Based on techniques from the state observer design and the pole placement technique, we present a systematic design procedure to synchronize a modified coupled dynamos system by a scaling factor ( projective synchronization ). Compared with the method proposed by Wen and Xu, this method eliminates the nonlinear item from the output of the drive system. Furthermore, the scaling factor can be adjusted arbitrarily in due course of control without degrading the controllability. Finally, feasibility of the technique is illustrated for the unified chaotic system.