Ok so here we go. I’m gonna need A little help here. I got this thing on the bench now. Basically it was a four input 76 master model. Somebody did the cascading Randi Rhodes MOD and made it into an 2 input 800 block up two inputs. But before I even begin and hook up a speaker load I noticed there was another mod back here in the speaker input section. is this extra hole a effects loop?