DI Ground issues

MetalJonesy

more metal, more booze!!!
Ok..so i use my active di box to track guitars with active pickups..guitar in and balanced cable to my mic pre, however when i plug a cable into the thru jack into an amp i get hum on the amp..so i flick the ground switch and the hum on the amp goes, but transfers to the di track...

wtf is going on? every where i do this..and every di box i use i always get the same issue so can't be the setup..anyone have any ideas?

The DI box in question was the Samson DI, however i just used a palmer DI and it did exactly the same! :/ This doesn't just happen here at my house, but any studio i have been to, and with different guitars/amps, and even now in different countries.