Thorens TD124 “Mk1”/Mk2 plinth

Yes, it might be more of a theoretical, rather than a practical, issue.  My dealer puts very expensive cartridges, like Platinum Signature Rosewood Koetsu cartridges on modern tonearms (typically Ortofon, Triplanar, or Audio Noe) on idler tables like the Thorens 124 and Garrard 301 and 401 and Lenco tables.  Of these tables, he likes the Thorens 124 the most.  

A dealer in my area is a BIG fan of the 124 and has reconditioned dozens of them likes the ferrous subplatter much more than the non-magnetic aluminum subplatter.  He is not concerned with magnetic attraction from powerful MC magnets.  If you want something that has the sonic properties of the ferrous subplatter without magnetic attraction, a company named Schopper sells such a replacement.

The model this dealer prefers IS the Mk 1 with the ferrous subplatter.  Most fans of this table prefer the sound with the ferrous subplatter.  If I owned the table, I would go with the Schopper subplatter just for peace of mind alone.

It has a different resonance characteristic.

The after-market Schoppers subplatter IS made of a type of cast iron similar in acoustic properties to the original subplatter.  However, the cast iron is impregnated with a material that greatly decreases magnetic attraction; it was material supposedly invented for use in submarine construction where not attracting magnetic mines was a big help.

It has been been a while since I was on their site.  It was either Schoppers in the past, or some other company that offered the non magnetically attracted cast iron subplatter.  Schopper's current offering is bronze.  I have no idea if it is as non-resonant as cast iron.  Cast iron rings for only a brief moment when struck, I saw this demonstrated in a Fern and Roby turntable that was made of cast iron for that very reason (their first audio product).  

I have not heard a Thorens 124 with the aluminum subplatter so I don't know from my own experience if it doesn't sound as good.  I have only heard tables with the original cast iron subplatter.  I have helped with setup of cartridges on the tables with cast iron subplatters and did not notice any issue with magnetic attraction.  In any event, most of the tables reconditioned by this dealer needed nothing more than a good cleaning, a replacement of the rubber mushroom suspension parts and perhaps a gentle resurfacing of the idler wheel.  The braking mechanism almost always needs readjustment too.  

My local dealer likes this table so much that he recommends it for systems well into six figures where the customer would be willing to spring for something much more expensive.  He puts modern arms on the table and uses plinths from various commercial sources or plinths made by the person who makes his custom speaker cabinets.  These plinths are simple, somewhat light weight boxes; he prefers this to the heavier plinths that use much more wood to make them extra rigid.  

The Woodsong plinth I saw was exquisite in terms of appearance.  I have not seen an Artisan Fidelity table, but the pictures look very promising.

lewm,

It sounds like you employed some pretty heroic measures to get your plinth to perform as you like.  You certainly know more than most how resonant behavior affects the sound.  This is a tricky business as it is not simply the case of reducing or increasing some measure of performance so much as getting it to a point where it sounds right.  I have a table/arm combination-Basis Debut vacuum clamp/Vector tonearm--that is designed to damp resonance to the utmost, and while I like how it sounds, others find it is to damped and "dead" sounding; it really is a matter of taste and system matching.