The ML2-F plinth design for the TD124
Above: Cad render. The ML2-F waiting for its TD124 to be installed.
Above is a cad render of the core material within the ML2-F.
It is a rigid, yet lossy, material that is cast into a proprietary mold. The mold tool, in addition to being a casting tool, is also used to assemble and adhere the plinth structure that holds it. The object is to cast this material into a partially built plinth so that the material expands tightly against all surfaces which contain it. When the material is cured after casting, the top mold piece is removed. Then the cavity mold tools are removed. After this a plinth top plate is carefully fit and adhered into its mating parts to form an outer 'shell' that slightly bulges from the pressure of the cast material within it. Shell materials can vary. In this instance, the lower and outer side panels are cut from baltic birch multi-ply. The top piece of the plinth is cut from mdf. Once cast, and with the top plinth piece adhered, the entire structure is; first sealed per the needs of the material, then coated in a texture black enamel. Footers can vary. The first iteration makes use of heavy duty rubber feet. Hard cones can also be substituted.
Commonly used in surf boards as a composite core, Poly Urethane expanding foam is used in the ML2-F plinth as its core..left: td124 sn#13943 stands within the first ML2-F undergoing initial trials.
above: getting more serious. The rubber feet have been replaced with Golden Sound Large ceramic cones. The Neuance platform beneath. Above, the ML2-F polyurethane foam core plinth. This plinth does pass the 'knock' test. That is, with the sound turned up, stylus in groove, record not turning, knock on the chassis with one knuckle. No noise through speakers. Knock on plinth with one knuckle; no noise through speakers. This is dramatically different when the TD124 is mounted in an open box plywood plinth (with mushrooms).
Another concern: static electricity. It is Winter. The carpet is nylon. As pictured, I see no more static than is normal for this time of year. One noteworthy observation; when using a graphite platter mat, I see plenty of static electricity while handling records. Regardless of plinth. Graphite mats seem to be a problem. I've noticed it while the graphite mat was being used on another turntable.
Record playback. The Graham tonearm /Shelter 501-II combo is sensitive to vtf, overhang and zenith angle. Vta, --- not so much but best sound is with cartridge body slightly tail down. Vtf works best at between 1.7 and 1.8g.
I'm going to try a different armboard. The ebony board pictured transmits drive train vibes more readily than does the metal chassis of this player.
while this plinth does offer good isolation from external vibration, both surface borne and air borne, I have noticed some low frequency rumble while playing classical records that have quiet passages. Which led me to try this:
My trusty old heavy slate plinth. Guess what?!. The rumble went almost entirely away. A very dramatic difference..! That should tell me something. The ML2-F wasn't such a good idea after all. For now I'm back in slate and will attempt to "re-think" my foam plinth idea. Perhaps it isn't just as simple as a single type of foam that serves as a core within a wood plinth. Perhaps I need to consider using multiple density foams in the build with the 'lossy-est' foam at center and the denser, least lossy foam at the outer layers. Mean time, TD124 #13943 is sounding quite awesome within the slate plinth I have had since 2007. Maybe I'll shelve the foam plinth idea for a while.