Strings
Dan Trueman did extensive string tests when he got the very first hardanger d'amore. The strings he uses are:
C: Chorda silver viola 22.5
G: Eudoxa G 15.5
D: Eudoxa D 16.5
A: Eudoxa A 13.5
E: Gold Label E medium ball end
In December 2015, Salve Håkedal wrote the following message to all hardanger d'amore players at that time:
Strings: I send the Hd'A away with hardanger fiddle strings, because it's essentially a hardanger fiddle. (The C is Dominant viola, light.) You may use different strings, but I encourage to use thin gauge. It's not built for heavy strings or even medium gauge strings.
Bridge: As the G-string in the hardanger fiddle string sets are thinner than both the C-string and the D-string, I give the crown of the bridge a little hump under it. This is so the G-string will be lifted up to the bowhair. If you use normal violin strings, the G will probably be thicker, so the hump on the bridge curve should be removed for optimal playability.
Sympathetic strings: If you attempt to fit normal hardanger fiddle sympathetic strings to the Hd'A, you will probably struggle to reach the two pegs closest to the head. I have made Knut Oppheimsbakken at Valdres Folkemuseum make longer sympathetic strings and will try to keep them in store for you. But you won't have to change them often.