Thank you so much! I think the problem was not so much the difference between 2.5 and 4.5w, but probably the fact that I was way above this!
I found that 2.5 did not change volume so much in relation to 5w, at least not to my untrained ears, testing with both my headphones and the Zeppelin, but sound quality was a tad impaired at 2.5. Maybe my power source -- an old 5V / 0.5a adapter.
In any event, it's clear now that the power source matters a lot for the SU-1, so thanks for drawing my attention to that.
At proper 5w, things improved a lot. Maybe there was a combination of factors as the sound entered the Zeppelin at high volume and already somewhat clipped by the SU-1. The potentiometer was probably helping a bit (and I still need it), but it's much better now.
I still wish there was a way to half the SU-1's output, though.
I found that 2.5 did not change volume so much in relation to 5w, at least not to my untrained ears, testing with both my headphones and the Zeppelin, but sound quality was a tad impaired at 2.5. Maybe my power source -- an old 5V / 0.5a adapter.
In any event, it's clear now that the power source matters a lot for the SU-1, so thanks for drawing my attention to that.
At proper 5w, things improved a lot. Maybe there was a combination of factors as the sound entered the Zeppelin at high volume and already somewhat clipped by the SU-1. The potentiometer was probably helping a bit (and I still need it), but it's much better now.
I still wish there was a way to half the SU-1's output, though.