samsung ml 3561 n?

Hi I new to this forum and i've searched for some answer for my problem but was enable to find. My problem is this: some weeks ago i bought a used ML-3561N Samsung. It's working great, reliable and fast. But i think that the printing quality is a lot worse than it should be. I posted together a image of a text that i printed today, and the letters seen grainy and in low res, despite the fact that i used the max resolution. I also tried to configure in the computer and on the printer display, but i tried lots of different configs and the result is always the same. Does someone know how to fix it? Or which configuration i should use? By the way, the printer is on a network. This output comes from every task sendo to it by the users, including the autoprint test from the printer itself[ Thanks for now