@Triryche, thanks for your answer,
As explained in another topic, I'm from France, so i don't think i will be really understandable at phone for this very precise issue if I call Line 6 .... (My english language is very, very poor).
But I really want to help to solve this issue (i have seen some topics on the net from people who are interested for using Amplify 150 as a FRFR monitor for small gigs or at just at home, but don't need the "full power" of a firehawk 1500. it seems thats some of them will get this kind of issue with "flat & empty" preset at power ON
Is there an other way to open a ticket ?
Thanks,