SP10mk2: OMA Graphite plinth vs.Dobbins plinth

I am sure OMA thought about it, but my first issue with using cast iron for a plinth would be related to the possible effect of a ferrous metal on the function of the motor.  Theoretically, the iron surround could distort the magnetic lines of force around the motor and thereby suck out some torque.  Just something to ask OMA about.

 Dear Raul, the mat on my star sapphire series 3 was most assuredly the original felt mat. Perhaps the dealer glued it to the platter before he sold it to me, but for whatever reason it was glued to the mat, and the surface was a felt like material. Just for your information, it was only later, when I acquired much better sounding turn tables, that I discovered how muffled and recessed was the sound coming from the star sapphire, meaning no disrespect to current SOTA turntables. Even with vacuum applied.   The experience did not leave me believing that there was anything special about the mat on that turntable, except possibly that it was especially responsible for the unsatisfactory results. My next turn table was a Nottingham analog hyperspace. It ran rings around the star sapphire in every way. Even more so after I acquired a regulated power supply to supply AC to the Nottingham.

Fortunately, the ambient temperature in most of our listening rooms probably does not exceed 1000°C.

Raul, I am surprised that in your post above, you seem to be saying that the platter mat should be "seen but not heard".  That's a good goal, but in fact we know that the platter mat is always heard, even if it is heard to be neutral, which is the way I would put it.  Can you say more about the SOTA mat?  I used to own a Star Sapphire Series III with vacuum, and as I recall, it had a felt-like material that was glued directly to the main body of the platter; it did not have a removable mat.  And of course one could not put a mat on top, because it would interdict the vacuum.

Ferrari, Thank you for pointing out that the MS mats are gunmetal copper, not pure copper.  I did not appreciate that fact, because I have never seen, much less owned, an M-S platter mat.  I did read that the Tenuto mat is also gunmetal copper, not pure copper. However, my recent experience with a true pure copper mat that I had custom-made for my Kenwood L07D is consistent with your observation that pure copper seems to sound superb, and I do not really know why copper seems superior to all other metal mats I have tried, albeit on turntables other than the L07D.  Except whereas Raul concedes that a metal mat may function to block EMI, which I think has a lot to do with its superiority on my L07D. 

In this case, the pure copper mat replaced the OEM stainless steel "platter sheet" (Kenwood's term for it) supplied with the L07D.  Copper is superior to stainless as an EMI shield, which may account in part for my experience with the L07D. Both mats weigh about 5 lbs; I did not wish to greatly exceed the mass of the stainless steel platter sheet in creating the copper replacement, because the L07D platter is partly supported by magnetic repulsion, and also because I am categorically opposed to using after-market mats that are very much heavier than the OEM mat on DD turntables that rely upon a servo mechanism.  It may be OK to do it, up to a point (the capacity to tolerate a very heavy mat without disturbing speed stability) , but that point is likely to be different for different turntables.  One would have to test the speed stability on a case by case basis using sensitive equipment, in order to feel certain that no new problem is created by a very heavy mat.  And this is in addition to putting stress on the bearing and thrust plate.  Just my 2 cents on that subject.

I would keep in mind that the "CU" mats made by M-S are expensive not merely because of their association with M-S but also because they are made of copper, which is very expensive these days.  I recently had a copper platter sheet made for my Kenwood L07D by a very good machinist who is very reasonable in his charges; it ended up costing $700, more than $200 of which was the cost of the copper sheet that he started with. Well worth the expense; it replaces the stainless steel platter sheet that is standard on the L07D and seems to do a much better job of blocking EMI, even though SS is supposed to be a pretty good shielding material.  I too also use an SAEC SS300, which I bought from Raul years ago.  It's on my TT101 at the moment.  I am not sure what it is made of and would be curious to know, but it's not pure copper.

Chakster, We don't "need" anything, but it is in the nature of audiophiles to believe that we can improve upon what the factory (any factory) made for us by spending money on a fancy substitute or building our own.  This is not always borne out in actual practice, of course, but we audiophiles have the additional privilege of relying upon only our own opinion to determine success or failure. 

Also, for every SP10 Mk2 or Mk3, there is not necessarily a factory-made obsidian plinth to be found at a reasonable price, if there is one to be found at all.  So there is no shortage of aftermarket entrepreneurs to satisfy the need thus generated.  I, for one, am very happy with the 80-lb slate and wood plinth I had made for my Mk3, and I spent less than $700 to get there.  In my dreams, I would have wanted to remove the Mk3 motor assembly from its chassis and mounted that into the slate directly.  But it's too late for that now.

If you want to squeeze the most out of your Mk2, I would vote for the Dobbins plinth PLUS the Krebs upgrade. The Krebs mod is very reasonable in cost (about $700, I think) for the level of improvement it affords. In fact, if cost is a major issue, I would advise just go for the Krebs mod and use your existing plinth until you can afford a Dobbins (or Artisan Fidelity, etc). My reason for preferring the Dobbins is that it gets rid of the SP10 chassis. Artisan can do the same. Possibly OMA can do that too. (I've lost track of the latest and greatest.) That's the way to go, IMO.

I use all-slate plinths for my Lenco and Denon DP80. I am very pleased, particularly with the Lenco in slate. But in some respects this is a subjective judgement. For my SP10 Mk3, I added a hardwood layer to the base of a large slate plinth, firmly fixed to the bottom surface of the slate. This was done empirically, but it actually did seem to make the turntable more neutral sounding when a priori I heard no real problem with the all-slate original version.