The location of the armtube on top of the counterweight box allows it to extend forward above the top of the post that supports the filaments, effectively hiding the bearing arrangement from view. Like I said – simple and incredibly elegant. Even better, it doesn’t rely on super exotic or expensive materials, precision construction or vanishingly small tolerances. It offers, to all intents and purposes, the benefits of a uni-pivot without the oft-quoted challenges when it comes to rigidity and stability. If there’s no way that a gravity dependent bearing can deliver rigid coupling, at least the Supatrac solution opposes the damaging horizontal impulses that act at right-angles on a conventional uni-pivot, making them so hard to resist. It’s so simple that it almost qualifies for “why didn’t I think of that” status – except that once you look at the implications of the execution, the simplicity becomes buried amongst the mechanics.
The Blackbird arrives, beautifully (and very safely) packed in a foam-lined pelican-type carry case. In fact, everything about the package – from the box to the superbly clear instructions, the complete set of tools and multiple spare parts – rise well above the norm. Supatrac’s presentation is a model of professionalism that belies the ‘just got started’ status of the company. Aside from the arm-mounting collar (Linn-type, but with a collar and parts to allow its adaptation to the SME slot, while other popular mounts are also available) the arm consists of a mounting pillar, the arm-wand and a bunch of hardware. The wand is constructed from a pair of rectangular carbon-fibre tubes, bonded together along their long sides to create a rigid, figure-eight double box. The business end of the arm is cut at an angle to allow access to a pair of short cartridge mounting slots, the two tubes being internally reinforced with aluminium channels to prevent over-exuberant users from crushing the carbon mounting surface. The box section arm-tube carries the signal wires in one side and damping foam in the other. It can also be cut to any length, allowing SupaTrac to offer 9” and 12” arms as standard, but also to entertain orders for special lengths as required. The open tube arrangement allows for special wiring (“You have your own, preferred internal arm-wire, or need six wires to run a field-coil cartridge, that’s no problem sir.”) but it also allows the owner to vary and fine-tune the arm’s effective mass. This extremely unusual facility can be achieved in two different ways. The standard 9” Blackbird runs an effective mass of around 10g – which is light by today’s standards. But Supatrac provides a rod and coupling wedge that can be inserted into the tube that carries the wires, complete with a tethered thread to adjust its position or retrieve it. A formula is provided to calculate the correct position of the internal weight. Then there’s the option to use an under-slung carriage weight, which clips over the arm-tube and can be positioned at any point along its length. Finally, the Blackbird can be ordered in either standard Baerwald geometry or Stevenson: the latter optimises tracking towards the end of side, where many classical pieces have closing crescendos with heavily modulated grooves. So, here you have an arm that is adjustable for effective mass, adaptable to specific cartridge requirements and in which both length and geometry can be specified – and I’m just getting started…
