Just discovered that my xtant 403a has a jumper switch that turns the input signal into a balanced signal. This effectively boosts the input to 17 volts according to the manual! In addition to that you can increase the input gain. These two features combined act in the same manner as a line driver and gets rid of any ground noise/excess noise. My sound is so clean after discovering these two features. I'm so happy. I'm gonna do a write up on this amp in the review section after using it a bit more. Wanna see if it can hold up with my sub wired parallel at 1 ohm load. If it can do this without frying (which it's been fine so far) I'll be thoroughly impressed. Any other amps out there that have this feature? I found it quite awesome.