Originally Posted by foreign
No it's still there the distortion using RCA is at low level volume aswell as high. It's as if the stx isn't shielded properly as the tube amp is quite powerful it picks up everything. If I use any other source there isn't distortion no matter what volume is set at laptop, iPod , CD player , DVD player. So its safe to say its the stx and not my as you put it consumer grade tube amp :-).
Shielding should not affect distortion, only noise. Do you really get distortion (like clipping), or noise/interference that is there even when nothing is playing ? If the latter, and it only appears with the tube amp, you may have a ground loop. If it is really distortion, even at relatively low volume, you may have a faulty card, because it should not distort, even at 100% volume.