My First "Techie" - well part of it!

[Qwin]

Andy (plinth) by putting it in the bin!

The only original part of the superstructure I will be using is the Top Plate. I am casting a mixture of sand and fibreglass resin into the back of it. This will make it about 90mm thick, very heavy and inert as long as you keep the resin qty to the minimum required to bind the sand. It sets like stone.

The problem with just mounting the top plate on a slab of tree or whatever is the minamal contact area, this applies to the original rubber as well. By casting and sticking to the whole underside of the Top Plate it becomes one with the artificial sandstone block.

I won't really be binning it, I will have much of the original deck left over and plan on building this back up as a deck for my Girlfriend, in almost standard form. (strobe, cue light and pitch fader removed and a paint job)

[Qwin]

I’ve completed the bearing mods as above. See the story, which I’ve added to Ians thread “Can you improve the stock techie bearing???” at this location:

http://theartofsound.net/forum/showt...503#post413503

[Wakefield Turntables]

Ken,

Cant wait to see the new plinth and it looks like your quite handy with the bearing as well. The sonics of the 1210 may be altered significantly with your solution. I think most of us have the standard rubber / aluminium plinths. But, you could say that all people with modded 1210's have signficantly changed how there decks sound.

[Qwin]

Hi Andrew,
I'm hoping for something substantial, just hope it is an improvement and not a degraded sound, not every mod works the way you want. I've had my share of failures but have high hopes for this one.
I will be coupling the base of the bearing to the plinth with the old Blue Tak method. There is exactly 2mm clearance so a pea size piece should spread nicely.

[Qwin]

Back on track after the divertion for the bearing and getting ready to cast the plinth. Put the M6 threaded inserts in place for securing the tonearm. I used the threaded connectors that are for joining lengths of threaded bar or studding. I dropped in a couple of Aluminium tubes as tunnels for the cabling. I made use of all the redundant screw bosses, I used a large washer and screw to create lots of Mushroom head anchor points for the casting to latch on to.



Just waiting for the sand to dry out now, it has to be bone dry before adding the Polyester resin.

[Wakefield Turntables]

Ken, this has to be seen to be believed smart touch with the aluminium tubing its going to give excellent rfi and Emi coverage to your cables.

[Qwin]

Thanks Andrew,
nearly ready for casting. I've got a bad cold at the moment, but think I might be ok for the weekend. The sand is layed out on a big tray, approx 1m square. I keep raking it over and have a fan heater blowing accross it, but it is still taking time. I am a bit concerned about the mass, I am casting 9 Litres or there abouts and 80mm thick at the deepest points in the corners. The resin builds up heat when it is curing and a large mass tends to amplify this effect.
The last time I did this type of thing (20 years ago) the plinthe got so hot that it was smoking. I will be very carefull metering out the catalist this time. I think I gave it a shot for good measure last time, not being sure how it would set with such a large ratio of sand to resin and over did it.

You may have noticed I have not put any inserts in the corners for feet. I decided to stick simple Sorbothane semispheres directly on to the base. They are the best isolators I have come accross.

I came up with a design for adjustable feet using 50mm dia sorbothane feet. these were to be stuck to platforms attached to 1" threaded stainless bar. This would screw into captive 1" nuts in the casting and be adjusted from the top face of the top plate by a small allen key inserted through a hole in each corner. The 1" bar would have a small allen grub screw permanantly fixed in the end to take this. The problem with many adjustable feet is the threaded portion is too small a diameter and they need lock nuts to take up the chatter in the threads. By using 1" dia threads you can fill the thread with silicone sealant. When this dries and you insert the thread into the nut, it acts like a lock nut, stiff to turn but it has no chatter, stays where you set it and does not require additional lock nuts, which are allways difficult to get at. (ones at the back etc).

I decided not to go this route, my thinking was that all the extra metal work was likely to give a coupling path between the alloy top and the feet. So the simpler option seemed more appropriate. I will have to level the table it sits on but thats no big deal.

[Wakefield Turntables]

Sounds great so far, well done mate.

[Qwin]

Well that was a total disaster!

After 24hrs the resin sand mix had not set in the middle. It just had a 10mm thick crust which was rock hard, the rest was still soft enough to push your finger into. I used 2.4 L of resin/catalyst to 12 L of sharp sand. I know increasing the qty of resin will set but won't be as inert. My small test blocks were obviously setting like the skin that had formed and were not large enough to give a true representation, oh well, on to plan B.

I cleaned up the top plate, got all the gooey sand mix off with Acetone.
Salvaged the timber for the mould suround.
I will be returning to old faithfull and casting it in concrete instead. I nearly did this in the first place. Will have to coat the back with PVA for a good bond and add it to the mix. Got the materials lying around so will be doing this over the next couple of days.

[Qwin]

I cast the plinth in concrete.
Worked well, just waiting for it to dry out fully before I start filling any suface inperfections.



Must order some Walnut veneer.