Skeletal vs Plinth style turntables
Made a table a few years back from Cocobolo laminated with Aluminum, glued the 5 layers (3 cocobolo 2 aluminum) together with a 2 component Epoxy glue, still hold up very nicely. The aluminum layers were "timesaved" which is the typical graining you see on for an example your typical Face Plate. System 3 Epoxy Good Listening Peter |
Some 20 years ago when I was building my current SP10 MK3 plinth, I spent a lot of time experimenting with glues. I was using CLD on the acrylic top plate. In this case a 15mm layer of lead was to be adhered to the acrylic. I initially thought that a lossy type glue, such as ados, would be optimal but listening to the test pieces thru a stethoscope while tapping it gave a "thunk" type sound. This was not what I expected as I was trying to emulate the ideal water fall type plot as we see published in speaker tests. That is a sharp rise time with very little tail to the sound. I then started experimenting with epoxy glues and settled on an industrial araldite epoxy. This lead to protracted experimentation with harder and filler ratios. I found that I could further reduce the tail of the tapped sound by optimising the hardness of the glue. The final result gave a very short sharp "tic" when the workpiece was struck. The result was a kind of fusing the acrylic to the lead. In this way they behave as a intimate composite structure. Aiding this was massive clamping pressure while the glue dried. Over one tonne of cast iron billets were stacked on top of the plinth during the curing time. Epoxy heats up when mixed, so the glue becomes quite runny. The vast majority of it oozed out between the layers. Unwilling to let this excess set, which would have required expensive remachining, I spent almost all night until just before dawn removing the excess as it flowed out. Fun. |
Viridian et al, You guys may be missing the point of what Atma-sphere wrote (at least as I see it). The point is that whatever the resonant signature, it is critical that the tonearm and platter be "connected" so they resonate as one piece. The problem with outboard arm pods (again, as I see it) is that they separate the tonearm from the bearing/platter, and no matter what you do after that, the two entities are independently subject to environmental energy sources; they'll then move or vibrate differently in response. Best you can do is make them very very massive so that most energy is dissipated as heat rather than movement. This is/was essentially my longstanding argument with Halcro vis a vis outboard arm pods. My metaphor or thought experiment is: Think of yourself trying to cut a diamond while seated in a row boat floating on water. Now think of yourself trying to cut a diamond whilst you are sitting in one rowboat and the diamond and all your tools are in another separate rowboat. Which is easier to do accurately? |
Ct0517 and RichardKrebs, have you considered filling the webbed aluminum casting of an SP-10 with a dense hard mixture of industrial epoxy and crushed granite(similar to Verdier) or brass powder? This might give the casting the properties of a massive plinth, while performing in conjunction with a rigid skeletal "plinthless" sub-frame. I've been think of this for my SP-10 MkII, together with a turnbuckle between a threaded bearing well and the sub-frame similar but different to the Porter concept. |
Dgarrestson. I have removed the motor housing on my MK3 from the original square chassis See the triangular shaped TT on my krebsupgrade.com web site. The rather flimsy naked motor housing has been laminated ( epoxy glued and bolted) into a machined duralumin housing of 15mm wall thickness. This in turn is adhered to a 15mm thick lead disc. ( the piece that was cut out of the plinth to accommodate the motor) In my original post on this thread, I talked about minimizing material changes and joins in the platter arm loop along with consideration of propagation speeds, absolute dimensional stability and stillness. This leads to the conclusion that the chassis has to go. I also replaced the platter with an acrylic duralumin lead composite. Regards |
