A7#9 A dominant seventh sharp nine chord
- Notes
- A C# E G B#
- Formula
- 1 3 5 b7 #9
- Semitones
- 0 4 7 10 15 above the root
- Other symbols
- A7(#9), A7+9
A to C# is a major third (4 semitones), C# to E is a minor third (3 semitones), E to G is a minor third (3 semitones), G to B# is a perfect fourth (5 semitones). A dominant seventh with a raised ninth, B#. On the keyboard B# is the same key as the minor third, so the chord holds both a major and a minor third; it is written as a sharp ninth because it sits above the seventh and the letter names follow the stack of thirds.
A7#9 on the piano
Root position from A4: A4, C#5, E5, G5, B#5. Middle C is C4.
A7#9 on the guitar
Standard tuning (E A D G B E). Strings run low E on the left to high e on the right, frets downwards; × is a muted string, ○ an open string, and each dot shows the note it sounds, with the root in blue-green. Every shape below has A as its lowest note.
x 12 11 12 13 x (low E to high e)
Sounds A3 C#4 G4 B#4, fifth left out
The E-shape and A-shape grips are movable: an E-shape chord's root is the note under your first finger on the low E string, an A-shape chord's root is the note on the A string. Slide the same grip up or down to play dominant seventh sharp nine chords on other roots.
Inversions of A7#9
An inversion puts a note other than the root in the bass. The name is what semicord's chord finder calls those notes played bottom to top; a slash name like C/E means a C chord with E in the bass.
| Position | Notes, bass first | Named | Listen |
|---|---|---|---|
| Root position | A C# E G B# | A7#9 | |
| 1st inversion | C# E G B# A | Am7/C# (also read as A7#9/C#) | |
| 2nd inversion | E G B# A C# | A7#9/E | |
| 3rd inversion | G B# A C# E | A7#9/G | |
| 4th inversion | B# A C# E G | A7/C |
Where A7#9 fits
A7#9 has no place among the chords built from a major or minor scale: it holds a major third, C#, and the sharp ninth B#, which sounds the same as the minor third. That major–minor clash is the blues in one chord. It is used as the I chord of a blues or a funk vamp, and as a tense V chord in jazz; Jimi Hendrix's "Purple Haze" made E7#9 famous, which is why guitarists call it the Hendrix chord.