This project began in December of 1999 as a fellow audiophile and myself began discussing the possibility of designing and building our own turntable. This turned into a collaborative effort with participants from around the world. This page describes my implementation of a complete turntable using a bearing and platter design worked out by the Teres Team.
For more more information about the Teres project refer to the Teres turntable homepage.
From the often spirited discussions on the Teres list it became apparent to me that the coupling between the stylus and the spindle should be a very rigid loop, ideally holding both in perfect relation to one another. The use of very stiff arm wands and arm bases adds credibility to this notion. It also been reported that the choice of material used as a bearing thrust plate makes an audible difference with harder materials generally being favored. It seems that to accomplish rigid coupling you need to not only use a stiff material, but also something that is not compressible. Many layers of MDF would certainly be resistant to gross flexing. But because it is relatively soft it would would be subject to compression. If the choice of thrust plate material is audible, then certainly the hardness of the arm/base material would also be important. Based on these ideas I determined that I would use materials for the base and arm-board that are both stiff and relatively hard.
The importance of impedance matching and propagation of vibration was also
discussed on the Teres list, including an excellent treatise by Ivan Anderson.
Here is an excerpt from Ivan:
When a wave encounters a boundary of any description it is either
reflected, refracted, diffracted or transmitted (absorbed), or some
combination of these events.
...
When the characteristic impedance of the material after the boundary
matches the characteristic impedance of material in which the wave is
traveling, the transmittance is complete.
...
The main point? A medium can only dissipate/damp the vibration that
travels through it, and not that which it has reflected.
Here Ivan makes a good case for attaching the tone-arm to a similar material that
allows the vibration to pass through it so that it can then be dissipated.
Based on the above criteria I decided to use aluminum for my turntable sub-chassis. Aluminum, while not the most hard and rigid material, forms a good impedance match with the tone-arm, is relatively easy to machine and is inexpensive. However, aluminum is poorly damped and subject to resonance. So it was imperative that measures be taken to effectively deal with resonance. I came up with a design that is very rigid and at the same time extremely well damped. See the next section for the details.
The heart of my sub-chassis consists of a piece of 2 x 4 inch aluminum tube with 2 inches of each end filled with lead shot and polyester resin. The center section is filled with lead shot and mineral oil. This resulted in a bar that is rigid and absolutely dead. In fact it has a resonant signature more like a block of lead than anything else I can compare it to.
The post for the arm-board is of similar construction, a short piece of 3 inch aluminum tube filled with polyester resin and lead shot. The arm-board is attached via a 3/8 inch stainless steel cap screw through the center of the arm post (ala Verdier). This makes adjustment a breeze. Just loosen the cap screw and slightly rotate the arm-board. The arm-board is a sandwich of 3/16" aluminum and 1/2" clear acrylic.
To provide more damping and also isolation from external sources the sub-chassis is embedded in a box (tank) filled with a mix of sand, lead shot and mineral oil. A 10 x 12 inch piece of 3/16 inch aluminum plate attached to the bottom of the bar provides a large surface area that is embedded in sand/lead/oil. This large surface area provides better sinking of vibration as well good stability, holding the sub-chassis firmly in place. There is be no contact between the box and the sub-chassis (except through the sand/lead/oil) for good isolation from external vibration. Burying the sub-chassis in sand, lead, oil made a remarkable improvement in sound quality.
The following series of pictures illustrate how the components fit together.
The sub-chassis with the bearing installed
The box with about 1-1/2" of the sand/lead/oil glop in the bottom. It's a great damping medium, but really icky! The box is a wood (Granadillo) frame with top and bottom plates of 1/4" aluminum. The inside of the frame is coated with epoxy to make it oil proof.
Here the sub-chassis has been placed into the glop. I just squished the sub-chassis around to get it properly located and level.
Another 1-1/2" of the glop was added to bury most of the sub-chassis. The glop holds the sub-chassis firmly in place.
The top aluminum plate of the box is now put in place. The two small tubes toward the rear hold two color LED's that illuminate the platter to show the status of the motor controller. The tube toward the front holds the sensor to read the strobe disk attached to the bottom of the platter.
The finished Product! The lead, sand and oil are very heavy and the finished turntable weighs in at just under 100lbs!
Note the unusual arm mounting position. The Triplanar arm pivot is offset from the mounting pillar. Due to this offset it was easier to use this mounting position. While unusual the position is quite convenient. I also like having the fragile stylus farther away from the front of the turntable.
The motor pod is a length of thick wall, 4-1/2" aluminum tube. The pod is partly filled with lead shot to add mass and to damp out noise.
Last but not least the turntable is sited on a massive, rigid stand. The stand is constructed from MDF and the pillars are filled with concrete. A 3/8" threaded rod passes through the center of each pillar to attach the top and bottom plates. A 4" high sand-box sits on top of the stand. Large rubber stoppers (1" x 1-5/8") placed between the sand-box and the stand provide additional isolation. Rubber disks 3/8" thick are also placed between the sandbox and the turntable.
My arm is the outstanding Wheaton Tri-Planar series IV and the cartridge pictured is a Benz Glider. However, I recently upgraded the cartridge to a Clearaudio Accurate with stunning results.
To refine the physical appearance of my turntable I used Povray to create ray-traced images. Here is the the image of the final design. Povray allowed me to visualize a number of different base sizes, shapes and colors before anything was actually built.
