Intonation problem and string gauge.

Discussion in 'Acoustic Heaven' started by LowCaster, Feb 28, 2020.

  1. LowCaster

    LowCaster Tele-Afflicted

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    A friend of mine has an old and cheap acoustic dreadnought from the early 90's ( Hohner HG-3000 Made in Indonesia, laminated mahogany). Everything was off, strings unchanged from the first day as far as I can tell. I am trying to make it playable again (or maybe for the first time). Among other minor repairs I did the following:

    Filed the nut slots deeper.

    Adjusted the trussrod, neck is straight.

    Leveled the frets to take care of wear and high frets.

    Replaced the straight plastic bridge saddle with a new compensated graphtech saddle and lowered the action to 2.5mm (12TH fret).

    It was strung with really big strings like 13 or 14s'... Hard to say with the rust...

    The idea was to lower the action and use a lighter gauge of strings if possible. So I replaced the strings with a set of 13-54. The action is low and it plays smoothly.

    My problem now is that the intonation is off, the note played at the 12th fret is flat by nearly 10cent . The beginning of the neck is OK but you can hear it when playing from the 8 or 10th fret and it goes worth .

    How can I correct this?

    I think about raising the action a little, or trying a higher string gauge like 14-59 (those are not stocked by guitar dealers in Paris, I would have to order) or 16-56. Maybe need a different tuning then. Would this be enough? I don't want to sacrifice playablility either. Any advice is welcome.
     
  2. rangercaster

    rangercaster Poster Extraordinaire

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    Put a noncompensated saddle on there... see if that helps ...
     
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  3. LowCaster

    LowCaster Tele-Afflicted

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    I might go as far as putting back the original plastic saddle. However as I see it, the compensation only affects the B string. A noncompensated saddle could help the intonation of the B string, not the E string, where the position is alredy optimal (forward). The graphtech has the same pattern as that one:
    [​IMG]
     
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  4. Obsessed

    Obsessed Telefied Ad Free Member

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    Which string is that far off from intonation? Most acoustics are strung with 12s, so that might be a place to start as well.
     
  5. LOSTVENTURE

    LOSTVENTURE Tele-Afflicted

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    You realize that fret placement is critical in order for intonation to be correct. If the frets were not properly placed at the factory, nothing you do is going to fix the problem. Unfortunately, I've seen this problem a few times, usually with the less expensive acoustics.
     
  6. Obsessed

    Obsessed Telefied Ad Free Member

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    Just read your new post. The B string spot on the saddle could be modified.
     
  7. Obsessed

    Obsessed Telefied Ad Free Member

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    +1 I have seen that as well setting up beginner guitars for friends and relatives. A very good possibility.
     
  8. LowCaster

    LowCaster Tele-Afflicted

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    All the strings are similarly off, flat when played at the 12th fret (and around). Of course it is most annoying for the high E when you want to reach those high notes.
     
  9. Ditchgator

    Ditchgator TDPRI Member

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    Guitarnutbuster.com says that their product solves tuning problems no matter what guage of strings, term or no, acoustic, electric etc...
    Reviews and videos are encouraging.
    Kinda ugly tho.
    No modifications at all. Huh.
    Kinda pricey, but transferrable to whatever guitars you've got.
    Just goes to show that problems are the mother of invention. ;):cool:
     
  10. LowCaster

    LowCaster Tele-Afflicted

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    :eek:

    I'll try to check the fret placement (good challenge for me), but the neck seems well made. I'd tend to suspect the bridge placement instead. Anyway I won't try to relocate the bridge either. Or am I?
     
  11. Obsessed

    Obsessed Telefied Ad Free Member

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    Bummer. I would say that a custom made nut is your solution, but others on this forum are much better qualified to come up with a solution. Hang in there, someone will help.
     
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  12. PhredE

    PhredE Tele-Meister

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    LowCaster,

    Just want to toss out a couple of things (that, I hope, weren't covered already..). It would be nice to see pics of nut, saddle+bridge, areas of fretboard where the notes are a problem.

