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Thread: Intonation Mystery

  1. #1

    Question Intonation Mystery

    Hello all - Im in a bit of a pickle. Background: i know my way around working on instruments, novicely. On my Eastman mandolin - tune to pitch, check harmonic nd 12th fret...they are the same, so that tells me the bridge is proper in place. BUT when I fret, for example, 5th or 7th fret (bot exclusively) they go sharp? Is this a fret problem? Or is the neck bowed r something? Thanks in advance.
    Last edited by EddieFrank; Nov-23-2021 at 2:11pm.

  2. #2
    Registered User sunburst's Avatar
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    Default Re: Intonation Mystery

    Only 5 and 7 are sharp? If it is two frets only, and all strings are sharp at those frets, that is inaccurate frets. If other frets are also sharp, it could be the string nut; either string notches too high or inaccurate placement. If only some strings are sharp it could be the strings or the string set.
    BTW, it is impossible to get all strings of a set in perfect tune at all frets (the closest I've ever accomplished was +/- 3 cents everywhere, and at that point improving one string/fret was going to make it worse at another fret.

    Going through a step by step set up should minimize intonation issues.
    1. check neck relief
    2. check frets, If they are not properly level they must be attended to before a set up can be accomplished.
    3. adjust string height at the nut if needed
    4. adjust action height at the bridge
    5. re-check neck relief under string tension and adjust as needed

    If the frets are in good shape and properly leveled, if the neck is properly straight (a tiny bit of relief is usually good), if the nut slots are correctly cut for string height, if the action is reasonable, and if the strings are relatively new and in good condition, we've eliminated all of those things as the cause, so any intonation problems are the result of some inaccuracy somewhere.

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  4. #3

    Default Re: Intonation Mystery

    Hey thanks for reply - No, it's not only 5& 7, I just used that for example. I will edit the post. Thanks for the tips.

  5. #4

    Default Re: Intonation Mystery

    I can say its probably not the strings themselves, as it is an ongoing thing I've been trying to figure, at least 3 sets worth( meaning probably 4 months)

  6. #5
    Registered User sunburst's Avatar
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    Default Re: Intonation Mystery

    If it's other frets also, I'd check the string height at the nut first.

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    Registered User Mike Conner's Avatar
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    Default Re: Intonation Mystery

    If I understand your description correctly, the 12th fret harmonic and the 12th fret fretted pitch are a good match. Most mandolin bridges have a staggered compensation for the individual string pairs - the A strings saddle point is typically moved back towards the tailpiece. Sometimes, and I have seen this several times on imported guitars, the intonation can improve for frets 3 through 7 by moving the nut slightly towards the first fret, leaving all the other fret positions per the standard calculated distance from the first fret.

    On my guitar and GOM builds I incorporate this compensation in my fret position calculations and cut the slots accordingly. The compensation I use is 0.013" less from the nut to the first fret. When refretting guitars a new nut is usually needed also, and I have a razor saw with a 0.013" kerf blade, so it is easy to saw between the nut and end of the fretboard, file everything clean and smooth, and glue the new nut in the modified position.

    Follow Sunburst's guidance first, and if everything else seems correct, perhaps consider whether moving the nut slightly closer to the first fret could help.

    Before reworking the nut position, I would move the bridge slightly towards the tailpiece, letting the 12 fretted pitch be slightly flat, and see if this moves your other fretted pitches in the right direction. Easy test to perform before starting any surgery ;-)

    If you are anywhere near Murphy NC I would be happy to help...

  9. #7

    Default Re: Intonation Mystery

    Hey thanks for the info - I had thought about trying to position the bridge so that 12th fret is a hair flat - I nearly never play those notes.
    Oddly - Im in Asheville! I love the Murphy area.

  10. #8
    Registered User sunburst's Avatar
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    Default Re: Intonation Mystery

    Quote Originally Posted by EddieFrank View Post
    ...I had thought about trying to position the bridge so that 12th fret is a hair flat - I nearly never play those notes...
    Many people don't play those notes regularly, and I have suggested to them to place the bridge for better intonation on the frets where they do play regularly.

    BTW, I shorten the distance from the nut to the 1st fret on new builds but only occasionally do that to a completed instrument. If the nut slots are cut correctly (so that the string height is the same as the fret height or perhaps a couple of thousandths higher) the first 3 frets are usually no more than 3 or 4 cents sharp, and most people can live with that just fine. The effect on intonation of shortening the fingerboard is pretty much the same as lowering nut slots that are too high.

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    Registered User Mike Conner's Avatar
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    Default Re: Intonation Mystery

    Quote Originally Posted by EddieFrank View Post
    Hey thanks for the info - I had thought about trying to position the bridge so that 12th fret is a hair flat - I nearly never play those notes.
    Oddly - Im in Asheville! I love the Murphy area.
    If in the end you are not satisfied with your results, or if you happen to plan to be in the Murphy area, message me and I'll try to help.

