Power Supply Noise Problem

[thyristor44]

As I wrote some time ago in another forum ("Class D"):
"You should connect all ground lines together

I am working on that but its difficult to earth the Pi also the dac is non powered, USB only.

 

[den_hr]

I am working on that but its difficult to earth the Pi also the dac is non powered, USB only.

You don't need to "earth" the Pi (unless it's in a metal case, in which case it's a good idea to "earth" it by connecting minus (ground) power to the case).
You just need to tie the power ground of the Pi and the power ground of the amp to the same point.
As for DAC, see my crude illustration of how I connected my components in my project.
Granted, my system is a bit different, since everyting runs on 5V.

 

[thyristor44]

I like the idea of your pcm5102 dac, seems a much better solution than my usb dac. I tried your star earth idea but no better. Will try again when I get a 12s dac. I will have to wait to get one from China as I have spent far too much already.

 

[bobo1on1]

Creating a star ground doesn't work in this case, the rpi and amplifier will still use the same wires for power ground and signal ground.

Here's a simple and cheap solution, a USB isolator: USB To USB Isolator Industrial Grade Digital Isolators With Shell 12Mbps Speed ADUM4160/ADUM316 USB Isolator Drop Ship-in USB Gadgets from Computer & Office on Aliexpress.com | Alibaba Group

 

[thyristor44]

Creating a star ground doesn't work in this case, the rpi and amplifier will still use the same wires for power ground and signal ground.

Here's a simple and cheap solution, a USB isolator: USB To USB Isolator Industrial Grade Digital Isolators With Shell 12Mbps Speed ADUM4160/ADUM316 USB Isolator Drop Ship-in USB Gadgets from Computer & Office on Aliexpress.com | Alibaba Group

That looks a good solution. Pi usb into isolator and run the DAC from the isolator. Have you tried this or is it theoretical. To me it should work. Has anyone any experience of this.

 

[bobo1on1]

I have used a usb DAC on a PI with such an isolator, the multimeter showed that it provides isolation, but I did not test if it avoided any ground loops.

 

[thyristor44]

I have used a usb DAC on a PI with such an isolator, the multimeter showed that it provides isolation, but I did not test if it avoided any ground loops.

Thanks bobo1on1 I will try one.

 

[thyristor44]

Exactly, the culprit is the ground loop. Fortunately your TPA3116 amp has balanced inputs, on some boards quite easily usable. It worked in my case very well Adding an Amp into Thin-Client PC

Brilliant phofman.
Got amp as you advised and did your mod and dead silent. So thanks for that.
Only problem, one capacitor cracked so I need to replace it Is it tantalum and does it need to be 63v if I am running on 12v.
Thanks.

 

[phofman]

Very well, congrats.

As of the broken cap - if it works, I would just fixate it with hot glue. If not, any 1uf >12V cap should do, it just transfers common-mode ground noise to be subtracted by the amp's differential input.