Same issues with my brand new Pro Keyboard, but it is only truely annoying when a connection via USB is made. This is regardless whether the power adapter itself is used or not.
The moment the USB is disconnected and connectivity is only using DIN MIDI (which is opto-isolated) no undesired output occurs anymore.
This renders the USB connection practically only useful for firmware updates
.
I checked if I can get the software editor working via DIN MIDI so I'm not having the USB issues, and this is workable: both software editor and hardware synth can be kept in sync, except when real time changing the parameters on the synth in which case the editor does not update itself. Have I missed something?
In any case I heavily suspect this USB issue being a hardware design flaw
, and not really correctible. I'm using more than ten different hardware synths via USB and none of them have this unmusical behaviour. Luckily there is DIN MIDI as a workable alternative, if not I would have had to return the this rather well sounding device