A75 SieteQuinto

The SieteQuinto tuning takes the six strings you already know and tunes them up from G to G, like putting a capo at the 3rd fret. Every chord shape and scale you know still works and keeps its fingering; it simply sounds three half-steps higher, in a bright register.

Then the seventh string adds the bass. It is tuned to a low C, the same note as your 5th string, one octave lower. You get the sparkle of a capoed guitar with a real bass string underneath.

Example
Play the A-minor shape you already know. On the A75 it sounds as C minor, and the open 7th string adds a deep C under it: the note of your open 5th string, an octave lower.