quote - "the string width at the nut is 6.1mm and 7.9mm at the bridge. "
Slaven, this seems a little unbelievable, just checking, are those really the right measurements? Your fingers must be as thin as pencils!! I had terrible difficulty trying to adapt to 7.5 at the nut and 10 at the bridge, although I did think that I would be able to achieve it if it were my only guitar, but switching back and forth with my other guitars with wider spacing proved impossible. (Perhaps if I played electric it would have been possible.) Somebody else also commented on this earlier in the thread.
I am not surprised that you found the high A too tense at 630, particularly a .028. D Addario makes strings as thin as .018 to my certain knowledge, google this -
D'Addario NYL018 Classical Guitar Rectified Nylon .018, single string
A friend of mine here has a straight-fret eight string made by Javier Pascual with a 630 scale. He is using a fluorocarbon Seaguar Fluoro Premier .405 mm string. It sounds a little bit twangy, but this may be what all high A strings are going to sound like. I have at this writing 4 instruments in the house with high A strings, a requinto at 540, my prototype nine string at 560 (with fanned frets and the low string at 680), and two straight fret seven strings at 580 millimeters (which are my wife´s instruments and which have D Addario .022 high A strings.) . . . they´re all a little twangy and require a special touch on the high A.
I am thinking about 600 mm for the high A on the next nine string, which is now on the drawing board (though when I can afford to build it is another question entirely).
It might be interesting to start a thread about high A strings - ask everybody who has one on any plucked instrument to chime in and say what the length is, what material and tension they are using, and how well they like it on a scale of 1 to 10.
Playing a guitar with a high A string, and being able to use the same guitar to play 16th c. lute music, has given me some very interesting insights in the thinking of 16th century musicians which would be much more difficult to understand if the two instruments were separate, and even more so if they were tuned to different pitches. Thinking of the high A string as "La" in the modal sense, (regardless of the actual pitch,) is one although only one of the possible mappings of the gamut onto the fingerboard, but it is the one Luis Milan chose to use for the entire first half of his book when showing the modes to beginners. In order to understand the modal system it has been necessary for me to learn to analyze and translate harmonic concepts into modern thinking in various ways while reading tablature. This is much easier on a high-A instrument which overlaps directly with the guitar. When I listen to recording of G-tuned lutes it bugs me at first to hear the Dorian mode played in C-minor! until my ears adapt and I can get clear about what I'm hearing.
I have thought a great deal in recent years about the high A string as a historical exhibit... It disappeared from the vihuela, leaving the Baroque guitar in its place, and the lute dropped its highest string first to G and then to F over the course of the seventeenth century. In light of this it is interesting to contemplate the phenomenon of the two pitch standards of the Baroque, "Choir Pitch" and "Chamber Pitch" - some Bach scores for instance have the string parts written, say, in E Major while the organ part is in D. Considering that some evidence - I am thinking of both Luis MIlan and Vicenzo Galilei, both of whom I have been studying recently for insight into the modal system - shows that there really was no fixed pitch concept among lutenists in the 16th century, I guess that at some point around the early 17th century guitar and lute players were sucked into the game of the rising pitch standard and were no longer able to acheive a high A with gut strings, perhaps not even at "Chamber Pitch", much less organ pitch. (the New Harvard Dictionary of Music has a list of historical pitches mainly from organs which go as high as about A-500 if I recall correctly). Even today, I´m sure that you could not put a gut string on your A at 630. Aquila Nylgut won't do it either. And even on my 560, I have broken an awful lot of high A strings over the two years that I have had it, of every material I could get my hands on. Right now I have a Seaguar Red Label .47mm fluorocarbon string on it and it has been there I think for a couple of weeks without breaking. Maybe its the one. It sounds pretty good. I tried a nylon DÁddario .020 just before and it broke immediately... it was the only one I had. I sanded the nut slot a little more (in case that was the reason) and moved on.
Slaven - maybe this is too radical for you, but I really like the low B on my prototype nine string, which is now the lowest string since I took the low F-sharp off and made it an eight string. The low B is now at 680 millimeters and I really like it. You might consider going a little longer on the low end than 660. If you went with 610 to 680 it would only be a 7 centimeter fan. The fan on mine is a total of 12 centimeters difference, which may be about as extreme as you can go, but it is perfectly playable after some practice. The problem is with the sound of the G and high B string on the upper frets - the intonation there is uncertain, and the frets are close enough together to be a little difficult, and so this is why I will go with a longer design next time (600 - 720 is my current drawing.) I will, however place the right-angle fret at the third fret on the next build, in order to minimize the angle at the nut and increase the angle at the bridge. (this creates a structural problem which I have a solution for on paper but have to run it by my luthier when the time comes to talk seriously.) The electric players usually put the right-angle fret up around the 7th or 9th fret.
And Slaven, bravo for using Grand Staff! Maybe you would like to play my waltzes - which I wrote out in grand staff - they are posted here --
over and out.
The next nine string is on the way...