DIY tensioned string suspended tonearm

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To make this toy I sacrificed my nicely working “Schroeder clone” for parts and rebuilt it without magnets in the bearing (I still use magnets to correct antiskate). I don’t know if this kind of tonearm bearing was built before. With exception of the tonearm lift, some fasteners and the spring, I made all parts at home! I am not a machinist, but I have universal milling machine that I bought for $500 from Harbor Freight.

The wand hangs on a string tensioned with compressed spring. The string has few millimeters of solid contact with brass part of the wand (which allows efficient transfer of sound waves out of the wand), but the string enters and exits the brass part from the same tiny hole. So, the bearing practically has a single point of suspension and minimal stiffness when the tonearm operates in its normal range of movements. To limit vibration and horizontal movement of the string, it passes just below the wand through a hole of a diameter close to diameter of the string. The lower part of the string and the spring is submerged in silicon oil.
Feel free to criticize and ask any question publicly,
Marek
 

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Thanks,
I made the new tonearm to replace the first “Schroeder clone” and on preliminary listening it sounds as good as the clone, but I only heard them both with a cheap cartridge. I need to make some small changes to the string before I try it with my good cartridge, and that will take some time. I hope to make it sound as good as my second “Schroeder clone” (the mutant which I was comparing to two conventional commercial tonearms). You can read about it in my thread: Magnetically suspended DIY tonearm – post # 18.
Marek
 

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Michael, I do not know if you are still interested, but I have the answer to your old question “Do you know a better method to soak wood with oil?”
I diluted Tung oil, which is very thick, with lighter citrus oil. For pernambuco wood I used a 50/50 blend. I don’t have a strong enough vacuum pump so I used DIY (cost $10) compression chamber and applied 800kPa of pressure for a couple of days. After the treatment the wand sweated oil for a long time…

The top half of the device (picture below) is a compressed air reservoir with filter (folded rag) preventing vapors from reaching and damaging the valve located on top. To save oil, the bottom part is narrow with a wider chamber just big enough to accommodate the headshell.

One more thing, I noticed that people have problems working with Vectran. In my new tonearm, Vectran string is snaked through 5 holes 0.8mm in diameter and raps around two parts, so my snaking technique may interest you…
Marek
 

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The Vectran thread I use to make the string consists of 300 loose fibers 23 micrometers in diameter. When folded in half (600 fibers), it can easily be pulled through 0.8mm hole, but that would be too thick a string. Both thickness and vertical tension of the string determines how antiskate force changes across the LP. Unfortunately twisted string gets more twisted when tonearm moves across LP increasing slightly antiskate force when skating force decreases. Therefore, I use magnetic antiskate correction. To make a thinner thread I cut twice the required length, divide it into thinner threads, then grease one thread slightly with silicon oil to straighten and hold the fibers together. I fold the new thinner thread in halve and using thin copper wire, starting from top I pull the thread through all the holes. At the bottom end I replace the puling wire with a small brass bar to hold the thread there without making a knot. Then I make a knot on top of the assembly. The brass cylinder in the wand has three interconnected holes - the thread enters the first hole, exits through the second hole (on the other side of the cylinder) wraps around a section of the cylinder, enters into the third hole and exits through the first hole.

To absorb some of the sound waves induced in the wand by vibrating stylus, I made part of the wand on which the counterweight slides hollow, then filled it with fine metal powder (W, Cu, Pb) saturated with oil. On the other side of the bearing I used metal powder mixed with soft wax. The counterweights and tonearm wire look weird but there are good reasons for that arrangement.

