buzzing - truss rod, setup, or fret leveling?

[jim19]

I've gotten out my rarely used Stewart Macdonald kit mandolin. I built it in about 1980 and it has never been taken to a luthier. The only places that don't buzz are the open strings and frets from above (highest notes) the 15th.

I'm attaching a photo and wonder if it can help diagnosis.

If I put a machinists rule on the fretboard it will touch at the 1st fret and also between about the 12th and 15th fret. On the other frets, I can slide a piece of paper between the fret and string. If I slide the rule down off the first fret, it will touch the second fret, then third etc.

In the photo, the green tape marks where a fret touches a string - the lower two tapes mark four consecutive frets that touch. I expect those 4 frets are the problem.

Does this give any clues? I'm sure the setup I initially did wasn't very good.

Jim

[dhergert]

I'm not a luthier, but as an early start to answers, here are some things to consider that our luthier folks can probably provide more information about...

Has the mandolin been stored un-played under normal string tension for a long period of time?

How does your mandolin's neck heel joint look? Are there any signs of movement in the finish around the neck joint, or in the button area?

The high fret pattern you've described suggests that the neck may have pulled forward, allowing the extension fingerboard over the body to flex relative-upward at about the 12th fret.

If the neck joint has not moved, the neck itself may have developed a forward-bow, which might be remedied by adjusting the truss rod.

Whether or not to slack strings when an instrument is in storage is a good question... If you don't slack the strings, the neck and the neck heel joint are under constant tension. If you do slack the strings, the neck might back-bow. So it's hard to know what is best.

[Nevin]

The truss rod is to adjust the amount of relief in the neck. Most mandolin players prefer between none and very little. A fret level is done when the frets aren't level. To diagonse this, rather than a long straight edge, you need a short one that just spans three frets. When you span three frets and the frets are level, the edge will sit evenly on all three. If there is a gap or the edge rocks in the middle, you have uneven frets and need to level them.

[keith.rogers]

The bridge is too low seems obvious from the description and picture, at least as much as I can tell. But I would get the setup PDF that is frequently mentioned here and just do a complete and proper setup, because you have other issues that should be addressed and doing it right should be your goal.

https://www.mandolincafe.com/forum/threads/98399-Mandolin-Set-up-E-Book-by-Rob-Meldrum

[ProfChris]

From your description, I'd start by slackening the strings and then adjusting the truss rod until the neck is as flat as you can get it. Ideally, your straight edge will contact all of frets 1-12, and there will be a slight air gap under 13 upwards.

I suspect you'll see gaps on some of 1-12, in which case you need to level and recrown the frets.

Once done, restring, set the relief, probably adjust nut slots, then set 12th fret action.

If 15 is higher than the plane of 1-12 once straightened, then your neck joint has rotated some - take pictures and ask again!

[jim19]

Thanks - I don't think the neck joint has moved - it looks good against the sides and the back was glued over the neck heel and also looks good. Of course the neck could have warped...

I will look into some of the other ideas given.

[rcc56]

The instrument should be evaluated and, if necessary, adjusted using the following steps in order to determine whether or not there is a problem.

1. Adjust the truss rod so that there is little to no relief between the nut and the body joint. Check by simultaneously fretting each string at the first fret and at the body joint. The strings should just clear the 5th and 6th frets without touching them. Do not adjust the rod so tight that there is any back-bow.

2. Fret each string between the 2nd and 3rd fret and ensure that the string barely clears the first fret. If the clearance is large, the nut slot can be lowered slightly. If the string touches the first fret, the slot must be raised.

3. Measure the distance between the top of the 12th fret and the bottom of the strings with a good rule-- the 6" machinist's rule available from Ace Hardware for $5 will work. Adjust the bridge until the distance between the top of the 12th fret and the bottom of the strings is 4/64".

This is the standard set-up procedure for a mandolin and will put the instrument in spec to play with reasonable action. If the mandolin still does not play without buzzing, you may have high or loose frets, or a fingerboard that is not sufficiently flat, or other problems; and the instrument should be taken to a good repair person to diagnose and correct the problem.

The set-up procedure is similar for guitars and banjos, except that when setting the bridge height for these instruments, the string height above the 12th fret will need to be greater: i.e. 6/64" under the treble string and 7/64" under the bass string for medium action on a flat top guitar, higher for a heavy strummer, lower for a player with a light touch.

[EdHanrahan]

I'm sure the setup I initially did wasn't very good.

Yeah but...

Between 1980 and now, the neck has been thru several dozen cycles of seasonal swelling and contraction; maybe not much in any one year, but cumulatively... Yikes!!

In my humble & highly amateur opinion, it's possible that the once nicely-seated frets are no longer quite so aligned; they may have moved and/or partially risen in their slots. So, while a straight-edge is an important tool, I also find that simply sighting along the tops of the frets while reflecting a light from the far end can help find areas of discontinuity in the reflection pattern. It's quite possible that some frets, maybe at just one end, need to be gently tapped back into place. (I aways protect the fret with a wood block, rather than tapping directly on the fret.)

That's a prudent step to take before a fret leveling, as you'd hate to file a fret's top off only to find later that the bottom should be lowered back down.

And, not to be alarmist but to complete the thought because nobody has said it: In the worst case, the neck has warped (over the past 40 years) and needs to be planned flat before a full re-fret, but hopefully not!

[Mandobart]

I'll play Mr. Obvious here - how is your action at the 12th fret and bridge adjustment? Have you tried raising the saddle height with the thumbwheels? I have a couple instruments that need minor seasonal tweaking of the saddle height.