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Old 7th November 2006, 07:53 PM   #1
marekst is offline marekst  Poland
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Default Magnetically suspended DIY tonearm

My second tonearm is ready; you can see pictures in my gallery. It is based on excellent idea patented by Frank Schroeder. My second tonearm is so different from the original, I do not call it a clone, I call it a mutant.
The main difference is that it does not hang by a thread. The arm hangs by magnetic field. The thread keeps the distance between magnets and supplies some of antiskate force. Why did I turn “Schroeder” upside down? Because with a heavy arm wand my clone had stability problem. To ease the stiffness of the suspension the string is attached to the magnet in the way that the pivot point is close to magnet gap. In my first, ultra light clone the center of gravity of arm wand is above the pivot point. In my “mutant” with heavy ebony wand the center of gravity of the wand is below the pivot point.
Frank Schroeder has a secret how to make his tonearms not wiggly and not stiff. Cloners who asked him privately disappeared from discussions on the Internet, even their posts disappeared from archives. I did not want Frank to use his magic wand on me and shut me up, beside the cloners honor would not let me ask. It would be like a defeated hacker asking for a password. I shaped ends of the magnets, one conical, one semi cylindrical. That solved the wiggly arm problem many cloners reported.
The second, more audible difference is that I added a second pair of magnets to correct the antiskate force. Not quite as good implementation as Carlo Morsiani’ but the same reason. One very small magnet is on the end of counterweight shaft and a bigger one is fastened to adjustable bras wire arm. To hold the magnets in place I used small pieces of latex tubing. The magnets are pulling on each other, that adds extra antiskate force where it is most needed. The system is not perfect but the antiskate force decreases as the skating force decreases. Distortions caused by skating force are not audible any more. Before, either the beginning or the end of LP sounded bad. When the needle is lowered down it gently skates out into the starting groove.
To adjust the antiskate I made my own test record, I sanded an old LP to a smooth finish. The record sounds like hsshshhshsshh and gives the needle a bit more drag than uncut LP. I know that only the tip of the needle is working and it is not the same as the needle working in modulated groove but it works for me. I have also used uncut spaces between tracks on Hi-Fi News test LP and of course I have used good music and my ears.
There are other small differences: wiring, counterweight, headshell, my aluminum wand shafts are filled with fluid and lead powder etc…
Finally I am happy with the way my tonearm operates though it is a pain to adjust it. Too many parameters affect each other. The sound is excellent!
Recently I learned about Morsiani tonearm. If I had to start from the beginning I would buy or clone Morsiani.

An amateur has the right to be wrong, when a pro is wrong he has to be the Pope to be right.
Marek Stojek

http://gallery.audioasylum.com/cgi/v...erImages=21150
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Old 9th November 2006, 03:03 AM   #2
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Default Beautiful thanks for posting...

stellar work! Thanks for posting I have made a copy just in case the bad guys send your post into cyber pergatory. Best regards Moray James.
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Old 9th November 2006, 06:15 PM   #3
JesseG is offline JesseG  Canada
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Very, very, very nice.

I especially like the way you have built the main post assembly - this could be adapted to a number of projects.

I have lately become interested in trying an update on the Irish Vestigal tonearm from the early 80s (?). It would require a pivot point that could be easliy implemented using your design.

How do you handle VTA?

Quote:
My second tonearm is so different from the original, I do not call it a clone, I call it a mutant.
IMO there is a huge difference between ripping off a designer and developing a design idea to the next level. I think your work, although based on Schroder's idea, is a step beyond his and is not a clode at all. After all, the guy at Ford who came up with the V8 engine just married 2 four-bangers together, but he (or his estate) holds the longest-lasting patent in engineering.

Bravo!

