isolated armboard

[just an idea]

Having finished making my first TT about a year ago, work on the Mk-II is just about due.
I've been really happy with the results of my first attempt, basically it's made using the motor, subplatter and bearing from a rega p2-24 along with the rb300 arm. I has an acylic platter made. The motor is housed seperatley in a solid wooden box, the rest of the table is made from 2 sheets of granite sandwiching a sheet of cork to dampen the ringing from the granite.

For the Mk-II I plan to use something other than granite... just because granit is so difficult to work with, but experiment more with different materials to sandwich. Can anyone recommend any combinations...?

I am also considering having a sprung or isolated armboard. I have been looking at sandbox insolation platforms and have been thinking on how to build one into a turntable to place the armboard on, isolating it from the rest of the TT.... Before i start trying to figure out how to cope with the rega mounting system running through the sand, are there any other problems I haven't thought of?
has anyone done this before?
is it a good idea?

Thanks

 

[YNWOAN]

The arm and the platter should remain in a fixed relationship to each other - compliantly mounting one, relative to the other, is not a good idea IMHO.

 

[just an idea]

but how about sprung arm boards, like the LP12?
I see your point, backed up by rega putting those metal braces on their better TT's to increase regidity between arm and platter bearing... so have I missed something or are there 2 very different schools of thought here?
what are the pros and cons of both methods?

 

[YNWOAN]

In the case of the LP12, and similar designs, the armboard and the platter are attached to a single, rigid, chassis (the sub-chassis); this assembly of chassis, armboard, platter and arm is then decoupled via springs from the plinth (to which the motor is attached via the top-plate). The arm is not decoupled from the platter (well, not in the way you suggest at any rate).

(this much is TT design 101 )

 

[just an idea]

but what I was trying to suggest is similar... I think. Imagine i had an LP12 and instead of springs under the armboard, I put a sand box for the arm board to lie on.... don't worry I'm not going to do this.

 

[YNWOAN]

There is no harm in trying it - in fact, I would encourage you to experiment.

But what I am describing is not what you are describing (at least, not if I am interpreting your posts correctly).

In the case of the Linn (and all similar decks), the springs are not under the armboard on its own, they are under a secondary structure to which is attached both the platter and the armboard.

 

[just an idea]

oh really, i have to admit never seeing one in real life. I always thought the armboard was free to wobble inependantly of the rest of the turntable.

I'm seeing your point... out of interest I will experiment, but I suspect there are numerous problems with this idea... we'll see.

 

[YNWOAN]

Of course, placing the armboard on sand is a very different proposition to mounting it on springs.

 

[Bibio]

instead of sand try a bicycle inner tube pumped up with air or even take the valve out and fill it with sand then cap it off. that's the great thing about mechanical things like TT's as it's only your imagination that holds you back.

 

[just an idea]

I've experimented a little with the bike tube, but it's a little cruder than I want... I would like to be able to use about a 5 inch section of the innertube, sealed at bothends with the valve in the middle... so I could pump up individual balls to adjust the height with the valves protruding through the bottom of my shelf. But I can't find a way to seal the cut ends of the tube.

Filling the tube with sand is an idea... I'm not sure yet if it's a good one or bad one. To make better use of the sands properties, maybe a tube of thinner rubber might be better.... all I can think of is sand filled condoms.