Oops! I forgot to say multiply the measurement by two! So your scale length is 24-1/2"

From your description it seems likely the problem is at the nut/zero fret. I forgot to ask which you have. If it is a zero fret, you might try slipping a thin palette knife under it and gently pry it up a bit. Not a long-term solution, but if it decreases the buzzes that's a clue the you need a zero fret with a slightly higher crown.

If your dulcimer has a nut, there are two options:

1. Examine the top of the nut to see whether the strings are in slots deeper than the bass string. The bass string should not be much lower than its diameter (so its top surface in its slot should be about level with the top of the nut, perhaps a frog's hair lower). Over time with much playing and re-tuning, strings can wear the nut down, digging deeper into their slots and begin buzzing. Since this is a donated dulcimer, there is no telling how well it was treated before it got to you.

2. If the strings look fine in their nut slots, there remains the possibility that the nut never was high enough. Ya never know what some else is able to tolerate (or play around, despite) in the way of odd buzzes. In this case, pry the nut loose and slip a piece of business card stock, sized to fit the base of the nut, in as a shim. Retune and check for buzzes. You may need two such shims.

But more than two shims would suggest something even more fundamental and dire is going on —such as the whole tailblock becoming loose from its glued foundations in the sides and back, and cocking up when you tune the instrument. Let us then pray...

updated by @dwain-wilder: 05/22/24 02:23:27PM

Hi Dwain; here are my answers . Thanks for your help

Are all the strings buzzing? YES
Are the buzzes on a single fret or a group (or groups) of frets? Mostly from fret 2 and up.(the lowest string is not as bad)
What is the scale length (measure from the nut or the center of the zero fret to the 7th fret to get the nominal scale length).

12 1/4 inches 

What are the string gauges? .012 .012  .020 ( ( think)
What is each one tuned to? D A D 
Can you slip a nickel coin between the last fret and the bass string? YES
Is there any buzzing on the open (not pushed down at any fret) strings? Yes but its slight and intermittent.

 

Hi MJ, we'll need more info about buzzing before giving advice:

Are all the strings buzzing?
Are the buzzes on a single fret or a group (or groups) of frets?
What is the scale length (measure from the nut or the center of the zero fret to the 7th fret to get the nominal scale length).
What are the string gauges?
What is each one tuned to?
Can you slip a nickel coin between the last fret and the bass string?
Is there any buzzing on the open (not pushed down at any fret) strings?

A string buzzes if it's too loose, or if the next fret up from where you're noting is too tall.  The tall fret needs to be filed down slightly so the string doesn't hit it. 

You could also try raising the nut with a shim, or raising the bridge with a shim.  All of the frets need to be level with each other to keep the buzzing away.

Thanks for the good advice about anchor pegs- that dulcimer  now has a new anchor, loop end strings and her owner is delighted.  

Now I have a new question. Is there an easy way to fix buzzy strings.  I recently replaced friction tuners ( no screw on the end- just pegs) with geared tuners - in order to make a donated dulcimer tunable and playable. the Strings buzzed before I changed to geared tuners, I think it is slightly better but I was wondering if there is an easy fix for buzzy strings.