VPI TNT Bearing question

I did something similar to a TNT with a non-inverted bearing by extending the threaded thrust rod outside the bearing well. A massive brass donut threads onto the rod, with an extensible footer that drains vibration into the platform below. One of many modifications to TNT. I'm not a fan of inverted bearings. The non-inverted bearing stays better lubricated and puts bearing noise down below, where the brass coupler can absorb and drain it into the platform. I also replaced the steel ball bearing with a ceramic ball that floats between dual plastic thrust plates. Two points of contact spreads the load for reduced friction and stress at the thrust plate-- allowing for a heavier platter.

Adding mass and coupling to the platform should help an inverted bearing too.

Whatever VPI has done with subsequent iterations of the platter bearing to improve coupling between the bearing housing and the plinth, my point is that massive brass coupling of the metal bearing housing to the platform below will surpass the acrylic plinth in dissipating parasitic vibration from the system. This is based on several modifications to TNT spindle bearing and suspension I've performed that substitute brass for plastic. If you have access to a machine shop, try it you'll see. The construct can be extended to a brass pedestal that extends from the tonearm pedestal through the plinth to the platform. I've done it and it works. After enough of this the acrylic plinth becomes little more than a means of locating the spindle and tonearm in the horizontal plane.

I took a staged approach developing the corner towers, evolving from sorbethane of the original TNT Jr., to springs, to a rigid mass-loaded approach using solid hardwood and later brass in feet, and finally to brass with a DIY Stillpoints-style core. There are a few others who have adapted Stillpoints or rollerballs to the TNT. With a chrome spring-steel hole plug from Lowes and 1/4" and 3/8" ceramic ball bearings from Boca Bearing, it is possible to emulate the Stillpoints idea inside the VPI stock elephant feet, which further benefit from being recored in brass. To solidify and better couple the now unsuspended plinth, I eliminated the threaded leveling mechanism from the suspension tower and substituted a leveling mechanism underneath the platform supporting the TT. With this last step the TNT and its platform perform as a system.

It requires a lathe to make a spindle bearing. There are several plastic materials harder and less compressible than delrin for thrust plates, and ceramic balls that sound better than steel for various reasons. AFAIK, I am unique in encasing a floating ball in a donut between dual thrust plates. I considered updating to the inverted bearing, but rejected this for the reasons stated above. Having owned and discarded the TNT 3-pulley system, I was curious to find a better way to center the spindle bearing that would also support thread drive. Theoretically the centering mechanism should lessen somewhat the need for closer clearance tolerances between the spindle and its cylinder. In fact, once the drive system finishes torquing through start-up, there may be reduced friction/noise with a bit more clearance. IMO the unfocused sluggish sound of soft rubber belts is the Achilles heel of all VPI designs. The idler wheel that I added centers the platter and provides better traction for the thread. Thread drive is the best thing that can be done to realize the potential of these TTs.

Mark Kelly's AC-1 sychronous drive controller kit has been out of production for several years. I believe he does similar work for OEMs and perhaps custom jobs. I've never compared it directly to an SDS or Walker controller, but the AC-1 killed the PLC in my system. The fact that the AC-1 is a two-phase controller has advantages. The SDS is a single-phase controller that works with a phasing capacitor.

The TNT offers simplicity and lots of space to work through DIY mods, which is the main reason I've stayed with it since the mid 90's.