microphone double adaptor

[sockknitter]

sorry, i know this is slightly OT but i really need some help. i want to build a microphone double adaptor so that i can put an sm58 to two differnt places. ie one to an effect unit and the other to a PA. this way i can have both raw and processed sounds at once.
i already have a pickup in my acoustic guitar but i want to utilise the mic for a different sound quality.
it seems to me to be a fairly simple thing but i'm a bit of a noob when it comes to electronics. would anyone have any circuit diagrams that could help me split a mic signal into two without losing juice.
cheers.
tom