Hello Linus,
I have the same head and the same problem. I've described this problem to ashdown, and ask them for the acceptable limit for hiss, but have not recieved any answer, yet. Next week I will test this Head in our local music shop (ashdown dealer) to ask them for their opinion. I think the hiss is too loud. I wonder, if this would be covered by the warranty....
Have you got any progress on this issue ?
Regards
stephan