Technics SL1200 plinth damping

[Marco]

LOL, Tony!

Nick (and others), with respect, I think some of you guys have too much of a penchant for fiddling instead of just sitting back and enjoying music!

I don't doubt what you say is right, but the fact is I simply never have the inclination to 'look under the bonnet' because it sounds so bloody good as it is...

Having said that, I'm sure there is indeed plenty of mileage in providing a better plinth for the 1210, and that the sonic rewards are not inconsiderable. However, realistically, it's probably a bridge too far and one is simply better buying a separate motor unit and tonearm in a dedicated plinth, a la SP10, or your rather lovely Denon

Later in the year, with that in mind, I'll be going for one of Dave Cawley's fully refurbished SP10s, fitting a 12" Jelco to it, and putting the lot into a nice slate plinth - then it'll finally be 'job done'

Marco.

[scoobs]

LOL, Tony!

Nick (and others), with respect, I think some of you guys have too much of a penchant for fiddling instead of just sitting back and enjoying music!

I don't doubt what you say is right, but the fact is I simply never have the inclination to 'look under the bonnet' because it sounds so bloody good as it is...

Having said that, I'm sure there is indeed plenty of mileage in providing a better plinth for the 1210, and that the sonic rewards are not inconsiderable. However, realistically, it's probably a bridge too far and one is simply better buying a separate motor unit and tonearm in a dedicated plinth, a la SP10, or your rather lovely Denon

Later in the year, with that in mind, I'll be going for one of Dave Cawley's fully refurbished SP10s, fitting a 12" Jelco to it, and putting the lot into a nice slate plinth - then it'll finally be 'job done'

Marco.

Amen to that. I am done with fiddling now, there's no way I'm messing about with my Denon. The whole project has dragged out longer than expected and I've missed out on the music for too long as I cant stop my grubby little mits from twitching along the way.

It's feet up and from here on in.....well, once I've replaced the tonearm it will be

[DSJR]

Surely the best way to economically deal with any possible mass issues with older direct drives is to carefully site them on a specialised turntable support/wall shelf, away from bass nodes in the room and as far away from the speakers as reasonably possible, thereby avoiding the problem in the first place? I only suggest this as I remember my SL110 being VERY sensitive to feedback issues and supporting it properly, together with better feet perhaps, must improve the sound this gorgeous looking deck would give.

Audiotech used to do a great and neat wall shelf which works for all sorts of turntables and CD players, not just the LP12 it was designed to go with originally (much better than the Sound Org wall thingy and better in the bass than the Target TTW1 [with original supplied boards obviously]).




P.P.P.P.S. Thorens apparently supplied rubber "mushrooms" to replace the springs in the TD125 once upon a time for certain purposes (some were used in night-clubs I understand). has anyone here got any experience of these?

[mulane]

Marco, fair enough but as I was already under the bonnet fitting my new armboard I could not help but notice the poorly fitted layers. And I love experimenting and tinkering with what I already have rather than lashing out on new stuff . And if your Mana'd SL came within 95% of the slated SP10 then I have to wonder if an SL with an "optimised" plinth might get to 98% which would probably do me fine.

Thanks for the tip re the Arboseal Scoobs-I will see if this stuff is available here.

[mulane]

DSJR, yes a good support and feet are important but its really locking the gate after the horse has bolted if the plinth is inadequate, as the plinth is the first "support" really. I think a cure could be very simply done and should bring significant improvements for those of us who plan to keep our decks.

[Tony G]

Further points following on from the above -
The resin block would appear to be likely to be a polyester bulk moulding compound, possibly glass reinforced and probably mineral powder filled for bulk and mass.
Yes, technics no doubt did their homework, however I imagine their intended (and actual) market saw their priority as reducing or eliminating the ingress of vibration to the turntable from external influences (DJ decks work in an unfriendly environment in that respect) rather than controlling resonances emanating from the cartridge/disc interaction.
I see the design as utilising a rubber cradle and flex feet to isolate the playing gear from its support surface and the mass block as being intended to firm up the resilience of that rubber, much as vibrapods and foculpods function most effectively at their designed loading.
The issues I have described arise from generating greater reactive forces during playback than would have been intended or envisioned in the specifications of the arm, which, after all, is of medium mass and intended for medium compliance cartridges.

The main issue to be addressed is the breaking of the mechanical feedback from stylus to record, since this interface is where the reactive forces are generated a mechanical feedback loop exists which passes from the cartridge to the arm to the arm mount to the plinth and hence back to the platter where its effect is magnified.

