I played a show last night and was setting up my gear. The amp was a Blackstar HT. i use an AMT C2 pedal so went about setting it up. I plugged into the effects return (as i always do with other amps) but there was no sound. If i plugged into the front of the amp there was no problem, so all the cables worked fine. So what was i doing wrong? Why was there no sound when i went straight into the fx return?