Aquila Flat Spiral U•BASS® Set

Purchased a used Oscar Schmidt OUB500K-A-U which came with Aquila ThunderGut 68U's. They sound somewhat mellow and are easy on the fingers but I don't like the rubbery feel. I researched several non-polyurethane type strings, specifically flat wounds. I chose these Aquila Flat Spirals as my first attempt.

I also purchased the U-Bass TUSQ nut for Flat Wounds. The nut width was about 1mm wider than the fretboard but that's ok. The nut height was about 7mm too tall. The attached image shows how much material needed to be removed from the bottom (compared to the original nut). I did not file the grooves at all. It took several iterations to get this just right. I ended up taking a bit too much off the bottom but corrected that by using just enough mylar shims to eliminate the slight buzz on the low E. A mere .35 mm worth of shims made all the difference. Used a dab of wood glue to secure it in place. There is zero buzz on any open strings.

The ThunderGut strings did not have any washers inside the soundboard. Don't know if any poly strings use washers. No washers were provided with the Aquila Flat Spirals. I installed 4 brass washers that I chamfered on the ID to better seat the beads at the end of the strings. One edge (D string) had to be further modified as the internal brace was not exactly centered.

Lastly, I tightened the single action truss rod about 1/4 turn to further improve the overall action. Measured at the 12th fret, E is 0.09 in. and G is 0.10 in. Still no…