain to use) - no variation can be detected.
I also did some motor breakthrough and low frequency isolation tests - very pleased with the result of both of these.
I also built a simple test rig to look at bearing stability and the effects of increased load on the magnetic bearing. early indication is that the more compressed the magnetic field the greater the 'cogging' effect is. At present the magnetic gap is 4mm. I have ordered a large ring magnet to invetigate further.
I also did some motor breakthrough and low frequency isolation tests - very pleased with the result of both of these.
I also built a simple test rig to look at bearing stability and the effects of increased load on the magnetic bearing. early indication is that the more compressed the magnetic field the greater the 'cogging' effect is. At present the magnetic gap is 4mm. I have ordered a large ring magnet to invetigate further.
YNWOAN said:
[note to self: ynwoan too heavy for platter construction]
I'm not sure if you said that, if I'd seen it I wouldn't have asked. But for a ring magnet that will fit inside the circumfrence of the label, I think you could almost certainly find something premade on the net; I think one of the sites already posted had something close (http://www.engconcepts.net/List_Of_Ring_Magnets.asp). No idea how much repulsion you'd get but some of them look pretty intense.
I was only thinking of how much a custom one would be because I haven't seen anything that would fit round the circumfrence of the disc it's self, and can't really think of any standard applications that would need something like that. If you could get one to go round the circumfrence of the platter, it'd make it a more stable structure; holding a plate with your finger tips spread round the circumfrence is much easier than pinching them together and balancing the plate in the centre, if you get what I'm jibbering about.
YNWOAN said:
Those look pretty. What kind of CNC gear do you have available?
That makes sense, the effect should be next to zero for an actual ring magnet; not quite if you want to start getting ultraphile, since the magnet has discrete domains in it, but seriously....
YNWOAN said:
I meant to say earlier but I've been really busy, I have a few high sensitivity Hall sensors left over from something I was doing last year. I'm pretty sure they're still stored in my "collection of important stuff, not junk". If you like, I'll have a quick look, see if I can find you one and put it in the post.
They're really simple, three pins. You just need some voltage on two (I think I used a 9V batery) and you read the voltage off between the ground and third with a DMM. Being Hall sensors, they'll detect DC fields.
You could wave one over the platter and see if you can find the field. It'd give you a quantitative measure of the actual field present.
Given all the talk earlier about the lack of give in the vertical plane of the platter, would it be so crazy to consider replacing the remaining radial bearing? I suppose unless you were using very strong magnets, using a belt drive wouldn't be a great idea.
If you were to make the shaft of the platter reasonably long and then put a ring magnet pair at the top and the bottom, it would obviously be a lot more resistant to tilting than if you were to just drop a single pair of magnets in where the original bearing was.
Only problem with replacing the radial bearing is I don't think neodymium likes being magnetised in that particular geometry. The ring magnets I've seen magnetised in that orientation (90 degrees to the 'thrust' magnet you're working with) were composites made of a few magnets I think, which could be better. I think they have to be over a certain dimension before you can get them as one solid magnet.
I have access to both a CNC milling machine and a CNC Router.
The shielding disk element is turned on a Lathe.
Err, yes, very kind offer. If you have some way of accurately measuring the magnetic forces I would most grateful.
I think I have overstated the level of stability the magnetic ring offers. The magnetic field appears to be relatively un-compressed - hence, cogging is very minor. I doubt that even a ring magnet round the rim would be sufficient to stabilise the platter to an adequate degree. The ring magnet I have ordered is from a site posted by another contributor to this thread but is a little larger than ideal. Hopefully, its continuous construction will produce a greater level of magnetic force and I can therefore use fewer magnets in the upper element of the bearing.
The shielding disk element is turned on a Lathe.
Err, yes, very kind offer. If you have some way of accurately measuring the magnetic forces I would most grateful.
I think I have overstated the level of stability the magnetic ring offers. The magnetic field appears to be relatively un-compressed - hence, cogging is very minor. I doubt that even a ring magnet round the rim would be sufficient to stabilise the platter to an adequate degree. The ring magnet I have ordered is from a site posted by another contributor to this thread but is a little larger than ideal. Hopefully, its continuous construction will produce a greater level of magnetic force and I can therefore use fewer magnets in the upper element of the bearing.
YNWOAN said:
Okay, always the way, it's in your way when you don't need it and disappears when you do, but I found them... if you PM me your address I'll post one tomorrow. I did a quick check and I think you'll need 4.5 to 5.5Vdc for the power, I probably used a 9V battery with a pot across it.
If my memory of which one I got is correct, you'll be able to get an absolute measurment of the field, not just relative.
With the magnetic ring, my thoughts were along the lines of how easy it is for imperfections to make it wobble/tilt on its axis for the same field strength. The smaller the OD of the ring, the more it becomes like a plate spinning on a finger, so any slight mistake will make it start wobbling, even if it's virtually impossible to press the platter down any further against the magnet supporting it (think of a small OD magnet like a jewel pivot). For the same field strength, it'd be harder to make it wobble/tilt if the support was around the circumfrence, thinking about moments of forces rather than just the repulsive force alone. A small OD ring is more like a pivot, whereas a large OD (even if it has a large ID as well) is more like a support. For the same strength of magnet, it should be harder to make the platter wobble/tilt if magnets are round the edge of the platter.
