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Thread: how to fix this intonation issue ?

  1. #1
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    Default how to fix this intonation issue ?

    First this is not a mandolin question as mandolins usually have floating bridges, so I don't have issue like the one below:

    I bought a brand new guitar (classical, nylon string) last December. After playing for 3 months, I realize that the intonation is not that good, I can heard notes and chords being a bit off-tuned. At fret#12, the chromatic tuner shows that all the 6 strings are sharp, and I can hear the notes being sharp too.

    So I measure A = nut to fret#12 (the fret, not the wood)
    and B = fret#12 to the tip of the saddle where the strings make contact
    I found B = A + 0.5mm approx.

    From my tenor ukulele building experience, I had to give B = A + 2.5mm so I have room for saddle compensation and its intonation at fret#12 is near perfect, the tuner shows exactly one octave higher.

    Since the guitar has fixed bridge, what would be the best recommendation to remedy this intonation issue ? (without having to unglue the bridge and reglue it at the proper position, I would create a mess on the top sound board if I had to do it this way).

    BTW, this guitar has an under the saddle transducer (classical , electric).

  2. #2
    Robert Fear Folkmusician.com's Avatar
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    Default Re: how to fix this intonation issue ?

    Hello,

    The first step here would be to make sure your action is where it should be. If you can lower the action, it may be enough to get the intonation in. Changing strings to a lighter tension will also help.

    Aside from this, warranty it or doing bridge work would be the fix. If is has a saddle slot that can be filled and recut, I would go that route rather than re-position the bridge.

    How many cents off is the intonation?
    Robert Fear
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    Default Re: how to fix this intonation issue ?

    Quite possible that you need a lighter gauge string, Also since it has a fixed bridge maybe the saddle is tilted a bit forward....I`ll let some of the builders chime in but I would check those two things first...Keep us posted and let us know what you find out,....

    Willie

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    Default Re: how to fix this intonation issue ?

    One empirical method for figuring this stuff out is to remove the saddle and replace with a series of 6 triangular pieces of something hard that will bridge the slot. Move these mini-saddle chunks around until the intonation makes you happy. If you can somehow carve a bridge that will accommodate the compensation that process reveals, go for it. If not, do whatever the usual fix is for the issue. Fill and recut, or whatever is appropriate.
    Stephen Perry
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    Default Re: how to fix this intonation issue ?

    The strings on my guitar appear to be the normal tension strings. I have tried (on other guitars) the hard tension and the light tension ones so I can tell. I will try a light tension string to see how better it gets.

    How many cents off is the intonation?
    I do not quite understand the word "cents" here, but I guess it mean how many percent?
    If 100% off mean it sounds 1 full note off, then should be 25% as my e-tuner shows around 1/4 step off

    The saddle slot fit the saddle snuggly, so the saddle stood very straight.

    One empirical method for figuring this stuff out is to remove the saddle and replace with a series of 6 triangular pieces of something hard that will bridge the slot
    I really understand the description of the empirical method, and I will use it to determine the best saddle position for best intonation, per string. I will use a small triangular stick , in place of the saddle, laying on top of the bridge, sort of a floating bridge as on a mandolin. Thanks for the suggestion which so obvious in the mandolin world, but never occur to me when holding a guitar !!!

    somehow carve a bridge that will accommodate the compensation
    This gives me a good hint, I believe it means carving a saddle, not the bridge. I plan to glue on the side of the saddle another piece of plastic to make it thicker (leaving the part that dip in the slot intact, so it still fit in there). then I will file an angle at the contact point such that it get moved farther away from the neck, ideally to its correct position. The worst thing that can happen is I lose a saddle and have to get a new one.
    If I can make it, it will look pretty weird, but the intonation should be much better.

    Thanks for all the suggestions here. I will post the "uggly" photo of my saddle.

  6. #6
    Registered User Tom Cherubini's Avatar
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    Default Re: how to fix this intonation issue ?

    If your saddle has an ivory (plastic) insert there is something you can do. Usually those inserts are a bit over 1/8" thick. What I did on a nylon-string classical guitar was to file little slopes on the top of the insert at a 45 degree angle just wide enough for one string. If I needed a shorter dimension between the saddle and fret 12, the highest part of the slope was toward the fret board. This has the effect of moving the spot where the string crosses the saddle by the thickness of the ivory insert.
    To lengthen the distance from the 12th fret and the bridge do the opposite. I tuned every string separately for perfect pitch.
    It sounds like this method will correct the 0.5 mm discrepancy you have.

