I may be working out some simplifications to avoid some of the long jumps sometimes needed between bass positions. of course i find i'm surprisingly accurate a lot of the time, but if, say, you go from E to Db it gets chancy. if you get it wrong it's awful. i must say, now i'm improving, i can see how you could think in terms of major and minor thirds and find it somehow useful. I might say in passing that my 80 bass accordion has no dim7 row.

for instance if you want to avoid going the distance to Db major from E you could play the third and fifth notes of the Db major chord as an F minor chord, even though it results in a C note played instead of Db itself. think of it as a Dbmaj7 without the Db note.

on the other hand if you want to avoid going up to G# major from, say Bb, you could play the upper third interval of G# as part of a C minor chord. think of it as the G#maj7 chord without the G#.

this may apply just as easily from a minor chord. G#minor might be changed to Emajor, i suppose.

At least this is one way to stay closer together with your chords.

Tell you what i've seen - a 140 bass accordion which includes an extra row of flatted or minor third basses before the major third or "alternate" bass row. A total of 7 rows. A rethink for the jazz accordionist!

But i'm sorry if i seem confused but which am i to understand, that fifths are omitted from the 7th chords? or is it thirds? i think i read the latter in this thread if i'm not mistaken.

can somebody please explain what notes are missing from each of the various chord types. that might be even more useful yet.