Terrible intonation problems on Bowl Back mandolin.

[ZacGordon]

Greetings,

Recently i have bought a bowl back mandolin to play at historic fairs and such. the instrument as a whole was in great condition, needed cleaning - New strings - and minor tuning peg repairs. I did all that and then restrung it, I decided to use GHS ultra light gauge strings on it. After stringing it up and tuning it, There is a very obvious intonation problem. Just going from the open string to the 2nd fret sounds noticeably out of tune. I thought it could be a bridge/saddle problem so i sanded that down a bit since the action was a bit high as well. No change. Can using ultra light strings be causing this massive intonation problem?? Any thoughts or advice is greatly appreciated.

Thank you.

[sblock]

No, it's not the strings. First determine that you have the bridge in the proper position. Do the octave harmonics and fretted notes match at the 12th fret? If not, then move the bridge until they do. If that doesn't correct it, check that the nut is not too high (which would cause fretting the strings to make them go sharp), or if the slots are cut wrong (releasing the string away from the front edge), or if the entire nut might have been displaced (away from the fretboard) for some reason. These two issues -- the bridge position and the nut -- are the most likely culprits. If not that, then you probably have some frets in the wrong locations, although that is much less likely, and also not something you can easily fix yourself.

[John Kelly]

Just as a first thought - have you moved the bridge while changing the strings? If it is in the wrong place then you will have big problems with intonation. Try positioning the bridge so that when you play a string at the 12th fret and then play the harmonic at the same fret you have the same note. If you find that the fretted note is flatter than the harmonic then the bridge needs to move towards the nut, and if it is sharper, then the bridge has to come back towards the tailpiece.

The neck may have moved, as you say the action seemed a bit high and you lowered this by sanding the bridge foot. Have this checked if the bridge position is not out of place.

If your new strings are not fully seated in the nut slots this too can affect intonation. Perhaps they do not quite fit the original nut slots?

[Tavy]

This sounds more like a nut problem to me. What you need to do is:

* Tune up, and with your regular tuner, check the pitch at fret 12.
* If sharp at 12 move the bridge towards the tailpiece, if flat, move towards the nut. It's not uncommon to find that the ideal bridge position is pretty much right on the cant, and/or to run out of adjustment room.
* Now with the strings in tune open, check at the second (or first, or third) fret. If they're hopelessly sharp then your nut is too high. Note however, that there are better more reliable ways of checking for nut height, but this is a simple way to at least begin to diagnose the issue. Also note that if we were setting up properly, the nut should really be adjusted first, but again lets eliminate the easy stuff (bridge position) before worrying about the nut.

So.... more information required, but I'm afraid it is not uncommon for Neapolitan instruments in particular to have serious intonation issues. They can all be fixed though.

[MikeEdgerton]

We had one that appeared here a few weeks ago with the bridge glued in place. If it isn't floating you've got that issue to deal with first.

[ZacGordon]

Just as a first thought - have you moved the bridge while changing the strings? If it is in the wrong place then you will have big problems with intonation. Try positioning the bridge so that when you play a string at the 12th fret and then play the harmonic at the same fret you have the same note. If you find that the fretted note is flatter than the harmonic then the bridge needs to move towards the nut, and if it is sharper, then the bridge has to come back towards the tailpiece.

The neck may have moved, as you say the action seemed a bit high and you lowered this by sanding the bridge foot. Have this checked if the bridge position is not out of place.

If your new strings are not fully seated in the nut slots this too can affect intonation. Perhaps they do not quite fit the original nut slots?

It's hard to move this bridge while replacing the strings, Because it's glued to the soundboard. Ive never seen one like this but i measured it and it is in the perfect spot. The neck is not bent, I checked all these. I made sure that the strings will fit and they do fit in the slots, Perhaps what sblock said is true about the nut being high.