Jess
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Old 10th November 2006, 12:24 AM   #4
marekst is offline marekst  Poland
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Thanks James and Jess.
I have no “on the fly” VTA adjustment. There is an Allen grub screw in the aluminum ring, the 2.5” long main post slides up and down manually. On the picture the main post is not visible; the mutant is at its lowest position.
Some details that may interest you: I cut the main post and the lower horizontal support from one piece of aluminum on a lathe. I installed the upper support and brass pillar on lower support and than spinning the whole assemble on the lathe I drilled a hole for the upper magnet. This way both magnets are perfectly on axis.
With my rather primitive machine the biggest challenge was drilling a hole for the magnet exactly in the center of the aluminum wand shaft.
Marek
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Old 14th November 2006, 08:27 AM   #5
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Hi Marek,
Congrats on your implementation of the bearing principle. Btw, if I really had a way to make people disappear, it be most likely certain politicians that would vanish, but never audio diyers ;-)

On a more technical note: the reason for choosing the hanging versus the "upside down" arrangement is not only dictated by the desire to achieve utmost stability(self aligning, self centering), but also by the bearing geometry that will compensate for the otherwise inescapable susceptability to warp wow when using a bearing with a pivot point above(or below) record level. using the hanging arrangement, any movement upwards will result in the bearing assembly/armwand moving ever so slightly backwards as well, compensating for the shortening of the eff. length that is caused by a warp. You have to realize that the bending point of the thread is NOT the pivot point!
Your arrangement will emphasize the warp wow, but, at the same time, reduce the effects of any magnet misalignment.

Keep up the good work and good luck with a future Morsiani project,

Frank
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Old 15th November 2006, 01:36 AM   #6
marekst is offline marekst  Poland
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Hi Frank,
Thanks for your reply. I am glad that it was not your black magic. Maybe now posts by InDaGroove and others will reappear. It is interesting that only you and two brave Canadians commented on my tonearm. There was one other guy but he only dared to contact me via email.
On technical points you are absolutely right. My arrangement did move the pivot point up (about 1/4”) in relation to record surface. I compensated it a bit by moving the head of the headshell up and lowering the tonearm a bit. I am not going to argue on this mater as I do not know the subject well.
Marek

And now for the benefit of future cloners:
Remember what Frank said about the geometry of the arm. Also, it is much less work to make Franks clone than my mutant.
To drill the magnet, use 1/32” and 1/16” carbide drills from mcmaster.com part No 2841A92 and 2841A94. Drill the hole with 1/16”bit for the knot first. On the opposite side drill 1/16” hole to the depth of about 1/3 of the thickness of the magnet. Finally drill through with the 1/32” bit. This way the fragile 1/32” drill bit will have a shorter distance to go. Be careful when you drill a hole in the screw holding the thread, as brass or aluminum is more likely to break the drill. It takes a few minutes to drill the hole.
Mcmaster.com also has all the metal you will need.
After you tie the knots pull on the thread very hard to test if knots do not slip through the holes. God have mercy on your cart should the thread slip through later on…
For Shelter cartridge I made the wand from ebony wood. After cutting a piece of wood in half length wise, I turned and flipped the top piece to increase stability of the laminate. Before I glued the wood together I made 2 parallel 1/32”deep grooves in each piece from one end to the other. When I put the wood together the grooves formed 2 guiding holes. This way I was able to drill two 1/16” holes trough the wand for left and right channel wires separately. The ebony is very oily so before gluing it together the surface has to be degreased with alcohol. If you opt for drilling one hole for both wires it is possible to use one solid piece of wood as bigger diameter drill won’t drift sideways so much.
For my Shure cart I made ultra light wand out of pernambuco wood drilled with ¼” bit and I filled the inside with balsa wood.
I hope I did not bore you with details, any questions?
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Old 15th November 2006, 01:28 PM   #7
jugi63 is offline jugi63  Finland
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Well Marek, I am probaly to be counted in the category you specify as making the disappearing act.. Just for the record, I don't consider myself as disapeard if I spend less time by my computer ja more time listening to music. And also - it has nothing to do with Franks magic. It is just plain curtesy not to spread out in the open all the plans or information about something that belongs to someone else.

There is a difference in mostly figuering out things for your self and then getting a little help, apposed to having everything layed out for you.

