How disable dithering on Dell 1700?

Hi:

How do you disable the dithering on a Dell 1700? 

I've gone to the trouble of creating a nice sharp text page (black text with blue signature) from a 600 dpi scan, and all the pixels are very clean.  But printing to the Dell 1700, I end up with (what I presume is called) a dithered rasterized print, about the quality you would get from a 150 dpi fax. 

I'm into this experiment about 15 printed test pages already, varying all the printer controls.  This is a pdf in Adobe Acrobat, confirmed in prepress as 600 dpi.  Color management from printer/Adobe has been varied.  Any insight into this problem would be appreciated.

-- Roy Zider