My friend got a new Bongo double humbucker for his b-day and we both can't figure out the knobs. It has 2 normal and 2 stacked. The first one we know is volume and we have other ideas but dont know for sure.Any help would be apreciated, Thx p.s. I know how many bongo freaks there are so I'll tell u the color. Its black with black pick guard but I gave my friend the idea to get a green pearl and hes going to go for it, I think it will officealy be the sickest bongo ever.