View Full Version : DIY Clone Tonearm
Audioflyer
03-08-2014, 16:46
Would you make a tonearm that looks like this? I was give one that was damaged beyond repair after my friends young daughter used it as a hammer. :spank:
The files below are in pdf format one 2D/3D files.
I’ve modelled this up in a cad package by reverse engineering the damaged arm.
https://www.mediafire.com/?uug5vocja6dd9rv
https://www.mediafire.com/?j7p9of0t2ql82qi
Sharif.
That ought to make an interesting project Sharif.
Being a unipivot design makes it easier to copy. What does the unipivot needle run in - an inverted cup or a miniature ball-race? If you can copy the dimensions exactly and use the same materials, the Aro copy will have the same effective mass as the original.
If you take the cartridge wires out to a separate plug and socket, situated near the pivot end of the arm, you will be able to make and use exchangeable arm wands, should you want to experiment with different cartridges.
Keep us posted once you decide to embark on the project.
Good luck! :)
Audioflyer
03-08-2014, 17:59
The pivot needle run in a sapphire cup I found a source for them and the arm tube is made from an aluminium archery arrow shaft the rest of the material is of the shelf.
I was hoping to get a small batch made but my brother in law had a serious motor bike accident early this that’s left him unable to stand for long periods.
:(
I've been thinking about the connector and may try using the miniature plug/socket as used for a ps/2 keyboard.
Sharif.
sq225917
03-08-2014, 21:17
Sharif speak to ynwan he's been looking at super miniature Lemo plugs recently.
Sharif speak to ynwan he's been looking at super miniature Lemo plugs recently.
They are already used by a few arm manufacturers.
the arm tube is made from an aluminium archery arrow shaft the rest of the material is of the shelf.
When you go to order the arrow shaft, it may have a size such as "2114" or something cryptic.
Luckily there is a method to the madness, however it's still an odd sizing convention: (And this applies to aluminum only)
The first 2 digits are the shaft diameter in 1/64ths of an inch, so the diameter is 21/64"
The 2nd two digits are the wall thickness in 1/100ths of an inch, so the example has walls 14/100"
Carbon arrows use a different system...
One thing worth looking at, there are some aluminum-clad carbon shafts available now, they are the best sounding when tapping and listening to it ring. Also most archery ranges have a bent/broken arrow box, you will probably be able to get as many as you want for free or just a few bob. (and as you only need 8-9" of shaft for the arm, there will be plenty of useable shaft on a discarded arrow)
I've been thinking about the connector and may try using the miniature plug/socket as used for a ps/2 keyboard.
That's a mini-DIN of some sort. It should work really well.
I might suggest making your cable from Mogami W2929 or something with a similar construction (4-conductor+shield, small and flexible)
And there is an excellent DIY cable recipe here - http://www.takefiveaudio.com/mall/shopcontent.asp?type=DIN_phono
I love the idea of your project, please keep us informed of any progress and take lots of photos.
Cheers!
Audioflyer
12-08-2014, 23:21
Jim (6L6) thank for the explanation of sizing the aluminum arrow shafts that was some thing new I've learn't.
I am hoping to have a set of CAD drawing for the tonearm finished soon, I will put them up on the forum for suggestions and comment.
walpurgis
12-08-2014, 23:42
Interesting project. I've been considering constructing a unipivot tonearm for a while, I've thought of using hard oak as a wide rounded bearing cup and stainless steel as a less rounded pivot point. My opinion is that the pivot contact has to be as directly in line with the stylus vinyl contact position as possible (this has to be approximate as it varies by cartridge obviously). My choice of arm material for a medium mass arm would be Tufnol or Paxolin sheet, which I have actually obtained (both) and would make a braced, skeletal arm form from. I may actually get around to starting soon.
Sharif, are you making an entire new arm, repairing the one you have, or fabricating only the damaged bits?
I ask merely from curiosity.
Sharif speak to ynwan he's been looking at super miniature Lemo plugs recently.
I recently got this delivered:
http://i62.photobucket.com/albums/h90/markemark_2006/Hi-Fi/37C8214F-C3A0-4941-94BE-550EAF58FB99_zpsqesny1cw.jpg
It's a custom latching 5pin - ordered directly through Lemo (the cartridge is just for scale).
Also made a proof of concept of an arm - it's not based on an Aro though:
http://i62.photobucket.com/albums/h90/markemark_2006/armdevelopment2_zpsde7cc3c4.jpg
Audioflyer
14-08-2014, 07:17
I recently got this delivered:
http://i62.photobucket.com/albums/h90/markemark_2006/Hi-Fi/37C8214F-C3A0-4941-94BE-550EAF58FB99_zpsqesny1cw.jpg
It's a custom latching 5pin - ordered directly through Lemo (the cartridge is just for scale).
Also made a proof of concept of an arm - it's not based on an Aro though:
http://i62.photobucket.com/albums/h90/markemark_2006/armdevelopment2_zpsde7cc3c4.jpg
Those connectors look good the plug looks a little tall.
That's the first time I've seen you concept of an arm looks very interesting.
Audioflyer
14-08-2014, 07:21
Sharif, are you making an entire new arm, repairing the one you have, or fabricating only the damaged bits?
I ask merely from curiosity.
I'm planning to make a new arm well at less four of them.
Naim may not be keen on you making an Aro clone other than for yourself - have you enquired?
Those connectors look good the plug looks a little tall.
That's the first time I've seen you concept of an arm looks very interesting.
The connector does look long but it has to be put into perspective - it's only about 6mm diameter so in reality it isn't very tall (the end bit is a cable strain relief/reducer too).
The arm tube (well, not a tube) will probably be a CF fabrication or possibly 3D printed. The details of the bearing have been blurred out at present as it utilises a technique not currently used in arms. Lots more development to do yet.
