ground loop

Hi there, I recently got an old GoldStar GSM-6330 and wanted to add an internal Bluetooth-receiver to it, without sacrificing any of the existing functionality. I decided for some cheap Bluetooth receiver board. You can see on this image, how I wired everything. (I stole the +-12V from the...

Hi there A bit of an electronics novice here, forgive the lack of knowledge. But I'm trying to record my voice to my laptop via a USB-powered audio interface (it has USB cable for both power and data). A low hum has appeared which gets worse if I touch my mic body, and almost goes away...