The input connection has broken (the soldering) now since i've soldered ?

Usually feeback in electric guitars comes from either poor connections or, more commonly, poor grounding. I recommend searching on Google for the wiring diagram for whatever guitar you're playing and checking all your connections, especially the ground to your bridge. If not, possibly try cleaning the contact which you worked on with a contact cleaner (which you can buy at Radio Shack) and re-soldering the connection. Hope this helps!

Baliga Lutherie
June 2009