Abstract: Methods and apparatus are provided for preventing ink clogging in impulse ink jet printers. In preferred embodiments, the ink jet printers include at least one nozzle for ejecting ink droplets in response to a sequence of control signals and a control means unit for generating and applying the sequence to the nozzle and for controlling the amplitude of the control signals. In preferred methods, the control unit generates a plurality of mutually asynchronous firing signals on demand, the firing signals having amplitudes which are effective to eject droplets of ink from the nozzle. The control unit also generates a plurality of mutually synchronous sub-firing signals after a predetermined interval following the firing signals, the sub-firing signals having amplitudes which are effective to prevent clogging of the nozzle yet which are ineffective to eject droplets of ink therefrom.