Just a stupid, short question: do I need a pre-amp when I want do connect a electric bass guitar to the mixer or not? Hope you can help me

no, u don't 'need' one, the bass should be able 2 plug straight into the line input of the mixer and give u a workable sound and level with just the mixer's built in preamp (all mixers have a preamp of some sort on the inputs). However, a good preamp or 'D.I.' box will improve the tone of the bass considerably. I use a SansAmp bass driver as a preamp for my musicman stingray and it sounds wicked. Plugged straight into the mixer, it works but sounds weak and thin. good luck, bjkiwi