Harsh overtones -- nut?

[Strabo]

I tried various strings on my 1921 Gibson A and finally bit the bullet and installed Thomastiks about a month ago. They play beautifully with even tone across the strings and virtually no noise from slides.

Recently I noticed that the two e strings sound different. The one on the treble side seems to have some harsh overtones that I do not hear on the other one. I also discovered that this occurs only with the open (unfretted) strings; when fretted, both strings sound the same and the harsh overtones are absent. This leads me to believe that the problem might have to do with the nut, not the string itself.

The nut appears to be original, though of course there is no way to be 100% certain of this. Close inspection of the nut shows no cracks or other visible defects. There is very little apparent difference in how the two e strings lie in their slots. The top string may lie just slightly deeper in its slot that the lower one, but any difference is very, very slight. I'll try to attach a photo below.

I don't think it's a good idea to start by butchering a near-100 year old instrument without fully understanding what's happening here. Can anyone suggest how I can best proceed to investigate this problem?

Thanks in advance for any help!

[sunburst]

That sound is usually a result of the string not lying right at the front (front being toward the bridge) edge of the nut so that there is a slight sitar effect. The slot can be worn from string vibration, there can be something packed into the slot under the string, but whatever it is, a light stroke or two with an appropriately sized file will generally clean up the nut slot and the sound of the string.
I would probably simply clean up the slot (and perhaps the others as well), but if you want to visually check first, use magnification and good light. The string contact area in the nut should show up as a glossier area. If that does not go right to the front edge of the nut, the slot probably needs adjustment.

[sblock]

+1 What John said!

[John Kelly]

What John says. Looking at your picture there might well be a bit of rounding at the fingerboard edge of the nut, but you need to check the base of the slot to see if there is some wear there too.

[Willie Poole]

I have one mandolin that is just backwards of yours, mine notes good open and when I play up past the 7th fret it has those overtones. I installed a new Bridge saddle and it helped but I still get it slightly, when we do some recording I never hear it when played back so I don`t bother with trying get it perfect any more...None of the band members say they can hear it so I chalk it up to my old ears...

Willie

[Strabo]

John's explanation makes sense -- a slight gap at the front of the nut slot would allow for the "sitar effect". That also helps understand how this condition might have developed over time. I'll give it a close look and then maybe a stroke or two.

[EdHanrahan]

While the prior opinions (from folks far Far FAR more qualified than I) are definitely valid, I have a suspicion:

... The top string may lie just slightly deeper in its slot that the lower one, but any difference is ...

... just enough to cause the outter open E-string to touch the first fret when vibrating, thus being another possible source of the "sitar effect". You can see in the photo that the E's are much closer to the 1st fret than the others, and the outter E, per your description, is closer yet than the inner E.

Short term cheap & simple exploratory fix: Shim the outter E at the nut with paper and (possibly) hear the overtones go away. Longer term fix: Fill and re-cut the E slots (I've done that more than once), or replace the nut (ditto).

[Strabo]

Good thought -+ I'll measure the clearance at the first get.

[Strabo]

(I meant "fret").

[colorado_al]

If you suspect it is the original nut and want to keep it, I'd just fill the nut slot and cut it again. If you use super glue and bone dust to fill it, you should have a good hard surface that will cut well and resist wear. If bone dust is hard to find where you are, then baking soda will do.
Otherwise, just replace the nut and cut new slots in it.

[Strabo]

You were right, Ed. The top e string did not even clear my thinnest feeler gauge .006" at the first fret. The second e string was only a little higher. I filled both slots but didn't gain much, though it seems to have solved the problem for the time being. I'm guessing that I'll eventually need to shim the nut. I'd like to keep the instrument as original as I can.

It's interesting to me that extended use does indeed wear down the nut. In this case that's 95 years, so maybe that shouldn't be a big surprise. After all, you can wear out a car in 20 years or less!

[pops1]

Bone is not even density so yes it can wear. Shimming the nut is easy and only takes a thin shaving to do what you need. I would use a tapered shaving so as to not change the bass if it is ok now.

[Larry Simonson]

Being unfamiliar with sitars, I am wondering if someone would describe the "sitar effect". Thanks

[EdHanrahan]

... if someone would describe the "sitar effect".

If you listen so some of George Harrison's later Beatles songs, there's lots of buzzy-sounding instrumental, that being Indian sitar, a la Ravi Shankar. I won't try to describe one; you probably wouldn't believe me.

I recently had a chance to try a (late-'60s favorite) Coral electric sitar. Looks like a solid-body guitar w/ slightly exotic shape and a bunch of sympathetic non-fretted treble strings. But the real crux is its bridge: Adjacent to each of the 6 strings is a metal tang that doesn't touch a static string but does intrude into about 90 degrees of a plucked string's possible vibrational swing area. Because strings rarely vibrate in a constant plane, a plucked string will quickly come into contact with the metal tang and take on a bunch of buzzing (irregular overtones) that fades away slowly, while the string is effectively pushed back into a plane that places it away from the tang where it can vibrate freely and in tune. Of course, the string's plane of vibration may well swing back into alignment with the tang, re-starting the buzzing.

Yeah, this description IS a bit mystifying, but this might help:
https://www.youtube.com/watch?v=Wqt_iZBvtCo

It's an interesting effect in small doses, but not what most of us want from our E-strings!

[Hendrik Ahrend]

John's explanation is spot on. Solved this problem with one or two file strokes more than once - but I've never been able to actually see what caused that sitar effect.