Abstract: An apparatus for developing a latent image recorded on an imaging surface, including a housing defining a chamber storing a supply of developer material including toner and carrier, a donor member with an electrode array on it, spaced from the imaging surface, for transporting developer material on the surface thereof to a region opposed from the imaging surface; a closed-loop grid, spaced from said donor member, having an electrode array on the outer surface thereof, which faces said array on the donor member, said arrays including a plurality of spaced apart electrodes extending substantially across width of the surface of the grid and the donor; a magnetic roll for loading developer material onto said grid, and multi-phase voltage sources operatively coupled to said electrode arrays, the phase being shifted with respect to each other such as to create traveling electrodynamic wave patterns for moving toners along the surface of said electrode arrays, and with bias voltages controlling transfer of toners be