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In Reply to: Re: Same protractor for all arm lengths. The problem is ... posted by Sea Monster on September 9, 2006 at 18:39:18:
the effective length is 307mm and the overhang is 12mm.Using JE's baerwald spreadsheet an arm of 307mm effective length will have an overhang of 13.3mm and a spindle to pivot distance of 293.7mm.
Obviously the 295mm distance is wrong for the Baerwald null points. And I suspect the Orsonic headshell may have changed the effective length but that is another problem.
If we solve the equation to determine the effective length using the spindle to mounting distance of 295 and the Stevenson null points of 60.5/117 we get 306.7mm effective length.
As is the case with many Japanese tonearms they often are designed for Stevenson null points which gives the arm a different linear offset and headshell offset angle.
I suspect if you were to align the cartridge with Stevenson null points it will work.
Send me an email and I will mail you a Stevenson protractor you can printout. It works for any length tonearm.
Follow Ups:
Got the Stevenson protractor from vinylengine. No need to send me. Thanks.Still does not work. Since I am very sure about the effective length and the cartridge tip to headshell base measurements, seems something is fundamentally wrong. In this case I will need to increase mounting distance to get the proper alignment. Would it be possible there is something wrong with the manual?
and the problem most likely lies in the fact you are:A) not using an Ikeda cartridge
B) using a different headshellAs you noted most other non-Ikeda cartridges donot fit inthe Ikeda headshell which was designed for an Ikeda cartridge as shown above. The Ikeda cartridges have a vertical cantilever which extends downwards at about the position of the mounting holes. A normal cartridge has the stylus about 9-10mm in front of the mounting holes.
So when you use a different headshell, which is probably longer than the Ikeda, and a "normal" cartridge the effective length has be increased. How much? Probably 10mm or more depending on where the cartridge is located in the headshell.
As I mentioned earlier I encountered the same problem as did Allan below.
The manual is correct only if using all original Ikeda parts, as it was intended.
Yes, I suspect you will have to move the mounting point outwards. How much? Measure the distance from the pivot point of the tonearm to a point midway in the slots in the headshell. Add 10mm for the cartridge and that will give you the new effective length.
Then you can calculate the new mounting distance using the null points you wish to use to align the cartridge although I am pretty sure the offset angle of the headshell (fixed in this case by the bend in the armtube) is assuming Stevenson null points and the original 307mm effective length.
So unfortunately you will probably end up with an alignment which does not match any of the physical parameters of the arm.
Garth,Thanks for the reply and it is helpful.
Something still bothers me on what you said. The manual says 50 mm from the stylus tip to headshell base so in theory it should not matter what cartridge you use as long as you fix the cartridge so that the stylus tip (diamond) is 50 mm from the headshell base. As the base connector is identical for Ikeda and Orsonic headshells so as long as the 50 mm distance is correct we should not care whether it is a Ikeda headshell/cartridge combo or Orsonic/Ortofon combo. Am I missing anything here?
If it can't be aligned there is only one cause...just like experienced and Allan too, the mounting distance is wrong for the headshell/cartridge you are using.The Ikeda data is correct assuming null points of 60.5 and 117mm namely the effective length is 307 and mounting distance is 295.
So if you can't align it with the Stevenson protractor then the effective length is different due to the different headshell/cartridge.
Forget the 50mm thing for now. What is the distance from the pivot of the arm to the midway point of the slots in the new headshell? Add 10mm and that is approx. the effective length with the cartridge mounted at the midway point.
I moved the arm outward a bit until the cartridge shows alignment with the Stevenson protractor. I believe this is less elegant method but feel that the sound is more right after doing this.
I'm sorry but the Ikeda people expect the arm to be used as intended and if done so the dimensions they give in the manual are correct. If you change the effective length the mounting distance can no longer be correct.Be happy you have it working.
It was definately intended to be used with Stevenson null points too. The first mistake might have been to use Baerwald null points.
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