Edit: for anyone interested, I got rid of the ground loop by putting a Ebtech Hum Eliminator between the output of the switcher and the input of the Mesa Formula. Works great!
Cheers,
Chris
Thanks for your your reply! Yes, I came to the same conclusion after a whole day of searching and trying what the problem could be. I think it’s actually the external switches of the Mesa Formula preamp that are causing the main problem. Is there anyone by coincidence who happens to know more about that?
Cheers!