Audioflyer
14-08-2014, 07:45
Naim may not be keen on you making an Aro clone other than for yourself - have you enquired?
I had thought about that and will only make my four arms for myself though I will make some changes to the design.
I don't think there is much you can change in a simple unipivot design but to make it look like the ARO would be a bit of a cheek.
I'm suprised that nobody has cloned it before as they like to clone their amplifiers.
My experience is that a lot of DIY audio is electronics based. Of course there are loudspeaker projects, but fine engineering is less common.
I think there is quite a lot that can be done differently with the unipivot concept :).
There is no need to use the cable strain relief of the Lemo plug.
Regarding Naim's possible objection to a copy/clone of their Aro arm - well they would only have cause to object if the copy were to be sold on as an Aro arm. That would be fraudulent and the copy a forgery. There is nothing to stop anyone making a "chinese copy" for one's own personal use.
Audioflyer
25-08-2014, 22:13
I've made a bit more progress on a my diy unipivot arm the Naim can wait another day.
Left hand side of the drawing showing bearing post with VTA adjustable mounting.
Tone arm base will use Rega's three point fixing.
Right hand side showing an overview of tone arm with Rega geometry.
The flanges on the side of the yoke are placed low down and should add further stability to any side way forces.
Counter weight stub will be rigidly coupled to the yoke with the counter weight decoupled with two 'O' ring inserted with in.
http://i681.photobucket.com/albums/vv175/audioflyer/Un-pivot%20Tonearm/PTTAView22082014.jpg
Sharif
How do you think those weights will impact on the arm when tracking warps?
According to your dimensions, your arm has the following geometry:
Effective length: 237.034mm
Offset angle: 21.033 degree.
According to the vinylengine.com, they differ from those of the Naim Aro arm, which has the following geometry:
Effective length: 230.5mm
Offset angle: 24 degree
(Overhang: 18mm)
The Aro arm conforms to the Bearwald geometry for an arm of effective length 230.5mm.
How did you derive the dimensions for you arm?
How do you think those weights will impact on the arm when tracking warps?
If they are offset at the same angle as the cartridge slots, it will be completely fine.
If it's not, then the whole gimbal vs. unipivot religious argument will start...
Or am I missing something? (I hope so...)
Ok, then what are you referring to? (And why is it taking 3 posts for you to explain?) :)
Audioflyer
27-08-2014, 15:27
How do you think those weights will impact on the arm when tracking warps?
My thinking for the extra weight to the bearing cup/yoke was to see if the I could increase the arms stability.
After talking to one of the structural engineers the extra weight would not make any difference.
As the weight was going to be place either side of the bearing I can see no reason wraps would be a problem.
If they are offset at the same angle as the cartridge slots, it will be completely fine.
Since the axis of the vertical bearings is not at right angles to the cartridge slots, the arm will 'roll' slightly (counter-clockwise as viewed from the front) when the arm rides any record warp. Just as the J-shaped SME arms do.
Or is your arm still a unipivot design? It's not clear from your drawing.
Audioflyer
27-08-2014, 15:38
According to your dimensions, your arm has the following geometry:
Effective length: 237.034mm
Offset angle: 21.033 degree.
According to the vinylengine.com, they differ from those of the Naim Aro arm, which has the following geometry:
Effective length: 230.5mm
Offset angle: 24 degree
(Overhang: 18mm)
The Aro arm conforms to the Bearwald geometry for an arm of effective length 230.5mm.
How did you derive the dimensions for you arm?
I'm planning to use the Rega geometry.
Drawing the arm to the Rega effective length and pivot to spindle distance I could not get the offset angle right,until I found it was for their cartridges only.
If I've read the effective length for other cartridge set-up will be approximately 239mm.
Audioflyer
27-08-2014, 15:45
Or is your arm still a unipivot design? It's not clear from your drawing.
Yes it still a unipivot design.
As the weight was going to be place either side of the bearing I can see no reason wraps would be a problem.
So the pivot is in the same plane as the weights?
Audioflyer
27-08-2014, 16:38
So the pivot is in the same plane as the weights?
Yes the weights are in the same plane as the pivot.
I was thinking that by applying the principal axes for aircraft it might help with a with a tone arm design.
If the pitch axis is along the arm tube towards the counterweight.
The yaw axis was the arm moving over the record.
The roll axis was the bearing cup/yoke with extra weight to the lower half.
http://i681.photobucket.com/albums/vv175/audioflyer/Un-pivot%20Tonearm/PTArmYoke22082014.jpg
I'm planning to use the Rega geometry.
Drawing the arm to the Rega effective length and pivot to spindle distance I could not get the offset angle right,until I found it was for their cartridges only.
If I've read the effective length for other cartridge set-up will be approximately 239mm.
The Rega arm geometry is:
Effective length: 237mm
Overhang: 15mm
Offset: 21o,
with radial null-points at 57.2mm and 120.4mm.
This corresponds to neither the Baerwald, Loefgren, nor Stevenson geometry; though it is closest to Stevenson's:
Overhang: 15.42mm
Offset: 22o.
There's some dispute over the actual Rega measurements if you speak to http://www.audiomods.co.uk you'll find these figures derived from practical measurement recommended: Pivot to spindle distance 222.25mm. Offset angle 23 degrees and the effective length 239.5mm with an overhang of 17.25mm
There's some dispute over the actual Rega measurements if you speak to http://www.audiomods.co.uk you'll find these figures derived from practical measurement recommended: Pivot to spindle distance 222.25mm. Offset angle 23 degrees and the effective length 239.5mm with an overhang of 17.25mm
That makes more sense - with those measured figures, the arm geometry is now virtually identical to Baerwald (offset angle: 22.96o, overhang: 17.28mm).
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