can spark owners please try this : pitch problem when USB is plugged in computer
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bypass all effects on your spark to get un processed guitar sound, plug the usb cable into the back of the amp. Play a single note on your guitar, and while the note is ringing, plug/unplug the other end of the usb cable in a running computer's USB port.
Do you notice a shimmer/chorus like effect kicking it whenever it is connected to the computer, and that stops when unplugging ?
it seems like there is some issue going on with the internal clock of the spark digital processor that causes the pitch of the amp to fluctuate up and down. When superposed to the direct sound of the guitar it gives a chorus effect. -
don't confuse the R&D guys at PG,
they haven't even got the grounding power supply hum right yet.