I thought I would document the process....
so here it is:
First I thought about the roll of plasticine / plasti-clay....
1) It adds mass (mass loading) - converts HF vibration to lower Frequencies (which are more easily damped by various mechanisms)
2) It is an elastomer - it squishes, and converts vibration to heat
3) Elastomers work most efficiently in vibration to heat conversion when constrained (Hence Constrained Layer Damping - CLD)
4) There are two primary vibrating surfaces - top and bottom of plinth - various reports on the JVC's have used damping on both surfaces (brass weights on the top, sitting the plinth on damping rubber/cork/etc... on the bottom)
5) By providing a link between the two surfaces, and doing so using a CLD under a little pressure (compress the spring...) both surfaces could be damped
6) No way of filling the plinth with plasticine as there are circuit boards that require space and ventilation - and plasticine by its nature will under pressure mold itself and change shape until all compression is effectively gone.
So I needed a way to constrain the plasticine, while filling the space between top and bottom of plinth with it......
My high tech solution involved..... Toilet roll cores
I cut them so they were between 1-2 mm shorter than the space from top to bottom (the additional space will be filled with plasticine.
Then I filled each core with Yellow (why yellow... it was the first colour out of the pack...)
I also used the cores to get a mound of plasticine into places where manual spreading would have made it difficult (close to boards, etc...)
And I positioned them in the open spaces furthest from the supporting plinth walls - ie where a spring between top and bottom plinth will provide the most damping effect. (A better long term solution might be a bunch of actual springs located where the rolls are currently, and kept inside tubes [toilet rolls?] which are immobilised used modelling clay.... )
Then I started building up the modelling clay from the plinth edges working in, and using it to immobilise the rolls....
The modelling clay was built up to be about 1mm higher than the edge of the plinth - to provide some compression when the base is put back in.
I was uncomfortable having loose modelling clay right next to the motor - where when compressed it might push into the works.... felt a lot safer with the clay constrained in the rolls:
A number of people are welcome to come out and say "I told you so"....
I ran short of modelling clay - not by much, and I don't think what I've done is inadequate, but I could have used another 500g or maybe even another Kg.
I also soldered in some captive leads (BlueJeans LC-1 low capacitance) - and measured the resulting C at around 100pf (yay finally!)
I used more modelling clay around the cables to provide support so load on the solder joints gets minimised.
On closing the plinth I had to push down quite firmly, and screw things down tightly.
The end result has the bottom fibreboard bulging a little - this shot shows the way the base was being pushed up after I screwed down the other side... this was then forcibly pushed down and screwed down. (tried to take photos showing the slight bulging but it just wasn't visible in the shots)
I also picked up several Ikea Lack tables for my new turntable rack, and have been reorganising the listening room....
Things are not done yet, as I am missing several sets of spikes - for between the Lack Tables (stacked on top of each other) and for under the TT... - I also have a collection of sorbothane hemispheres and pucks of various sizes...
So I cannot yet report on the end result...
I'm picking the spikes up on Monday so things should be up and running either Monday or Tuesday,
bye for now
David
