Chord · A Dominant 7♯9 (Hendrix)
A7♯9 Chord
A7♯9 is A, C#, E, G and B# — the Hendrix chord. Bluesy and aggressive.
A7♯9 on every instrument
The same 5 notes, 2 sets of hands. Open a diagram for alternate shapes, audio and the mistakes to avoid.
What A7♯9 is made of
A7#9 (A seventh sharp nine) is built from the notes A, C#, E, G, B#, with the interval pattern 1, 3, 5, b7, #9.
Stack 1, 3, 5, b7 and #9 on a root of A and you get A, C#, E, G and B#. That interval recipe is what makes the chord a seventh sharp nine chord — move the same shape to another root and the character travels with it, which is why C7♯9 sounds like a transposed A7♯9.
Dominant 7♯9 (Hendrix): The Hendrix chord. Bluesy and aggressive.
Spelling: the notes above are written the way a score would write them, not simplified to the nearest piano key. That is why this chord is spelled with C♯ rather than its enharmonic equivalent.
Keys that contain A7♯9
No major or natural-minor key contains all 5 of these notes — this one gets borrowed.
Chords like this one sit outside the diatonic set — they arrive as secondary dominants, borrowed chords or passing harmony. Browse every key to see which progressions pull it in.
Other chords on A
Same root, different colour.
The same seventh sharp nine shape, moved
The identical interval recipe, built on other roots.
Questions people ask about A7#9
- What notes are in the A7#9 chord?
- A7#9 is made of A, C#, E, G and B# — the 1, 3, 5, b7 and #9 degrees of a seventh sharp nine chord built on A.
- What keys use the A7#9 chord?
- No major or natural-minor key contains all 5 notes of A7#9. Chords like this arrive as borrowed harmony — secondary dominants, harmonic-minor colour, or chromatic passing chords — rather than as one of a key's native chords.
- How do you play A7#9 on guitar and piano?
- This page shows A7#9 on guitar and piano — 5 voicings in total. Each diagram links to the full instrument page with alternate shapes, audio and common mistakes.
Learn the theory behind it
Why A7♯9 behaves the way it does — the guides that explain the chord instead of just spelling it.