Technics EPA-250 Cartridge Matching Concerns


Hi, I am awaiting delivery of a Technics SP10 mkII with EPA-250 arm (i.e. EPA500 armbase & EPA-A250 Wand). Documentation states that Effective arm mass: 14g (without cartridge). Separately, I've read that the Technics headshell weighs 7.5g (with option to add 2g or 4g weights when needed). As I study up on this arm and try to narrow my sights for a cartridge purchase a couple of headscratchers are bogging me down. Any insights are appreciated.  

1) For use of resonance calculators does the 14g effective mass include or exclude the 7.5g headshell?  

2) The EPA-250 owners manual includes a little chart showing "Suitable Cartridge Weight & Compliance Relationships". It suggests adding headshell weights w/carts from 3g-6g; No headshell weights with carts 6-8g; and adding the auxilary counterweight for carts weighing 10.5-12.5g. No mention is made of the range 8g-10.5g! Of course, this range fits a number of my cartridge candidates. So what's the best way to adjust for that? Specs show "Cartridge weight range 3,0g – 12,5g".

3) In general, I've read that moderate mass tonearms are good companions for moderate to low compliance cartridges. One of the carts I'm considering is AT ART9, which is rated  18 x 10-6 cm / dyne (@100 Hz),  35 static. Formulas I've read suggest that to convert to 10hz calculations to multiply the 18 by 1.5-2.0. So that would avg. a compliance of 31.5.  The other method suggests halving the static figure, which would lead to compliance of 17.5. Using the first method concludes that with a resonance ~7hz my tonearm is not a good match. The second method yields more favorable results.  What's the real world result more likely to show? I've read all the raves on the ART-9 already, but want to focus on whether or not its compliance is too high to mate with this arm? Would a lighter than the 7.5g headshell help and are their any particular ones that you'd suggest. Most of the headshells I see are heavier.

4) Any EPA-250 users care to share their preferred cartridges on this arm? 

Cheers,
Spencer


  
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You got some pretty precise responses over on Vinyl Asylum.  Mine was perhaps the vaguest, but I stand by my opinion; the equation(s) used to determine tonearm/cartridge matching may give precise numerical answers, but the data inserted into the equations is always a bit shaky, always an "estimate" or based on a manufacturers published specifications, which may or may not describe the characteristics of your particular sample, especially where cartridges are concerned.  Furthermore, the range of acceptable results for resonant frequency (at the very narrowest, between 8 and 12Hz), actually permit a fair amount of latitude in effective mass and compliance, especially when you consider that F is a function of the square root of the product of those two parameters.  So, I say go for it, provided the compliance of the cartridge and the Meff of the tonearm are even in the permissible ballpark of a good match.  Far too much time and effort is spent worrying this subject to death, again, in my opinion.

Lew,

I appreciate your comments and concluded as much from the other commentary from the esteemed John Elison, our friend (also esteemed!) @dgarretson and yourself. Given the flexibility of this arm I should be in good shape with all the carts under consideration and most others. It's not going to be a constraint. Cheers,
Spencer
Thanks to your post on VA, I found out after decades of ignorance that my Technics EPA-500 tonearm is actually identical to a Technics EPA-250, save for the nature of the arm wand.  So, thanks for bringing up this question.
@lewm It's amazing all that there is to learn! Just today I went through a panic when the seller told me basically that there is no room on the EPA-250 for an "additional weight" and that the arm I'm buying only has one weight. I sent him pdf of the owner's manual showing him figure #17 which shows the "additional weight" which screws into threads on the back of the main weight. Meanwhile while waiting for a reply I found weights for sale but most were described as for SL1200 and costing $10 or less. The lone vendor with an EPA250 weight wanted $40 and weeks of shipping from Japan. 
Lo and behold, the seller saw the pics, confirmed that a) He does have the weight to send me and B) Yes 100% interchangeable with the SL1200 weights. Lesson learned. Cheers,
Spencer
Yes, the aux weight that came with the EPA-A250 is identical to the aux weight for the SL-1200MK2, et al. 


Sbank, If JP says the two are identical, you can "bank" on it.  However, if there is a problem, any good machinist can make you what you want if you give him the specs.  One guy is Colby Lamb out in Oregon.  He is an audiophile/machinist par excellence.

After 40+ years, I think I know everything there is to know about what equipment was made by whom and when, but every once in a while I have an epiphany like this that reminds me I really don't.  Now I just need to find a B250 arm wand for MY B500 base.
Sorry, that's "A250" arm wand.  There I go again.

Thanks, guys. 
@lewm If I run into anyone selling one of those A250 wands, I will point them in your direction. Cheers,
Spencer
Careful Lew - that's what I said 15 armwands ago! 
Funnily enough, I had put my A500 up for sale.  Now I am reconsidering. You've really got 15?!

16, but one is a partial I bought for parts to fix two others.  I've two bases as well.  Fantastic system. 
When I need a wand, I now know who to pester, @jpjones3318! Cheers,
Spencer