    Tom
    So chi sono.

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    Default Re: how to fix this intonation issue ?

    I don't know what an ivory insert is. I guess this must be some sort of thin piece of plastic.
    I have an old white saddle that I can cut pieces to be glued on the guitar saddle to make it thicker.

    About the idea of using 6 triangular pieces, I just spent 10 mins going the easy way. I took a bamboo chopstick with square section, cut lengthwise at 45 degree and I got two long triangular sticks, as the moving bridge.

    Using this one, I determined that the strings contact points should be moved about 2.5mm further away from the neck to get "perfect" intonation at fret#12, all the 6 strings.

    I just glued the pieces cut from the old saddle on to the new saddle, it's now 3mm thicker at the top, the glue should dry tomorrow for me to file the slopes.

    One stupid question though: how come guitar/ukulele makers tend to make this same mistake ?
    We all know that we need room for saddle compensation, but some are built with very little room.
    I have read the same thing in an ukulele kit instruction: glue the bridge such that fret#12 is exact at the center between the nut and the saddle !!! this means no compensation and bad intonation.

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    Default Re: how to fix this intonation issue ?

    This morning, I file the slopes on my modified saddle and do a quick test run.
    The string contact points now move away from the neck by 2.5mm approximately, and fret#12 intonation is perfect, shown by the e-tuner (which shows a needle with a screen light, amber if off tune, green if in tune).
    Since my guitar has an under the saddle transducer, I got to make sure the extra pieces I glued on the saddle do not touch the surface of the bridge, this way, the saddle is still in full contact with the transducer.
    The new saddle does look weird, but it's important to get good intonation. No one looks at the saddle when I play the guitar.
    Here is the "triangular stick" that I used to determine the proper saddle placement:
    Click image for larger version. 

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    and here is the modified saddle:
    Click image for larger version. 

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    Default Re: how to fix this intonation issue ?

    That's a bit odd! I'd be filling and cutting.
    Stephen Perry
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    Default Re: how to fix this intonation issue ?

    Just for information, one hundred cents make one semitone, twelve semitones make up the chromatic scale. Cents are figured logarithmically, so it is not exactly percent, but close enough. If your strings are set at a reasonable height then yes, your bridge is located in the wrong spot. If you want your transducer to work correctly you need to fill and recut the saddle slot, which will mess up the string angle a bit, but help restore the downward pressure on the transducer. It seems a bit counterintuitive but the longer nylon strings on a classical guitar should need less compensation than the tenor uke. (I also build tenor ukes.) A quarter tone off would have me seeking a refund.

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    Default Re: how to fix this intonation issue ?

    Hi Philstix,

    thanks for the explanation. Based on this info, my guitar is about 30 cents sharp as shown by the etuner (which show the number on it). I always set my instrument for low action, that's the first thing I do on any guitar/ukulele or mandolin I get.
    I understand the need for the saddle to put pressure on the transducer, I have not test plugged in yet.
    Visually, the contact point move 2mm away from where it was. And the transducer is the flexible kind, not the hard one.
    I am hoping the pressure is still strong enough to work well.
    My main concern is the string pressure has the tendency to pull the saddle away from the neck and this could either:
    1) break the saddle OR
    2) crack the bridge
    I may have to shim under these "sticked out" pieces to counter this undesired pull. This way, the entire saddle "assembly" still get vertical pressure to the bridge. This entire work only modifies the saddle so far.
    If this turns out to be bad at the end. I guess I have to unglue the bridge and re-glue it at the right spot.

    I should have checked the intonation before buying this guitar !!! I was so excited because it really fits my need:
    1) thinner, easy to hold, 1.75" nut width
    2) acoustic / electric and it sounds really good plugged in
    3) lower cost (new for 300$ and I got it for 240$).
    Most of the guitars at this price range I tested have this kind of intonation issue.

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    Default Re: how to fix this intonation issue ?

    Oh well, those little pieces that I glue on the saddle could not hold under string pressure. The glue gave up and they fall out.
    I am back to the original saddle now, with about 1mm more for compensation, not perfect but better than it was.

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    Default Re: how to fix this intonation issue ?

    If you put something on the bridge to raise the string higher above the frets than the existing saddle lifts them, that will affect the intonation. You have to push the higher string down farther and harder, and that stretches it -- pulls it sharp. Good luck.

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    Default Re: how to fix this intonation issue ?

