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DIY Tonearm

Home Theatre Systems

jls001

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I have been following the Nanook 219 tonearm build thread on diyaudio. It is a very simple unipivot tonearm, with the arm tube usually made from an aluminium arrow shaft, the tip of a Parker ball pen refill cut off and used as the male bearing, and various types of female bearing arrangements - from simple brass pieces to jewel bearings - having been used by various builders. In its rawest form, it is just the basic arm tube, bearing arrangement as mentioned above, a suspended counterweight to lower center of gravity, and some sort of headshell arrangement ranging from the elaborate to really simple ones.

But the central idea behind this build is to utilise easily available parts to make a good sounding tonearm. The original build costed $ 2.19, hence the name Nanook 219, Nanook being the diyaudio user name of the Canadian gentlemen who adopted and improved the Altmann "joke" arm.

I have spent lots of my evenings and weekends planning how to go about this build. The biggest challenge for me at the outset was to figure out what to use as the female part of the bearing. The male bearing was easy as I happened to have a couple of Parker ball pens.

The next decision was whether to use aluminium or carbon fiber arrow shaft as arm tube or make something out of wood. Aluminium is the most commonly used among builders of this tonearm. Each has its advantages and disadvantages. Aluminium or carbon fiber arrow shaft would not need any shaping as they're already tubes, close tolerance ones at that. Both would need some amount of internal damping. I knew that I won't get ready-made wooden rod of my required diameter. And even if I got one from somewhere, there is the question of how to drill a hole all along the length of the arm tube.

I chose to go with wood as wood is usually known to have good sonic properties (different types of woods are used by builders as tone wood in tonearms). Plus wood has adequate damping property. And I am more familiar with woodworking than working with metals. I have zero working experience with carbon fiber. Moreover I didn't exactly set out to build a very light arm. It was my intention to have a medium to heavy mass arm so wood seemed like the best choice for the purpose.


So here's where I am at now, temporarily rigged up with a counterweight borrowed from another tonearm and suspended from the counterweight "stub" with a thickish solid core copper wire:




Top view, temporary setup to check trackability. There is no wiring yet. After setting the tracking weight and fixing it at the correct mounting distance (I am using 294 mm pivot-spindle distance), it tracks beautifully without jumping or skipping. I didn't bother with correct offset angle yet, though I had offset the headshell by rough estimate (I am guesstimating approx 18 degrees):




Right now the two halves of the arm tube are tied together with cable ties, and need to be glued together. Since I didn't have a chisel that could cut away a semi-circular section, 5 mm wide, I had to improvise my own chisel by sharpening the pointy end of a metal file (the end that usually goes into the handle). But the metal I used was not tampered and therefore quite soft. It needed constant sharpening on a sharpening stone.

Some more build pictures below. Except for some parts, it isn't difficult to build an adequately working model. Fit and finish perhaps is where the skilled will come away looking good. And if my fit and finish leans on the agricultural on the aesthetics scale, you know just where I stand on the skill divide:lol: But it has been an immense learning experience for me.

This is the starting point: D section wood decorative moulding, 13 mm diameter, machined teakwood. It is dirt cheap - Rs 53 for a six and half feet length. Buy the full length, as you need to cut off at least two straight segments of 15 inch each. More often than not, these mouldings are hardly arrow straight. Also one needs to choose good looking grain structure. Buy something with the least blemish (and the straitest, of course).




The groove for passing the tonearm wire is manually carved out:












In the picture above, the extended part on the right hand side of the picture (topmost piece) was an afterthought. After making two of equal length, I was suddenly faced with the problem of how to make the headshell. I thought one might as well make the headshell an extension of the arm tube itself to avoid the complication of joint, and also to maintain as much structural rigidity as afforded by this piece of wood.

More build pics to follow:)
 

Record Player

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WOW. Excellent work me friend. Joshua in his element :). Great to see such levels of DIY efforts coming out in our very own forum. Looks much better than what you showed me earlier.

Following this thread closely now. The build itself will be a great achievement, but very keen on its performance.

Cheers
 

jls001

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Making the female bearing:

The raw material was a piece of brass plate. I compared the profile of the ball pen tip and the tip of a center punch I have, and the center punch have a slightly larger angle, so a hole punched with it would fit the ball pen tip with some allowance for tilt in all directions.