    1). You leveled the frets, but did you follow with a good crown (and polish)? 'Flat' (uncrowned) fret tops can be a cause ..

    2). Have you checked the bridge condition, saddle fit, etc? Wobble of the saddle could be a problem, and a lifting bridge? (/ugh)

    3). Sounds like you swapped the nut out -- what does new one look like? (I ask because I also had a similar situation arise after I changed a nut out (on the high E), it turns out (despite my best efforts..) I didn't angle the string slot downward enough (nor did I sand/file enough on the tuner-facing side of the nut).. net result: the string was traversing down to the tuner from an almost flat travel across the string slot in the net -- this proved to be the cause of a couple related problems. After I shaped and sanded properly these problems went away (!). Might be worth double-checking..(?)
    See: https://www.classicalguitardelcamp.com/viewtopic.php?t=90982&start=15

    (Look for the post by Trevor Gore date/time: Friday 14 November 2014, 23:44 pm)
    I ended up filing my nut as in the 4th photo from top) -- it is very 'thin' in the lengthwise body direction [top of headstock to beginning of fretboard direction). It is same size at base in the nut slot, but I filed it an angle to where it is parallelogram shaped from a side profile, but has a top 'flat' surface of about .125"
     
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  13. Freeman Keller

    Freeman Keller Friend of Leo's

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    First of all you need to know that your saddle slot is in the correct location to even allow compensation. My general rule of thumb is for the center of the slot on the high E side to be at the scale length plus about 1/16, on the low E side I like plus 3/16. That assumes a 3/32 slot and should give you enough adjustment for most string gauges. Don't just assume its in the right spot, remember that group of Martins where it is at the scale length and the only way to get it right is fill the slot and reslot it.

    My trick for compensating an acoustic guitar saddle is to start with it flat on top. Get the action close to the final value but maybe 10 thou high. String it with the strings you are going to use. Now take a short piece of thing wire - a piece of B string (16 or so thousands) works well, put it on top of the saddle and tune up. Move the string until the intonation is as good as possible, mark both sides of the string with a pencil and then do the others strings. When you shape the top of the saddle make the break point for each string between those lines.

    Last but not least, you can actually calculate where the break point should be for most string sets and scales using this

    https://www.liutaiomottola.com/formulae/compensation.htm

    Some minor points to remember - the thicker the CORE wire of the string, the more compensation it needs. The high the action the more you stretch the string and therefore the more compensation you need. I have a jazz playing friend who likes his guitar set very slightly flat - he says he can always sharpen a string when he frets it but he can't make it flatter. And audiologists tell us that most people can hear 5 cents of sharpness or flatness but only few can hear less.
     
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  14. LowCaster

    LowCaster Tele-Afflicted

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    @PhredE : The top of some of the frets is still a bit flat, I crown lightly, to avoid ruining the frets, I’ll give it another try next time I take the strings off. However the problem is present everywhere, not like one flat spot that would make the pitch shift on one note, and after a closer look I don’t think that’s the problem.

    IMG_0656.jpg

    Here is the bridge. Nothing moves, the saddle is a good fit in the slot.

    IMG_0657.jpg

    The nut is original (pure plastic), I filed the slots to adjust the height. They don’t look nice with graphite powder on, but I think they are OK. I’m sure the nut is not the problem, I checked intonation using a capo at the second fret. There is still the same difference in pitch between the harmonic and the fretted note at the 14th fret (12+2).

    IMG_0654.jpg

    This is the reason why I hope that I can correct the intonation by using thicker strings and higher action. But that would make the guitar harder to play.

    5 cents would be OK, but it’s 10 cents flat and I can hear it clearly.

    I will take the time to make the measurements and calculations and report what I found.
    Thank you Freeman Keller for all the precisions.
     
  15. PhredE

    PhredE Tele-Meister

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    Lowcaster,

    Thanks for the info and pics. I am still examining these...
    Hopefully, someone else more skilled than I chimes in too.

