I designed this circuit which will provide a reference for PWM comparators based on both a manual control and an external control voltage. The only way I could think of to do it is more complicated than I'd like, and I wonder if anyone knows a simpler way.
The point labeled "SIG_REF" will be -1V to +9V based on the pot position. The control voltage coming in the TRS jack will be 0 to +5V. The output labeled "PULSE_REF" needs to be at least -1V to +9V. When no connector is plugged into the TRS jack, the pot should cover the full range, and should sit at the midpoint +4V when set to 50%.
So the problem is that the control voltage needs to be amplified by 2 and offset before summing with the SIG_REF, but PWM_EXT needs to be 0V when there's nothing plugged into the jack. That means the + input of U13A needs to be grounded, and the inverting input can't be offset when there's nothing plugged in. Neutrik makes a jack that has a normally-closed tip switch to cover grounding the + input, and a normally-open sleeve switch which could be used to ground the gate of a PMOS transistor to apply the offset voltage when the control voltage is plugged in.
Is there any simpler way to do this?

The point labeled "SIG_REF" will be -1V to +9V based on the pot position. The control voltage coming in the TRS jack will be 0 to +5V. The output labeled "PULSE_REF" needs to be at least -1V to +9V. When no connector is plugged into the TRS jack, the pot should cover the full range, and should sit at the midpoint +4V when set to 50%.
So the problem is that the control voltage needs to be amplified by 2 and offset before summing with the SIG_REF, but PWM_EXT needs to be 0V when there's nothing plugged into the jack. That means the + input of U13A needs to be grounded, and the inverting input can't be offset when there's nothing plugged in. Neutrik makes a jack that has a normally-closed tip switch to cover grounding the + input, and a normally-open sleeve switch which could be used to ground the gate of a PMOS transistor to apply the offset voltage when the control voltage is plugged in.
Is there any simpler way to do this?

