Official Luthiers Forum!

First I apologize, don't post much, read a lot. Don't have much experience so I don't give much advice, and I don't build much, would like to but you know day job, family, ect.....
Just finished #5, well 7 if you count electrics, a classical (classical #1) built from the Bogdanovich book and plans. This guitar is a college graduation present for my son a good classical guitarist playing a respectable factory guitar, but he needs something better. He is heading for grad school and I wanted to give him something special. First the good. I am very happy with the sound overall, bass is amazing trebles seem ok, but getting better each time I play it. Made a few mistakes along the way some I fixed, some become design features.
Now the problem, the D string has a buzz when played open I can not track down, it buzzes action high or low, I releveled the frets none seemed high. The weird part that my son pointed out to me is that it only buzzes when played with a down stroke not when played on an upstroke no matter how hard you strike it.
I do a lot of repair work on guitars and mandolins mostly refrets and have chased down a lot of buzzes but this one has got me. My only experience working on classicals has been a few bridge reglues. Ideas or advice?

Classical guitar strings are notoriously inconsistent. I am assuming you have noticed this problem on more than one D string. If so and if the string buzzes only on the open string then you have a rattle in the nut. In order to function correctly the string slot must be the correct diameter, not too deep, and if the slot goes "up hill" just a tiny bit, the string will rattle. By up hill I mean the slot is deeper at the front of the nut than in the middle. If you take the string out of the slot you may even be able to see a bit of metal from the winding in the front part of the slot, if your slot is sloped down towards the front.

_________________
Stay with the happy people.
--Reynolds Large

Thanks TRein, I haven't checked the nut, thought I did a good job, but I've been wrong before, your diagnosis makes sense. The nut is still a bit high but very close. I'll look at it tomorrow eve. I've switched from late night luthier mode to beer. The trebles are getting better. It amazes me how a guitar evolves and changes in the first few hours of its life.

Hi Chris,

Although a buzz within the nut slot is quite probable, you may also simply have a nut slot too deep. The buzz would come from the string that hits the first fret while it vibrate. To check that, press on the third fret and check the clearance between the top of the first fret and the bottom of the string. Like shown in the picture:



You should have somewhat the thickness of a sheet of paper between the two. if not, than your problem comes from there.

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

It might be worth putting a scrap of paper in the suspect slot, replacing the string, and seeing how it sounds. If the buzzing changes or goes away, the cause is either the height at the nut or some defect in the slot. I only mention this because it's a 30 second job, and might help others trying to track down a buzz.