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In Reply to: RE: High compliance, low output MC? posted by John Elison on February 28, 2017 at 23:10:28
Hi John
Thanks for posting up the formula! I confess I got lazy and just quickly scanned the graph on the HFNRR test disc sheet.... Cheat sheet!
While we're on the subject of effective mass specs...Have you seen JoshT's q on the SL1301 arm? They quote 22g including cartridge mass of 6g. Headshell is 9.5g. I thought at a glance that it was really 12g, but checked the instruction manual for the 1301 and also the EPA-100 out of curiousity and that quoted 22g as well. Is the effective arm mass really about 16g? I've never seen it specified the way Technics have done in this case. Also really surprised to see the strange geometery with the offset at 21.5degrees. They look to have applied Lofgren B to a very narrow envelope so they end up with ~3 deg error at 146mm! Crazy stuff...
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
Follow Ups:
Hi Anthony,
> They quote 22g including cartridge mass of 6g. Headshell is 9.5g.
That's interesting and very commendable on Technics part. They also state the VTF of 1.75-grams. This represents a very precise way of presenting effective mass because effective mass actually varies slightly depending on the position of the tonearm counterweight. Therefore, knowing cartridge weight and VTF pins down the position of the counterweight precisely.
The effective mass of the tonearm without the 6-gram cartridge might be slightly greater than 16-grams since the center-of-mass of the cartridge is probably not concentrated at the stylus but is slightly behind the stylus. For example, suppose the center-of-mass of the cartridge were 7-mm behind the stylus. The cartridge's effective mass would be calculated as follows:
Cartridge Effective Mass = 6*223 2 / 230 2 = 5.64-grams
Now, if you removed the cartridge without changing the position of the counterweight, the tonearm effective mass would be 22 - 5.64 = 16.36-grams. However, we normally don't go into this kind of detail so we simply approximate tonearm effective mass as 22 - 6 = 16-grams.
With respect to tonearm geometry, the Technics SL-1301 reminds me of the geometry of the early SME III. Compare the two graphs below:
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Hi John
Thanks for the information! It's interesting how one gets a sense of the quality of engineer involved in designing a product based on how the specifications are presented - particularly when comparing to other similar products. I'm always suspicious of products (in the audio field especially) where the technology or specifications are concealed. For example Power Conditioners or cables where they claim no active components, but then try and cloak the details in some mystical explanation!
I thought your curiousity would be piqued by the tonearm geometry for the 1301 when I first plotted it out. This MUST have been a conscious design choice by the designers and not a mistake...surely!
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
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