Without much of customization (just adjusted effective mass) I tried the tonearm with three different cartridges: Shure M97xE, AT 440MLa and Shelter 501II. The tonearm sounds more dynamic and detailed which makes it sound a bit brighter than the Clone - more like gimbaled tonearm I had before, but better. I hope to get the sound I like by changing wood, headshell plate material and better dampening of tonearm stand - it will take months.
Cheers,
Marek
 

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The motor is from Teres. It is installed in DIY housing that doesn’t dance around. My setup allows and requires setting the belt tension before every session to match thermal expansion of the platter as my room temperature varies from day to day. The setup also allows setting the motor to lean slightly toward the platter so the belt doesn’t slip downward as I run it with very little tension. The belt is DIY made from ½” leader tape. I find VCR tape too flimsy and holographic tape too crooked and not suitable for the application. The platter is from VPI Scoutmaster, but the side is covered with copper and grounded (through the bearing) to prevent static electricity build up - plastic belt shouldn’t be used on acrylic surface.
I will be gone for a while, pile up the questions and comments,
Marek
 

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Hi Marek,
Good solid job as usual! I do not really understand what keeps your arm from falling down - kind of knot on the thread? Anyway, what is the advantage over conventional unipivot design? - your's shall have more resistance for the arm moving up and down (but in the same time it shall be less prone to lateral rocking I guess).
Thanks for wood saturating advise - I will try it.
Regards,
Michael
 
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Joined 2003
Hello marekst, I should have recognised the leader tape - but I'm used to seeing 1/4". I like your tensioner. I'm thinking of making some variation of the Altmann turntable and was thinking of using 1/2" VCR tape, but leader is also a possibility. I will use a motor from a 5 1/4" floppy drive.
 
Marek,

I've been working along similar lines trying to design a tensioned string alternative to Schroeder's magnets. I was stuck about how to position the arm on the string if I was going to use a single string. Your bar idea is an elegant solution. Thanks for posting.
 
Hi, I am back home, thanks for comments.
I am including a sketch (diagram) of the bearing.

What is the advantage over conventional unipivot design?
These are my personal, unprofessional opinions:
Tensioned string drains sound waves out of wand more efficiently than the needle point.The wand is lighter around pivot point than wand of a conventional unipivot - it stores less energy. The sound is more dynamic, detailed and cleaner.
Compared with gimbeled tonearm there is a lot less friction and no bearing rattle.
Compared with magnetically suspended tonearm, there is no advantage but my new bearing has less tension (resistance), the pivot point is not imaginary
and i believe the tonearm is not protected by patents, but I may be wrong.

Marek
 
another tensioned string arm

This is a prototype I've come up with that uses an expansion of Marek's string tensioner. It's appearance-challenged, but works surprisingly well. There are two strings, upper and lower, which support and pivot both the outer ring and the wand. It's critical that the strings at each pivot point be quite close together or they become a parallelogram, which causes unwanted stray tensions. The strings, in this case, are dial strings, which I had available. They're a bit stiff, but don't stretch much. The arm is salvage and the cartridge is a Shure. The outer ring is PVC pipe.

My conclusions about this kind of arm are the same as Marek's, despite the different approaches. My immediate reaction to hearing this arm was that the sound is delicate - it is transparent and nuanced, the notes are made by instruments played by musicians.
 

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Ingenius design. I see you maneged to make gimbal tonearm without rattling bearings -congratulations. You are right about unwanted stray tensions, that's why I made 1/32" holes for the string. If you make a metal version with vectran string, dampened spring and well treated wooden wand it could outperform anyting out there. One question: why two springs?

Marek
 
Thank you, Marek,

I'm guessing that your question is 'why two "strings?"' There are no springs in this design. I did figure out a single string version, but the tension was huge in order to make all the connections. Some string broke - radio dial string - and some - nylon kite string - introduced stray tensions, which moved the wand horizontally. I still like the idea of a single string gimbal and I'll keep working on it with high tech string and better machined surfaces that will reduce friction on the string as it's being tensioned. I haven't explored your damped spring, yet, but I plan to.

I work mostly in wood because that's what I'm used to and my shop is set up for. On the other hand, there's this machinist here who likes to do audio related work - - -

You and I seem to be all alone out here in Tension String Land and that's a shame because it's such a great way to DIY an arm.
 
