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R5. 

An external power supply will switch the turntable on and off.  The armboard shown is cut to fit an SME 3009 tonearm.  Armboard materials will receive some experimentation.  Current thinking is toward constrained layer builds of different materials for the best combination of rigidity and resonant absorption capabilities.

The goal is to retain the traditional appearance and layout of the original table while substantially upgrading the sound over the original design.  This is still a suspended layout that hangs the subchassis by three bolts attached to a rigid top plate.  

 

Above: Just for reference, the standard TD150 sub-chassis and suspension assembly.  Compare that to the image below.  The goal for the more rigid and better damped sub-chassis frame is to eliminate both sub-chassis flex and to reduce if not eliminate the propagation of bearing noise traveling through the frame material out to the tonearm.  If you don't believe that the standard sub-chassis will flex from the mere weight of its own platters check this link...

Q: So what is wrong with a little sub-chassis flex you ask....? 

A: When the sub-chassis flexes the following takes place:

The distance between motor pulley and driven pulley changes
When this distance changes the elastic drive belt either stretches or contracts
When the belt length changes, pitch speed is momentarily altered
We lose pace rhythm and timing
Tonearm geometry is altered, changing the all important alignment between the stylus and record groove.   Musical detail is then lost

The whole point to the increased rigidity is to improve pace, rhythm and timing, and detail....to get closer to the sound of the original master tape. 

Constrained layers construction is used in three structural components; the base plate, the subchassis frame and the top plate.  The materials in the constrained layer build-ups are 5052 aluminum, pvc type 1 and polyurethane adhesive. The aluminum is chosen for its rigidity.  The pvc is used as the alternating layer within the build to serve as a resonant damper.  The thick bottom plate will add structural integrity to the cabinet.  A large opening is cut into the bottom plate to allow air-born resonance to pass freely out of the cabinet.  The opening also allows access to adjust platter level. 

 

Replacing the conical compression springs are three assemblies of the unit pictured above.  This isolation unit is much less compliant that are the Thorens coils.  Listening tests have proven this design to offer greater pace rhythm and timing as well as increased details.  These units isolate the sub-chassis from the main chassis, which carries the vibrating motor but with the added benefit of a more stable sub-chassis that remains largely without motion during play.

 

 

R5mtrplt_1.jpg (58624 bytes)  R5mtrplt_2.jpg (65704 bytes) click on thumbnail to view full size image

The motor mount plate is slotted to allow adjustment for belt tension

 

 

Three BDR cones are used as footers.

With exception to the rigid bottom plate, the interior of the plinth is identical to the standard TD150 cabinet and assembles in the same way.  However a significant difference lies with.................

the interior wall construction of the cabinet.  Provision is made for the cabinet sides to hold lead shot to damp resonance. Cabinet material will be 1/2 inch Baltic Birch multi-ply.  The cabinet assembly does not used mitered joints.  Instead, the plates are cut precisely to fit square with overlaping joints.  The two vertical braces to each side not only provide structural integrity, they allow the cavities to be filled with the shot in a methodical way during assembly.  Fastening is accomplished with adhesives.

The finished cabinet will be covered in Black Walnut veneer.   The veneer is to be cut to have the appearance of a mitered construction for aesthetic reasons.

 

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