  13. #10
    Dave Sheets
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    Default Re: Intonation Mystery

    Strings too high off the fingerboard at the nut cause this effect, as mentioned earlier. That might not be your problem, but I've seen it on many, many instruments.

    Good luck with it, if it's the problem at the nut, it's an easy fix.

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    Registered User briankwood's Avatar
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    Default Re: Intonation Mystery

    I've found that shortening the distance from the nut to first fret a few thousandths helps this problem. It can be done by cutting the fingerboard. Try experimenting by sliding an E string under the strings against the existing nut. That will shorten the distance to the first fret by half the diameter of the string and give you an idea if that's enough or too much compensation.

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    Default Re: Intonation Mystery

    Most of the time, sharp intonation on the lower frets only is caused by nut slots that are not correctly adjusted. Occasionally I see a nut that has been rounded at the front, causing the strings to come off the nut too far back. I would be at least mildly surprised if a modern factory made fingerboard had been cut off too long. The large scale manufacturers are all cutting their boards with CNC now. I have seen some mis-cut boards on older instruments, also on some hand-made instruments.

    At any rate, the instrument needs to be correctly set up before a diagnosis can be made.
    The steps are, in order:

    1. The truss rod must be set for minimum relief.
    2. The nut slots should be checked and adjusted for correct height and back-angle.
    3. A fresh set of strings should be installed.
    4. The bridge height must be adjusted, then the bridge position adjusted so the 12th fret harmonics match the fretted tones.

    Note: Step 3 is very important. Old strings can raise havoc with an instrument's intonation.

    It is only if you still can't get it dialed in after the above that you get out your rule and start measuring. Cutting, if necessary, should be left to a professional.
    Measure not once or twice, but several times before cutting.

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    Registered User Tom Wright's Avatar
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    Default Re: Intonation Mystery

    Of course eliminate the likely high nut and use new strings. But shortening the fingerboard is filing, not cutting, at least in my case. I removed the nut, made a sanding block on a stout file, and aimed at about a business card change, or ten thousandths. I snuck up on it with a couple of tries on my third mandolin, as the ebony was very tough. On three instruments, .010" was just right.

    It is not a problem to go too far, as one can shim the nut backward easily. I find this solution better than trying for an overhanging nut.

    I only speculate as to the cause, but suspect the change in deflection angle that happens only at the nut, because the upward-angled string is bent downward. This does not occur between frets, only from open to first or second fret.

    A strobe tuner will tell the tale. If new strings and very low slots (angled upward) don't solve the issue, consider shortening. I hear Taylor does on their guitars.
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    Registered User sunburst's Avatar
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    Default Re: Intonation Mystery

    Quote Originally Posted by Tom Wright View Post
    ...I only speculate as to the cause, but suspect the change in deflection angle that happens only at the nut...
    The cause is string stiffness. When deflected from straight, the stiffer the string the more is stretches and thus pulls sharp. That is why heavier gauge strings need more "compensation" to play in tune (and why nylon strings require much less compensation).
    When we deflect a string nearer the end of it's vibrating length (the nut or the bridge) it is stiffer than it is nearer the middle, so when fretted on the first few frets (nearer the end) it pulls sharper than it does on upper frets (nearer the middle). That is why strings fret sharp on lower frets; they are nearer the anchor point so the string is stiffer.

    (BTW, files cut.)

  19. #15
    Registered User Mike Conner's Avatar
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    Default Re: Intonation Mystery

    To be clear(er), I have razor saws with 0.010" and 0.013" kerfs. If the original nut is intact, it's easy to use it as a guide, rubbing the saw blade against the nut while cutting down through the fretboard. This is much more reliable than removing the nut and attempting to use a file to remove the material parallel to the frets and keep the end at 90 degrees to the neck surface. Easy clean up with needle files after sawing.

    Sunburst's explanation of why this compensation is needed is spot on IMHO. That's the same reason for the pitch going sharp when the nut slots are too high - the string is getting stretched sharp even more if moving a greater distance. With the typically short mandolin scale lengths, a small change can have much larger effects than with longer scales (like guitars).

  20. #16

    Default Re: Intonation Mystery

    Looks right, John. On a zero fret design, I guess a new, larger fret could be put in and crowned asymmetrically, no?

  21. #17
    Registered User sunburst's Avatar
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    Default Re: Intonation Mystery

    Quote Originally Posted by Richard500 View Post
    ...On a zero fret design, I guess a new, larger fret could be put in and crowned asymmetrically, no?...
    I don't really know, I normally don't work with 0-fret instruments. There's not much to be done to adjust zero fret, but I suppose crowning it off-center is a possibility if it starts out big enough.

