I bought a used Peavey Foundation bass guitar a long time ago, and I really liked the original strings. The sound was very warm and mellow, a lot like an upright acoustic bass. At one point I experimented with other strings because the original set was wearing out. I tried D'Addario XL Semi-Flatwound Half Rounds medium gauge ENR72, which sounded a little too clangy to my ear, and D'Addario XL nylon tapewound medium gauge ETB92, which sounded even more clangy. I experimented with a piece of foam under the strings near the bridge with one of the replacement sets, but I didn't get the sound I liked, it was too dull rather than warm, and of course the sustain suffered.
The original mystery set is also medium gauge, but round wound, which is actually supposed to sound brighter, at least when the strings are new. Finally, the E string snapped at the bridge, so now I have to use something else. An interesting thing about this bass is that the two pickups are connected in counterphase, I'm not sure whether it's by accident or by intent, or how common this is, but I actually like the sound.
Here is an example of what it sounded like:
Could anyone suggest similar-sounding strings to try?