How good is the Obsidian plinth of Technics SP10 ?

I worked directly with a quarry in Pennsylvania, Structural Slate in Bala Cynwyd, PA, I think.  They cut a slab to my specifications: 23x19X3, and honed both sides, as I recall.  I then contracted with a water jet company in York, PA, to cut the slate using a pdf file to program their water jet; I think that pdf was available for the Mk3 chassis from Soundfountain, on the internet.  So that cost me total less than $500.  I then contracted with an audiophile/carpenter in Houston to make me a base out of cherry wood and baltic birch with a cut-out for the mass of brass which acts to dampen the Mk3 bearing, a la Albert Porter's idea. Albert uses a piece of solid iron; I was leery of putting such a big hunk of iron so near to the magnetic rotor of the turntable, so I chose brass, etc, etc.  I drilled the underside of the slate slab for female threaded bushings that I glued into the slate with liquid weld, and I then bolted the wood base to the underside of the slate. Total cost was probably around $800, even including the piece of brass (from On-line Metals) that I drilled and tapped so a threaded rod could pass through it and contact the base of the bearing housing, a la Albert. I am not going to pretend there was not a lot of physical labor involved.

Thank you very much Lewn. It's good to know I don't have to spend crazy amounts of money to get a good plinth! Especially a slate one.

In my opinion, the Obsidian plinths of Technics circa 1980's were a complete sonic disaster.  Anemic, flat and homogenized sounding.  My first Technics Sp10Mk3 had one, it was abhorrent and I thought at first it was just the turntable.  After purchasing my first properly designed bespoke plinth ~ Panzerholz constrained layer based, it completely changed my mind about the potential of the Mk3 and what a direct drive can really sound like.  After that, I tried a Slate OMA plinth, and although it was neutral, focused and slightly better in my system that the Obsidian,  I completely lost the tonality of the Panzerholz and exotic wood based plinth I had owned prior.  

Perhaps it has something to do with level one plays back music and the feedback generated? I recall Peter Aczel initially not caring for the sound of the SP10 until he mounted it in the Cotter base, realizing then that the sound pressure generated by his current Janis woofers excited the obsidian base to the point of negatively affecting the sound. So those using the obsidian at more moderate levels and better platforms may well experience no sonic deficiencies. Just sayin.. Our opinions of products are almost always based on our listening environment, which may be hugely different from someone with another opinion. I’ll never forget a friend coming over, listening to my Trenner & Friedl speakers and ordering a pair the next day. But in his room they absolutely sucked. No bass or body whatsoever. I realize speakers are totally room dependent, especially in the bass regions, but I think the principle holds for everything. Widely-varying listening environments make for widely-varying opinions. Peace.