Designing a DIY TT

[Dougie085]

Ok so I've been thinking up a DIY turntable design to build for my self. Some of the design idea's are questionable and lots of people have said they don't think it will work. The parts that I would have to replace are relatively cheap so I'd like to give it a try. Here are a couple pictures of my rendering so far.

[IMGDEAD]https://i24.photobucket.com/albums/c30/Dougie085/TTbase.jpg[/IMGDEAD]

Just a note the blue line represents where the platter's edge will be in association to the base. Also for some reason Sketchup kind of squares the edges but its actually a circle.

[IMGDEAD]https://i24.photobucket.com/albums/c30/Dougie085/Platterbottom.jpg[/IMGDEAD]

This is the top of the base plate and bottom of the platter. The small holes are for magnets. I understand some people think that this may cause issues with the needle and cause noise issues. I'm aware of this but the magnets I'm going to use aren't extremely strong and the platter is 4" thick. So there is 4" of hardwood between the needle and the magnets. In the center of the base plate there is a pole piece that will hold the platter in place. The platter will have a bearing that will go in the middle that will help reduce friction between the pole and the platter. The pole will extend up and will actually be the center pin for the vinyl it self. Some have expressed concern that there may be ruts between the magnets where it would sort of hang a bit and cause bobbing. I think that the way I have it planned right now it shouldn't be a problem because they are relatively close together. If this does prove to be a problem my idea to fix it is to have a second row of magnets that would be in between the magnets on the first row but further back so there would be no space where there wasn't a magnet. As for the tonearm I'm still undecided, one idea is to buy a Jelco SA-750D (http://www.jelco-ichikawa.co.jp/e_tone_arm.htm). I haven't decided if I want to try and build a tonearm as I'm not sure I can match the quality of something like the Jelco. I'm still looking for ideas for the motor and speed control. I've thought of maybe just gearing it only for 33 1/3 rpm as thats more then likely the only thing I'll ever play on it. So anyone that can offer advice or what not greatly appreciated. If you want to offer criticism I don't mind I've heard a lot of people say they don't think it will work but I'm still willing to try this out. If in fact the magnets don't work I can easily pull them out and add a bearing.

 

[harwoodspark]

You won't know unless you give it a go. There are one or two decks that use magnets to lift the platter, usually a pair of ring magnets. Maybe you could find a pair large enough for your project then you would have a seamless travel. You can usually put magnets under aluminium and the lines of flux don't pass through.

Good luck, Si.

 

[Dougie085]

Yeah I've been looking into ring magnets but they are all quite strong something like 36lbs of pull (the one I've found thats big enough anyways) which I think is a bit much considering 2 of them will be pushing against each other. I'm not sure I'm still looking into this. This project is in the early planning stages right now.

 

[Dougie085]

I've also been wondering what is a good DIY Phono stage I could build? Something that I could either order a PCB or there are eagle files available would be nice. I'm not sure if I want to do tube as vinyl is typically not all that bright sounding if done properly. Of course I saw a phono stage kit from a company thats supposed to be very transparent. Generally though I'm one that likes to hear it the way its supposed to be rather then listening to tube coloration but thats not to say I don't enjoy tubes. Kind of contradicting I know.

 

[planarboy]

ive been thinking my riaa stage lately is letting me down, but it probably is.
Ebay special...yaqin 12b tube preamp with phono stage, very noisy, pretty ordinary.
People have suggested to me to get graham slee, but i might just watch this thread and copy what doug ends up doing.

 

[YNWOAN]

I experimented with a magnetic lift bearing some months ago. The concept I used was not unlike the one you propose (I did post about it on this forum at the time). However, a couple of differences did exist, my magnets were closer to the main bearing and they were also closer together. Even then I did find some element of cogging between the magnets did exist and my final design used a ring magnet for one element of the magnetic circuit - this cured the cogging issue.

[IMGDEAD]http://www.markholterman.pwp.blueyonder.co.uk/1171979234.JPG[/IMGDEAD]
[IMGDEAD]http://www.markholterman.pwp.blueyonder.co.uk/1171979178.JPG[/IMGDEAD]

The pics above are of the MK1 prototype.
I then modified it a bit to look like this and incorperate some shielding:

[IMGDEAD]http://www.markholterman.pwp.blueyonder.co.uk/1173473257.JPG[/IMGDEAD]
[IMGDEAD]http://www.markholterman.pwp.blueyonder.co.uk/1173473112.JPG[/IMGDEAD]

I then modified it again to use a ring magnet for the lower magnet and fewer magnets in the upper magnet array.

 

[harwoodspark]

That's real nice YNWOAN. Linn bits?

 

[YNWOAN]

Thanks Yes - some bits are.

 

[Dougie085]

I'm not sure I have the MFG capabilities you have there . Those look awesome though! So you used a large single ring magnet on the bottom and then several magnets on the platter part. Is there any reason you didn't just use another single large ring magnet for the platter part? How much pull force did the large and small magnets have?

 

[YNWOAN]

What does MFG mean - sorry if it’s a dumb question (is it 'manufacturing'n not heard that before)? I used a CNC router to make all the bits for the bearing. The pics I have posted are with the structure made from acrylic though the final model was made from HIPS.

The reason I did not choose to use a ring magnet for the platter part was because I wanted the magnetic field to be reasonably compressed, I did not want to increase the mass of my platter so could not use another ring magnet. The effective strength of the magnetic repulsion could be controlled by reducing the number of cylinder magnets in the platter section; this also had the benefit of reducing the magnetic field propagated towards the platter surface.

