Abstract: An ink jet printer includes an image transfer drum and a print head for ejecting drops of ink toward the image transfer drum as the drum rotates relative to the print head undergo. A control mechanism controls operation of the print head relative to rotation of the drum in response to a dot clock signal. The control mechanism includes a position encoder which generates an encoder signal at a frequency dependent on rotation of the image transfer drum and a digital phase locked loop circuit which receives the encoder signal and generates the dot clock signal at a frequency equal to the frequency of the encoder signal multiplied by a rational number.