Add Voltage Controlled Pulse Width Modulation to your PAiA FatMan with one LM324. See drawing PWM.GIF.

The summing amp sums the control voltages. This sum is then summed with a bias voltage. This final sum is compared to the inverted FatMan ramp waveform. The output of the comparator is then conditioned for the PAiA FatMan filter input. Note: The bias pot is a panel control. As well as setting the bias level for your control voltage inputs, it acts as a simple knob control for pulse width. To use it as a knob, turn all CV inputs to minimum.