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Joined 2003
Excellent stuff.

This looks like a very interesting idea. I've always used unipivots (ball point pen into PTFE block) because I felt that rattling bearings could be heard, but your string-driven-thing idea solves the rattling bearings of gimbals and wobble of unipivots whilst retaining the unipivot's manufacturing simplicity.

Love the "rustic" look.
 
Doug,
My mistake, I am seeing things, my brain assumed that inside that white thing on top of your screw is a small spring and another below the support. In your prototype the wooden support bends and acts as a spring. With stiff metal support and stiff string some kind of spring is necessary to compensate for thermal expansions and for changes of the length of the string when it twists as the arm moves. Otherwise tension will change, sound will change and antiskate force will change. By the way Schroeder tonearm is another string suspended design with a pair of magnets acting as a spring, many try to copy that, we are not alone.
Marek
 
Good Morning EC8010 and Marek,

Thank you both for your responses.

I was interested in unipivots, but there's the wobble thing --- I built a wood version Schroeder arm (pg 31 "DIY Schroeder Tonearm?") which worked well, but there's the patent thing --- The yoke on the Schroeder led to the gimbal. Marek and an artist named di Suervo provided important positioning solutions.

As a very rough analogy, I think these arms are like the softer, better damped suspensions on modern cars - less bump and rattle, better control. Suspensions like that require strong, stiff frames as Marek correctly points out. The difference, and the critical factor, between tensioned and conventional arms may be that tensioned suspensions are unified - when under tension, they inherently become one piece instead of separate parts.

I hope more people get in on this idea because there is more potential still.

The small white things at the top and bottom are wood plugs with a vertical hole through them and a horizontal slot. A small metal bar drops into the slot and the string is tied over it. That's another reason I went with two strings - tying off one string made me nuts - I never got it figured out, really.

"Rustic" was kind and a good laugh this morning.
 
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Because of wood cutting mishap my wand ended up shorter and consequently lighter than intended and I had to make a heavier cartridge mounting plate. I thought adding weight to the headshell is a cheap solution good only to make commercial tonearms universal, whereas on custom made tonearms the extra mass could be better used to make the arm stronger. I guess I was wrong, the results are better than I expected just from getting the effective mass right. I am not sure if the improvement is because the headshell plate is heavier or made of different material (brass in place of aluminum) or because consequently the counterweight was moved to different location where my interior counterweight shaft dampening is more effective, but I like what I hear. I never make things identical for A/B testing, I do not like changing cartridges back and forth for comparisons, but I know that now my baby sings like never before and it does it with inexpensive cartridge AT440MLa. A bit of glassines in the sound of violins disappeared, focus improved – the tonearm is ready.
On the picture is a new headshell plate - the plate is brass the threaded part is aluminum.

dtut,
Thanks for explanation. Your design has one advantage over mine: it doesn’t need counterweight with low center of gravity which positively changes the way tonearm reacts to record’s moguls. I could easily achieve that by making a bearing with enough restoring force (two points suspension, one couple millimeters above another) but I believe that that would be worse than low counterweight! The disadvantage of your concept is extra ring between the wand and the support (extra part, longer, more complicated string path, possible resonances etc). “The wobble thing” is not an issue as my tonearm is stable, some minimal friction of string around pivot point stops wobbling. Conventional unipivots have a heavy bell around pivot point which reinforces wobbling effect.

About the “patent thing” I don’t plan to sell anything but I have extremely strong opinion on it…well, I’m sure it would be erased by the moderator. I will soon rebuild my other magnetically suspended tonearm as string suspended, anyway.

About more people getting on this idea – it’s a shame that your original, ingeniously designed, totally DIY tonearm had almost no response... Hmmm… what does that say about our DIY forum which falls over expensive, commercial designs…

Good luck in developing your tonearm I am glad to share this thread with you,

Marek
 

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