2. analog
  3. 1265063971

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
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
lewm
12,483 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.
Ag insider logo xs@2x
rauliruegas
12,810 posts
 
Dear Derekmur: I want to assume that all what I posted you already checked and is fine.

Two things: check through a microcospe/loupe if the stylus is in pristine condition and second from what you are go up at least 10mm-12mm up at the tonearm pivot ( don't be affraid to do it, can't do harm to anything. ) and listen and see what happen and follow testing from that high VTA/SRA down till you find the cartridge sweet spot.

This time just forget about tonearm/cartridge resonance frequency because the important subject is that you achieve the best performance from the 20FL.

Btw, the MP-50 is very nice cartridge.

Regards and enjoy thye mmusic,
Raul.
More to discover