Sharp along the board but perfect at 12th

[Mandoak]

I have noticed an intonation problem with my manolin.
It is perfectly tuned on 1st and 12th fret but anywhere from 2nd to 11th frets notes are slightly sharp (the dial thing goes up to 3/4 way to the right while showing the note) by varying degrees. It is more or less the same for all 4 strings.
1. Does this mean my fingerboard is curved?
2. If the first answer is yes, then I guess truss rod has to be adjusted (right?). Should it be tightened or losened?
3. Can I do this myself (it is a KM150)?
I searched the forum and strangly enough there was no such question previosuly (this things only happen to me !)
Thanks in advance
Mandoak

[sunburst]

It probably means the strings are too high at the nut, but it could be other things...

FWIW, we can move the bridge for good intonation at the 12th fret regardless of what intonation problems an instrument has, but that does not necessarily mean it will be in tune anywhere else. Any time you hear or read that setting the bridge for correct intonation at the 12th fret means you're done with setting intonation, whomever said or wrote that is not entirely correct.

[Paul Hostetter]

The easy-to-ascertain other thing it could be is that there's too much distance between the nut and the first fret. To check this, capo to the first fret, move the bridge so the intonation at the new 13th-fret "octave" is correct, and then check intonation in between.

[Willie Poole]

You should be able to sight down the fret board and see it it is bowed to excess, if it is get a luthier to correct it because if you have never tried doing that you could be causing some damage and there are probably other problems along with that...Pauls advice on checking it with a capo is great advice....

[Folkmusician.com]

Mandoak,

Do you know what year the KM-150 is?

Does it look like this?

[Paul Hostetter]

You should be able to sight down the fret board and see it it is bowed to excess...

I seriously doubt a bowed neck could account for this issue. The capo check takes but a few minutes.

[Mandoak]

Thanks everybody for your comments and answers.
Willie I could not be sure even with magnifying glasses.
Paul I did the capo test and problem was still there. Although reading your reply again I jsut realized that I did the test wrong. I just caped the 1st fret and retuned without moving the bridge.
One other observation that might be useful to somebody else: I tune CGDA. As part of these tests I tuned back to GDAE and problem was significanlty less.
However your reply made me curious about effect of nut so I changed the nut I had made for the one that came with the instrument originally. problem went away! The one I made was exactly the same height and width so the only difference must have been the dept of groves. The original nut sound is a bit dull (or may be it is just knowing that is plastic) so I guess now I have to make another nut but this time correctly (I noticed you have alot of great article on your site including one about nuts. I have to read it before starting).

Robert yes the mandolin originally looked exactly as the photos you posted. Altough I have changed the bridge, tail piece, nut, tuners and revoved the finish complegely and put a different finish. It has imporved the sound (still not happy with the fourth set of strings- sound too muted).

I am amazed that dept of groves can make so much difference. I am glad I posted this question before mesing up the truss rod. I have learned more from this fourm than I can describe, thanks.

[Dale Ludewig]

It may not be the depth of the nut slots, but the angle. You should check that they're sloping down toward the headstock so their contact is on the fingerboard side. Otherwise, you are in essence, changing the nut position.

[sunburst]

Correctly cut nut slots will slope back toward the tuners, as Dale says, about half the angle of the string across the nut. The proper depth is level with the frets. In other words, the strings should rest in nut slots so that the bottoms of the strings are the height of a fret above the fingerboard. There are easy ways to check that, many of us do it like this.
If, as I suspect, your slots in the new nut are not deep enough, you will not have to make a new one; only deepen the slots to the correct depth.

[John Kelly]

John, that's an excellent set of pictures and accompanying text in your reference to setting up a nut. Everything here that someone needs to be able to get that end of the instrument playing at its best.
Many thanks.

[Mark Levesque]

Mandoak,

You have changed the strings, right?
I know of a guy who sent his guitar back to a builder for a similar problem and the builder just changed the strings and it was fine.

[Rob Meldrum]

John had it right on. Great pictures and explanation.

Rob

[Walt Kuhlman]

Lower your bridge if possible
Change our strings to a lighter gauge

You can check the nut as it may not be cut deep enough, but if this where the case the first fret would be sharp as well.

Walt

[Mandoak]

Yes I have changed the strings. As a mater of fact I tried different types all the way to thin wires to see how it would sound and if it can imporve (thin wires sound nice but went out of tune every 2 minutes). My mandolin is an experimental lab for me (I have less then 2 months experience with mando so everything is new and really fun).
I have read the articles you guys have generously put on your sites (thanks) regarding making a correct nut.
Just one questions: is there a technique in making sure you are cutting to the right dept or is it trial and error and a lot of patience?

[John Kelly]

The way I was shown to get an initial height on the nut is to take about three inches of ordinary pencil and plane it in half along its length, so that the lead is visible all along it. Place this on the frets, lead down, and draw it across the nut, which is sitting in its slot. This pencil line, which marks the height of the frets at the first fret gives you a reference for your initial cutting and then you can fine-tune from there, using trial and patience and filing a very little at a time. Look at John Hamlett's link above to see the height he is aiming for and how he achieves this.

[sunburst]

The "half pencil" is pretty standard for establishing the preliminary height for the nut slots. The link I posted above is, of coarse, to Fret.com, and clicking to pages 1 and 2 (the link is to page 3) will fill in the procedures done before adjusting the string height.