Electronic circuitry compensates for variations or sags in electrical voltage within a thermal ink-jetting (TIJ) printing apparatus. Ground potential and other supply-related voltages are monitored and corresponding signals are provided. The signals are used, directly or by other circuitry, to affect the biasing of one or more transistors coupling TIJ resistors to supply voltage or ground nodes. Printing errors and related problems associated with voltage variations are reduced or eliminated accordingly.