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Old 21st March 2008, 03:28 AM   #1
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Default Designing a DIY TT

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.

Click the image to open in full size.

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.

Click the image to open in full size.

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.
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Old 21st March 2008, 03:58 AM   #2
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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.
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Old 21st March 2008, 04:01 AM   #3
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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.
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Old 21st March 2008, 08:45 AM   #4
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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.
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Old 21st March 2008, 09:12 AM   #5
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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.
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Old 21st March 2008, 09:52 AM   #6
YNWOAN is offline YNWOAN  United Kingdom
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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.

Click the image to open in full size.
Click the image to open in full size.

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

Click the image to open in full size.
Click the image to open in full size.

I then modified it again to use a ring magnet for the lower magnet and fewer magnets in the upper magnet array.
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Old 21st March 2008, 10:57 AM   #7
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That's real nice YNWOAN. Linn bits?
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Old 21st March 2008, 10:59 AM   #8
YNWOAN is offline YNWOAN  United Kingdom
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Thanks :-) Yes - some bits are.
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Old 21st March 2008, 05:58 PM   #9
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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?
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Old 21st March 2008, 06:28 PM   #10
YNWOAN is offline YNWOAN  United Kingdom
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What does MFG mean - sorry if itís 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.

Iím afraid I donít 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.
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