Thorens TD124 “Mk1”/Mk2 plinth

Larry, I don't claim to know much about resonance control, except by observation and an attempt to apply some logic.  Also, I never know if I have achieved the best result possible based on the science.  I only go by what I hear. For example, I listened to the SP10 Mk3 in its heavy slate plinth alone,first and for several months. It sounded fine that way. Then I got into some conversations with Albert Porter who was kind enough to share some of his secrets, mainly as regards damping the platter bearing. That prompted me to add the cherrywood subplinth with the built in massive lump of brass to damp the bearing, and I do think the sound got "better".

Porchlight, When I decided I wanted to own an idler drive TT, I auditioned a Garrard 301, a Lenco L75, and a TD124.  All of them had been upgraded and tweaked, but given that each was in a different system and in a different listening room, etc, to make precise comparisons among the 3 would not be fair.  Nevertheless, I liked the TD124 least of all, and it wasn't a close call to eliminate it at the start, mainly due to noise.  So I don't doubt your impression that the TD121 may be superior. I subsequently acquired an NOS Lenco L75, dumped the plinth, the chassis, and the tonearm, mounted the works on a PTP3 top plate (see Lenco Heaven), had the platter sprayed with a dampening paint, had a 50-lb plinth made from PA slate, and added a Phoenix Engineering motor controller with Roadrunner tachometer, to drive the OEM Lenco motor.  Totally by the seat of my pants. The SP10 Mk3 and Lenco projects were fun, but I would never do it again, which is why I won't sell them.

I can believe that cast iron is relatively nonresonant, if only because Albert Porter uses a large cube-shaped cast iron block to dampen the bearing inside his Panzerholz plinths for Technics SP10 mk3s and Mk2s. When I was creating my own plinth for my own Mk3, Albert advised me to use iron for that function and for the reason that he felt it was nonresonant, but I was fearful that such a huge chunk of iron would affect the massive magnet that is fastened to the Mk3 platter, which functions as the rotor of the massive motor, thereby possibly reducing motor torque.  So I went with brass instead, inside my Mk3 plinth which is made from a huge piece of slate cradling the chassis. Then the slate cum chassis sits on and is bolted to a cherrywood base that harbors the large chunk of brass. In both Albert’s plinths and my one-off plinth, there is a threaded rod that passes through the chunk of metal (iron or brass in my case) and snugs up against the base of the mk3 bearing housing. Interestingly, you can tune the result by tightening or loosening the contact between the rod and the base of the bearing housing. Not too tight sounds best.

I think but am not certain that there is a layer of bronze in the 21-lb Mk3 platter.

Schopper call it “bronze”.

Which is an alloy of mostly copper and some tin. No iron content.

Maybe. But if it’s the resonance of iron , then why would a nonferrous aftermarket subplatter suffice as a substitute where the mk2 nonferrous sub platter is judged to be inferior?

Why (for what reason) does anyone think the ferrous subplatter would sound best? I wonder.

Ignore my post of 07-08 at 4:30 PM.  The test I described is to detect whether the weigh pan of a digital VTF scale is ferrous (some are); it obviously won't work to detect a magnetic attraction between the cartridge magnets and a ferrous platter or subplatter.

psf, After stating that you have no issue with the TD124 platter, you go on to describe what I would call an "issue".  Anyway, it sounds like you know how to deal with it satisfactorily. I don't know about the strength of the magnets used in Grado cartridges, but I do know that my Ortofon MC2000, which seems to have its magnets in the "belly" section of the cartridge body, hanging close to the LP surface, definitely does have issues if you try to use it with even a stainless steel platter that has significant iron content.

Larry, you fail to specify whether the TD124 that causes no issues with the various cartridges you name is a mk1 or mk2 type. One sensitive way to check for magnetic attraction is to set VTF with a digital gauge and then, with the gauge still in place, gently raise the headshell by a mm or 2, and see whether the gauge goes negative briefly in the process.

I think the main difference is mk1 had a ferrous platter that can play havoc with a LOMC, whereas the mk2 platter is nonferrous. So yes there probably is no difference as regards the plinth. If I’m in error I trust I’ll be rapidly corrected.