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M20FL Super Compliance?

I recently purchased one of the NOS M20FL Super carts from William Thakker on Ebay to use with a VPI Classic. The compliance he states is 20mm/µN. I used Vinyl Engine Resonance Calculator to estimate the resonant frequency in my tone arm (JWM 10.5i SE):

http://www.vinylengine.com/cartridge_database_tools.php#ResonanceCalculator

Arm Effective Mass: 12.3g
Cartridge Mass: 5g
Fastener Mass: 1g
Cartridge Compliance: 20mm/µN

This gave me an estimated Resonant Frequency of: 8.31Hz A little low, but workable.

When I received the cart, I mounted it and aligned it with a MINT Protractor. The VTF was set to 1.5g. And the VTA was up a little in back. (I read that this cart likes a positive VTA setting.)

I tested the M20FL with the Hi Fi News Test Record on the resonant frequency sweep test on side 2, the cartridge would wobble somewhere between the 7 and 5 voice announcements, showing a resonant frequency of around 6HZ! This is too low and the cart was susceptible to footfalls and woofer pumping.

Using the Resonant Frequency Calculator I would need to put in a compliance figure somewhere closer to 35 to get this low of a resonant frequency with this tone arm.

Is the figure quoted by Thakker wrong, or can these NOS cart vary wildly in compliance?

Has anyone else tested their M20fl compliance?

I wanted to make sure I'm not missing something in my calculation before I contact William.

Thanks for any insight.
derekmur

Showing 3 responses by lewm

lewm
12,456 posts
 
Keep in mind that the cartridge is "NOS", which literally means new OLD stock. So for one thing the compliance may no longer be what Ortofon said it was 20 or 30 years ago (or however long ago the thing was built). Moreover, that equation is flawed in many ways in terms of its ability to predict reality. In sum, your results do not surprise me. But at 6 Hz resonance, I am a little bit surprised that it is so sensitive to footfalls. You might try isolating your table a bit better. (I bet you hoped no one would say that.) I have one of these, also purchased from Thakker. I am using it in a Dynavector DV505 with its 11.2 gm headshell, which darn near must approximate the effective mass, since the rest of the vertical pivoting arm is so vestigial. So, not too different from your setup in terms of the parameters. I am having no problems with footfalls, on a Lenco in a heavy but totally unsuspended slate plinth. I have no idea what this means, but maybe it helps you.

I just thought of one more thing. Over on the VA, some experts have noted just in the last day or two that the HFN test LP is very inaccurate in that the actual frequencies recorded are not as labeled, another source of error. The Cardas LP is recommended as being more accurate.
lewm
12,456 posts
 
Guys, Bottom line is that the HFNRR test LP is not good for determining tonearm/cartridge resonance because the actual recorded frequencies do not necessarily match what the label says, at least as claimed by several knowledgeable contributors on VA. Stringreen, might not the expected extra stiffness of the suspension, due to age, just about counteract the error you note above regarding tonearm mass?

Raul, Thanks for the poop on the DV501. If the information is correct, and if it does apply to the DV505 as well, it would seem that I would be advised to find a very lightweight headshell for auditioning high compliance cartridges. Something that is not much more than 5-6 gm. Do you have any candidates? The DV505 stock does work well with the Ortofon M20FL Super, however, possibly because it is not so high in compliance compared to other MM/MI types.
lewm
12,456 posts
 
Dear Derek, I think up above you wrote that the predicted result was 8 to 9 Hz, using the equation and the parameters you note above. So if ALL of your input data are off by a little bit (due to age of cartridge, the variability of dynamic compliance, etc, etc), the interaction of these errors in solving the equation could easily give you any number +/-50% of predicted value. Plus, we know that your test instrument (the HFN LP) is inaccurate. What is the mystery? Garbage in/garbage out.
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