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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 1 response by derekmur

derekmur OP
6 posts
 
Thanks Raul,

I'm having a hard time describing the sound I heard from the m20fl. It seemed to be picking up lower frequency unwanted resonances from things like a small warp in the record. It sounded odd to me so I tested it on the Hi Fi News record. When i got such a low resonant frequency it made me wonder if something was wrong with the cart.

I realize that the Hi Fi News record isn't accurate, but it seems to me that this cart would need to be much more compliant than 20mm/µN to get this reading.

My current cart is a Nagaoka MP-50 and it's resonant frequency is close to what the Vinyl Engine calculator predicts.

I guess my question with all of this is:

How can a cart with a 20mm/µN compliance spec give a 6hz resonant frequency in a 12.3g effective mass tone arm?

Stringreen, I have the stainless armtube. Mike @ VPI told me that the effective mass of this armwand is 12.3g (the aluminum armtube is 10.9g)

Thanks
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