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Topic: Knee lever change returning sharp. |
Dave Hepworth
From:
West Yorkshire, UK
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Posted 12 Jul 2021 6:28 am |
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Hi All
Can anyone explain this ( emmons setup).
I have a top B raise to D on LKV .If I engage A pedal before raising to D and keep A pedal engaged when lowering back down to C# then C# is just sightly sharp.The true pitch of C# is returned by coming off A pedal and then repedalling A.The same phenomena is there but slightly less sharp if I use the C pedal.
Thanks for looking. |
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Jon Light
From:
Saugerties, NY
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Posted 12 Jul 2021 7:11 am
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| I think I may have once had a glimmer of understanding of what was happening there, physically, but I no longer remember. Suffice it to say that what you describe is a common and widely suffered occurrence. |
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Earnest Bovine
From:
Los Angeles CA USA
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Posted 12 Jul 2021 7:17 am
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This happens to some degree on all steel guitars, and I don't think you can fix it. You can learn to mitigate the effect as you play by briefly letting up a bit on the A pedal as you release the raise from D to C#.
It is not related to roller nut problems or string hysteresis. Rather, it happens because when you raise string 5 to D, there is no tension on string 5's pull rod, so the A pedal's cross shaft feels different forces, and the ends of shaft move a bit in their bearings. You can even see it in some cases if you watch carefully. You can also notice that C# on string 10 will be higher after you release the D raise on string 5, which shows that the cross shaft is not where it was before you raised 5 to D.
So the problem is not so bad on guitars with tighter tolerances (snug fit on the cross shafts). But even on the same guitar, this can vary from one pedal to another. For example, on my Franklin, I raised 5 to D with LKV and it came back only a 1 or 2 cents sharp. But after I had Big Paul add some pedals, and move the B-to-D change to the rightmost pedal, the release down to C# came back around 8 cents sharp, which doesn't sound so good.
I just checked the 2 that are set up right now:
On the Sho-Bud, it comes back about 5 or 6 cents sharp.
On the GFI, it comes back about 4 cents sharp. |
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Dave Hepworth
From:
West Yorkshire, UK
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Posted 13 Jul 2021 12:02 pm
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Hi Earnest,
Thanks for the informative reply.Ill check the low B pitch as you explained and get back to you.
Regards |
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Dave Hepworth
From:
West Yorkshire, UK
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Posted 14 Jul 2021 5:05 am
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Hi Earnest,
I checked the low B as you suggested and it does NOT return sharp after top B TO D raise !!??
I was wondering if it was due to a thought I have which is..
The raise to D is quite a long travel for the pull rod.The changer hole will arc very slightly as it goes to D and therfore the straight pull rods would "see "at some point a fortshortened hole ....an oval .This would cause a very slight interference fit on the rods and on returning to C# would hold the finger slightly off.
If the rods were slightly skimmed at the changer end to give a bigger gap between them and the changer hole to accommodate the arc would that alleviate the phenomenon?
Regards Dave |
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Earnest Bovine
From:
Los Angeles CA USA
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Posted 14 Jul 2021 8:01 am
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| Dave Hepworth wrote: |
| I checked the low B as you suggested and it does NOT return sharp after top B TO D raise !!?? |
Very interesting. So your cross shaft does not end up in a different position after the lever temporarily takes the tension off one of the pull rods. I would guess that the cross shaft fits nice and snug, at least on the low-string end.
I just tried my Sho-Bud, and the low C# on string 10 moves up about 4 cents after I raise and release C# -> D -> C# on string 5.
| Dave Hepworth wrote: |
The changer hole will arc very slightly as it goes to D and therfore the straight pull rods would "see "at some point a fortshortened hole ....an oval .This would cause a very slight interference fit on the rods and on returning to C# would hold the finger slightly off.
If the rods were slightly skimmed at the changer end to give a bigger gap between them and the changer hole to accommodate the arc would that alleviate the phenomenon?
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I'm not sure about the interference part, and I don't understand "skimmed". But you do raise a good point that we could look at what comes back different where the tuning nut meets the changer's raise bar, after tension on the pull rod goes to zero then comes back.
There are only a couple of other strings where this might occur:
String 4: Raise to E# with the F lever, note the pitch, mash and release the C pedal, and see if you E# is still where it should be. It comes back about 8 cents higher on my Sho-Bud, but I don't think I would ever do this so it doesn't really matter.
A lot of U-12 players go B to C# to D on the middle B string (string 9) so they would have the same problem that we have on string 5. |
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Dave Hepworth
From:
West Yorkshire, UK
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Posted 14 Jul 2021 8:45 am
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Hi again Earnest,
Glad you see my theory.Skimmed as in reducing the diameter slightly....not sure how tho.If you have the wherewithal to do this let me know the outcome.
My steel is a Mullen RP and not old.I did try initially the E to F and F# test and all was OK! I suppose it's not such a long linear pull.
Regards Dave |
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Jon Light
From:
Saugerties, NY
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Posted 14 Jul 2021 9:03 am
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re: other places that this is an issue:
While trying to retain a plain 6th string to keep the lower lever throw short, I put a 6th string raise compensator on the F lever to counter the 6th string cab drop of the A pedal. In combination with B pedal usage, this was an absolute fail. Even as infrequently as I might combine F lever and B pedal, the return problem, just during the transitional overlap during chordal movement was gruesome. |
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Earnest Bovine
From:
Los Angeles CA USA
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Posted 14 Jul 2021 10:52 am
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| Dave Hepworth wrote: |
Hi again Earnest,
Skimmed as in reducing the diameter slightly |
I don't think this problem, or any problem that you can reproduce so consistently, is caused by friction between pull rods that should slide freely past each other.
Here is a way to check: Mash the A pedal, raising your string 5 to C#. Now raise it to D, but not with the knee lever. Instead, do it by pushing real hard on the raise bar right next to the tuning nut. (You will need some kind of poker such as a screwdriver to do this.) When you release, if it still comes back to C# a few cents sharp, then you know that the problem is not cause by the pull rod that raises to D, since you didn't use the pull rods. All you did was release the tension of the C# pull rod for a moment, allowing something to move a little and come to rest differently when the tension came back on that rod.
On my guitars, when I do this, the C# comes back a few cents sharp just as it does when I use the pedal to raise to D. |
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Steve Mueller
From:
Cincinnati, Ohio, USA
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Posted 14 Jul 2021 1:28 pm
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I think that's called "Floating the changer" when you activate one change on a string and then are on and off a second one with the result not returning to pitch. I had that issue on E9 string 7 in the pedals down position(7 has a temperment comp slightly lowering it), then activating a raise to G# and coming off it while keeping A and B down. It returned sharp. I switched to a heavier gauge string and adjusted the bell crank slots, now it works perfectly and both my steels. Not sure if this would work on the 5th string change you describe.
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2016 Williams D12 8 x 8, 2015 Williams D12 8 x 8, 2023 Williams S12 4 x 5, Milkman Amps, 1974 Gibson Byrdland |
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