Re: Bad hum from amp
Gonzoso, if the hum dies when you put your hand on the strings the first thing to do is to ground your strings. If this is a electric instreument it should have the strings grounded usually through the tailpiece to the output jack or somehow to the cable braid going to the amp. Perhaps this has come disconnected or not done. With a multimeter check for continuity between the strings and the metal on the cable connector. If there is no continuity try to find out why. Reconnect it if it was there. If it hasn't been done run a small wire from the output jack ground to the tailpiece and connect under one of the tailpiece screws. If you want it hidden remoce the strap peg and file a very small geoove for the wire, run the wire down through the F hole and out throught the groove and reinsert the strap peg. Grounding the strings should alleviate the hum. Good luck.
'52 Martin D-18, Taylor 510, Heiden A , Eastman 805E