DIY Uni Pivot Pics

I am designing a Uni-pivot for my 10 year old Rega Planar 3.

I have attached pictures below of my idea.

I will revise the design a little as the center of gravity of the pivot assembly seems a bit high.

I have 7mm Carbon fibre tube for the arm, brass for the pivot assembly and counterweight, Stainless Steel for the pivot point and aluminium for the head shell. I can make all of the parts myself. Will try to source a sapphire for the pivit bearing face.

Does this look like a good idea? Are the materials suitable?
Check the "what to do for a tonearm" thread just below on analogue.

Dice45 has put a link in one of his posts for site that sells sapphire bearing cups.

They also sell 1/8 sapphire balls for $4 us a throw.

instead of the cup/spike option why not do a trio of balls on the post and a single ball on the arm that rests in the centre at the top of the pyramid. (a nippy's "tetra pak" made of sapphire balls)
This is the unipivot setup used in the ACT one tonearm.

16 bucks US for a perfectly setup pivot point sounds good to me and the sapphire balls should last forever.


Nice pixes. Which pix program did u use? or was it a real 3D CAD? which one?

However, your arm design misses the sideweights i was suggesting in my earlier unipivot posts to increase rotational inertia w/o increasing efective mass. So you'll get deep bass only with ultra-high-compliant cartridges like the Shure V15.

Please do a search of my posts with the search keyword "unipivot". You'll find a lot of info concerning that. If you have questions, come back, i'll answer them. :)
DIY Uni Pivot Part 2


I have added more pictures as per your input and previous posts.

They are Revised design Figs 1, 2 and 3.

The program is AutoCAD Mechanical Desktop and it is a 3-D solid modelling program.

I have added counterweights which hang under and towards the pivot point.

I will try to do some inertia calculations around the pivot point and post results.

I am thinking carbon fibre for the arm, but as mentioned before it may not be suitable.

The CAD pictures in your tangential tonearm site is most impressive.
Tonearm wire

I am progressing slowly and need to know where to connect the Earth wire to the tonearm.

Do I connect it so it is in electrical contact with the headshell. The arm itself is carbon fibre, so non conductive. I am using the jewel bearing and pivot point. The jewel bearing is aslo non-conductive anyway.

Can anyone suggest where it should be attached. I am ordering the wiring for the arm and I need to know how much I need.

great to hear, you are progressinig faster than me :) too much projects in the pipeline and other things out of balance.

Anyway, for the case you need shielding, you can linen your tonearm wand's bore with, say, alu foil or copper foil, thin!, lightweight. To this shield you connect the 5th. the earth wire. this earth wire can be cheapochaepo IMO, provided it is utterly flexible as the other wires.

But i would be very surprised of you need shielding. I never did, in nine out 10 cases mx SME V's earth wire makes no difference in hum&noise whether connected or not. In the 10th case it slightly alters hum&noise W/O cancelling it (i mainly use LO MC cartridges however.). I'd suggest you omit shielding, unnecessary shielding hurts sonics.

Suggestion: try out 0.1mm thick enamelled copper wire for tonearm wiring before you spend $$$ for Cardas or the like. Although it is solid, not stranded, it is thin enough to be flexible. I costs almost nothing and sounds gorgeous. Unbeatable and unquestionable with MM cartridges, it even sounds fine and works well dynamically with LO MC cartridges. Which is a surprise as 1.2m of ths wiring build up 10 Ohms DC resistance.

Make two twisted pairs of this wire, one for each channel. Just don't twist them too tight. :)

J Epstein

2002-02-08 7:24 pm
I had very good results (by that I mean the cable performs well sonically and is also very soft which is important for my air bearimng tonearm setup) by using desoldering braid as a miniature shield braid. You need to compress it along its axis like Chinese handcuffs, and then you can run a stiff, folded wire through the center ("catheterize" it) to open a channel down the middle. Then pull the tonearm wires back through using this wire. It's nice and small and easy to work with.

I fopund my phono preamp would get unstable if I had too long an antenna at the input ;)