VTA and HTA overhang

Sarcher30

Actusreus, your fork analogy does not work. If you could lift the rear of the fork straight up without letting it move forward as you lift it would pull the front back. This is quite easy to test with your tonearm. Just setup your alignment protractor and play with VTA. It's easy to see.

Sean and Peter,
Remember that you're not actually moving the tonearm, but the VTA tower or essentially the column that is supporting the tonearm. So in my fork example, if you threaded the back of the fork and inserted a screw that would allow only vertical motion, you could move the back of the fork without pulling it in or out.

I will adjust the VTA today on my table just of out curiosity. I know Doug adjusts the VTA for each record so it'd be interesting to hear his opinion on the matter.

Audiofeil, I'm with you there. I don't personally adjust VTA for every record either, but I think it is important to know how different adjustments effect things. Especially when setting up a cartridge.

If you don't adjust VTA for different height records then make sure you set your alignment on a medium thickness record. Unless you mostly listen to 120 or 200 gram pressings. This is what I do.

All that said I can understand why someone might want to adjust VTA for different record heights. Most people don't have the time or patience to fiddle with it. Myself included.

Actusreus, The only way the offset would not move when adjusting VTA up or down is if the tonearm post was curved. Lets use your fork as an example. If you lift your fork without moving the front at all it will trace an arc in the air. Turn the fork on it's side and put it on a piece of paper. If you attached a pencil to the end and rotated it keeping the tongs centered, it will trace an arc. Unless the tonearm post can trace that same arc it will effect overhang when adjusted.

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.