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VTF, VTA, SRA, and 92 degrees - question

I'm familiar with the logic that has been out there for a while about setting SRA at 92 degrees for what is considered the optimal styus position, based on a lot of analysis done by Elison and others. My question is, if VTF and VTA are set per cart maker's recommendations (let's discount Anti-skate for this discussion even though it would come into play), then wouldn't the SRA be automatically set optimally per the manufacturer's intention? Assume a cart that is built to the company's design parameters - no bent cantilever, no offset stylus etc.

Take a Benz cart for example. Many (if not all) of them specify a VTA of 20 degrees. So if VTF (and yes A-S) and arm height are set so that when all's said and done the VTA is 20 degrees, isn't that what it *should* be set at based on how Benz expects that cart to perform?

I ask because I set the SRA on my Benz to 92 degrees going by that camp, and when I checked the SRA it was at - guess what - about 22 degrees. That kind of suggests Benz expects the stylus to be at 90 degrees relative to the record. Isn't that how they've designed it? Don't I run the risk of having to compensate in other ways if the cart winds up exhibiting tracking problems at an SRA that does not support the specified VTA?
tonyptony
tonyptony OP
617 posts
 
I assume that you are using a digital microscope and overlaying the image with digital protractor to measure SRA. How are you measuring VTA?

Yes to your assumption. VTA is being measured in a similar manner, except for that I am measuring the angle of the cantilever relative to the horizontal surface of the record.

Using Expressimoaudio's 0 degree precision VTA block to insure measurement are with respect to an angle corrected image. Using a Supereyes B008 digital scope.
pbnaudio's avatar
pbnaudio
1,613 posts
 
I believe that the suggested 92' SRA angle is based upon that this is how most cutting lathes are set. SRA and VTA are completely aligned with each other, they change together. Again I'd state that the stylus to vinyl interface is the most important one as this is where the mechanical transfer happens.

On the other hand I don't loose sleep over the different thickness of the records I play, I set my SRA with a 180 GM record. Remember this is supposed to be fun not a chore, fretting about a different setting for each record is way beyond what I'd consider rational.

Good Listening

Peter
tonyptony OP
617 posts
 
Yes, you're right Peter. I guess my real concern is how much / whether a non optimal SRA can impact tracking ability. With everything set the way it is, I'm running a VTF of just under 2.1 grams for good tracking. That's a bit above the magic 1.9 grams that practically every bit on info I can find says is "correct" for the Benz Wood of my vintage. I'm not sure I understand what (if anything) the relationship is between SRA, tracking ability, and tracking force.
dinster
76 posts
 
The difficulty with VTA is that it is the angle between the record, and a line joining the tip of the stylus with the fulcrum...wherever that is. It is not the same as the "cantilever angle"! It is usually about 2 degrees more than the cantilever angle, depending on the length of the cantilever and height of the diamond. It seems that no cartridge has the "gold standard" setup (VTA 20 and SRA 92), they all seem to be out, often by quite a large margin. So I'm not sure what to do about this. Mine sounds brilliant with the tone arm near horizontal, which gives a cantilever angle of 22 degrees and an SRA of about 95 degrees, to correct the angles I would have to drop the tonearm base by about 15mm, and I'm sure the mechanical problems associated would make things worse (on an 11 inch arm 1 degree change in SRA equates to over 5mm change in arm height!!). I think the jury is still out on this one, perhaps the best is to set by ear from horizontal. I suppose I'm as confused as most everyone else:)
tonyptony OP
617 posts
 
Well, with all the measuring tools, calibrated blocks, and digital photos I have I think (!) I can get back to where I am now. I'm going to try again by starting with the cart at horizontal and see what happens from there.
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