Q: All of the sources coming into my mixer are extremely loud and distorted except for the microphones.

A: Most likely your line level source is overdriving an input configured for a microphone. All mixers that use the same physical input for both line level devices and microphones will have some sort of input gain adjustment. On some it may be an adjustable pot with a typical adjustment range of 20db to 30db. Others may use a simple push button or dipswitch that inserts a pad into the signal path. Again this pad will be somewhere in the range of –20db to –30db. Simply activating this pad should resolve your problem. If not it’s highly possible that you have a wiring problem such as incorrect pin configuration.