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!

17 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!

  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.


  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?

    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 !

    1. Hi Charlie,
      Yes I guess so but maybe face to face rather than trying to write it all down……maybe one day I’ll do a post on it!

  5. Hey George, so I have an titano accordion that has the same bass system and I realized that a couple of the buttons were bent upwards(It had fallen off the seat in the car a couple of days before) and I took off the treble side with the bellows attached and then I took out the reed blocks from the bass side. After I took them out, I flipped it upside-down, took off the cover and fixed the bent shafts. After that it was getting late so I went to bed, but in the morning when I woke up, I finished putting it back together but I didn’t realize that I hadn’t put the metal bracket back on that holds the shafts in place so once I put the reed blocks back in, I went to flip it back over to put the cover on and screw the hand-strap back in and about 15-25 of the shafts fell out. I just put them back in not realizing that they were supposed to go in a certain spot. I didn’t realize this until I started playing and it sounded off.

    Do you have any tips on how I can find exactly which shafts are in the wrong place and where they are supposed to go. I would really appreciate the help because I don’t want to have to go and spend a bunch of money to get something fixed that I can just do myself.

    Thanks, Hayden

    1. Hi Hayden,
      Ouch! I feel your pain – It’s so easy to make one small mistake that costs a lot of time! However you should be able to work out which shaft goes where. Each shaft has 3 (or on some accordions 4) pins on it. The row that fell out should be the 7ths and the Dims. So for each shaft you should be able to tell which levers it will operate so the pins have to be in a certain placing, and also the button should come nicely up to the hole. with a bit of trial and error you should be able to sort them out – be methodical! I’d put them in one at a time and check they make the right chord as you go. Best of luck. George.

  6. Hi George,

    Could you please offer any tips on setting up an Hohner 120 bass action so that the buttons maintain a good and more or less equal playing depth across the chords section? I am currently planning to at least renew the bass chord pallet lever springs in an attempt to gain better chord bass button height.



    1. Sorry this reply is so late – I have’nt been to my wesite in ages – for the record, not really since I’ve never done that but I’m not convinced that new springs will the height of the button. Depending on the type of mechanism you might bend all the levers (not really recommended) or re position the mechanism and/or the bass board so the buttons stick through more. Good luck and if you have a good success tell us about it!

  7. so here i took the first two rows without even thinking about it and now i have no idea what order they go back in, heeeeeeeeeeeelp please. its a 120 bass piano accordion Italian made no name brand on it or maker name.

    1. Hey Osker – Don’t panic – tricky and time consuming but very do-able! Each chord piston has 3 side lugs to pick up the levers and play a 3 note chord. There are 4 locations for these lugs so first sort all your pistons into groups that have the same configuration. The first 2 to go back on the left side with the buttons away from you are A7 and Adim. These are 3 note chords with no 5th A,C#,G for A7 and A,C#,F# for the dim. Check the 4 prongs by moving them and find out which is which. Now you can see what lug configuration you need and pick the piston that fits from that small group. Don’t be tempted to bend! The correct piston will just fit, and play the correct chord. Be patient and you will succeed! Good Luck and next time label them or put them in rows or something!!!!

  8. Hello, I just bought an old hohner accordion for ten bucks. I thought it was a cool decoration piece, but it’s grabbed my attention in more ways than one. I’d like to learn to play it, which I will do, but I want to make sure it’s working good first. One of the keys is stuck up. I figured out how to get at the keys from the inside, and noticed that it’s got a broken rod (am I saying the name of that part correctly)? Anyways, I need a part for it, do you perhaps have a rod I can purchase, or can you point me in the right direction. As well I’d like to determine the model and year. Any assistance would greatly be appreciated. Thank you.

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