Linear tracking turntables, whatever happened?

@ct0517 

Its DIY heritage begins with the original design by Poul Ladegaard. IIRC, he envisioned this as a linear tonearm that could be built at a kitchen table using basic tools and standard parts from a hardware store.  Vic at Trans-Fi turned that into a commercial offer, with a professional fit and finish and a steady stream of running improvements.  It's humble origin should in no way suggest that the design is unsophisticated. 

For the purchaser, the DIY part is principally the tank, pump, and airline.  This is no big deal, as all one needs is a low-pressure aquarium pump(mine is a Rena 400), a gallon plastic petrol can as a smoothing tank, silicone tubing, and brass nipple fittings from Home Depot.  The low operating pressure has design advantages, and avoids the complexity of the high pressure pumps associated with captured air bearings(e.g. extraction of moisture and compressor noise.)

Vic includes a Delrin tower on which to mount the arm base to a turntable plinth.  He builds each tower to the dimensions of platter height and armboard of the customer's TT. Alternatively, the customer can fabricate a tower with better metal materials such as brass or stainless steel.  I made a custom brass turntable base that drops into the stock collet of a Kenwood L-07D.  This preserves the VTA adjustment of the original Kenwood tonearm.      

Set-up is straight-forward, but it is critical to align the air manifold such that the stylus tracks a perfectly straight line from the perimeter of the LP to the center of the record spindle.  For a template, I took a 12" strobe disk and scribed a radius from the center of the spindle hole.  Once the manifold is painstakingly aligned, you wouldn't want to ruin that by pivoting it to change records.  The cue bar raises the wand enough to allow careful sliding of the LP in from the side.  This is only a hassle if the turntable has a really tall spindle.

One must carefully dress the flying tonearm wires through the supplied gantry to avoid torqueing the wand as the sled travels across the air manifold.  This takes practice, particularly with high compliance cartridges. 

One area ripe for DIY improvements is adding mass to the front of the flat wand in order to optimize vertical effective mass across a wide range of cartridge compliances.  I found it useful to machine a kit of small brass weights that can be dropped into the large holes in the wand between the cartridge mount and the vertical pivot bearing.

It's a neat high-performance arm.  IMO, it's only shortcoming is that it doesn't leave enough room to mount additional pivot arms to the TT.       

@ct0517, to add to Dave’s excellent comments, and in the cause of clarification, let me say no, record changes are NOT made by sliding the LP under the cartridge/stylus (and the arm wand onto which is mounted the cartridge). At the end of an LP side, the wand is returned to it’s rest position, at the far right end of the arm’s manifold, where it is out of way of the LP. The LP DOES however need to be slid under the manifold, which is locked in position over the back of the LP, about half way between it’s center hole and it’s perimeter. Other linear trackers avoid this by having a longer arm wand, making it possible for the arm’s main structure to be located beside the table’s platter, not positioned over it.

The manifold being suspended over the LP makes possible a shorter arm wand, which has benefits (lower mass, inertia, and resonances) and one penalty (greater changes in VTA and SRA when navigating warps, resulting in possible "warp wow"; a table providing LP flattening---via vacuum hold down or a clamp---is good for the arm). One thing I like about the Terminator is the arm wand/cartridge/stylus facing the operator, rather than being 90 degrees perpendicular as with other linear-tracking arms; makes cueing much easier!---Eric.

Bdp24 - The LP DOES however need to be slid under the manifold, which is locked in position over the back of the LP, about half way between it’s center hole and it’s perimeter.