What angle should I set the VTA on my VPI turntable?

9 out of 10 of us wouldn’t be able to measure SRA accurately even with a USB microscope. For most of us that method would be a waste of time and money, unless maybe one has been trained by an experienced person, like MF or Peter L. This has been shown more than once on various vinyl forums. IMO, the best advice is to set the top of the headshell parallel to the LP surface, then go up or down from there if the initial setting does not yield good tonal balance. As many others have already written.

what @lewm & @whart said!

IME, some carts demand frequent VTA adjustment to sound their best while others seem pretty damn happy and less sensitive to small adjustment. Cheers,
Spencer

bifwynne,
I see you upgraded to the VPI stainless arm with VTA adjust.  My experience with the original stainless unipivot is this: When VTA is changed, adjusting the tail up decreases VTF.  Adjusting it down increases VTF.  A lot.  If VTA isn't close, the adjuster won't make much difference in sound.  The fix was procedural.  I began using a VTA/VTF gridded block to level the cartridge and closed in on the VTA from there, readjusting VTA then VTF and repeating.  With the Lyra I imagine the situation is compounded by its' sensitivity to VTF.  You may have arrived back at the sweet spot of coil alignment but not SRA.  When in the ballpark, the range of the adjuster will take you from murky to shrill and finding the VTA sweet spot is easy.

Another VPI owner. With my Sussurro, sounds best when arm is slightly higher in the back 

wlutke

When VTA is changed, adjusting the tail up decreases VTF.

Just the opposite: Raising the "tail" (pivot) will increase VTA.
See VTA/SRA diagram here.