[ZacGordon]

This sounds more like a nut problem to me. What you need to do is:

* Tune up, and with your regular tuner, check the pitch at fret 12.
* If sharp at 12 move the bridge towards the tailpiece, if flat, move towards the nut. It's not uncommon to find that the ideal bridge position is pretty much right on the cant, and/or to run out of adjustment room.
* Now with the strings in tune open, check at the second (or first, or third) fret. If they're hopelessly sharp then your nut is too high. Note however, that there are better more reliable ways of checking for nut height, but this is a simple way to at least begin to diagnose the issue. Also note that if we were setting up properly, the nut should really be adjusted first, but again lets eliminate the easy stuff (bridge position) before worrying about the nut.

So.... more information required, but I'm afraid it is not uncommon for Neapolitan instruments in particular to have serious intonation issues. They can all be fixed though.

Thank you for the response! Its not the bridge i know, And it couldnt be moved easily anyway since the bridge is glued on to the soundboard. I measured it though and it is in the right position.

[ZacGordon]

No, it's not the strings. First determine that you have the bridge in the proper position. Do the octave harmonics and fretted notes match at the 12th fret? If not, then move the bridge until they do. If that doesn't correct it, check that the nut is not too high (which would cause fretting the strings to make them go sharp), or if the slots are cut wrong (releasing the string away from the front edge), or if the entire nut might have been displaced (away from the fretboard) for some reason. These two issues -- the bridge position and the nut -- are the most likely culprits. If not that, then you probably have some frets in the wrong locations, although that is much less likely, and also not something you can easily fix yourself.

Well, the bridge cant be moved. Its glued in place, I measured everything correctly and it is in the right position. When i press down on the 12th fret its sharper than the harmonic. Even at the 2nd fret its a lot sharper than it should be compared to the open string. The nut may be high, i noticed that could be a problem.

[MikeEdgerton]

If you could put a towel on top of the bridge (perhaps folded) and put a hot iron (like you use to iron your clothes) on the towel for a minute then attempt to dislodge the bridge it might come undone. If you can't at least slide the bridge a little you're probably never going to get the intonation right.

[jesserules]

It is very possible that the frets are not placed accurately.

[MikeEdgerton]

It is very possible that the frets are not placed accurately.

I think it was a Lyon and Healy not a Gibson

I guess. When you look at the bridge it's glued right up next to the pickguard. I don't think it's in the right place. L&H was a little better than that.

https://www.mandolincafe.com/forum/s...12#post1666912

[ZacGordon]

I think it was a Lyon and Healy not a Gibson

I guess. When you look at the bridge it's glued right up next to the pickguard. I don't think it's in the right place. L&H was a little better than that.

https://www.mandolincafe.com/forum/s...12#post1666912

It is an American Conservatory brand bowl back, It is glued right up next to the pickguard, But its the same space from the nut to the 12th fret as the 12th fret to the saddle.

[MikeEdgerton]

It was built by Lyon and Healy that was their brand name and none of them had a bridge placed that close. You really need to be able to move it.

Gibson at one point had a problem with a fretsaw that had wrong spacing. I've never seen an L&H product with that issue.

[jesserules]

I think it was a Lyon and Healy not a Gibson

I guess. When you look at the bridge it's glued right up next to the pickguard. I don't think it's in the right place. L&H was a little better than that.

https://www.mandolincafe.com/forum/s...12#post1666912

Ah, I didn't know the brand.

Not that I was thinking of Gibson, although I have heard about that. I just have the impression that not all the less-expensive bowlbacks produced during the Great Mandolin Craze were made with as much care as might have been desirable.

[Charles E.]

That may be true but usually the bridge needs to be a couple of millimeters back from that measurement to account for string deflection. And the bass side of the bridge needs to be further back then the treble side to improve intonation.

[pops1]

It's hard to move this bridge while replacing the strings, Because it's glued to the soundboard. Ive never seen one like this but i measured it and it is in the perfect spot. The neck is not bent, I checked all these. I made sure that the strings will fit and they do fit in the slots, Perhaps what sblock said is true about the nut being high.

It is almost impossible to measure where the bridge goes as it goes behind the measurement you measure from the 12th fret. Different strings and different height action makes that measurement change so when you say it is sharp at the 12th fret the bridge is in the wrong place. Put some tinfoil right up to the bridge on both sides and heat it up with a 100w bulb in a bench light( while you are standing right there, don't move away) and get it loose and clean off the glue so it moves and I am guessing you will solve all your problems.