Lots of hammering later, this is the fit:




Size marked out for cutting:




After lots of filing and sanding, this is what we got:




Cutting out slots for the female bearing:










View from the bottom:




The pivot height is designed in such a way that the tip of the cone is slightly above the axis of the arm tube. This is mentioned by Viren in his build linked by Rajiv a few posts ago, and I also had read about it in a Graham Phantom arm review. When properly balanced, the arm is quite stable. One can rotate the arm on its pivot and it will spin 360 degrees (a few revolutions) without toppling over. And it comes to rest without wobbling. I guess it is a good start.

The next step is sand it down a bit further to thin the tube diameter and eventually to oil it (thanks Sachin for the advice on linseed oil - I bought a liter of it, some brand called "Kashmir" in a very industrial looking tin can). I will also rework the headshell design to simplify it and give it more rigidity. Need to do away with a couple of the linkages. For arm wire, I am cannibalising an unused mouse.
 

jls001

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Some more build pictures:

Board for mounting the arm base, arm lift, arm rest and male bearing. This is made from a piece of teak plank that was lying around. Need to figure out an elegant arm rest - it must both grip the arm securely when at rest and be aesthetically acceptable. I have used paper clip (the black coloured wedge type used for holding together very thick bunch of paper). But is is extremely difficult to work with that metal sheet as it is extremely hard and rigid, so shaping it to a desired bend or curve is very tough, though cutting it is quite easy. Being very hard and rigid it is quite brittle when bent to an edge like clamping it to a vise. Just bend it and unbend it a few times.




Three screws to secure the bearing barrel. Threading (M4) starts at the wood and goes right into the holes in the brass pipe:







The holder for the ballpen refill tip. It's a bit fugly in this picture but the final iteration is prettier:):




Another view of the holder:







The refill test mounted in its holder. After this picture was taken, I had re-shaped the holder to make a bit pointy, improved the roundness of the holder's shape, and gave a better finish to the edge where it meets the brass pipe.





In the picture below, note the screw hole on the brass pipe. That is for a 4 mm grub screw that will tighten to the brass rod that is passing inside the pipe. The brass pipe can be lifted by a maximum of 3/4 inch to allow height adjustment. I may have to reduce this height adjustability to about 1/2 inch as the overall height is taller than my liking. Rough height adjustments can be done by using different thicknesses of arm base (currently I am using 10 mm thick plywood but had made another one of 18 mm thickness). The grub screw adjuster can be used for final fine adjustments.




Total weight without counterweight and cartridge:



Need to reduce the weight a bit by shaving off some more and further sanding.

I am not happy with the rigidity of the headshell, so it is being re-designed. Also toying with the idea of making a Cartridgeman type foam isolation for the cartridge-headshell interface.

Also, need to test whether outboard azimuth stabiliser arrangement will be required. I am not planning on antiskating arrangement as this arm is a 12 incher and should work well without AS.
 

Sumanta

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Can't wait. Feeling like driving down to Mumbai to see your work with my own eyes. wonderful ideas.
Kudos to Mr. Bakshi too!
Question: Why were you not happy with the rigidity of the headshell? Why it should not be so rigid? How you measure rigidity? I guess too rigid a headshell will induce vibration. Is it?
 

jls001

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Question: Why were you not happy with the rigidity of the headshell? Why it should not be so rigid? How you measure rigidity? I guess too rigid a headshell will induce vibration. Is it?

The so called headshell in my case is nothing but an extension of the upper half of the arm tube. A slot of 1 inch was cut, through which one can pass a screw. In my previous design, the screw goes into a nut embedded in the top of the cartridge holder. This holder is also made of wood. The cartridge is held by two screws. The nut or the screw head needs some room, so I had put a spacer. I find that this spacer doesn't have enough strength, mainly because it is screwed to the embedded nut, which I was going to glue. I moved the embedded nut to the lower surface and now it works even without gluing. But to make this work, I had to sink the cartridge screw head into the cartridge holder. I'll post some pics later. It will explain it much better.

Rigidity is desirable in tone arms so that it doesn't get excited by secondary vibrations like the vibration of the motor that eventually travels to the arm via the plinth. The only motion that the arm must have is the motion due to the stylus tracing the record groove. If some other motion is also induced in the arm, it interferes with the primary motion. Also, the arm tube should not flex when it is in motion, because any flex induces unwanted motion in the stylus.
 

jls001

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What are the benefits in having such a tonearm?

There are many good reasons:)

Firstly, it is great fun building your own arm.

Secondly, it is within the reach of a low-skilled DIYer as the unipivot bearing principle is deceptively simple to build, but tough to perfect it.

It is cheap. Very cheap to build, in fact.

Other builders have claimed that it sounds very good. I hope it does.