I’m afraid I don’t know the specific strength of the magnets I used as most of my experimentation was empirically based. In the final design the two magnetic elements ride about 4mm from each other.

I also considered the second row of offset magnets idea, that you mention, but did not find it necessary.

I would encourage you to pursue this idea though as I did find it to be a worthwhile upgrade.

 

[Dougie085]

Do you know the size of the ring magnet you used? Also was it a rare earth magnet? I found one thats got a 4" outer diameter and a 2" inner diameter and is 1/2" thick. Has something like 90lbs of pull force. I'm liking the way you went about it. I think I'm going to edit my design now.

MFG = Manufacturing yes. My platter is going to be layers laminated together. I was thinking between one of the layers I would put a sheet of mumetal which is supposed to be the best stuff for shielding magnets.

 

[YNWOAN]

I got my magnets from this chap:

http://www.supermagnetman.net/product_info.php?products_id=418

the link above is to the ring magnet I used. I also used a disc of mumetal to shield the surface of the platter. I use an expensive, low otput MC cartridge and have experienced absolutely no problems.

I should warn you that the whole structure does need to be made to pretty close tolerances. In particular, the depth of the holes that the magnets will be held in has to be very even if the platter is not to 'ride' unevenly. However, if you are prepared to use a high mass platter then you could use two of the ring magnets which would make manufacture a bit more simple. I should add that I am not a follower of the heavy platter school of design, or mass damping as such - many are though.

I'm gald you like my work and I hope it has been of help to you

 

[Nanook]

mfg: = manufacturing

just "cross the pond" shorthand.
YNWOAN: your work looks very good.

Dougie085: I am sure your idea "wood work" (sorry for the pun, I can't help myself...). Obviously the strength of the field required will be determined by the mass and the possible magnetic properties of the materials used.

You can also use the magnetic "levitation" to reduce the load on a traditional bearing to good effect.

This approach has been used by Verdier for many years now. I don't think I've come across a negative review of any of his tables.

 

[YNWOAN]

Thank you Nanook

Actualy, I though the platter was fully levitated on the Verdier turntables - as is mine; I have heard of using magnets to relieve most of the load on the bearing though - I didn't experiment with this myself though.

 

[Dougie085]

Thanks for the link I'll check into it!

I made a couple new drawings with the modified design. How many magnets did you end up using on the platter and how big were they? The ones I was thinking of using are 1/2" diameter and 1/8" deep. I'm curious because I was wonder how many it took for it to actually levitate and was wondering how heavy your platter is. My platters is going to be rather heavy I think. Here are the new design.

 

[Vinyl-Addict]

Yeah I've been looking into ring magnets but they are all quite strong something like 36lbs of pull (the one I've found thats big enough anyways) which I think is a bit much considering 2 of them will be pushing against each other. I'm not sure I'm still looking into this. This project is in the early planning stages right now.

Doug, You can get a rough estimate of the repelling force by dividing the pull force by 3. IOW, 36lbs pull force will repel a 12 pound load with about 1/8" gap. This is just an estimate.

You really should experiment by building a model or jig to figure this out since it is very hard to get it right the first time.
I would avoid using a series of small disc magnets due to the cogging effect. Ring magnets are the best choice.
As was previously mentioned, precision is key when it comes to positioning the magnets, both concentricity and parallelism are of prime importance to the success of your project.
FWIW, I'm using ring magnets with 180 pounds pull force in my magnetic bearing. The platter weighs 50 pounds.

 

[Dougie085]

So even if your using 2 magnets pushing against each other its still divided in half? Or would it be like 18lbs x2? You don't think it would work as good the way that YNWOAN did it? With a ring magnet on the base and using the smaller magnets on the platter? And yeah I plan on getting pretty accurate placement of the magnets and the platter. I plan on using MDF I think for the platter which is generally pretty evenly dense and thickness. I will use a jasper jig to cut out the circles which is pretty accurate. If I end up using the smaller discs for the platter that will have to be carefully done. If I do 2 rings it should be perfect.

If you divide in 2 like that then the 90lb pull force magnets might actually be good to use. If I do an MDF platter I would probably veneer over it. I don't think that veneer adds enough weight or what not to really effect the balance much if any. These are just some of the ideas. If I use hardwood I think it would be much less accurate as far as weight balancing.

 

[Dougie085]

What is your platter made of? And how thick is it? How heavy do you think a 12" diameter platter thats 4" thick is going to be made out of MDF? I'm starting to think I should just go 2 ring magnets now. Which I was thinking for a while. But I liked how YNWOAN said he could adjust the height and magnetic field by using the smaller magnets on the platter.

 

[Vinyl-Addict]

So even if your using 2 magnets pushing against each other its still divided in half? Or would it be like 18lbs x2? You don't think it would work as good the way that YNWOAN did it? With a ring magnet on the base and using the smaller magnets on the platter? And yeah I plan on getting pretty accurate placement of the magnets and the platter. I plan on using MDF I think for the platter which is generally pretty evenly dense and thickness. I will use a jasper jig to cut out the circles which is pretty accurate. If I end up using the smaller discs for the platter that will have to be carefully done. If I do 2 rings it should be perfect.

If you divide in 2 like that then the 90lb pull force magnets might actually be good to use. If I do an MDF platter I would probably veneer over it. I don't think that veneer adds enough weight or what not to really effect the balance much if any. These are just some of the ideas. If I use hardwood I think it would be much less accurate as far as weight balancing.

Doug, I'm a machinist, don't work much with MDF. I edited my post, divide by 3.

 

[Dougie085]

Hmm ok so definitely need some strong magnets. I wish I had the equipment to machine a nice aluminum platter or something.