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I need some help with an intonation problem and was hoping some of you guys might have an answer for me. Ok, so the guitar I built for my dad sounds really nice, except for a small problem with the intonation. When a note is tuned open, and then fretted on the 12th fret, it is pretty much right in tune. The problem is, when the string is fretted on the 3rd fret, the note is off by about an eighth of a tone and then when the string is fretted on the 5th fret, the note is off by a full quarter tone. The biggest discrepancy appears on the low E string (string 6). I believe the frets are level...is this a truss rod issue? I have compinsated the saddle, do I need to do more work on it?   The problem really bugs me because he (my dad) uses the guitar at church a lot and there is a lot of playing using a capo.

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Joe Breault
Merrimack, NH
Perpetual novice

The only reason I can see it being a truss rod issue is that if you have WAY to much relief in the neck, you will be pulling the string further to fret it, thus pulling it sharp.
How is the action? If it's way too high, the same thing will occur. How is it at the first fret? If you nut it not cut deep enough, you do the same thing, pull it sharp when fretted. If, however it was a nut problem, it would be worse on the first frets and get better as you go up the fb.
Without seeign it, I'm thinking relief issue. Try this: fret the first fret with your left hand. With your right hand fret the 12th with your thumb and tap the string at teh 5-7 fret. It should just "click". Meaning you really shouldn't see any space under it but if you tap it it should indeed move a bit.

Did you slot the board for fretting yourself ??? Sounds like its not accurate enough.

If the open and 12th fret are close to being in tune and the 3rd and 5th fret notes are way out, then to me thats a fret placement trouble. No ammount of compensation will fix it. It will likely need a new board.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

The only thing I could add to what Tony and Paul have said.

Is that the neck is not perfectly aligned ?

Or if the fretboard was presloted but installed out of square to the centerline of the neck. or frets rolled when installed but this will show up easy.

     There are a few issues and without seeing the guitar I can't be sure . Along with some of the points brought up It may be a nut or saddle issue also.
     If you did indeed slot the board yourself it may be the slotting was not done right and the slot locations are off.
      Check the nut for square and the saddle. Also is this a steel or nylon? Also is it sharp or flat?
john hall

Sometimes the tang on the wire isn't perfectly centered and the fret will be installed "off". Is this an expensive guitar ( sort of doubt it) or is it a cheapo? Not knocking the guitar but the sort of problem you are experiencing I see mostly on poorly made low end guitars that use cheap wire and don't cut their slots/fretboards acurately. Have you measured the scale length and then recalculated where each fret should be? Then see if the frets are layed out where they are supposed to be. If you don't know how simply measure the scale( nut to center of 12th fret and double it) Then divide the scale by 17.817 that's the calculated distance from the nut to the first fret center. Subtract that number from the scale length and divide again and so on...Sounds to me like either the scale is off or the nut may be cut in the wrong spot/distance.

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Dave Bland

remember...

"If it doesn't play in tune...it's just pretty wood"

The guitar was built from a Martin kit. I doubt they would mis-slot their own fretboards. I suppose the frets could've twisted when I installed them, but I was very careful throughout the build. The neck had locating pins installed by Martin that correspond to hoels on the underside of the fretboard, so unless Martin had a big quirk in their shop, I can't imagine it being installed out of square.

Unfortunately, the guitar is in Maine with my father and I'm not there. I just wanted to get some ideas so that next time I'm up, I could bring the appropriate tools with me.

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Joe Breault
Merrimack, NH
Perpetual novice

Hi Joe,
If everything is basically as it should be in terms of bridge and saddle placement, fret placement, etc, then it could be the strings.

This was always a problem when I worked in retail, but it was especially noticable with lower tension Classical strings. I have seen it on steel strings as well, but not as often.

Take tuner measurements with the current set of strings, and then change them, tune up with the same tuner and do the tests again.

After that?

Good luck!

Howard

One other long shot: you say the notes at the 'third fret' and 'fifth fret' are off: ALL the notes on those frets, or just some strings? If the resonat frequencies of the top or the air in the box are too closely matched to frequencies the string is trying to make, the movement of the bridge can throw the pitches off a little bit. It's usually not much, but can be enough to be irritating. Again, this is a long shot, but worth checking.

Try putting a capo on the 1st fret and check the intonation of all the other frets. See if the 13th fret harmonic matches tone when the string is fretted at the 13th fret. Does the problem still occur? If the octave intonation is good with the capo on the first fret then the problem is with the nut and the nut might be in the wrong position or the slot may have a crown that is not at the leading edge of the nut. If the problem is the same with the capo, ie the 13th fret is good and the 3rd and 5th frets are off, then you might have a problem with the fret slots. Things can go wrong in manufacturing the fret board. It's been known to happen.