Bad feeback from mics/speaker.
I have a little home studio and sometimes want to amplify vocals etc if we are doing a rendition of a song. When i get the mics louder there is a really really bad screeching sound. The mixer output is going into a stereo system (no pro amp) , and i can't get the mics louder without a really loud screeching happening.
Sorry thats worded really badly but i hope you can undestand :)