background noise when i use usb as power supply

[martindunne]

love the preen most usefull of all my synths but seem to get noise if i use usb as a power supply. no noise if i use external 9v. is there any thing you can suggest, tried 3 different usb cable with and without sheilding no change. thanks

[Xavier]

Thanks 

Is the noise the same with your 2 preens ?
To be sure it's not a soldering problem with one on of them.

The more likely is that your USB 5V source is too noisy.
Is the USB cable plugged directly in the computer ?
Different suggestions :
. Using a USB power supply (but you'll lose midi over USB).

. Using an active USB hup... Can increase the 5V quality by providing it's own 5V.

. Trying to increase the 2 x 220uF capacitor circled in the attached picture (not the 330nF infor that is useless here)
You can first try to add an other capacitor in paralel. Put the two pins in contact (without soldering) and hear if that changes anything.
The 5V/ground pins at the bottom of the PCB can also be used for some experimentation. Try to manually put the bigest capacitor you have here while listening to the noise.
(Don't forget about the -/+ of the electrolyte capacitor and avoid shortcutting the 5V and the GND ).

Xavier

[martindunne]

cheers for the suggestions will try them out not a big problem tho can just use external 9v power supply