How to set SRA after determining true vertical?

Neil, how did you determine the 4mm => 1 degree? I'm not disputing it, just curious how you measured it.

Doug, I'll take that remark as a compliment? (unless informed otherwise.) Actually, this thread was partly inspired by the beautiful stylus pics you posted, plus people keep asking me how to do this. I know you adjust your SRA a lot, and I wish I could too, but the SME V was apparently designed in the "set it and forget it" days. I keep mine at 1.4 degrees which seems to work well for most recordings, but if anyone out there has an xtra Tri Planar for sale cheap, I'd be interested ;~))

Dan, I don't blame you for asking. It's quite simple really, and just a matter of geometry as you will see. Unfortunately, it would be a lot easier to draw it for you, but I'll try and explain it in words first, and maybe later I'll have time to make a diagram and post it. So please leave a post to let me know if the following makes sense to you:

A typical 9 inch TA measures 23 cm (or 230 mm) from the vertical bearing to the stylus tip. Imagine now that you lift your TA with the finger lift, but instead of setting it on the record, you just keep lifting it (magically of course) up and over the back of the turntable base, and continue under and up through the base to the armrest again.

OK? So you've just made a circle with the stylus tip; so far so good? The length of this circle's circumference (in millimeters) is PI times the diameter of the circle. The radius of the circle is 230 mm (the TA length) so the diameter is 460 mm. PI is 3.1416, so PI x 460 = 1445 mm (the length of the circumference traced by the stylus).

There are 360 degrees in a circle. So each (pie-shaped) degree of our circle would contain one three-hundred-and-sixty-eth of that 1445 mm circumference. Divide 1445 mm by 360 = 4 mm.

So if you raise the stylus end, OR THE BEARING END (which is what we need to do to create SRA at the stylus end) you are going to tilt the tonearm AND THE STYLUS (which is attached to it) exactly one degree!

If you have a cool tonearm like Doug's Tri Planar, you just dial up however many degrees (times 4mm) you want. If you're stuck with something less accomodating, I've found the best way is to use a stack of automotive feeler gauges to achieve the height you want.

Got it, Neil. The calculation makes perfect sense. Guess I was expecting that you had marked up some tiny protractor or something. I just have to run the numbers for a different arm length. This seems like another good method for getting started and then adjusting by ear. Fortunately, my Graham and TriPlanar both have VTA scales. The RB 250 I'm going to mount on a Lenco project doesn't have this but I plan on using an aftermarket Rega VTA adapter.

Dan_ed,

I too am curious but, he is right. I drew it out in Corel Draw and he is right on the money.

Converting:

Angular Tilts To Linear Measurements

1 arc second = 0.0000048481232363502727814651700363688 inch per inch

= 0.000048 inch per 10 inches
= 0.000058 inch per foot

Linear Measurements To Angular Tilts

0.000001 inch = 0.20626480624702760022105769979869 arc seconds per inch

= 0.021 arc seconds per 10 inches
= 0.017 arc seconds per foot