Sound Supports (tonearm plates and boards)

[YNWaN]

In Marco's case the geometry is slightly different because he uses an Ortofon SPU which is pre-mounted in its own headshell with no overhang adjustment. Therefore, the arm length is not adjustable and the geometry relies on the arm mounting hole being in a very specific location - I believe it is about 4mm different to that stated by Jelco (which assumes that you have the benefit of a slotted headshell to make fine adjustment).

[Marco]

Hi Mike,

How's it going, mate? Long time no hear!

I have copper arm board blanks which have not yet been machined for the SME (the majority of boards I make) I can machine one for you if you can give me the specs for the mounting holes and the relative location from the spindle.

Wow - that would be really great!

It would need to be further 'stepped down', though, than those shown on your website, and not simply a single flat, slightly sunken, plate. Basically, I'd need it to be similar to the one I had before, where the tonearm collar sits in its own recess (the recess should be around 3-4mm lower than the main body of the armboard):





Do you understand what I mean?

Otherwise, there wouldn't be sufficient leeway for VTA adjustment. The ortofon arm unfortunately doesn't have as much height adjustment as the Jelco... What's needed is an armboard very similar to the one for the Jelco, shown above, (with a round aperture cut out of the board), only of a wider diameter (the base of the ortofon arm is thicker than the Jelco) and a different spindle to pivot distance.

Anyway, I think you'll find most of the measurement info you need here (the tonearm shown is the one I have):

http://www.ortofon.com/index.php?opt...143&Itemid=146

Like Mark says, the crucial measurement is the mounting distance between the pivot point and turntable centre, which is 216mm.

I could also send you the tonearm mounting pattern template, which came with the arm, once I get my replacement tonearm back from Ortofon (long story!), which should be by the end of the week, if that helps.

And/or, Mark, as you've taken detailed measurements of the required armboard dimensions, perhaps you could supply Mike with any further info he may need?

Cheers, chaps!

Marco.

P.S Oh, and I'd like 5mm allen bolts, to secure the armboard, please, if you can do it, not screws or button-head hex bolts.

[Mike_New]

Hi Marco,
When I offered to make an arm board for you I forgot that you have never fitted my Bearing Base Plate. This serves two purposes, it stiffens the base area of the alluminium plinth and also raises the platter height by 6mm just enough to overcome the height restraints for most arms, I believe.

I have never made a two-piece arm board as I feel that the two pieces, can only degrade the stiffness in this crucial area and cause the arm board to act like a diaphragm.
There is mention of the need for absolute rigidity in this area in one of the SME technical bulletins.

The problem with the SL1200 is that there is a large hole to bridge when the existing arm/VTA assembly is removed. Unless this hole is sufficiently bridged with a rigid assembly then the thin metal double layer approach held together by three small screws, is not going to do justice to an expensive arm and/or cartridge.

I have however designed a single piece arm board specifically for the SL1200, with a suitable depression, which could fit all requirements. It would be machined from alluminium or brass and would be much thicker than the ones now available. This “thickness” is designed to be below the top surface of course.

There is marginably more machining to do but I will put a price on it of A$295.00 for the Alluminium version Inc postage. The unit will be a drop-in replacement for the existing Arm/VTA assembly.
Each arm board by it’s very design will be specific to a particular tone arm and spindle distance.

I have a SL1200 development test bed so I can accurately set off the required spindle-to-arm column centre distance with long-reach vernier calipers for each arm board I machine.

[YNWaN]

Hmm...what's that armboard in your pics Marco? It's not the one you had fitted to your deck when I saw it. Is it the acrylic one you mentioned?

[Marco]

Hi Mike,

Thanks for the information, and your points have been noted

I may well go for one of those armboards, but first of all I'd like to see what the one is like that Speedy Steve (on the forum) is making for me, out of a solid thick piece of ebony.

I should have this by sometime next week and will report back on its sonic effectiveness, or otherwise. I will then give consideration as to whether to go for one of your armboards, as a comparison to Steve's

Marco.

[Marco]

Hmm...what's that armboard in your pics Marco? It's not the one you had fitted to your deck when I saw it. Is it the acrylic one you mentioned?

http://www.ebay.co.uk/itm/Jelco-SA-7...item2569bf5587



Marco.

[YNWaN]

Hmm, black anodised aluminium and under £50 - it certainly isn't expensive!

[DSJR]

I wonder about all this rigidity thing, as one is in danger of moving the resonances somewhere else?????

Hardwood seems a good place to go and I always thought that a two-piece affair tightly clamped together would break up fundamental resonances and it may be a single plate that could act as a diaphragm - Linn and Thorens platter assemblies were two-piece for this very reason - has anyone ever owned a Fons turntable with its one-piece-bell clanging platter?

I'm not an engineer as you can see above, but in any case, the arm is adjustable for height, so there's a break at this point in any case, unlike with a Rega style arm which really does seem sensitive to what it's attached to..

[YNWaN]

Over the last few years I've done a lot of work with armboards, arm termination and the method by which arms and armboards are mounted. I've made a lot of prototypes, done a lot of modelling and done a lot of listening. What I would say is that my findings suggest that absolute stiffness and rigidity are not necessarily the optimum solution.

[DSJR]

As an aside, the ARO uni-pivot bearing are interesting, as the cup and associated spindle are a very close fit into the pillar assembly proper, putting a break there.. A classic one, the ARO, whatever I think of the final price and the exit cable, which I remember contributed more to the "sound" of this arm more than the mechanical nature of the arm itself...

Interesting concepts and forgive my engineering naivety