A line marker carries a spray nozzle assembly for marking or painting a line on a horizontal surface. The brush roller includes a shaft and a woven fabric brush including fibers planted in a strip-like base material, which is wound helically about the shaft with a helical winding gap. A plurality of gain networks and feedback paths from a reference voltage of the switching power supply are used to monitor the input power source and to modify the output voltage based on characteristics of the input power source. The single pressure plate design is compact and minimizes axial space requirements for the apparatus.