Dumb VTA Question

OK, I've read Michael Fremer's comments regarding SRA and VTA and am still confused about the difference. Perhaps someone here can put this in perspective for me (and maybe a bunch of other folks)!

As I understand it, you change the VTA by lowering or raising the pivot point of the tonearm, which also changes the SRA. I had always thought of it that way since making those changes alters the angle at which the stylus contacts the record surface, hence trying to immitate the angle at which the record was cut. So, what's the difference between the two???

VTA/SRA can also be changed by lengthening/shortening the effective tonearm length, also called overhang I believe, but it still affects both of these parameters so, again, what's the difference?

Raising or lowering tracking force also changes the angle in both cases. I'm missing something here and would sure like to know what? Anyone else confused by this?

In reality, everything affects everything. You aren't done when you change the height of the arm..you must recheck how the raising/lowering affects the downward pressure. Once that is adjusted, you must make sure the stylus still sits in the absolute correct spot of the alignment gauge,...and then understand that all of that has to be checked and adjusted again, and then again, until gradually you are satisfied and can walk away (for a long drink and well deserved rest).

Excellent post by Jcarr. As usual.:)

"However, as I recently wrote in Stereophile, the
construction of every tonearm that I am aware of (with the
sole exception of the Eminent Technology linear trackers)
guarantees that altering SRA will simultaneously cause the
effective length to change, along with the tracking force.

To make sure that any SRA-induced audible changes are truly
attributable to SRA rather than sundry alignment shifts that
came along for the ride, you must recheck the overhang and
tracking force and "put them back" to what they
were prior to the VTA change.

At the end of the day, you may ponder about the real value
of "VTA on-the-fly" mechanisms (grin).

kind regards, jonathan"

I would just like to add that IMO overhang should be the
last adjustment done after changing the other parameters. We
could argue the order but I think it should be SRA first,
then VTF, and finally Overhang last.

Then there is Azimuth. If you have a linear tracker or a
pivoted tonearm that adjusts Azimuth in the same plane as
the offset angle then adjusting Azimuth should not effect
the other settings much at all. On the other hand most
pivoted arms adjust azimuth at the back of the arm.This
adjustment is not in the same plane as the offset angle.
When this is the case, changing azimuth will effect all of
the other settings (VTF,SRA, and overhang). In this case I
would do it in this order. SRA, Azimuth, VTF, and then
Overhang.

As said above, this needs to be done multiple
times by ear to dial it in.

Sean

I might add my tuppence here.
Firstly, Adjusting SRA/VTA makes a huge difference to tracking force on most arms. What you hear is the alteration in tracking force predominantly, unless you reset this after each adjustment....which defeats the purpose of VTA on the fly. Just try it out.
Second point is that to make a substantial difference to SRA you will need to change the base of the tonearm some 10mm to achieve 1 degree change in SRA (depending on the length of the tone arm, 15mm on a 12 inch).
My final point is I took a lot of brilliant photos of my stylus on the record, and measured the SRA repeatedly. I did it so often, I damaged the suspension, and required a cartridge rebuild.....and never managed to achieve 92 degrees. So now I set tone arm level, play around a bit from there, until it sounds right, compensating for tracking force with each change, finally I reset overhang, and alignment.
As illustration, just putting my record weight on my ClearAudio CMB, increases the tracking force by 0.02 grams (it compresses the magnetic bearing and lowers the whole platter), so I can see how a thinner record will see a greater tracking force than a thicker record, the change in SRA will be much < 0.1 degrees. Since not all records are cut at precisely 92 degrees, I'm not sure that this is the holy grail.
I'm sure the debate will go on but after much trouble, I have concluded that the changes in tone arm base height relative to the change in SRA are too great to make a meaningful difference in SRA, but what they do do very effectively is change the tracking force. The change in overhang is tiny, just check geometry with different systems Baerwald/Lofgren/Stephenson, and see the differences are not that small, which to me means a range is acceptable?
I must conclude that I am not an "expert" by a long way, but have had a painful and costly experience with this question, and read just about everything I could lay my hands on, and then did some basic trig on the angles.

I thought I read that M. Fremer wrote that with a 9" arm, a 4mm change in height amounts to a 1 degree SRA change. I have a 12" arm and adjust my SRA for different LPs. I move my arm up and down in a 3mm range which amounts to about a 1/2 degree SRA difference. That sounds tiny, but it is audible and worth the effort to me. I don't then also adjust VTF and overhang, though I know they are effected.

I mark my LPs with the best setting height for reference and this does not correspond to the varying record thicknesses. For example, I have lots of LPs that are say 160g and they cover the full 3mm range of best VTA. Same for my 180g LPs.