Excel U-12 mechanical questions

[Niklas Widen]

I’m having some trouble with my 2018 Excel U-12 and I’m wondering if anyone of you Excel players will recognize this.

The following is what’s up:

- The 9th string B-D raise seems to make the fifth string A pedal raise go further by ~ 10 cents when the a pedal is activated. It doesn’t raise the B string by itself.

- The lever that lowers the E’s and lowers the 2nd string to C# makes the 9th string B-D string raise a few cents further when that raise is activated.


There’s good slack in the changer on all changes. Do you have any idea what might be causing this? From what I’ve understand, various degrees of cross shaft and/or changer axle flexing or twisting seems to be a common problem with U-12s. Any takes on this? Any fixes or is it something you just have to learn to live with?

Thanks,
Niklas

[Ian Rae]

The 9th string B-D raise seems to make the fifth string A pedal raise go further by ~ 10 cents when the a pedal is activated. It doesn’t raise the B string by itself.

The B-D lever can't act directly on the 5th string, so you should look at how the A pedal is adjusted in relation to the 9th. Do you also lower 5 or 9, maybe on a vertical? And do you split to B#? I would temporarily slacken the small split tuning grub screws until the initial problem is solved. I can't say more without being there!

The lever that lowers the E’s and lowers the 2nd string to C# makes the 9th string B-D string raise a few cents further when that raise is activated.

I have those changes on the same knee, and I'm not sure why you'd want to use them together. They don't affect any of the same strings, so it must be some sort of mechanical interference underneath the guitar. These things are best investigated with the instrument the right way up (uncomfortable, I know!) but when you turn it upside down things can sometimes settle into misleading places.

When I got my Excel I had to adjust the levers considerably. They have plenty of adjustment, the downside of which is that they can end up making unexpected contact with other parts. Flexing is not an issue with these instruments. Good luck.

[Chris Reesor]

Hey, Niklas,I have pretty much completely re-rodded my Superb in the process of adding two more knees and relocating others, so perhaps I can assist you.

If the rod for the string 9 B-D raise passes through the bell crank for the A pedal, the rod could be dragging on the bell crank, or more likely, on the pull pin.

The B-D raise probably also lowers string 2 to D, while your E lower levers also lowers string 2, in this case to C#. This is the common area where I would start looking for mechanical interference.

It may be possible to spot the problem with the guitar in playing position, but you really need to turn the guitar upside down, operate the offending lever and closely watch what is happening. Some sort of stand that allows you to reach under the guitar to pluck strings, which can then freely ring is pretty much essential for this work.

Good luck, CR.

[Ian Rae]

Yes, I didn't make it clear that you need to be able to examine the instrument both ways up

These guitars are very neat and dainty underneath, and although I've never had any problems there isn't much clearance.

[Jim Palenscar]

In addition to what has already been said, there are times that, when the A pedal is depressed and then the B-D lever on the 9th string is activated, the change on the torque of the A pedal cross shaft having the stress reduced by the B-D change can cause what you are noticing on the 5th string. Sometimes that can be minimized by putting the 9th string bellcrank on the B-C# change closer to the rear apron.

[Chris Reesor]

Interesting observation, Jim.

I'll have to see if my guitar does that, and how much. I know I would notice 10 cents, but I don't use that maj7 rooted on string 9 at D. Too many good alternatives handy on the Uni 12.

[Niklas Widen]

Thanks for your replies!

I think Jim is onto something. I have worked on enough guitars before to feel confident that there’s no binding or overtuning going on. It makes sense and ’ll try what you suggested.

Thanks
Niklas

[Chris Reesor]

On further thought, Jim's observation does seem to explain both the issues you raised, Niklas.

I wonder if a steel cross shaft would also reduce this, by reacting less to torque changes than the aluminum.

Where are the mechanical engineers and materials scientists when we need them?

Seriously, though, welcome to the very exclusive Excel Superb owners' club.

[Ross Shafer]

I ran into this a couple months back on a guitar I built. It puzzled the crap out of me. As per Jim's advice, it was indeed flex (doesn't take much) in the A pedal cross-shaft (stainless steel). I was able to alleviate the problem by making the A pedal change as light and long as possible (bell crank close to the cross shaft and changer further from the pivot).

Good luck! Breath carefully and stay well!!

[Ian Rae]

I got my Excel out (it's my gig guitar and it wasn't expecting to be disturbed) and to my surprise it does exactly what's being described.

The reason I've never noticed is that I tune in natural intervals so the effect is to turn the third between 5&6 with the pedals down into an equal-tempered one which doesn't register in the heat of battle.

Like Chris, I don't use it for the maj7 chord anyway, but I do use the B-D raise with just the A pedal to do a 7#9 - but the #9 is kind of wild and bluesy anyway so it doesn't matter.

Well spotted Niklas!

P.S. My Williams with the same setup does not do this at all.

[Michael Johnstone]

Sometimes cross shaft flex can be a problem on a loaded guitar like a U12 - especially if the bellcranks are located toward the middle of the shaft where the flex is more pronounced. If the problem shaft is aluminum, you can just run off a copy made of hard steel and stick it in there. For me it was the shaft that lowers your Es to Eb. And then when you lower the Ebs on down to D from a slave shaft, it's lowering from an already lowered position and the flex is different. I did that shaft replacement on a Sierra and the improvement was substantial. My 2005 Excel keyless has a well engineered compensation system where you can tie the floating tuning head to any or all pedals and really zero out any little split-the-difference temperment stuff that I used to have to live with. It's startling how in tune all the combinations are now. You just have to anylize the linkages from A to Z until you identify the problem. You only have to do it once.

[Ian Rae]

This particular issue isn't causing me any grief, so I won't be doing any fixes. But thanks Michael for the explanation and the remedy - you never know!

[Niklas Widen]

Thanks, it feels good to some more of you are experiencing this, that makes it easier for me to accept it for what it is. I actually use that change in combination with the A pedal quite a lot, but temperament and bar control makes it work.

A small flaw on an otherwise, pun kind of intended, superb guitar.