I'm just about assemble this VU-meter with LM3916, and I have seen diagrams and so on, but when the leds only can take up to 3v, shouldn't there be a resistor before the leds when i'm using 12v? On all of the diagrams I have seen there hasn't been used any...
You don't need resistors because the LM3916 outputs are current regulated (constant current). If you read the data sheet you'll see it's adjustable from 1mA to 30mA (I know, real electronikers don't read data sheets). You just set the current for the rated current of the LED and it provides that current, independent of the supply voltage.