Wizard, ground loop problem

OWL Wizard
#1

My Wizard has been tested with two different laptops and three different USB audio interfaces. Same problem every time:
a high pitched probable ground loop whine (only) when the Wizard is simultaneously powered by the computer and connected to the audio inputs of the interface.
Is this fixable, or is it intrinsic to the components being used?

#2

Thanks for bringing this up here.

Iā€™ve found something similar when plugging in a particularly power-hungry MIDI controller. Sounds like a ground loop hum modulated by the LED: you can somehow hear the LED changing colour. Is that similar to what youā€™re experiencing?

Thereā€™s a number of potential solutions, Iā€™m going to experiment a bit with the LED PWM and report back.

#3

Thanks for the reply, yes it seems that the LED is somehow connected to this issue, a definite correlation between colour changes and timbre, but colour changes are made through turning pots, soā€¦hard to be certain of course.

#4

Iā€™ve run into a similar problem with a project I was working on, if itā€™s the same thing, then itā€™s not a ā€˜ground loopā€™ in the conventional sense, but instead itā€™s the resistive voltage drop across the USB cable (it only takes a few microvolts). In my case, the solution was to isolate the USB power and data. I have an external USB isolator I can test with, Iā€™ll let you know the results.

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#5

I was just testing the wizard yesterday with some new effects pedals - massive ā€œground loopā€ overload ahoy! (when powered by USB bus from laptop). But it absolutely pertains to non-isolated USB connections.

USB isolator with Magus?
#6

Hi, again, so I just tested it with the Olimex USB Isolator (USB-ISO) (~$30 Euro), and it seems to eliminate the ā€˜groundā€™ noise and has enough power for the Wizard. (side question: whatā€™s the policy about mentioning specific products by name/price?)

#7

Just to confirm - I also solved this problem by getting a USB isolator, in my case this one:

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