From quite a few years ago, this was my version of a Uni-pivot tonearm design by the late Dave Whittaker, creator of the Aura Turntable.
Dave knew that wood would provide good damping – he chose to use lightweight Balsa wood.
He thought also that the open truss structure would be low in resonances.
Dave’s own Balsa wood tonearm below, with Transfiguration AF-1 Cartridge and on a Acos Lustre GST-801 arm base:
My construction drawing – Effective Length 245mm is based on the Fidelity Research FR64 tonearm:
The uni-pivot point was made from a ballpoint pen (the ball is epoxy glue fixed solid).
Mounted onto an arm-base & arm-lift taken from a Hadcock GH228 tonearm.
The heavy brass ‘boss’ contains the uni-pivot contact ‘thrust plate’ inside (see drawing). We used a sapphire thrust plate – but you can simply use something like a M6 Hex-head machine screw, which has a nice conical shape inside the head (see below).
The completed tonearm mounted on an Aura turntable, with Cardas 33ga wiring from cartridge to phono input:
The brass bearing ‘boss’ has outrigger balancing weights on each side, for Azimuth adjustment.
A uni-pivot tonearm needs some mass at the bearing, for stability – for good bass performance. There is a lot of power / energy in the low frequency range.
(The arm counteriweights are also taken from a Hadcock tonearm.)
Top view below showing the screwed connection of the Balsa wood tonearm to the brass bearing ‘boss’. The wood is glued to a metal (copper) plate and the screws fix the plate to the brass boss under.
The Counterweights are mounted very low – this is not ideal, they would be better mounted higher, closer to stylus level – Vertical Tracking Force tends to vary more. As the tonearm is moved up and down, counterweight distance varies more. (See diagram below.)
A minor enhancement – the headshell also has small outrigger weights (non-magnetic brass and aluminium) – they help stability I think, but also provide a handy ‘finger-lift’:
The sound – the attributes of a uni-pivot bearing are audible – fatigue-free treble, clear, non-aggressive tone.
Next time – a DIY 12″ solid wood tonearm.
Please feel free to comment!