Technics SL1200 plinth damping

[mulane]

Very nice deck scoobs. Sorry to hear you gave up on the Technics though. Anyone else have any thoughts on this? If the layers are all rattling together then surely they would be INDUCING resonance rather than supressing it as intended! What about the "super" SL 1200s with copper mats and SME arms etc - are they just rattling away like ours?

Cant remember where I saw this but here's one person's solution:

[Tony G]

From the look of that stand and the points under the deck I have a feeling that I have seen that "mod" here somewhere in the last 6 months.
My own recent experiments with my 1200 indicated that the two under layers act more as ballast and shock absorbing mounting cradle rather than CLD.
My experiments with this table are proceeding at a rather leisurely pace enforced by a severe bout of fiscal depression preventing me from throwing money at it like I might otherwise.
You mentioned using a dampening layer in your armboard or considering it - doing what I can afford ATM and having a "non-recommended" spare RB250 lying around I gave it a spin on the 1200. Having already ascertained that, to me, even with extra ballast and modded counterweight, the stock arm was not up to running either a DL-103 or the AT-Mono cartridges that I wanted to run, and knowing that they perform well on my Tecnoarm on my other deck.
That particular experiment indicated several things, one was that most of the limitations of the stock RB250 (it does have a counterweight mod) demonstrated themselves and showed why Michell did what they did to it to produce the Tecnoarm.
Another was that, particularly when clamped firmly to the armboard, the 1200 was particularly affected by what was used in the way of feet, foculpods were the worst, then the stock feet and the best were points threaded into the mounts for the stock feet.
Best result with the Rega arm was to place a suitable sized 2mm thick "O" ring between the base and the armboard and barely tighten the nut by finger to only just prevent rotation of the armbase.
This indicated to me, that the arm was transmitting too much energy into the alloy casting and it was not being properly dissipated before making mischief.
Not that I particularly wanted to use a Rega arm on the 1200 anyway, for me it obviates most of the reason for owning one, which is the ease of swapping cartridges.
The stock arm really does offer the best of everything WRT easy cartridge swap and adjustment of VTA and VTF - shame it cannot handle pushy MCs as well.
Even the Jelco does not offer the same facility either for VTF or VTA.
I digress, I do feel the alloy plinth, being part of the motor system, requires the arm decoupled or an arm capable of dissipating the excess energy from an overenthusiastic cartridge.
Dependent on that, it may also benefit from different feet; the benefits of different types may not be as I found, as I suspect that may also depend on the substructure (stand or support).
Still haven't given up on it, but it is on the back burner for now while I catch up with listening to some music rather than the gear.
Have fun.

[mulane]

Interesting re the O-ring under the arm base-I have been using a lead washer under the arm on my other deck for years. Sounds like you also think there is room for improvement in the plinth.

I wonder what the material they use in the IDL actually is. It feels and rings like a fibreglass composite, maybe with carbon added. I also wonder if this material is ideal as a damping layer and whether rubber is the best material for a base, although you would think Technics did extensive research into the subject.

I think using a silicon layer between the top plate and the IDL could work well and the best thing is that its reversible. The other more permanemt idea that springs to mind is cutting the IDL into smaller seperate blocks or sections and permanently gluing them where possible to the aluminium top plate, maybe with hot glue. What could be a better material to damp the top plate with-acrylic? Panzerholz a la Clearaudio?

[twelvebears]

One slightly bonkers option I'm considering with the assistance of John from Slateage, is to find an old knackered 1210, take it apart and see whether it possible to remount the essentials in/on a machined slate plinth....

[mulane]

Doesn't sound bonkers to me but then.... Do you think therefore that slate is closest to the ideal plinth material?

[mulane]

Clearaudio aluminium and Panzerholz plinth-candy?

[scoobs]

Doesn't sound bonkers to me but then.... Do you think therefore that slate is closest to the ideal plinth material?

I know mad Marco has previously threatened to go after a bespoke slate plinth for his 1210. No doubt there would be a great deal of effort needed to work one, and the final cost would be pretty high. Slate doesn't ring like granite and it's density and weight will damp out most resonance, but some feel that it isn't the last word in resonance damping.

Regarding your 1210, as I mentioned earlier, I attached the the single middle solid resin layer to the underside of the chassis (top plate) with silicone sealant, which didn't really achieve what I was hoping for, but whilst removing the resin layer, I ended up breaking it into 3 pieces and inadvertantly found that this improved the situation when I re-attached the pieces with sealant as there was no rattle, and 3 separtate pieces are easier to fix down securely than the one large piece. In addition I filled the voids in the resin block with Arboseal compound which is what Michell use under their Orbe chassis. This final iteration of scoobs style reverse engineering was the most succesful at removing the rattle and adding additional mass and damping. Once I replaced the stock feet with threaded RDC cones things improved further.

[Marco]

Interesting reading this, but what pray tell is this "rattling" that you speak of?

I can detect no such thing on my 1210 - perhaps the 17 layers of Mana underneath zap it into non-existence!

Marco.

[scoobs]

Yes fair point Marco. It is not something you can detect when the 1210 is fully assembled. If the rubber base is removed the resin block is exposed, whereby when tapped with the finger the block will not so much rattle, but will not sound securely coupled to the underside of the chassis, one gets the feeling of it ringing or rattling...however when the rubber base is replaced and is secured to the block by another approx 5 screws then things begin to solidiy a bit more as the block is now secured from above and below. But having looked under the bonnet one is left with the impression that the resin block is not really doing much other than adding mass, and I felt that if it the block could be bonded or coupled to the chassis by more than 5 or so piddly screws then it would impart greater damping qualities on the deck as a whole.

[Tony G]

Mana from heaven ?