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    Default Re: Intonation Mystery

    If you put in a larger zero fret you raise the string height at the nut, so to speak, compounding what you are trying to eliminate. I see zero frets larger and usually replace them with the same size as the rest of the frets. Makes more sense to me. They can always be replaced if they wear, and will give a a better action.
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  23. #19
    Registered User briankwood's Avatar
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    Default Re: Intonation Mystery

    Quote Originally Posted by pops1 View Post
    If you put in a larger zero fret you raise the string height at the nut, so to speak, compounding what you are trying to eliminate. I see zero frets larger and usually replace them with the same size as the rest of the frets. Makes more sense to me. They can always be replaced if they wear, and will give a a better action.
    Normally a larger 0 fret doesn't make sense, as you say. In this case though, I think the idea of a larger fret that is selectively reshaped has some merit, assuming you can start with a large enough fret. Most mandolins don't have 0 frets anyway, though.

    So, as mentioned before, I suggest using wire of whatever diameter that will slide tight under your strings and against the nut. If you need to use smaller dia. wire you can shim it up with a feeler guage blade tight enough so the strings won't buzz. That will tell you a lot before you do anything else. You can test intonation and play your mandolin like that as long as you like before deciding to move on to actually changing things. When you use wire, 1/2 your wire diameter is the amount you are shortening. You can estimate if you need to change more or less from that, or maybe decide your intonation problem isn't related to that at all.

  24. #20

    Default Re: Intonation Mystery

    Actually, adding a wire is what I did, although not for pitch correction. It was to raise a zero that someone had leveled even with the others, which doesn’t work very well. That is, I did it to get 0.010 more height, which turned out to be one of the wound string diameters. I mentioned it here, but the more serious folk said I should have done a proper repair by replacing the fret. Been playing my accretion for a couple of years, unaware that I might have fixed a problem I couldn’t hear!
    Like the rich guy in Moliere’s Bourgeois Gentihomme, I was speaking prose without even knowing it.

  25. #21
    Registered User sunburst's Avatar
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    Default Re: Intonation Mystery

    Quote Originally Posted by Richard500 View Post
    ... a zero that someone had leveled even with the others, which doesn’t work very well...
    When done correctly it works fine (until it wears down), especially with a small amount of relief in the fingerboard. It is essentially the same as using a capo.

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  27. #22
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    Default Re: Intonation Mystery

    Zero frets are in right now. It's partly due to successful marketing by the manufacturer of "Zero-Glide" nuts . . . which I have dealt with once on a customer's instrument, and am not particularly impressed with.

    I lived with a factory installed zero fret for years on my first good electric guitar, which was a Gretsch that I bought new in 1971. I saw no advantage to it at all.

    At any rate, if you understand the geometry of fretwork, a zero fret should be the same height as the rest of the frets, as long as the neck is straight and everything else is in order. If it is higher than the rest of the frets, it will cause the same problems as nut slots which are not correctly adjusted for height. The intonation will be sharp on the lower frets, and the instrument will be harder to play in the first position.

    I will mention that I rarely see a new instrument that has had the nut correctly adjusted at the factory. And many of the handmade instruments I see have the same problem.

    Keep it simple. Have the instrument set up according to the standard procedure listed in post #12. Chances are 95%+ that everything will come in where it's supposed to be. If that doesn't take care of the problems, then find a luthier who understands the math and geometry behind fretwork and intonation. Let him take the measurements and find the best solution.

    Untrained instrument owners taking files, sandpaper blocks, saws, chisels, etc. to the end of an instrument's fingerboard is an invitation to a big repair bill, and sometimes cosmetic damage that cannot be reversed without major work.
    Last edited by rcc56; Nov-28-2021 at 10:48pm.

  28. #23
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    Default Re: Intonation Mystery

    Quote Originally Posted by sunburst View Post

    (BTW, files cut.)
    Some of mine don't . . . anymore . . .

  29. #24

    Default Re: Intonation Mystery

    “As long as the neck is straight and everything else is in order”
    Well, yes. And there are luthiers who are skilled in this (obviously high skill) area. But there are tens of thousands of mandolins out there that are, because of low value, ignorance, ownership by amateurs, passage of time; not going to get optimum maintenance. And we also have been told that even moderately expensive, brand new instruments often are not set up optimally at the factory, let alone to a purchaser’s preference.

    I’ve been, as a hobby, salvaging very old mandolins that are otherwise wall-hangers or trash, and amateur, possibly wrong repair is appropriate. Necks are very often not straight, nuts originally too high, parts missing, almost inoperable tuners, etc. Getting to some semblance of playable is an objective, and even hearing them awake after very long slumbers. Most have had little or no prior use, and certainly no maintenance, which is slightly sad, but hardly tragic.
    The best instruments, for the best players, should be serviced by the best qualified; leave the rest to us duffers.

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