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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
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rauliruegas
9,123 posts
 
Dear Derekmur: I find these statements in other forum that I think comes from you:

++++++++" I guess I don't mean footfalls. I'm trying to describe what a low resonant frequency sounds like. I guess I mean the arm cart combination is accentuating low frequencies that don't necessarily coincide with musical information. Also the lower frequency spectrum sounds muddy with these artifacts. Is this what you hear with this kind of a mismatch? " +++++

IMHO I think ( like I posted ) that in extreme conditions ( TT set up, LP heavy waves/off center, tonearm poor bearing or faulty bearings, cartridge suspension out of manufacturer design, etc, etc, speaker heavy feedback, , , . ) it could happen what you posted even a deep msitmatch could make that the cartridge skip/wobble over the recording.

Are you on some " extreme " conditions?

Regards and enjoy the music,
Raul.
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rauliruegas
9,123 posts
 
So you have muddy bass performance, right?. Other that that " mistmatch " I think that you have to check that the TT and tonearm are perfect level, you have to give 20 hours that cartridge to settle down, after these 20 hours make a check on set up on overhang, VTF, load impedance, capacitance, cleaning the cartridge pin connectors, checking the tonearm wire connection with the cartridge pin connectors, make changes in cartridge/tonearm VTA/SRA set up, azymuth set up ( this cartridge is very sensitive to this parameter and with an unipivot tonearm this is a critical factor. ), antiskating, I don't know which kind of damping " mechanism " ( oil or whatever. ) has that tonearm but you have to play with too, try to find if exist a recording where the cartridge performs great to analize differences, etc, etc.

Regards and enjoy the music,
Raul.
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
6,770 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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rauliruegas
9,123 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.
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