Tuning problem

[Jakup Zachariassen]

Hi
I have a Mullen G2.

I have a knee lever that raises the B string to D.

When I press the A and B pedals, everything is in tune.
When I press the A and B pedals and the knee lever, everything is also in tune.

However, when all 3 pedals are down (A and B plus the knee lever that raises B string to D), and I release the knee lever from D back to C#, the C# is too sharp. I have to release the A pedal and press it again to bring it back into tune.

Is there a way to fix this?

[Lane Gray]

Finding the problem will be harder than fixing it.
I can almost guarantee that whatever is binding, and something is definitely binding, is only binding when the guitar is up on its legs, and the problem goes away on the bench.
Look for signs of rods rubbing, and either hit them with a PTFE spray, or rearrange them so they're not rubbing or binding anymore.

You might have to be underneath it as someone activates the changes.

[Lee Baucum]

Here is a recent discussion;

viewtopic.php?t=409610

~Lee

[J D Sauser]

Hi
I have a Mullen G2.

I have a knee lever that raises the B string to D.

When I press the A and B pedals, everything is in tune.
When I press the A and B pedals and the knee lever, everything is also in tune.

However, when all 3 pedals are down (A and B plus the knee lever that raises B string to D), and I release the knee lever from D back to C#, the C# is too sharp. I have to release the A pedal and press it again to bring it back into tune.

Is there a way to fix this?

If I understand your issue correctly, it occurs when you raise the B string(s) three half-steps, then release it while the A-pedal (two-half-step raise) is already engaged.

If so, this behavior doesn't seem totally surprising to me.

The most likely cause suggested here will be string hysteresis — the tendency of the string behind the nut (in the keyhead) to expand and contract with a slight delay. This occurs on all raises (string returns slightly sharp) and lowers (returns slightly flat). Usually, a little playing or tugging restores neutral pitch. This results from the downward pressure of the string over the roller nut, which creates friction.

However, if the effect is more pronounced in your case, the lowering scissor (held against the stop plate by the return spring) may be getting pulled off its neutral resting position in one of two ways:

1) The three-half-step raise lifts the lowering scissor off the stop plate

Even a tiny lift can cause unstable tuning. The fix is to increase the return-spring tension so the lowering scissor stays firmly planted against the stop plate, even during the three-half-step raise.

To check:
• Observe visually whether the lowering scissor lifts off the stop plate during the raise.
• Test mechanically by gently trying to lift it; it should stay tight and snap firmly back to the stop plate.

2) Geometry shift when the raising scissor moves

When the raising scissor leaves the stop plate, it pulls the lowering scissor with it at it's pivot point. This changes the angle of the lowering scissor, lifting it slightly (NOT "lifting off" as described in #1, but, going up VERTICALLY against the stop plate!) and causing friction against the stop plate. When you release the three-half-step raise into the A-pedal’s two-half-step raise, this friction can cause the mechanism to “hang up”/using "play" momentarily, affecting the pitch it settles on.

What to do
• First ensure issue #1 is solved — return-spring tension must be sufficient, but not excessive.
• Optionally, add a lowering rod linked to the A-pedal raise to slightly co-pull the lower.

With this method, you tune the A-pedal raise slightly sharp, then counter-lower to pitch. This keeps the lowering scissor off the stop plate, eliminating friction issues.

Note:
This co-pull method can negatively affect tone and sustain, because — similar to a split note — both scissors are now “floating” in the linkage instead of at least one resting firmly on the stop plate.

I realize this is complex to describe mechanically, but I hope this explanation helps clarify the thought process, diagnostic steps, and solution options.


... J-D.

[Lane Gray]

• Optionally, add a lowering rod linked to the A-pedal raise to slightly co-pull the lower.

With this method, you tune the A-pedal raise slightly sharp, then counter-lower to pitch. This keeps the lowering scissor off the stop plate, eliminating friction issues.

That's some clever stuff.