A9 guitar chord
The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped.
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About A9 — drop 3 voicings
A9 is A, C#, E, G and B — A7 with the ninth stacked on top.
It sounds bright and full, still clearly pulling. The ninth adds height without softening the tritone underneath it, which is why funk and soul comp on this rather than on a plain 7.
A9 notes and formula
| A | C# | E | G | B |
|---|---|---|---|---|
| 1 | 3 | 5 | ♭7 | 9 |
Dominant — the same pull as a 7, with more colour.
Also written Adom9 or A dominant 9. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play A9
The same operation one voice further down: the third voice from the top falls an octave and becomes the bass.
That leaves a bigger hole under the top three notes, so a string gets skipped: the muted string in the middle is the shape, not a mistake.
A9 has 9 of them, on strings 5-3-2-1 and strings 6-4-3-2, from the 2nd fret up to the 14th — every inversion the chord has: A in the bass, C# in the bass, G in the bass and B in the bass. The one to learn first is the B shape at the 2nd fret.
5 of them sit on strings 5-3-2-1, so you can run the inversions up one set without changing strings — which is the whole reason to learn them as a family rather than as separate grips.
Start with 542000 — no barre and 3 open strings. 2 of the 10 shapes here sit in open position. 5 of the 10 need a barre. Together they cover the neck from the 2nd fret to the 12th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x22223 | 2nd fret | B, 9th in the bass | G | barred |
| x02423 | open position | A, root position | G | 1 open string |
| 542000 | open position | A, root position | E | 3 open strings |
| 522423 | 2nd fret | A, root position | G | barred |
| 5454xx | 4th fret | A, root position | B | all fretted |
| 575457 | 4th fret | A, root position | B | barred |
| 575657 | 5th fret | A, root position | B | barred |
| xx7687 | 6th fret | A, root position | B | all fretted |
| 9x7987 | 7th fret | C#, 1st inversion | B | all fretted |
| x-12-11-12-12-12 | 11th fret | A, root position | E | barred |
The same notes rebuilt from scratch give 4 shell, 12 drop 2, 14 rootless and 6 open string voicings, each on its own page.
Tensions. A shell of A9, root, third and seventh, leaves a string free, and the tones that belong over it are the #11 (D#), the b13 (F) and the 13 (F#).
How to use A9
A9 is the V of D, and that is where it goes if it goes anywhere: the third and the flat seventh are a tritone apart, and both resolve by a semitone into D.
Voice by voice, A9 → D. 2 voices move by a semitone, and one note is common to both chords.
| In A9 | Moves | In D |
|---|---|---|
| A, the root | stays where it is | A, the fifth |
| C#, the major third | rises a semitone | D, the root |
| E, the fifth | falls a whole tone | D, the root |
| G, the flat seventh | falls a semitone | F#, the major third |
| B, the ninth | falls a whole tone | A, the fifth |
In which keys. Every note of A9 belongs to D major (the V, the dominant) and B minor (the ♭VII).
What to play over A9
Every note of A9 is in A mixolydian and A lydian dominant.
Chords near A9
Change one note of A9 and you have Amaj9 (the flat seventh becomes a major seventh), Am9 (the major third becomes a minor third), Aadd9 (drop the flat seventh), A69 (the flat seventh becomes a sixth), A7 (drop the ninth) or A9b5 (the fifth becomes a flat fifth).
A9 is a dominant chord — root, major third, fifth, minor seventh. Dominant seventh chords on every root.
On A9’s sound and use this page follows Mark Levine, The Jazz Theory Book (Sher Music, 1995). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.