I used stewmacs nut and bridge files to cut the grooves, and yes it is only on the open string note.
Thanks for the suggestion, I will give it a try
I agree with Ken about the likely culprit, although are all notes affected or just open string? I'm just now getting back to dulcimers after a 40 year hiatus with little knowledge except for something like your problem. If the string is not in firm contact with the bridge at the point of exit to the playing area, then what you describe could happen. I had something similar but it was a little easier to troubleshoot since it only made the noise as an open string. With no zero fret, the problem was easily isolated to the nut where the string was actually only touching it at a point farthest from the frets. Odd resonance on the far side of the zero fret might happen, but if it is, then muting that area with your finger should change the twang.
BTW, why a 30" VSL, etc. I will be using your info in trying to re-string the big boys in my picture whose dimensions are nearly identical to yours.
I have built several dulcimers from 16" to 30" VSL. The latest one has 30" VSL, Lower bout is 8 1/2", upper bout is 7" and is 2 " thick. Sides and back are walnut and top is ambrosia maple.
I started out with 12,12,16,24 strings and the melody and bass sounded fine, smooth and mellow, but the middle string has an odd twang . I used Struthers string gage and it recommended 9,9,12 and 18. after switching, I used 10,10,12,20. the middle string still has that strange twang. My instruments all have zero fret but could the problem still be in the nut that keeps the strings in position? the bridge was originally ebony but I changed that to bone . Still get that off sound. Action is very low as I dish the fretboard slightly midway to allow a lower bridge, could it be too low? No buzzing
I appreciate any thoughts
Hey , I agree with what Richard has said. Initially follow whatever recommendations the luthier has for your instrument. But you should also experiment a little to discover your own preferences. You may find that you want one or more strings a little heavier or lighter than what the luthier suggested. And you may find that different dulcimers respond differently to different string gauges. Learn what you prefer for each of your dulcimers and then you can buy single strings in bulk.
As Richard says, in general, nickel-wound strings have a brighter sound and bronze-wound strings have a mellower sound. I much prefer bronze-wound strings, but that is a matter of personal preference. I also use so-called "squeekless" strings for my bass strings. They reduce the sound of your fingers sliding up and down. If you play in a drone style and don't fret the bass string, that is obviously not an issue for you. And some people don't like some of the squeekless strings because those that are coated with a plastic to fill in the grooves supposedly have a muted sound (something my ears don't hear).
You might also want to make use of the Strothers String Gauge Calculator . You enter in the VSL (vibrating string length, or the distance between the nut and the bridge) and the note you want the open string to play. The calculator will then estimate a good string gauge to use. Note that the calculator errs on the light side, so feel free to try out stings one or two notches heavier than indicated.
Just think of this as one area you can explore to help develop your own preferences and thereby, your own sound.
Starting out it is best to follow manufacturer recommendations. As you discover the sound you prefer there is nothing wrong with experimenting and strings are inexpensive enough before telling the spouse you need another dulcimer to get the sound you prefer.
Nickel vs bronze vs phosphor bronze wound. So many decisions about strings. There is some difference. Many consider the nickel wound to be somewhat brighter. With aged ears and hearing loss I doubt I could hear much difference. Some folks use plain steel rather than wound for the bass string. Ken H. on this site is one who does that.
Juststrings.com offers single strings in loop end or ball end. Their website is very complete and it may take some exploring to find what you need. They are very helpful by phone or email if you have questions. I tend to purchase all ball end. A couple of snips with wire nippers on the ball will break the soft material and then you have a loop end.
Keep asking questions. That is the way to learn.
I've read the recommendations for string gauges and know that they can be purchased individually, rather than as sets. I'm interested in a few recommendations. Is there a difference in nickel wound vs bronze wound bass strings? If the dulcimer maker recommends (or sells) certain strings is it best to go with that recommendation?
I suspect it's useful, as a beginner, to experiment with different strings, but it would be nice to have a bit more focus than I have right now.