An Automatic Ab/Bb Trill Mechanism Retrofit – Bassoon Repair
July 21st, 2014 by Trent
Cross posted from Trent’s personal blog. Repair tech Eric Anderson and bassoon specialist Trent Jacobs team up again for more creative bassoon keywork ideas.
About two months ago I had a shower thought of how I could simplify the thumb Ab/Bb trill mechanism on my bassoon. On the standard Heckel system bassoon, the movement from Ab to Bb in the low octave and the overblown octave requires the third and fourth fingers to move up and the thumb to move down (all on the right hand). This makes for a rather awkward movement when an Ab/Bb trill is required. You can get away with trilling the third finger of the right hand on some bassoons, which provides a sort of solid Bb, but it’s pretty weak and that’s a difficult finger to trill all on its own. Or try any of the other fingerings here…
So there are several solutions common for an Ab/Bb trill that is not only easier but sounds better. The most common is an additional key for the thumb that opens the Bb pad and a new pad/tone hole. When fingering Ab, you trill this key, and the additional tone hole opening with the Bb tone hole provides a solid and tunable new Bb pitch.
This extra thumb key is sometimes tricky to get to because of where it is relative to the F# and back Ab keys. Some bassoons have it in line with the rest of the thumb keys, either between the F# and Ab (or replacing the Ab all together) or on the far end beyond the Ab key. There are other mechanisms as well, but they usually have trade-offs in what you can do for multiphonics or full fingerings in the upper register. The “Articulated Ab-Bb mechanism” (which forces the Bb pad closed when you press the G key), for instance, does not allow you to play the single most common multiphonic and prevents the “full” fingerings for high Ab and A.
My thought was to link the mechanism of this additional tone hole to the pinky Ab key, so that when both the Ab pinky and Bb thumb keys were pressed, the additional trill tone hole is opened.
This would allow for an nAb/Bb trill by playing Ab, and trilling the normal Bb key. Sounds perfect, so what would be the problem? There are only 3 other pitches on the bassoon that have normal fingerings involving both the Ab and Bb keys. High D, Eb, E, and F. Luckily, it’s easy to test how this would affect these notes: play those notes with the Ab/Bb trill key instead of the normal Bb key so both pads are opened. Low and behold those notes are better with the extra tone hole opened!
Figuring out how this would work required a bit of thought. But essentially it meant doing three things:
- reverse springing the Ab/Bb trill tone hole so that it would be held down by both the Ab and Bb keys
- adding two arms: to the Bb pad cup over the trill key lever, and on the back Ab linkage mechanism over the trill key pad
- adjusting the springs around the Ab key mechanism to operate the stuff on the back side of the boot when the pinky key is depressed
Luckily for me, I discovered that on my Moosmann 222A, the trill tone hole key was actually already sprung open! I think the reason for this was to allow for a lighter action on the Ab/Bb trill key. At any rate, this meant I wouldn’t have to rebuild the trill key lever to accommodate the arm attached to the Bb pad cup.
After coming to all of these conclusions, I discovered one instrument where this was done. It confirmed everything I had determined on my own. Heckel #9980 has this mechanism.
So now came the part about doing the modification. I had Eric Anderson do the work at Midwest Musical Imports. The first step was easy: remove the Ab/Bb key and posts. Get them out of the way. Then the new arms were made and soldered to the existing mechanism. Finally, re-assembly and adjustment of the springs in such a way that the keys were regulated and doing what was intended.
Eric tells me that what make this mechanic difficult to deal with is that you’re regulating what is already the hardest pad to seat on the bassoon (the Bb pad) to another key. So you have to really line up everything right. The option for Heckel 9980 had adjustment screws on both of the new arms, but I trusted Eric to be able to set it up right, so I just had him make solid arms with no adjustment screws. I don’t want to futz with this anyway.
So when it was done, it works!
I still have to have the soldered bits silver plated yet, so they’ll match better. And I’m awaiting dummy posts that I can screw into the empty post holes. The wood holes are sealed, so it’s functional now, but it’ll look better with silver balls in place of the holes. I didn’t want to try to match wood stain color by plugging them, and I wanted to be able to revert back to the original key if I wanted later, so leaving the post holes seemed like the right option.
Shoutout to Bret Pimentel for his fingering diagram builder.
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