+1 to what Kevin said. Why does this need to be in pedal format? There should be many small mixers out there that do exactly what you want. Even the really really cheap ones are astonishingly good these days. If it has to be a pedal, you can just transplant the guts of a cheap Behringer mixer (or whatever meets your needs) into a pedal housing. If you want to make it yourself, just trace the mixer of your choice and start modding from there. That would give you the schematic and a prototype, problem solved. If you want someone here to take enough of an active interest to walk you through a design process, you will have to divulge a lot more information. Right now it's a bit like you are going to a restaurant and when the waiter wants to take your order you say you want food, delivered on a plate, in exchange for money. Not nearly enough information. Also, this here is, for the most part, more teatime at aunt Ida's, where a bunch of old ladies exchange recipes, than a restaurant.
Not sure that helps but hope so anyway,
Andy