    Brainstorming a bit, maybe (??) it might be worth a try to swap back to straight (non-compensated) saddle AND try a different gauge of string? I like Freeman's suggestion above too; maybe you could try some of both and then check intonation say, on the b string or e string ?
    Any reason you wound the E and e strings inward on the tuner peg (instead of the other way)? Just curious.
     
  16. LowCaster

    LowCaster Tele-Afflicted

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    I should have mentioned that I tried 12s’ first, and it was worse (flat at the 12th fret, more than 10cents), going to 13s’ improved very little and did not solve the problem. Maybe 14s’ would help to gain a few more cents enough to make it usable?

    I prefer the three tuners on each side to act in the same way when tuning. It didn’t cause any tuning issue so far.
     
  17. Dreadnut

    Dreadnut Tele-Holic

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    Important question to consider: did it have the intonation issue before you worked on it?

    If not, my first try would be switching back to the original saddle.

    Also a point of clarification: adjusting the truss rod should not make the neck straight; it should have a slight camber to it. The truss rod adjustment makes for more or less camber; when adjusted properly, it should show equal spacing of the strings off the neck at the first fret and the 12th fret when pressing down at the 6th fret.
     
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  18. Freeman Keller

    Freeman Keller Friend of Leo's

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    I'm assuming that means that when you play the harmonic at the 12th fret it is in tune with the open string only one octave higher. When you fret the 12th fret the note plays flat. That means you have too much compensation for that gauge of string. The harmonic will always be in tune, but as you fret a string two things happen. First, you stretch it pulling it down to the fret - that raises its pitch. Second there is some bending stiffness in the string (the classic formula that we use to calculate frequency and tension based on length and material properties assumes an "ideal" string). We "compensate" for that by making the string longer from the fret to the saddle - it is still in tune played open but is not a bit longer when fretted to the frequency drops.

    The amount that the string sharpens when stretched does depend on the core diameter - the winding is just there to add mass. The fatter the winding the more it goes sharp so the more we need to compensate - that is why the unwound 2nd string needs more compensation than the 1st or 3rd (which has a smaller core). That explains the little notch for the B string.

    You are correct that if a string is playing flat when fretted you can raise the action (which will stretch it more sharpening the note) and/or go to a string with a fatter core (which will also raise the pitch) but both of those things will make the guitar harder to play - the eternal compromise. I would start with very careful measurements of what you currently have - measure the nut to 12th fret carefully and double - that will give you the scale length that the guitar was built to. Measure carefully to the break point of the saddle - that is the compensated scale length. Go to Mottola's calculator and enter the information from your strings and the actual scale length - that is the calculated compensated scale - it is theoretical but I have found it to agree remarkably well with guitars that I feel are properly compensated.

    If there is a significant difference then you might need to move the saddle. That is not trivial but it happens - some guitars simply have them in thw wrong place. My rule of thumb as I said before is that I locate acoustic saddles with 1/16 of compensation on the high E and 3/16 on the low - with normal string gauges and my little wire trick I can get the intonation within 5 cents - I've even done this on my 12 string guitars - the saddles end up looking like a rip saw blade but the guitar plays in tune.

    Here is worst case option - I have filled the slot with a piece of rosewood and am routing a new saddle slot with the bridge on the guitar.

    IMG_2724.JPG

    Actually this is being done for a different reason - this guitar had one of those adjustable saddle assemblies and I'm converting it to a solid saddle.

    Anyway, take the measurements and report back
     
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  19. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    I'm far from an expert, but I'm thinking that if the frets are not located properly, they are probably all incorrect together, since they were put there by machine. I'm wondering if the bridge itself can just be removed and glued back down closer to or further away from the neck. in other words, the frets relative to each other might be exactly where they need to be, but the bridge might have to be moved.
     
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  20. howardlo

    howardlo Tele-Holic

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    Seems like a lot of time, cost and effort for a guitar that probably wasn't that great to start with (unless it has some sentimental value).

    Especially when you can get a really nice playing and sounding solid top Yamaha FG-800 for less than $200.
     
    Last edited: Feb 29, 2020
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