Accordion · 6 min read

The Stradella bass system, explained

Six rows of buttons arranged by fifths: counter-bass, bass, major, minor, seventh, diminished. How the Stradella layout works and where free bass takes over.

2026-08-20

The layout in one paragraph

Look at the left-hand side of a 120-bass accordion and you see six diagonal rows of twenty buttons. Reading from the row nearest the bellows outward: counter-bass, fundamental bass, major chord, minor chord, dominant seventh chord, diminished seventh chord.

Along each row, adjacent buttons move by a fifth. Find C, and the button below it is G, the one below that D, and so on around the circle. Go the other way and you get F, B flat, E flat. The whole system is the circle of fifths laid out under your fingers, which is why the same accompaniment shape works in every key, just shifted along the diagonal.

The counter-bass row sits a major third above the fundamental. If your middle finger is on C in the bass row, the button diagonally up on the counter-bass row is E. That is how you play bass lines that walk in thirds without leaving the position.

Why the chords are presets, and what that costs

Each chord button opens several pallets at once and sounds three or four reeds. You do not choose the notes and you do not choose the inversion. The instrument picks a voicing, usually compact and near the middle of the bass range, so chords do not muddy at the bottom or thin out at the top.

The benefit is enormous for the beginner and for dance music. One finger produces a full chord in tune, in a sensible register, instantly. An accordionist can supply a complete accompaniment alone, which is the historical reason the instrument travelled the world.

The cost appears the moment you want a specific voicing. You cannot play a first-inversion chord, you cannot omit the fifth, you cannot place a note in a particular octave, and you cannot write independent bass lines. The diminished seventh row is genuinely diminished, and the seventh row usually omits the fifth, which surprises people when they analyse what they are hearing.

It is also worth knowing that the bass reeds typically sound in more than one octave at once, so the left hand is thicker than the notation suggests.

Finding your way without looking

You never look at the left hand. The keyboard faces sideways and your head cannot get there. Orientation is entirely tactile, and the instrument helps: certain buttons have a dimple, a roughened surface or a small indentation as landmarks, most commonly C and E, sometimes A flat.

So the practice discipline is to learn the geography by feel from week one. Find the marked button, count rows outward with the fingers, and build muscle memory for the standard shapes. The bass-chord alternation of a waltz or a polka, the two-five-one, the walking bass in thirds using the counter-bass row: each of these is one hand shape that moves bodily around the circle.

Students who learn this properly in the first six months stop thinking about the left hand entirely. Students who peek at it for a year develop a habit that is unpleasant to unlearn.

Sizes and what you actually need

120 basses is six rows of twenty. Smaller instruments cut the number of buttons per row, not the number of rows: 96 basses is six rows of sixteen, 72 is six rows of twelve, 48 is six rows of eight. Losing buttons means losing the remote keys at the ends of the circle, which for most repertoire below Grade 5 is no loss at all.

Weight is the honest argument. A 72-bass instrument is dramatically lighter than a 120 and a beginner will not run out of buttons in the first two or three years. Buy the range you need for the music you play, not the number that sounds most impressive.

Free bass and the converter

Free bass abandons the preset chords. The left-hand buttons become a chromatic keyboard of single notes, laid out in rows of minor thirds much like the right-hand button system, covering four to five octaves. You choose every note, so you can play a fugue subject, voice a chord any way you like, or run a genuine independent bass line.

Most concert instruments are converters: a lever switches the same buttons between Stradella and free bass, sometimes mid-piece. Dedicated free-bass-only instruments exist but are less practical. Converter models cost considerably more because the bass machine has to do two jobs, and they are heavier for the same reason.

The sequence that works is Stradella first, for several years, then free bass when the repertoire demands it. If you are weighing up which instrument to buy, come and try both at A&G Academy in Singapore before spending the money, because the difference in feel is not something you can read about.

Frequently asked

How does the Stradella bass system work?

Six rows of buttons run diagonally across the left-hand side. Two rows give single notes, the fundamental bass and a counter-bass a major third above it. Four rows give preset major, minor, seventh and diminished chords. Adjacent buttons along each row move by a fifth, so the whole layout follows the circle of fifths.

What is the difference between Stradella and free bass?

Stradella gives preset chords: one button sounds a complete major, minor, seventh or diminished chord in a fixed voicing you cannot alter. Free bass replaces those rows with single chromatic notes across four or five octaves, so you choose every pitch. Free bass is required for fugues and most concert repertoire.

How many bass buttons does a beginner accordion need?

Seventy-two is plenty for the first few years, and forty-eight is workable for a child or a very light instrument. All sizes keep the same six rows and the same fingering shapes; smaller models simply drop the remote keys at each end of the circle of fifths. Weight matters more than button count.


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