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Leave it alone at 12v - if it ain't broke, don't fix it. If you get 0 - 10v on the analogue output, you'll be fine.

great to see you have it working even if your not 100% sure which connection you re-made during your investigation

your connection to the VFD looks correct

in practice using the 12V supply...

So you are using a USB cable from the PC?

does it still make a noise if you remover the jumper to disable the relay ?
(I can't think of anything other than the relay that could make a noise)

having a quick look at the data sheet for...