Hello all. I’m new at this so excuse my somewhat ignorance to perhaps the obvious. I am using a nano and the tea5767 FM radio module with a rotary encoder for tuning. I also have a Bluetooth board running and a relay module in place to switch the audio signal between the FM and Bluetooth modules. The relay sends the audio signal to an amplifier board. All devices are powered from a 5 volt power supply module via the rail on my protype board. All is functioning well aside from what I believe to be a ground loop issue. With the Bluetooth board audio enabled, there’s a background digital sounding whine present. As well, between stations, when tuning, I receive a similar noise through the FM tuner. When locked to a station there’s no noise. I have tried isolating power to each module with a DC to DC converter, using an audio isolation transformer on the audio path with no great success. All device grounds lead straight to the neg rail with no daisy chained components.
Any suggestions on how to manage this suspected ground loop issue would be most appreciated!
I'm not going to look up all that gear but did you ground all the DC adapter powered stuff, too? I mean, if it's using an AC/DC wall adapter and if it doesn't have the all three connections to the wall (ie no earth, just neutral and hot) then you can run into this. Neutral goes to the electrical panel (and then earth, or your copper cold water pipe), only earth is earth (at least in NA).
My stereo had this issue coming from the turntable preamp, as it is DC powered via wall adapter. All the equipment goes back to a UPS and power conditioner and still had the issue.
To fix it, I crimped a ring terminal to just the earth wire of an old three-prong AC cord I had and disabled the hot and neutral. Then I used the ground screw on the preamp and affixed the frankenwire to it, then plugged it in to any old available plug on the power conditioner.
Not sure if this makes sense to your equipment but hopefully it helps.