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Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
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Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
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In Reply to: More newb questions... posted by Kiwi Brian on November 14, 2006 at 02:26:10:
Overhang IS the difference between effective length and pivot to spindle distance. How you adjust it doesn't matter.For the purposes of calculating the arm parameters overhang is not important, it is simply a consequence of the choice of the other parameters. Rather than use a spreadsheet you can refer to the following two equations which will allow you to calculate the necessary parameters to achieve a given linear offset.
Le^2 = Lm^2 + N1*N2
and
Sin(theta) = (N1+N2)/(2*Le)
You have obviously run into one of two general limitations in tonearms which may prevent them from being aligned to any given pair of null points. Either the offset angle or effective length cannot to set to achieve alignment based on the actual distance the arm is mounted from the pivot.
However I cannot understand why you say you cannot achieve alignment with Baerwald null points except that you simply mounted the arm too far away or too close to the spindle. You should be able to rotate the cartridge to the correct offset angle defined by the equation above however you will also see that given the constant of the two null points (linear offset) and the pivot to spindle distance the correct effective length may simply be too long for the arm or too short.
It is not true, contrary to what many think, that one can use any set of null points one wants to align any tonearm. Once one chooses the null points and therefore establishes the linear offset only specific combinations of effective length, mounting distance and offset angle solve both equations.
Since in your case you have made no provision for adjusting the effective length, pivot to stylus distance, you must mount the arm at a location so you can solve the first equation with the Baerwald null points and the adjustment you have allowed for at the base. If the mounting location you picked is wrong for the fixed effective length no amount of cartridge twisting will align the stylus at both null points.
The best type of protractor I feel is the type that uses the linear offset, based on the two null points chosen, to "point" the protractor at the pivot point. This places the inner alignment point at the correct offset angle for the actual pivot to spindle distance. The cartridge is then simply moved back and forth to get the correct effective length (overhang) for the actual mounting distance and rotated to achieve the correct offset angle. If this is carefully and accurately done there is no need to check at the outer null point. It MUST be correct.
I believe the now discontinued Schröder Model 1 did not have a slot at the end of the arm-tube but rather effective length was adjusted by sliding the complete arm-tube back and forth in the cradle. I had one for only a short period many years ago. I now have a Model 2 and Reference which have a fairly long (12mm) slot to adjust effective length (overhang if you will). I see no compromise in strength but I guess it depends on how it is done.
Using equation 1 above you can easily see the difference in effective lengths for a given pivot to spindle distance is not very much for the most popular established linear offsets (null point pairs). They are:
Assume 222mm the popular Rega distance
Loefgren "A" 239.3mm
Loefgren "B" 239.7mm
Stevenson "1B" 237.0mmLikewise assume a fixed effective length and you will see the mounting distances vary by a range of about 2-3mm depending on the actual length.
These are distances which should be easy enough to achieve without "pushing the mounting board around the plinth". :-)
What protractors/alignment gauges are you using? What null points have you tried?
Hope this helps and I answered your question(s).
Cheers!
Garth
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Follow Ups
- Re: More newb questions... - Garth 11/14/0604:51:13 11/14/06 (1)
- Thanks Garth - Kiwi Brian 02:38:10 11/15/06 (0)
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