Stradella Bass Mechanism

Inside an Accordion Bass Mechanism

I needed a part so I started to dismantle an accordion bass mechanism that I had in my accordion graveyard. Most piano accordions have Stradella basses comprising 2 rows of bass notes and 4 rows of chords.

Stradella Bass Mechanism
Stradella Bass Mechanism

Accordion Bass Mechanisms

Each button in an accordion bass mechanism has a flat shaft with pins that operate levers to sound the appropriate reeds. In the picture above the shaft on the left has 4 pins so I suppose it’s from the 7th chord row and the ones with 3 pins are from the diminished chord row. Looking at the picture the shafts are out of order (4 pins and 3 pins should alternate) so it’s a good thing I never intended to rebuild it! Most accordions use a 3 note 7th chord but this Marinucci must be like a Weltmeister and have a full 7th chord. (I never heard this accordion play because it was given me for spares and it immediately had all it’s reeds taken out!) I do accordion repairs for private customers and The Accordion Shop. If you want help mending an accordion yourself try this great website run by George Bachich.

Why Remove an Accordion Bass Mechanism?

You might have to remove the bass mechanism on an accordion because it’s the only way to work on the pallets below if they are broken or leaking.

After removing the 7th and Dim buttons I found that I could get the Major and Minor chord buttons out in one go. I was just breaking this old Marinucci for parts so I knew I would never have to re-assemble the bass mechanism. If you did need to re-assemble, you would have to carefully keep track of each part.

Accordion Bass Mechanism Half Dismantled
Accordion Bass Mechanism Half Dismantled

Removable Accordion Bass Mechanisms

This modern Hohner has a removable bass mechanism – you can get this far very quickly by undoing 6 bolts! The pallets are under a protective aluminium plate. Most Scandalli and Weltmeister accordions also have removable bass mechanisms

Modern Hohner With Removable Stradella Bass Mechanism
Modern Hohner With Removable Stradella Bass Mechanism

This Scandalli Scott Wood Four is old (40’s I think) and amazingly they had already developed a removable Stradella bass mechanism.

Scandalli Scott Wood Four wirh Removable Stradella Bass Mechanism
Scandalli Scott Wood Four wirh Removable Stradella Bass Mechanism

The Deeper You Go…

The last 2 rows of buttons are the bass buttons and have the longest shafts. I found them hard to remove without bending some of them. In this case bending parts didn’t matter but it might be tricky if you are intending to re-build.

Marinucci Accordion with Bass Mechanism Mostly Removed
Marinucci Accordion with Bass Mechanism Mostly Removed

I needed to dismantle this Vignoni bass mechanism and it took so long that I had to leave it overnight. I had nightmares about a cat walking along my windowsill and muddling the bass shafts. (We don’t have a cat!) Come the morning I managed to re-build it without too much trouble.

Vignoni Bass Mechanism
Vignoni Bass Mechanism

Rollers or Pipes

Last of all I removed all the “rollers” or “pipes” These are the 24 long bars (in the centre of the picture below) that lift each of the 24 pallets and have levers where needed to be activated by a button. For example the C pipe associated with the chords would have levers for all buttons playing a chord with the note C in it – like C major, C minor, A minor, Ab major etc.

Stradella Bass Mechanism Removed and Pallets Accessible
Stradella Bass Mechanism Removed and Pallets Accessible

To be honest I’m unlikely to need any of the complicated bits for repairs because they tend to be slightly different on every accordion, but I have a store where I keep bits and they sometimes turn out to be useful. For now I’m just glad I don’t have to rebuild this accordion’s bass mechanism!

7 thoughts on “Inside an Accordion Bass Mechanism”

  1. Fascinating, the Stradella mechanism is an incredibly ingenious design, maybe you’re now ready to dismantle a free bass converter (I’m having palpitations just thinking about it).

    1. Thanks Brian. I saw a free bass converter being built in the Excelsior/Pigini factory when I visited Castlefidardo. (I blogged about it here) but I haven’t had to do one myself yet. If I do my mantra will be “methodical with lots of photos” which should help me on the way back!
      Cheers
      George.

  2. Thank you for unveiling the unseen intricacies of the bass mechanism. It’s very clever, isn’t it?

    What might be interesting for the future is a look at how treble and bass register switches work.

    Regards
    Pál

  3. Good morning I was hoping you can help me, I have a Hohner Morino V N with a broken button a G I think is it possible to replace it without removing the mechanism , it is not completely broken it just looks ugly

    Regards Seán

  4. I think I have a unusual free bass converter system on my Bugari Conservatory 3RC Bayan ‘C’ System
    It’s a ‘rotated’ version of the right hand, rather than mirrored, so that the top C#6 is at the chin end, and the bottom E1 is down the leg end.
    The unusual bit is that the C’s are in row 6 (Stradella diminished row) and goes chromatically up from row 6 to 4, leg to chin.
    This suits me, having come from piano, where the lower notes are played with the little finger rather then the thumb.
    I’m assuming that a standard rotated system would normally have the C’s in row 4, and go chromatically up from rows 4 to 6, bottom to top, which may be a little more comfortable for the left hand.
    Maybe you could confirm?
    Thanks
    Brian

    1. Hi Brian, I’m no expert on free bass but I had a look around and yes I think it’s unusual! One of the best sources of bass diagrams is the manual for Roland’s FR-8 which being purly electronic can be set to lots of different standards. You can download the Owners Manual here (P103 has 5 free bass systems) and also the “improvements” manual which describes another 4 Systems! None of them are yours I think !
      https://www.roland.com/uk/products/fr-8x/support/

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