Hello,
I know this is a question coming up quite frequently but I still can't wrap my head around it properly, apologies for this. I'm trying to build a fairly basic guitar amp, more of a test frame for some effect I want to work on in the future. So I'm using a 12V power supply to power a class D amp, which is taking its inputs from Bela's stereo output (I'm using only the L output.) Likewise, I'm using the stereo in (L) for the guitar input. When powering the Amp from the power supply and the Bela from the laptop everything works fairly fine, there is a little bit of hum but nothing out of usual. However, if I power both the amp and Bela (from the barrel jack) from the same power supply there's a significantly higher hum. This goes away the moment I plug the laptop back in. I'd assume there is a ground loop situation going on but I can't be 100% sure. The 12V power supply is a cheapo switching one so I'd assume there is some noise coming from that one as well. I tried 2 ways of bringing the 12V down to 5V for the Bela, one using a CPT DC-DC converter and the other using a 7805, both having the same amount of noise.
How would you advise powering everything up using just one power supply, is there a way to isolate a separate 5V from the 12V power supply?
Best,
Bogdan