The acrylic at 12mm thick might be light enough to be supported by that flimsy aluminum clutch operated platter. Nice idea.
re: that TD124 clutch operated platter; It has its complications.
I've had a few expensive daydreams. Increase thickness of it. For material, perhaps machined from a solid billet of high density graphite. Thicker in the record support area by at least 1/2". Of course you'd need a bearing with a longer spindle pin. Thorens was never generous with their spindle pin lengths. I did mention that this daydream was expensive.
But the acrylic idea could be done much more affordable.
-Steve
I have one of Mirko's stainless steel platters and prefer it slightly sonically to the stock cast iron platter with my (2) Windfeld and SPU A95 cartridges and Schick arm. The SS platter is completely non magnetic, but does ring like a bell, perhaps comparably to the zamac platter. I've applied some damping on the interior which is marginally helpful.
I suspect that the powerful magnets in modern MC cartridges like my SPU A95 and Windfeld are inducing eddy currents in the platter and interfering with the internal fields in the cartridge as well. These cartridges generate substantially more than 0.5gm of down force magnetically. (I've measured as much as a gram depending on the mat used - not a fan at all of the stock mat)
Based on long term use of the Mirko platter I have come to believe that investing in a better non-magnetic platter for the 124 is not an entirely misplaced notion if you are using an MC with very powerful magnets.
This might make a significant difference on warped records where significant changes in distance between the cartridge magnets and the platter will result in significant changes in tracking force.
I solved the problem on the other table which has a cast iron platter by going to an oh so trendy
Panasonic strain gauge cartridge.. (Specifically an EPC-465C)
I suspect that the powerful magnets in modern MC cartridges like my SPU A95 and Windfeld are inducing eddy currents in the platter and interfering with the internal fields in the cartridge as well. These cartridges generate substantially more than 0.5gm of down force magnetically. (I've measured as much as a gram depending on the mat used - not a fan at all of the stock mat)
Based on long term use of the Mirko platter I have come to believe that investing in a better non-magnetic platter for the 124 is not an entirely misplaced notion if you are using an MC with very powerful magnets.
This might make a significant difference on warped records where significant changes in distance between the cartridge magnets and the platter will result in significant changes in tracking force.
I solved the problem on the other table which has a cast iron platter by going to an oh so trendy
Panasonic strain gauge cartridge.. (Specifically an EPC-465C)
I have one of Mirko's stainless steel platters and prefer it slightly sonically to the stock cast iron platter with my (2) Windfeld and SPU A95 cartridges and Schick arm. The SS platter is completely non magnetic, but does ring like a bell, perhaps comparably to the zamac platter. I've applied some damping on the interior which is marginally helpful.
I suspect that the powerful magnets in modern MC cartridges like my SPU A95 and Windfeld are inducing eddy currents in the platter and interfering with the internal fields in the cartridge as well. These cartridges generate substantially more than 0.5gm of down force magnetically. (I've measured as much as a gram depending on the mat used - not a fan at all of the stock mat)
Based on long term use of the Mirko platter I have come to believe that investing in a better non-magnetic platter for the 124 is not an entirely misplaced notion if you are using an MC with very powerful magnets.
This might make a significant difference on warped records where significant changes in distance between the cartridge magnets and the platter will result in significant changes in tracking force.
I solved the problem on the other table which has a cast iron platter by going to an oh so trendy
I agree with all of the above. There are avenues available to improve the TD124. The Mirko SS platter is one method. I also like the the non-magnetic iron platter that has been available from Schopper. Expensive as it may be.
I question if this is not an opportunity to increase the moment of inertia by machining a thicker (and heavier) platter from non-magnetic materials. Or go denser material using same external dimensions to get greater weight. In Bung's book he mentions that prototype TD124 motor units were produced with brass platters, but that this was abandoned for production use due to the expense of working (and buying) that material. Brass and bronzes can be a challenge to machine, depending on which alloy. And these materials are not given away freely. That Japanese notion of using the fabled 'gunmetal bronze' material for a platter does seem interesting for a one-off experiment.
But then Brass and bronzes do in fact ring loud and with a long sustain (depending on the alloy) since these are traditional materials used in bell making.
Austenitic iron alloys with a high graphite content could be studied for compatibility. The higher the graphite content, the lesser the tendency to ring, I should think.
I had some communications a year ago with an individual who thought that manganese (difficult to machine) or Tungsten in its softer condition might be suitable candidates for the main flywheel of a Td124. It does pique some interest. (without yet doing any research on densities and tendencies)
-Steve
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The acrylic platter was the idea of Pink Triangle. I think their idea of sonic neutrality is reasonably true. It has low mass compared with many things we might use. I think it might help the zinc alloy platter also. The cork in neoprene mats which I think I might have invented with the help of the young engineers at James Walker is an ideal interface. Cork is chaotic and maintains that quality when set in fake rubber. Chaotic materials are be their nature linear. Now if that isn't up there with quantum theory I don't know what is. If you want resonance same sized particals helps greatly. Rubber is also a resonant material except it has a suck out peak. Again, that is not what you really want unless you hit the exact frequency required ( the music on the LP can never be that ). Setting cork in rubber gets you what you want. I dare say simple cork is just as good except not very durable. This idea has been copied many many times now and forgets Loricraft and James Walker. If the cork-neoprene looks dull after a few years sanding restores it. As the cork usually comes in two pieces ( that certainly was my idea ) use the flat one zinc/iron to acrylic and the hole version on top. MDF should work well as a platter add on if wanting to get an idea. Bakelite is first class. I have used 78's as add ons.
