So the other day when the the Praise Team was practicing for Chapel at my school (had already set up mics and monitors and such). I started getting horrible feedback (this is a new system and we are using a Yamaha LS9-32). So of course I grabbed the Master and pulled it down and even turned it Off, but that didn't stop the feedback. The meter showing db was as high as it would go (surprised it didn't blow our new speakers) and I noticed the Reverb (I think it's called "Stereo Send" that it is being put through. Not too sure though as the board is pretty new and is my first digital board) was also at max. I didn't think much of Reverb and just remembered it later. I got the feedback to stop by pulling ALL the channels down. So I think it had something to do with the Reverb. Of course since singers and violin players are sound experts they all were convinced it had something to do with the monitors (but the feedback was over the mains). Another strange thing was right before it I noticed the EQ on vocals was weird (sounded suppressed), but the EQ was flat (I even turned off High Pass to make sure). So my question is, any ideas what caused this (I noticed that when it was set up, one of the monitors was close to a vocal mic, but I don't think that was the problem)? Do the Stereo Sends bypass the Master and go straight to speakers? Any way to prevent this in the future?