I no longer use a digital microscope to set SRA. I tried that, and it is pretty precise for getting in the ballpark. For that it is an excellent tool and worth the effort, IMO. From there, listening will tell you how far you need to deviate from the 92, or whatever angle you use, for the best sound. Knowing the exact angle is not what I think is important. The reason is that it can vary between different LPs, regardless of thickness, or record weight.
So Christian, if I understand you, you have found an SRA angle that you think sounds best on a variety of LPs. You then make note of that angle by looking at the Graham bubble. In this way, you assure yourself of repeating the same SRA angle for different LPs, regardless of thickness, by always returning your arm to that same bubble level mark for each LP. Does this describe your methodology correctly?
That makes a lot of sense but only up to a point. If this indeed describes your method, my question for you is this: How does this method account for different cutting head angles? You can always return to the same angle for your arm (VTA) which assures your SRA is always the same when it hits the groove. The problem is that the ideal angle in the groove varies and it is not dependent upon record thickness. Ideally, what you are trying to do is match the original cutting angle.
I have a friend who had a very precise set of calipers and he measured the thickness of each LP before he played it. He had a chart which showed which setting to use on his Graham arm (if I remember correctly) for each LP thickness. You are right that not all 180g LPs are the same thickness. He adjusted for that. What he failed to realize is that his method was very good at assuring that his arm was always at the same angle and that his SRA was always the same for each LP he played. What he did not understand was why some LPs sounded right and others did not. He did not account for different cutting head angles. This means that the ideal SRA angle truly varies from LP to LP. To my knowledge, there is no cutting head angle standard, or if there is, it is not always adhered to. Perhaps Andre would know more about this.
I fully realize that many people don't want to go through the hassle of figuring this all out, especially considering that cartridge suspensions sag over time and people change cartridges, so SRA angles are in flux. And I also fully understand that an arm with on the fly VTA adjustment like the Graham is a lot more convenient that one like my SME is without it. But once you realize that SRA is a bit more complicated, and you decide to adjust for it for each LP, you will be rewarded with better sound.
