SRA change from 140g to 180g

Assuming there is 1mm difference in thickness betw 140g and 180g record and I started out with a 140g record with SRA at 90 degrees. When I put on a 180g record, SRA changed by 0.25 degree. (Provided I mantain the same VTF and using 9inch arm.

Is this correct? sin-1 (1mm/ (25.4mm*9))

I am amazed at how much I need to adjust VTA to maintain the same bubble reading on the Phantom 2.

I ultimately set by ear and ignore the bubble.
The bubble of the Graham II is a useful tool to see in what Position the Armtube is. Very useful when another Armtube is used for comparisons...or to get a Starting point with adjustment and it is always possible to get back precisely.
It has nothing to do with the result of reproduction, cartridges are different from height, needle angle/length..
To dial a cartridge "in" always has to be done while listening. Diamonds are different and more important, the polish of its sides are different, these make the contact area where the information is.
Yes, there are those height differences from the thickness of records, but this is only one chapter. Old records have different cuts and when you listen to a old Mercury Living Presence the VTA is even some more mm down.
Happy Listening
Thanks for answer. I realize that different records are cut at different angles. Different labels with same thickness will require different SRA, best done by listening.

What I am trying to get at is that variance in optimal SRA due to different record thickness is very small. However, different labels (3-4 degree variance in cutting angle) will require large changes in VTA.

To support the above argument, I would like to verify if the mathematics is correct.

Another mute point, I suspect the visual SRA is different betw static and dynamic situation. As the record is played, the friction must exert force at the diamond and affect the static SRA. Do you think this is true?

Well, with all your findings you are on the right track.
Static/Dynamic situation
Honestly, don't make you mad with that. Do your adjustments and that's it.
Most users think, their cartridge is perfect and it can't be improved. And when they go for a more expensive one, the improvements are a kind of magic...
The diamond itself has the most influence (there are lot of different designs ( Paroc for example, Shibata...) when adjusted right, the time differences are not subtle, they are easy to hear. Next is, how good is the cartridge made internally, channel amplification/channel separation? And the polishing of the diamond...all this has a dramatic influence, A good Lyra Delos with a top diamond will beat 70% of all cartridges out there. The other 30% are based on the kind of magnets they use and what kind of cantilever/winding they have. Of course, depends on the quality of the System.
It is an interesting chapter.
Hi, i haven't been one to fool with vta to much. I have a setting for 200 and
180 gram etc and kind of stick to that. Well, listening to a new speakers
corner lp i just got, sounded a little lame...moved the arm down a little and it
really opens up. (Using a TriPlanar)

You can almost go mad with all the vinyl tweaking possible !

Syntax, you're almost saying the arm is more important-maybe not that
strongly? Or possibly a easily adjustable arm...

Glai: any comments on the tri vs graham? is it more of a system matching
thing for you or a improvement? You've had some nice arms...
In terms of ergonomic, the magnetic azimuth is easier to adjust. The VTF adjustment is tiny bit easier as it screw in and out on the threaded shaft. As I have two Grahams on different tables, I can switch wands and carts betw tables easier. The triplanar is difficult to use with peripheral ring as the bottom of the wand would bump against the ring towards the inner half of the record.

The downside on the GRaham is one connection at the wand and another at the din cable.

As far as sonics, the triplanar is slightly warmer more coherent sound. The Graham counters with faster transient, more focus and bass punch. With cart that send a lot of energy into the arm, Graham can produce some treble glare. This arm relies on damping fluid to damp resonance. I prefer other type of damping or dissipation: via arm material, gimbal bearing , magnetic flux. I think I am over stating the point as this is nonissue for me on most carts.
I would add the Graham is more easily upset by floor bounce and suboptimal azimuth adjustment. I think this may be due to the unipivot design which lends the highly focused sound. I can see and hear the Graham wobbles for very short time when it is initially placed into the groove ( not a drop). The minus K platform also improve the Graham more than the gimbal bearing designs ( triplanar, davinci, TW 10.5). I cannot confirm whether this is purely due to design choice as I have only had Grahams unipivots. I have not had audiocraft or talea.

I also find the Graham extraordinarily sensitive to VTA adjustment. If my math is correct, 1mm record thickeness difference would yield 0.19 degree change in SRA on 12 inch arm vs 0.25 degree change on 9inch graham. 0.06 difference would be inconsequential.

I do set by ear. However, I like to gain geometric understanding to help me appreciate the designs.

Anyone can confirm the calculations? I am very far from my high school days.
Glai, thanks for the comments-appreciate it. Mid last year you posted several times regarding the Spiral Groove Centroid arm. Did you ever try that or explore this option?
You r welcome. I have not tried the centroid but feel that it should be at least competitive with the graham. I am waiting to see how the SG2 perform first.
Glai, read this thread I posted some time back (including pictures!) and all will be revealed: