I always use the Monitor output and the Direct output for my own monitor sound. For this I use 2 jack cables with a tip and a sleeve, like for my guitar and they are plugged in into my small 8 channel Soundcraft mixer. Also my XLR mike is plugged in into this mixer and 2 channels are for my guitar.
The main outs go to the PA with 2 XLR cables.
The trouble is that this all produces a serious (electric?) hum.This hum stays if I disconnect my mike. so it has to do something with the 2 ring - sleeve jack cables. I checked both of them but the solding is all right. I press both the ground switches at the back but the hum stays...
What can be wrong here?