When using the effects loop on my 700rbII, my amp gets very muddy with a significant volume loss. When running through my board into the input with out using the effects loop everything is fine. This makes me think that there is a problem in my amp as opposed to something in my board. I have had this amp for years, but I have never used the effects loop until recently. Could this be caused by a dirt or bad input jack on the effects loop or something internal?