EMI/RFI related.
Hook it up and try it. If needed; things to try: rotate the board so the audio rca is towards the top. Move the pi to the front of the crack.
If you built the code/configured the linux kernel, disable the functions you don't use such as the wire Ethernet, video. I not familiar with the pi development stuff, so all this is a guess on my part.
I design audio products (not tube) with a mix of DSPs, general purpose CPUs, FPGAs, along with network and bluetooth stuff. Rarely do I have to shield parts of the circuit. It is a matter of proper grounding schemes and power supply separation between analog and digital.
Now I need to go get a doughnut... thanks John
« Last Edit: November 15, 2014, 04:29:19 AM by elcraigo »
Craig Lewis (elcraigo is a nickname a good friend who grew up in Mexico gave me)