You pride in figuering out everything by your self but then you blame people who France has helped for not sharing private information with everyone else (including you)?? If plain curtesy isn't enough then maybe the old saying applyes here: "You don't want to bite the hand that's feeding you."
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Old 15th November 2006, 08:05 PM   #8
marekst is offline marekst  Poland
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Hi Jugi,
I remember you. I am glad that little help worked for you. And by all means keep the little secret safe. What troubled my mind was disappearing of posts with information on how to make parts not protected by patent. I am very fortunate and do not need help with manufacturing but some people do. I do not agree that discussing details of patented design is immoral. After all, the patent is there to protect Frank’s wealth and he made us more than aware of it.
What have you mostly figured out yourself? The pictures of Franks tonearms are out there, the patent drawings and description are out there, if you do not speak German, the US patent is out there. Not exactly top secret, right? You probably had Rega or similar tonearm to measure the basic dimensions. You built a clone and it did not work, right?

Marek

And now for the benefit of future cloners:
I do not know if I have used the right size and shape of magnets - that is Frank’s sweet secret. I will share what I did. I hoped to get magnets 3/8x3/8” but they were not available at the time so I used 3/8x1/4 in the wand and 3/8x1/2 in support. I tried to figure out the shape of the pole peace to make the magnetic field concentrated more on axis to prevent infamous wobbliness. That is Frank’s other sweet secret. I tried different pole pieces and observed the shape of the ferric dust. I observed how close the iron needle would stay to the center of the magnet with different pole pieces. After a couple of hours of experimenting and not coming into any conclusions I did the obvious and “sharpened” the ends of the magnets. The further off center the bigger the distance between magnets. I think Frank mentioned that method in his patent. It did the trick for me. Contrary to rumors the magnets are not extremely hard and could be tooled like steel. Just do not heat them so they do not lose magnetism. As for pole pieces, I use soft steel 3/8” diameter about 1/8” high, shaped on end to fill the conical hole formed by the end of the drill. To keep magnets in place I used epoxy. Feel free to criticize.

And to bite the hand I have previously fed I have to say that my home made tonearm totally smoked out celebrated $1500 commercial design, more glory to Franks invention.
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Old 15th November 2006, 08:37 PM   #9
JesseG is offline JesseG  Canada
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Hi fellows:

I want to wade in here. I don't know if you folks in Europe have a very different convention on this that us here in North America, but here the rule is: YOU CAN BUILD WHATEVER YOU WANT TO BUILD, Patented or not, as long as it is not for resale. We are free to look up patents and use the information, engineering and trade secrets contained in them SO LONG AS IT IS NOT FOR RESALE.

There is no question that Mr. Schroder has solved a number of problems and built a very cool product. Long may he prosper. That does not give him, or anyone else, exclusive control of an IDEA; only the PRODUCT.

In addition, anyone who wants to take the time to look at commercial history will be able to see thousands of examples where encouraging non-commercial use of a unique design has only good results for the patent-holder. The more people who know about a design, the more popular it becomes. There are many, many people out there who will never want to build their own. Those people will just have to pay Mr. Schroder his justly-deserved money to buy one.

For those of us who are crazy enough to undertake building one based on a patented design, we would never buy one anyway - so Mr. Schroder is not out of pocket anyway.

IMHO, this forum is for people who want to exchange ideas and experiences about BUILDING hifi stuff, not for harassing inventive and ingenious folks who are doing what this forum is for: DIY.

Sorry, I don't want to offend anyone with my opinions, but that's just how I see things.

So, I say - BRAVO! marekst... Keep up the good work. I for one would love it of you posted some plans of your tonearm for those of us who are less ingenious (and with less time) than you.

Jess
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Old 15th November 2006, 08:51 PM   #10
SY is offline SY  United States
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YOU CAN BUILD WHATEVER YOU WANT TO BUILD, Patented or not, as long as it is not for resale.
As a practical matter this may or may not be correct, but as a legal matter, it is usually not so. You may build for yourself for the purposes of research or education, but NOT to avoid spending money on a commercial design. For example, if I wanted a tonearm to use in my turntable, it would be patent infringement to build a design which falls under an existing unexpired patent. If I wanted to explore a new way of damping resonance in a design, then it would be OK to build one for test purposes, but NOT to use in my living room.

Usual disclaimer: I'm not an attorney, but as a professional inventor, I have had deep involvement with the Patent Office and infringement litigation.
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