The means of doing this require the dissipation of this energy at at least one stage of the transmission chain, preferably more.
A heavier arm will absorb more energy without resonating, an overdriven lighter but rigid arm like the RB250 will transmit this energy (the tube will also resonate), fluid damping will help with resonance control, decoupling of the arm from the armboard will also help.

Bonding the mass layer to the plinth seems only likely to be effective if done permanently with something like a flexible polyurethane adhesive sealant (Sikaflex or similar) - since this would preclude access to the electronics it seems impracticable.
Without close coupling of the surfaces either by adhesive bonding or mechanical constraint there will be no CLD effect of energy absorbtion.

The only practical ways of breaking the mechanical feedback loop that I can see are careful arm selection (the Terminator obviously has the ability to isolate cartridge generated forces by its air cushion), the Jelco 750 has fluid damping and greater effective mass, and/or decoupling the arm at the armboard/armboard fixings.
Someone here made a rather nice looking armboard from an old technics armbase and a turned wooden block, I would imagine that to be effective as might various other approaches to decoupling.



Summarising, my conclusions are that replinthing or seriously tinkering with the base other than trying different feet are as Marco suggests and Scoobs found also, "a bridge too far".
Better to find a more suitable deck for those sort of things which could also provide the ability to use 12" arms, the new 12" Jelco looks rather tasty and affordable and as I think Marco has indicated elsewhere some more obscure broadcast arms still not fetching silly money secondhand that will even run an SPU.

My own trials will be confined to trying another arm on the Technics and possibly arm decoupling in one form or another. I have a Jelco very similar to the Sumiko MMT that will mount on a Rega armboard for the 1200 to try when I get around to it.

It is, of course, possible and most sensible to find a cartridge that will work happily with the stock arm, tweak the wiring and PSU and live happily ever after - but where is the fun in that.

X more posts while I was typing all this blather

[Clive]

A heavier arm will absorb more energy without resonating,

It's complicated, a heavier arm may absorb more energy or it may simply resonate at a different (lower?) frequency.

I did a huge amount or messing around with arm decoupling when building wooden CLD plinths for my idler. It certainly makes a huge difference to the sound, too much or too little destroys dynamics. The Terminator does indeed solve all this at a stroke.

[Tony G]

You are right Clive, my intention was not to imply that it would not resonate but rather that it would take more to excite that resonance. (or so I believe)
Would fully agree that arm decoupling is a fine balancing act as you describe.
It is interesting to note that after Gert Pedersen (sp?) did a deal in this area on Michell decks that Michell themselves took up the idea and produced their own version.
That was on a table where I would have imagined the arm to be fairly well isolated from the motor and platter bearing.
Perhaps the effects there are more due to helping the arm to dissipate the excess energy than to removing a transmission interface, perhaps this was also more the case with your wooden plinths ?

[Clive]

Hi Tony,

I think you're definitely on the right tack, your explanation of the issues is very well reasoned. We have bi-directional sources of vibration in our hi-fi (non-DJ) systems; motor to arm to stylus and stylus to arm. Some cartridges put a lot of energy into arms, idler and DD decks push energy into the arm (akin to DJ use) and then the stylus. Belt drive is probably kinder but has other issues. So finding the optimal decoupling requires a very experimental process. Isolation via an air cushion seems easiest and consistent but is not the only way.

[mulane]

I did a huge amount or messing around with arm decoupling when building wooden CLD plinths for my idler. It certainly makes a huge difference to the sound, too much or too little destroys dynamics.

What did you find was the best way to decouple the arm in your case then-a different type of wood in the armboard to the plinth? Would be intersted in your findings.

So you think silicone would not be an effective material to use to bond the damping layer to the top plate Tony G. I guess it is a very lossy material and so this may insulate the damping layer too much and not connect it to the top plate solidly enough. I'll have to have another look underneath to see how much of the damping layer can be permanently glued without denying access to the workings. If this is not feasible then it may be better to remove the damping layers altogether and have a "skeletal" lightweight aluminium plinth and place it on springs. Avid and Gyrodeck use this arrangement I believe. I do not see many high end decks using huge chunks of rubber in their plinths. Perhaps smaller pieces of different thickness aluminium could also be glued to the bare aluminium top plate to create a SDS-type sandwich, or even small pieces of SDS itself as I believe small squares of this material are now available for sale. Anyone know what the glue is that SDS use between their plates?

I also think your idea that the Technics damping layers are more about isolation from the environment than internal resonnances sounds probable.

I am in a good position to do a bit of experimenting in this area as I have two newly aquired used Technics decks and can easily compare the tweaked deck to a std one, so I'll have to get cracking on this. I had excellent results with my old belt drive deck using a particle board--MDF--particle board sandwich plinth and placing this on springs.