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In Reply to: RE: Ortofon 2M Black to replace Grado Platinum Reference ? posted by PAR on August 09, 2017 at 09:47:48
I'll see your pedantry and raise you.... ;-)
Mine is based on an actual measurement on a calibrated shadow graph. It is the height of the undeflected system and was actually 18.65mm averaged from 10 measurements. As you will no doubt have observed, I suggested using that as a starting position and fine tuning. The arm height scale on the SL1200 for example is based on an undeflected cartridge height. Either way 50um is not going to be resolvable by most people. 0.6mm may also be of little relevance if he doesn't adjust for individual record thickness! On the other hand setting 18.6 will provide a reasonable solution that covers thicker heavy weight vinyl and normal thickness LPs.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
Follow Ups:
Thanks but if the specification says that the height is 18.0 mm but your measurement indicates that your sample is 18.6 then the error in manufacture seems to preclude a recommendation based upon a theoretic standard. After all the OP's new cart may be 18.00mm high or 18.6 or 17.9 or anything in between (or either side).
Michael Fremer , a subscriber to the 92 degree SRA idea, has also found out that no stylus/cantilever manufacturer can guarantee SRA better then + or - 2 degrees. With a 9" arm that's a variation of 8mm at the pillar either way according to his figures.
So it seems that the only practical answer is to eyeball a level arm tube to start then vary either side up or down until the best sounding average over a number of sides is decided upon. Just what I have been doing for several decades :-)
I'm sure the intention is that a user may infer that this number (in the drawing) is the typical height after deflection when the VTA specification has been achieved.
However, without tolerances, those dimensions cannot be taken as "specifications". Different manufacturers seem to specify the dimensions differently, with varying deviation from the drawings. AT specify the AT120/440/etc as being 17.3mm. I have consistently measured between 0.05 to 0.12mm higher with an uncertainty of ±0.01mm. This suggests that the drawing assumes the ACTUAL undeflected height as being the more likely reference (allowing for about 0.5mm). My DL304 on the other hand measured 0.72±0.01mm higher suggesting that 15.5mm (unspecified tolerance) must be after deflection.
It largely depends on the cantilever length. The tip to mounting hole centre is the parameter that varies directly with cantilever length and so for a given VTA specification, the cartridge height will change.
I am measuring the undeflected dimension as the SL1200 arm height scale is calibrated to THIS value. Using the static compliance figure for the stylus, one can infer the deflection for a given VTF to be the "in use" height. I normally "fine tune by ear" at this point as there will be an uncertainty of roughly ±0.1mm in the drawing dimensions I would assume, so a rough guess would be to subtract about 0.5mm off the undeflected height taking into account recommended VTF (in combination with static compliance).
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
A good point about cantilever deflection which I had overlooked.
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