So I thought I would build a unipivot tonearm ,
In the pic immediately above you can see the pivot point , it is actually a sapphire ball 1.5mm diameter, this locates on the end of an m8 x 80mm stainless steel set screw . The sapphire locates into a 1.6mm hemispherical recess in a Teflon thrust pad ( actually a stack of 2mm Teflon discs) which are a light interference fit in the large sphere .
The headshell is a rough and ready test item to get geometry correct , the finished item will be heavier and much thicker as the test item has the arm mass at under 10g and I prefer around 11-13g with the option to add to this for low compliance denon dl103 and the like .
The arm will have adjustable viscous damping without the need to change oil weight , this simple idea was inspired by John Bicht and his wonderfully simple mission 774 arm .
The spheres are just gear knobs from eBay, the larger one is 50mm aluminium and the smaller counterweight is stainless steel m6 thread hole wound onto an m6 set screw which acts as the weight stub .
The armtube is 12mm aluminium but I will be swapping it for titanium lined with a secret damping medium just like the alphason arms , its not foam , I may divulge the secret sauce as the arm progresses.
Lots more to come on this poject
Titanium armtube fitted , damping trough fitted , SME style chrome plate brass sliding base fitted .
The arm base is available from eBay at a very reasonable price of £42 shipped and allows fore and aft adjustment of the whole arm , this saved me from needing slotted cart mounting holes in the headshell.
The damping trough is just an oil tank cap from eBay, 45mm id . Damping Oil is 800cst silicone damper fluid for radio control racing car’s and is readily available, as a rule of thumb the lower the cartridge compliance the slower or heavier the silicone , however this should be considered on the end arm mass as high compliance carts in high arm mass will also benefit from heavier oil ( to control any wayward arm movement around system resonance)
The titanium is 12mm OD and 10mm ID 6al/4v seamless which is very stiff , I chose it as the unipivot bearing system I have made has inherent compliance in the teflon thrust pad . I have still to line it with the secret sauce and am hesitating on this as the construction of the headshell clamp appears to be providing all the damping it needs .
All in all this arm is proving to be a scary device , for less than the price of a clean used rega rb250 its performance is up there and in some ways betters the alphason hr100s.
More as I clean up the cosmetics and try different headshell materials .