I performed a little unscientific experiment today.
I measured tracking force with my new record level digital scale on the stock rubber mat on the upper platter over the iron platter and got 1.89 grams.
I slipped a 1mm shim under the scale and got 1.785 grams. A difference of .105 grams.
I slipped a second 1mm shim under the scale and got 1.75 grams. A difference of .035 grams.
I slipped a third 1mm ship under the scale and got 1.715 grams. A difference of .035 grams.
I think I'd expect an increase in downforce as I move the scale higher if not for the magnetic attraction of the iron platter. Apparently 3 mm of lift wasn't enough lift to completely negate the magnetic attraction of the platter, but the biggest difference came with the first lift of 1mm.
I measured tracking force with my new record level digital scale on the stock rubber mat on the upper platter over the iron platter and got 1.89 grams.
I slipped a 1mm shim under the scale and got 1.785 grams. A difference of .105 grams.
I slipped a second 1mm shim under the scale and got 1.75 grams. A difference of .035 grams.
I slipped a third 1mm ship under the scale and got 1.715 grams. A difference of .035 grams.
I think I'd expect an increase in downforce as I move the scale higher if not for the magnetic attraction of the iron platter. Apparently 3 mm of lift wasn't enough lift to completely negate the magnetic attraction of the platter, but the biggest difference came with the first lift of 1mm.
Yes. I believe that the difference between the effects of magnetic attraction and the magnetic platter , and the lack thereof with the non-magnetic platter is demonstrated. But also there is another thing to think about; the higher the stylus rides the lesser the vertical downforce.
Hmmmm, when tuning vta/sra don't forget to check vtf settings afterward, I should think.
-Steve
If I may suggest, the best starting point is a flawlessly operating to factory spec machine. Only when that has been achieved can you know the potential of it.
-Steve
In my opinion, that's where you finish, not where you start.
And that's what I'm working toward.
That's very helpful. Don't forget it's distorting the magnetic field that could be important. Very slighty attraction could be an advantage. It would have an almost viscous way of behaving. My acrylic 12 mm platter ( thick mat ) might be doing all the right things for all the wrong reasons. That's why I said good for the zinc platter also.
My question is, at what point does it stop distorting the magnetic field and become a slight attraction with an almost viscous behavior.
The difference of .105 grams after one mm of lift as compared to .035 grams after the second 1mm lift has me thinking that thickening the mat by 1mm might be a good start.
The difference of .105 grams after one mm of lift as compared to .035 grams after the second 1mm lift has me thinking that thickening the mat by 1mm might be a good start.
Good argument I feel. 2 mm cork ideal.
https://www.mains-cables-r-us.co.uk...s-record-mat.html?search_query=mats&results=6
https://www.mains-cables-r-us.co.uk...s-record-mat.html?search_query=mats&results=6
The point of this brief experiment was to demonstrate whether or not the magnetic effect was still in play as I lifted the tonearm in 1mm increments to a total of 3mm above the stock mat, not to measure the effect with precision.
This experiment showed that magnetic attraction between the platter and the cartridge was still present with up to 3mm of additional space between them.
That's all it was meant to do.
It appears that the effect was diminishing. That's what we'd expect.
The most obvious and glaring evidence is that the same experiment over a non ferrous platter resulted in an increase in pressure, as compared to the experiment over the iron platter, which resulted in a decrease in pressure.
To clarify, I was adding distance over the platter in 1mm increments from the stock mat, which is just shy of 3mm thick.
Are you suggesting 2mm total, or 2mm over the stock mat?
Magnetic attraction.
Andrew, I have to agree with you. Basic fulcrum maths (I'm not a maths expert, but having to do applied maths for civil engineering, specifically finite element analysis, gives one some insight) will definitely dictate that increasing the angle of the arm tube relative to the weight at the back will cause the effective down force to decrease. The arm must be raised with the same shim thickness to give reproducable results.
My decks are in pieces, and will be for an appreciable time, or I would do some tests too.
Kevin
Andrew, I have to agree with you. Basic fulcrum maths (I'm not a maths expert, but having to do applied maths for civil engineering, specifically finite element analysis, gives one some insight) will definitely dictate that increasing the angle of the arm tube relative to the weight at the back will cause the effective down force to decrease. The arm must be raised with the same shim thickness to give reproducable results.
My decks are in pieces, and will be for an appreciable time, or I would do some tests too.
Kevin