I have a dulcimer that I converted to a bass dulcimer years ago (I didn't build it). Before people started talking about bass and baritone dulcimers. 4 equidistant strings. I use guitar strings on it (extra lights) tuned to guitar pitches. Keep it tuned to mixolydian A (AAEA high to low). It matches a standard A chord on a guitar.

I created it because I wanted an A dulcimer to go with my natural singing range. Tuning normal strings up to A just popped them. When I tried tuning them down to A they were way too loose.

Then I took a look at a guitar and thought, wait a minute, all the open notes I want are there. Bought a set of guitar strings, slapped 'em on the dulcimer, and the rest is history.

It has the tone of the gods and bass you wouldn't believe you could get from a dulcimer.