    Filling and re-routing the slot would certainly be the neatest option - I have remedied intonation issues that way on steel string guitars. However, I was once asked what I could do with a cheap 1/2-size steel-string with sharp intonation - it was bought as a conveniently sized and priced knockabout guitar for travelling on a pushbike. Perhaps for someone more router-happy and jigged-up than me, moving the slot would have been the quickest solution but, for me, that seemed a lot of hassle for a 30 guitar. My solution was to glue (with cyanoacrylate) an entire plastic saddle blank onto the back face of the original saddle, but positioned such that the base of the added saddle was clear of the top of the bridge. I then pared down the top of the added saddle flush with the original saddle, resulting in a saddle with an upside-down 'L' cross-section, double thickness at the top. I then shaped the top of the saddle to give the correct string heights and compensation. The guitar looked a bit odd on close inspection, but it sounded good (for a 30 guitar) - and the owner was happy.

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    Default Re: how to fix this intonation issue ?

    Filling and re-routing the slot would certainly be the neatest option
    This is probably the way I have to take as I like this guitar so much. However, I do not have the skill for doing this. Filling is the easy part, re-routing is difficult for me as I don't have the proper tool to do it. I will take it to a luthier to do this work.

    glue (with cyanoacrylate) an entire plastic saddle blank onto the back face of the original saddle, but positioned such that the base of the added saddle was clear of the top of the bridge
    This was pretty much what I did but using small pieces instead of an entire blank saddle. And I used expoxy which turn out to be a bad choice as it does not stand up the pressure and gave away.

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    Default Re: how to fix this intonation issue ?

    Yesterday, after going home, I found in my tool box an used blank saddle (and also a brand new saddle origianlly shipped in the box for this guitar, and a L hex wrench !!!). I don't know why the L hex wrench is shipped with this guitar as it has no truss rod to adjust.

    I lay the used blank saddle right behind the guitar saddle and cut the height so it is just a tiny bit taller than the guitar saddle (no glue yet). Then I tune the strings to tune. This alone brings the contact points to where I wanted and the intonation is near perfect. Then I test it plugged in, the pressure on the transducer is less as I had to crank on the volume to hear it loud thru the amp. To get back the normal pressure on the transducer, I have to glue the blank saddle to the original one making sure that
    the base of the added saddle was clear of the top of the bridge
    .
    I will put a very thin shim under the added saddle when I glue it, to create a clear space and to make sure it does not get glued to the bridge accidentally. Epoxy did not do the job, I just bough from Orchard something called "Plastic Welder", the bonding strength rated at 3500 PSI. Here is a link to it:
    http://www.ebay.com/itm/Devcon-Home-...item3f1cf046e7
    Don't know if this is a good glue for this job.

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    Default Re: how to fix this intonation issue ?

    I tested this glue on two pieces of hard plastic, about the size of half the saddle height.
    It got set in 15 mins, then I let it cured for 24 hours. The bond seems to hold pretty well. I can't break it off without breaking the plastic itself. I will use it on my guitar saddle this weekend.
    The goal is to restore the saddle pressure on the transducer and make the "enhanced compensated saddle" look better.

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    Default Re: how to fix this intonation issue ?

    KMM...If this is an oval hole guitar it may have a truss rod adjustment inside of the oval hole and not up at the peghead, look it over and see if you see a hex screw head inside of the oval hole...A lot of newer guitars are doing this now days, namely Martin which never had a truss rod for many years....

    Glad you seem to have the bridge problem fixed....

    Willie
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    Default Re: how to fix this intonation issue ?

    Willie,
    thanks for the suggestion about the russ rod. I looked thru the oval hole under the neck and IT DOES have a truss rod adjustment screw. And that's why the hex L wrench is included in the box. I feel so relieved knowing this.
    I glue the second piece of saddle on the back of the first one using "glue welder", with the original saddle in its slot, strung up at low tension to keep both pieces together then got interrupt by a 3 days business trip. I returned today and did some filing to get proper slopes and bingo, the intonation is now near perfect. I am very happy with the result.

    This is a very good trick for fixing guitar with not so good intonation.

    I will use this method on one of my new ukulele I bought, only two strings are sharp (C and E strings).
    I also have an Ovation mandolin (MCS-148) that has been setup by a pro luthier to address similar intonation issue. This mandolin has a fixed bridge like a guitar / ukulele. Even with a pro setup, I can hear the intonation is off for the E and A strings. I now know what to do with this, a bit tricky for Ovation as the saddle consists of 4 triangular pieces with the tip pointing up. And the entire saddle assembly contains the transducer in it !!!

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