Which bass system does my accordion have?

Question

Some time ago I inherited an accordion that is probably older than my grandparents.

Since then, incidentally, I've come to really love classical music and I really want to be able to replicate it myself.

The problem is I've never played an accordion nor any musical instrument. So I am going around Google to learn about accordions.

I think I understand most things now BUT I am so confused by the bass system.

The instrument is an 120/41 piano accordion with one bass switch and two treble switches. Brand is "Pollina".

I however don't know what kind of bass system it has only that there are 120 bass buttons, the middle C has an indent on the 2nd row from the bellows, when you press one bass button a couple more go down at the same time.

I have heard that there are two bass sysyems — free bass and stradella, and that they are very different from each other.

As I am an absolute beginner at this, I need this information to be able to start learning.

Answer 1

Most likely, it's a Stradella bass. The 120 buttons are arranged in a 20 by 6 array. The 20 rows are for 20 musical keys arranged in a cycle of fifths with some extras at each end so one doesn't have to jump one's hand up and down so far. (Works pretty well.)

The other 6 rows are arranged from bottom to top in a counter-bass row which is a major third above the second row, the bass (or root) row; then there are 4 chords; a major chord with root at the bass row, a minor chord, a dominant seventh with the fifth omitted (for sonic balance), and a diminished seventh with the fifth omitted. The dominant seventh (fifth omitted) can be used as an Italian Sixth a few rows away. The counter-bass line allows a major scale without reaching.