Since it is our own build, it can be tailored to suit our cartridge(s). So we can make it a low, medium or high mass arm. Mine is heavy.

It can also be made to a desired arm length. Here, the thumbrule is longer arm has lower tracking error, but needs more plinth real estate to accommodate. I chose a 12" arm. I also chose my own mounting distance and effective length, so I will generate my own protractor for proper alignment, etc.

Last, but not the least, one learns a lot in the process.
 

Sumanta

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I will ask many questions instead of reading. Is it okay? I will not mind if you say no, I can understand.
If you do not mind then here are my questions.

Why a tonearm (unipivot case forsay) can work differently being light or heavy when it is balanced and have the same VTF for a particular cart+stylus? Heavier one will induce more friction at pivot point and will have more inertia too. Is it intended?

Will wires when coming out of tone arm going into pivot axis induce inertia in the moving of the arm?

Some more photos please.

I find this idea as very intelligent. And I was thinking, if I can have two tone arm for one TT, I can have two different quality and cost based cartridge/stylus to play different quality records. It will be cheaper and less space consuming compare to having two TTs.

If it works, I just need to change RC connection to the phono stage.
 

jls001

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I'll post some pics later. It will explain it much better.

Some pics to explain:

The old headshell had a nut embedded into the top of the cartridge holder. The nut is supposed to be glued. But I had doubts it's not going to hold. The black plastic thing with brass threaded inside is meant to be a spacer between the headshell and cartridge holder, as the screws of the cartridge were not sunken initially into the headshell holder (the picture shows after countersinking was done for screw heads):




Here's how it looks. You can see that it is hanging by the spacer. Besides structural doubts, the stylus rake angle with this arrangement wasn't right, si I had to do something:




In the new headshell holder, the nut is placed below so that one doesn't have to worry about the strength of the glue. In fact one doesn't even need to cut the countersunk to the shape of the nut anymore - even a round one would do. If anyone wants to replicate something similar, making the countersunk part of the holes was a slow and tedious process. I used mostly larger drill bits to make the larger hole, slowly rotating the bit by hand. I destroyed one piece by trying to use a drill. A drill is just too fast and powerful and almost impossible to do such a delicate job without splintering the small piece of wood itself.

Now after one problem has been licked, another surfaces, namely wrong VTA:lol: The VTA was correct with the spacer. Now that it's removed, the headshell end droops. Need to figure out a way to correct it:eek:




Test fit of the new holder:




Managed to trim off and re-shape the headshell. Original was:




Newly fancified shaped:):

 

jls001

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Why a tonearm (unipivot case forsay) can work differently being light or heavy when it is balanced and have the same VTF for a particular cart+stylus? Heavier one will induce more friction at pivot point and will have more inertia too. Is it intended?

Will wires when coming out of tone arm going into pivot axis induce inertia in the moving of the arm?

Please ask questions - I will try to answer them to the best of my limited knowledge.

The unipivot is just a bearing and it can support light or heavy mass arm. You are right that once an arm is balanced, and appropriate tracking force is set for a particular cartridge, the force acting on the record is same whether arm is light or heavy.

But the combination of arm and cartridge produces a resonant frequency. The desirable resonant frequency must be in the range of 8 to 12 Hertz. The best combination to achieve this resonant freq is to use a high compliance cartridge with a low mass arm, and a low compliance cartridge with a high mass arm. Think of the compliance of the cantilever as the softness or (hardness) of a spring. If the spring is soft, you need less force to compress it, and vice versa. Why compress it? The cantilever is effectively a spring and we need a specific amount of mass to constantly press down on it so that it traces the tiny groove of the record correctly without skipping or jumping across the groove.

I hope that explains the principle of light/heavy mass in tonearms.

The tonearm wire when taken out from the arm tube (as is done in most unipivots) and not passed into the arm base like in gimballed arms, definitely can affect the antiskate. So one has to be careful to leave some slack so that it can be routed properly so that it doesn't produce a constant tugging force in one horizontal direction, or even affect the vertical tracking force. In my current arm, I carefully route the arm wire and tape it to the top of the plinth so it does not exert any force.
 
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Sumanta

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Superb!
Thank you for the patience.
Your explanation are very clear.
I was reading in Nanook post in diyaudio too and read the resonant frequency. How to calculate this resonant frequency? I am finding answers to many problems by your way of design and can easily follow your design. But effective resonance of my selected arm and cartridge assembly may vary.
What exactly "compliance" mean here? Compliance to its specification? Is it written in spec of cartridges?
 
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