the Soprano Guitar was inspired by tunings
that I had heard David Sylvian
and Robert Fripp were using

a normal guitar tuning
is based on 3 finger patterns.

i.e. you can play an entire major scale
without moving your hand using 3 finger patterns

mandolins, violins, violas, etc.
incorporate 4 finger patterns,
since the "frets" are closer together

If your fingers are agile enough,
you can play 4 finger patterns on the guitar

For this reason,
I decided to try and tune the guitar
in 5ths ( like a violin ) rather than 4ths

if a normal guitar were tuned in straight 4ths,
the high string would end up
being an F, rather than an E

this would make it difficult
to play bar chords,
so the decision was made 100s of years ago
to use a third between the G and B string

I could care less about playing boring bar chords

I'm more interested in extending the range
of notes that I can play in a set position

The hard part about designing the Soprano Guitar
was deciding what string gauges to use

My seven string guitar has a .050 low string
tuned to a low B

I decided to use a .052 low string on the
Soprano Guitar, and I tune it to a low Bb

From there we move up in fifths as follows:

    Bb, F, C, G, D, A

Note that the D string is tuned just below what
a normal guitar's high E string would be tuned to,
and the highest string is tuned to an A, which is
a full 5 frets higher than a normal guitar.
This is why I ended up calling it a Soprano Guitar

My first Soprano Guinea Pig was one of my strats

Here are the string gauges/tunings for all 6 strings:

    .008    A
    .009    D
    .013    G
    .028    C
    .040    F
    .052    Bb

The smallest string that I have been able to find
so far is a .008

It's not an easy task tuning a .008 gauge string
to a high A. If you try to just put the string on
and tune it up, you will probably break the string.

What I did, was to string the guitar, and then
gradually tune it. I would turn each tuning key
a full turn, and then let the guitar sit for a
few hours. Then I would come back and tighten it
some more. Eventually, I got it right, and the
thing is a blast to play.

The PrintChart program can generate scale diagrams for you