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How to set SRA after determining true vertical?

Here is a picture of a stylus with zero rake angle:

http://members.cox.net/nsgarch/SRA@%200.0%20deg.jpg

Since all modern styli are symmetrical in the x and y plane about the verical z axis, the tapered stylus and its reflection will make a perfect "X" when vertical (z axis perpendicular to the groove) and viewed from the side.

This condition is established by raising or lowering the tonearm pivot post. Once you find this point, and assuming you have a typical 9" tonearm (about 230 mm from pivot to stylus) then each 4 mm you raise the post from the zero
SRA point will apply one degrewe of SRA to the stylus.

A test setup is shown in these two pics:

http://members.cox.net/nsgarch/SRA%20setup1.jpg
http://members.cox.net/nsgarch/SRA%20setup2.jpg

Equipment includes:

a mini Mag-Lite flashlite,
a first surface mirror from old SLR cameras -- easy to find at photo repair shop)
a 50X pocket microscope
bean bags

Don't forget to first remove antiskate and set VTF.

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128x128nsgarch
gregadd
574 posts
 
A wrong theory carried to a ridiculous extreme.
dougdeacon
3,338 posts
 
Actually, it's a right theory carried to a ridiculous extreme.

A simpler solution is a tonearm with adjustable height. Then you can use any cartridge you like and play any record you like, while matching SRA.
gregm
3,405 posts
 
A simpler solution is a tonearm with adjustable height. Then you can use any cartridge you like and play any record you like, while matching SRA
Yes -- but by adjusting height you'll be changing the stylus overhang. As you note, having two arms is the right way -- but an extremist solution!
gregadd
574 posts
 
I am still looking for an article or picture that demonstrates that angled cutting head produces an angled cut. Has the angled groove been measured? All I have ever read is that it was just assumed.
thekong
203 posts
 
Dear Doug, Gregm,

Base on what I understand from your answers, it is the SRA that is important, not the VTA (of course, the SRA and VTA are interrelated). As long as you can adjust the SRA to fit the angle of the cutting heads, it would be ok. So, any cartridge (no matter whether it has a build-in VTA of 20 degrees or 22 degrees) can be adjusted to fit any cutting angle. Am I correct?

Now, my friend’s “theory” actual goes one step further, which I have hinted but didn’t really state out clearly in my original question. It goes like this:

Going back to my original example “say an Ortofon, with 20 degrees build-in VTA, will fit the Decca, and another brand of cartridge, say a Clearaudio, with 22 degrees of build-in VTA, will fit the EMI etc.”, his theory is that with a Decca LP, an Ortofon (due to the fit of it’s build in VTA) will always sounds better than a Clearaudio no matter how you adjust the arm/cartridge (even if you adjust the SRA/VTA for individual records), assuming the cartridges are in a similar price range. And vice versa, an EMI LP will always sound better with a Clearaudio. So, if you want to ideally play back all the LPs, you will need one cartridge with a 20 degrees build-in VTA, and another one with 22 degrees build-in VTA.

Well, based on the answers I got from you guys, I guess this theory is false.

Thanks again,

Michael
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