[LAU] Hum pickup in DI boxes

Not strictly a Linux problem, but I hope for advice. We're using a Behringer X32-Rack mixer for our church PA system. One of the inputs that we need is for people to plug in laptops - usually via the headphone socket into a Stagg dual DI box. We seem to get a lot of hum pickup on that, which I think is down to the proximity to the laptops. We have another identical DI box at the other end of the room which takes keyboard and bass and I've had no problems with that. Is there an alternative method we can try? We do raise the ground lift switch on the DI box, which reduces the hum somewhat but still get enough hum to be noticeable when nothing else is playing. I wondered if the matching transformers in the DI box are acting as pickups for the RF noise generated by the laptops. The mixer on EQ display with RTA shows noise across the audible spectrum, but most of the audible sound is mains hum. Bill -- +----------------------------------------+ | Bill Purvis | | email: bill(a)billp.org | +----------------------------------------+