VTA and HTA overhang

The problem is twofold, overhang changes with arm height and SRA varies from 91 to 95 degrees. Even Jon Risch* (the guy whose work this is based on) said that 91 degrees is right for 80% of all records. In reality, I think most people who occasionally change arm height for a record, usually change it a small amount. A 9" arm requires 4mm height adjustment for 1 degree change. Who set up the alternatives of changing for every record, or not at all?

If you use a Loefgren A or B alignment set at 92 degrees, then raising your arm slightly won't do much to alignment. Any two set of nulls between 60 and 121 mm, is a "good" alignment. Look at the nulls for Loefgren A, B, and Stevenson. If you're skeptical, get a straight line calibrated grid, raise your arm 2 mm and see where the nulls are. IMO SRA errors can be much more audible. Some people don't seem to hear it, but some people are nearly oblivious to speed variations.

Put a UHQR on your table, and in order to maintain your orig alignment the arm must be raised the same amount of extra record thickness. Look at the record and arm pillar as 2 sides of a right triangle. The arm tube to stylus is the hypotenuse. The alignment change is very small and SRA goes negative, Sound a little bassy?

*Audio magazine March 1981

One thought I have that has crossed my mind a few times in the past when thinking about LP's varying thicknesses. Why hasn't someone come up with either a shim or different thicknesses of mats. Then one could place a thicker shim or mat on the platter for standard pressings and revert back to the standard mat for the 220 gram recordings and have one of each for 120,140,180 gram etc.
I realize there may be different sonic signatures for each mat or shim, but would it be that noticable if they are all the same material. I am curious from a mechanical point of view that over time the constant changing of the tonearm in such a small incremented area of the adjuster, what wear will eventually reveal itself. Just a though and love to hear the shortcomings of this idea.

Sarcher, you are absolutely correct that raising or lowering the VTA the same amount as the LP thickness difference will preserve the original alignment. There, I knew I would learn something and this is so obvious.

However, some of the people I know change SRA for different records by listening and trying to duplicate the original cutting angle. This is independent of record thickness as there is/was no standard cutting angle, though most I guess were around 92 degrees. For these people, changing SRA does indeed alter alignment. Perhaps to such a small degree that it is not an issue.

And as Audiofiel wrote, life is too short. I set SRA with a 150-160g LP and leave it, obsessing no more. However, I do spend 20 minutes per side cleaning an LP, because it sounds better to me, so we make our choices, even if they are inconsistent.

Peter, The people that try to get the perfect SRA for every record must believe that it's more important than perfect alignment. I doubt there are many people that would go to the trouble of adjusting overhang for every record as well.

I'm sure someone could design an arm with a curved VTA tower with on the fly adjustment. It probably would not be worth the effort as I imagine it would be quite difficult to accomplish. It would be allot of work for a little gain in accuracy.

I adjusted the VTA today by lowering the back of the tonearm. I then checked the overhang, and the adjustment in the VTA did indeed appear to change the overhang, but too insignificantly to take notice. Admittedly, I changed the VTA very slightly, and I acknowledge that bigger changes might indeed affect the overhang to a more significant degree.

I find it curious that this is never mentioned when the VTA is discussed. As I mentioned in my previous post, you have to wonder about the utility of the VTA on the fly adjustments. To me the entire idea was that it allowed real time adjustments while keeping other variables constant. I suppose if the changes are minuscule, I can still see the benefit, but this does seem to warrant at least some discussion.

Btw, is Doug on vacation? This thread begs for his input. Doug, chime in!