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weird intonation issue on new build

Discussion in 'Luthier's Corner' started by danharris, Nov 26, 2017.

  1. IMG_20171122_102209. IMG_20171122_102242. IMG_20171125_200029. Backstory. Long ago, British Colombia Ministry of Forests had a seedling lot, Doug Fir, Hemlock and some cedar around the outside of the lot. the trees were ringed to stress them into mass producing cones. Bark is the life force of a tree, cutting the bark just deep enough to make it think its gonna die but not quite....

    ...Fast forward about 40 years, that old seedling lot is now a Ministry of Forests Fire Base. Quinsam Base. No longer being rung with a chainsaw every couple years, the trees are still sick and going to die. Every spring when the fire crews come back to work, we will fall one or two and mill them up for various projects. Last year some guys made a bike rack, a couple years before we built a fitness area with a big platform and squat rack, chiu up bars, bench etc. Currently, the original building falling apart and the gov is condemning it and building us a new facility.....right in the middle of the old seedling lot, most of the old trees were cleared this summer to make room for the new buildings. Needless to say, many firefighters from the last 30 years are very sad that those trees are gone.

    So i built a Quinsam bass, from the trees from Quinsam Base.

    Heres is my problem. its scaled at 800mm about 30.5". putting 12 @ 400mm and 24 @ 600, But everything is sharp... super sharp like, more than half of a half step. so i backed the saddles off all the way and its good enough but what the heck. the scale is now almost 815mm and its just getting playable...i still have to concentrate on playing flat to make stuff sound nice with open strings. Is this normal and what on earth causes this. It doesn't make sense to me.

  2. charlie monroe

    charlie monroe Gold Supporting Member

    Feb 14, 2011
    Buffalo, NY
    800mm would be the minimum scale length for the G string to intonate correctly. All thicker strings will require more length as their diameter increases.

    Do you have good witness points set?

    Looks like you have plenty of room, move your bridge.
    reverendrally likes this.
  3. What do you mean by witness points? I have drawn dots on the neck for fret markers, if thats what you mean. So ya Ill probably move the bridge, unfortunately the bridge routing is not square, its swoopy to match the slanted jazz bass look.. so the E is as far back as it can go. now funny enough the E is not that bad... its the D and G that are sharpest, i will probably move the 3 that have room back to match the swoopyness of the route and the body. I was not aware of minimal length for intonation. I guess i can get on board with that for now, if that is the case wouldn't changing string gauge change ur intonation too, or is it not enough to hear? interesting...I will be googling this later to get some scientific context.
  4. michaelwayneharwood

    michaelwayneharwood Builder of the Wastelands Commercial User

    May 1, 2014
    Owner Melodious Resonance Constructs
    This may help in understanding the issue, and in calculating nominal bridge saddle compensation measurements.

    Index of /formulae
  5. Yes, changing string gauge will change intonation, however slightly. Also check your nut, it should ramp up toward the bridge so the strings have a single breakover point, you intonate against that point. I had a poorly made nut (by me!) and had some intonation weirdness. I angled the slot up and everything got normal.
    T_Bone_TL and bastav like this.
  6. hey michael, that link is amazing. Index of /formulae There is a few hours of reading there. Its actually perfect for a hobbyist who has no journeyman or boss/teacher to learn from. I moved the bridge pieces back and re strung it with half flats so its still got a bit of grit but silky smooth. I never liked those strings before but they really sound "right" this bass. No pup in there at the moment so the true test of intonation will have to wait but it sounds like its supposed to. Only limiting factor seems to be my fingers. I put some strap buttons on and have a finger ramp/ trussrod cover to install. Over all i'm pretty happy with it. It s doug fir so its really soft, you could dig your thumb nail in a mm or two quite easily, but the tone sounds soft. I wasn't that big of a believer in tone wood until I made a walnut bass and then this little fir one. What a difference.

    Thanks for your help guys, till next time.
    michaelwayneharwood likes this.

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