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I read here that playing a string on the 12th fret will produce a note that is an octave above the note produced by playing the same string open (with no frets held down). For instance, if the bottom string is tuned to G, then playing the bottom string on the 12th fret should produce G also.

However, it seems that on my mandolin the octave is on the 13th fret. How should I fix it?

Playing a string on the 7th fret should produce the note on the next higher string (open), but it's almost a half-step off. I think this could be fixed by moving the bridge.

I didn't realize the bridge was a "floating" bridge, meaning it can be adjusted higher/lower with the screws. Could this be a simple matter of adjusting the bridge? I'm a little afraid to do so because I don't know which way to turn it. Also, there's a slight crack in the bridge right next to the screw: (I wonder if this is an indication that it's been "over-adjusted" before, leading to the intonation problems. That's just my guess though.)

There's a slight crack in the bridge, right next to the screw.

Here's a closer shot of the crack in the bridge (I've also highlighted it):

A closer shot of the crack in the bridge.

The neck looks straight enough:

The neck looks straight enough.

Other photos:

Bird's eye.

Bridge and tailpiece.

Headstock.

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2 Answers 2

up vote 15 down vote accepted

There are at least two things wrong in how your mandolin is calibrated, according to your excellent and helpful photographs.

  • Your wooden bridge saddle needs to be replaced because it is cracked in half, between the first and second pairs of strings. You can clearly see that the bridge saddle has collapsed and caved in, downward toward the top of the mandolin, where the wood has broken.

  • Your bridge is in the wrong horizontal position on the axis between the fingerboard and the tailpiece. It should probably be moved closer to the fingerboard. However, this is not going to help until the broken bridge saddle is replaced.

Look at your instrument again, more carefully. I have labeled where the problem really is.

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Take it to a qualified mandolin repair person. This should not be an expensive repair.

Here is an example of an inexpensive rosewood replacement mandolin bridge assembly for US $9.75.

enter image description here

A replacement bridge should be selected and installed by a qualified repair person, who can figure out what size bridge will fit correctly on your mandolin. It will require some modification to the wood to make it fit your mandolin correctly. You should also pay the repair person to do a setup on your mandolin, to calibrate several parts on the instrument to make it play properly in tune.

By the way, you do not understand what the term "floating" means in this case. This does not refer to the bridge's saddle being able to be raised or lowered vertically using the thumbscrews. The term "floating" means that the foot of the bridge is not glued to the top of the mandolin. The entire bridge is only held in its current position by the tension of the strings. The entire bridge can be repositioned by scooting the foot of the bridge horizontally, closer to the fingerboard or closer to the tailpiece, or even slanted slightly, to put it in the correct position for proper intonation on all four pairs of strings.

Get some professional help and your mandolin can play much more in tune.

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nice answer! feels good that people here care for other's instruments :) –  Sergio Oct 13 '13 at 0:51
    
Thanks for the great response. I was definitely confused about the floating bridge. I've added another photo that shows a closeup of the crack in the bridge. I don't think there is actually a crack between the first and second sets of strings like you said - it is coming in from the right, and it looks to me like that screw has been adjusted so it is much too high. Please check again and tell me if this changes anything in your response. –  Koveras Oct 13 '13 at 3:06
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@davidkennedy85 Even if the crack doesn't look like it would affect some of the strings, it introduces a variable that you can't reliably correct for until it is fixed. If the bridge was already intact, the fix would be to temporarily loosen all of the strings so that the bridge could be moved forward or backward (not up or down) to correct the intonation problem. –  NReilingh Oct 13 '13 at 4:32
    
Upvoted for being thorough and accurate. –  PSU Oct 14 '13 at 21:31

Following on from Wheat's superb answer, I'd initially use epoxy resin and a few hours in a vice to fix your bridge. This will obviate the need to replace - the existing one has the correct profile to fit the mandolin body. Upon re-fitting, make sure the intonation is good by checking open strings against 12th fret, both pressed down and with harmonics, sliding the bridge gently between neck and tailpiece.

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That would be a good idea IF you can properly repair the bridge saddle. If you buy a new saddle, or bridge, you should pay a repair technician to use their skill to carve the wood a little bit to make it fit for proper intonation. However, I think it would be worth it to pay a professional to fit a new bridge and saddle (make sure it is genuine rosewood or better yet ebony), because you will end up with a better-quality bridge and saddle, better-adjusted, than the original equipment on your cheap Johnson mandolin. This could improve the sound, playability, and intonation a great deal. –  Wheat Williams Oct 13 '13 at 12:54

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