Photoshoppers, quake in fear of my MS Paint skills!
An externally hosted image should be here but it was not working when we last tested it.
In the real world, if they were the same strength magnets, they'd be scaled in size a bit better (e.g. the small OD one would be thicker than the large OD one), and the large OD one should go just around the edge, not under where the disc would be, but it only took me two minutes in paint, so there's room for variations from reality...
Hello Iain,
Yes, I have experimented a little more. I did purchase a reasonably large ring magnet but I still intend to use a circular array of small magnets as the opposite 'force provider' so that I have more control over the strength of the magnetic field (i.e. more or less numbers of magnets used). To be honest my MK2 seems to work very well and I have been using it quite happily. I do intend to construct a MK3 version using the ring magnet - perhaps next week - the CAD just needs a little finishing off and I need to make a jig to test how many magnets will be required to provide the magnetic force I feel is appropriate.
I notice in this months Hi-Fi+ that Clearaudio have produced a turntable using a similiar (in concept, but different in detail) bearing. I was not at all aware that any 'reasonably' priced turntable had employed this principal. The bearing experiments are only a small element of a much larger project to engineer a whole turntable. I have already done this a couple of times but am intending to approach this new design from first principles. Like Clearaudio I intend to use a low mass acrylic platter (lower than Clearaudio though), although every other aspect will be quite different. I notice that Clearaudio have used a ceramic bearing shaft to stop it from conducting the magnetic field. The bearing in my current design (Linn main bearing) does indeed conduct the magnetic field generated by my magnetic bearing, but I believe this to be irelevant to performance - leakage from the spindle is very low and has no measurable effect on the cartridge that I am aware of. I am pleased however, that Hi-Fi+ seem to hear very much the same improvements I reported.
Yes, I have experimented a little more. I did purchase a reasonably large ring magnet but I still intend to use a circular array of small magnets as the opposite 'force provider' so that I have more control over the strength of the magnetic field (i.e. more or less numbers of magnets used). To be honest my MK2 seems to work very well and I have been using it quite happily. I do intend to construct a MK3 version using the ring magnet - perhaps next week - the CAD just needs a little finishing off and I need to make a jig to test how many magnets will be required to provide the magnetic force I feel is appropriate.
I notice in this months Hi-Fi+ that Clearaudio have produced a turntable using a similiar (in concept, but different in detail) bearing. I was not at all aware that any 'reasonably' priced turntable had employed this principal. The bearing experiments are only a small element of a much larger project to engineer a whole turntable. I have already done this a couple of times but am intending to approach this new design from first principles. Like Clearaudio I intend to use a low mass acrylic platter (lower than Clearaudio though), although every other aspect will be quite different. I notice that Clearaudio have used a ceramic bearing shaft to stop it from conducting the magnetic field. The bearing in my current design (Linn main bearing) does indeed conduct the magnetic field generated by my magnetic bearing, but I believe this to be irelevant to performance - leakage from the spindle is very low and has no measurable effect on the cartridge that I am aware of. I am pleased however, that Hi-Fi+ seem to hear very much the same improvements I reported.
Hi YNWOAN
Thanks for the quick respone.
I noticed that review which reminded me of your postings. I am using an Avondale 2 motor Genesis turntable with a TEAD Grove and generating a very good sound ( other stuff mostly Avondale too), the least transparency from vinyl is in the bass and your descirption of the improvement you gained is exactly what I think I need here.
I like the fact you have effectively raised the bearing up the shaft and floated it. You could have a great aftermarket product here.
I don't know if you have heard the Funk V, I haven't but the low mass multi drive approach apeals to me.
I am tempted to try something along those lines with a magnetic bearing and good isolation from the outside, but I would have trouble with the PSU and I do occupy heath robinson territory when I make something.
Anyway at the moment I am waiting to see how you get on and hope to try something similar on my Genesis so thanks for sharing
.And if you need a home for one of your prototypes.....
Thanks for the quick respone.
I noticed that review which reminded me of your postings. I am using an Avondale 2 motor Genesis turntable with a TEAD Grove and generating a very good sound ( other stuff mostly Avondale too), the least transparency from vinyl is in the bass and your descirption of the improvement you gained is exactly what I think I need here.
I like the fact you have effectively raised the bearing up the shaft and floated it. You could have a great aftermarket product here.
I don't know if you have heard the Funk V, I haven't but the low mass multi drive approach apeals to me.
I am tempted to try something along those lines with a magnetic bearing and good isolation from the outside, but I would have trouble with the PSU and I do occupy heath robinson territory when I make something.
Anyway at the moment I am waiting to see how you get on and hope to try something similar on my Genesis so thanks for sharing
.And if you need a home for one of your prototypes.....
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.