Adding voltage to a circuit

[mister_e]

I haven't place your circuit on a breadboard, but i have the following feeling.

Noise can come from each Opamp, and then mixed & doubled with the last stage. Higher your resistor values are, greater the chances to pickup noise... and then you also have the PCB layout, ground loops, PSU filtering etc etc etc.

You want to smooth everything from the port wiper with a capacitor, at the mix point (last stage), and probably at the output of the last one. Some op-amp may react weird with capacitive load so far. RC filter would help, while a bit useless in few cases. Software noise rejection is a common use.

I stick to the idea of a dual rail voltage. This can be easily produced with a simple PWM signal and a capacitive inverter. Match this to a low quiescent current OP-AMP and you're in business.

I have those AD5220 in stock, but not this specific op-amp.. got a load of others though.

I still not 100% understand why you can't trick the whole thing in software instead... i miss the whole idea. Anyways, you know where to reach me