I had a similar experience with Doc Watson, the first couple of times I heard him his sound was glorious, probably at the Cellar Door, later on at a larger venue, Constitution Hall, he'd plugged in and it just didn't sound right (but hell, it was still Doc Watson). I've heard the sound of those under saddle pickups described as "rubber bands stretched across a cigar box" and I have to agree but I was able to get a pretty decent sound from a K&K sound board pickup with a Baggs preamp, the kind you clip on your belt.