Mine sounds fine in almost anything I plug it into.
Headphones, mixing board, you name it...
But there was one time I used it and it just didn't sound good at all.
It was at a church I was visiting in Texas. They only had one set of speakers that the mics, organ and keyboard were routed through.
I couldn't get my amplug loud enough to play and compete without distorting a lot and it just sounded horrible.
I would up just taking it out and plugging directly into the sound board and diming my guitar volume.
Now...at my church...it sounds great!
But we have 2 speakers for each instrument and front and rear speakers for the mics.
"Talent instantly recognizes genius,
but mediocrity knows nothing more than itself."
-Sir Arthur Conan-Doyle