Help with Hum on Ian Canada streamer/DAC stack

Hi-

Have been playing in the Roon/Raspi streamer world and having plenty of fun with that. Am only proficient to a "simpleton" level as a tech, which is why I'm posting for helllllppp!!

Here's the current project from bottom to top of the Pi stack:

Ian Canada UCPi power supply-powered via USB-C using a Nirvana switch mode power supply
RasPi 4 rev B
Ian 9038Q2MPi Dual Mono Plus DAC HAT with the ESS controller of course
Ian OPA861 I/V output
To get started, I ordered a generic little 3.3/5v dual regulator board from Amazon to supply the DAC HAT and OPA861, powering the regulator with a 2.5 amp wallwart. That got the system working, sounding pretty nice while I saved up to start building up to better power supplies. It is likely this will get built into a nice case, it is enjoyable!
_____________________________________________________________________________________________________________________________________________________________________________________________
So now I finally got the Ian Dual Linear Pi MKII linear power supply powered with a Triad 2X 6vac 100va toroidal xformer. When I mocked up that upgrade was careful and methodical to match my skill level:
First wired the Xformer primary and tested the secondary winding outputs to be sure they were correct at 6vac X2.
Next connected 6vac to the inputs of the Ian Dual LInear unit and made sure i had the correct 5v outputs and polarity of DC voltage.
Then modded the jumpers on one Ian Dual Linear board to 3.3v and tested that power supply output for correct voltage/polarity.
Finally, connected the Ian dual linear PS up to the rest of the stack; the Ian DAC HAT gets all three of the single 3.3v power ins chained together with jumpers and powered by a single Dual Linear PS board. The OPA861 gets its 5v +/- from the other board of the Dual Linear PS that's configured to 5v. I did not connect the ground terminal of the OPA861 board to anything as there is no case yet.

That was last night, and as I fired 'er up in anticipation to be hearing some audio improvements from the better PS, just got only loud hum as the output of this RAsPi player stack!

So far, I have tried connecting the Ian OPA 861 ground terminal to the ground of an AC outlet and it still hums the same? So unhooked that.

But this is interesting and might mean something: I left the Ian Dual Linear PS board configured for 3.3v powering the Ian DAC HAT. But on the Ian OPA 861 I disconnected the dual linear PS and am powering its 5v with the Amazon regulator/wallwart. Powered like that, the streamer works normally with no hum, just nice music on the audio out. Can anyone enlighten me on what I missed, please?

mock up.png
 
You are probably asking in the wrong forum. Why don't you ask in an Iancanada thread?
A lot of people including sometimes Ian follow the thread at: https://www.diyaudio.com/community/...te-weapon-to-fight-the-jitter.192465/page-469

Also, do you have any test equipment? A digital multimeter? An oscilloscope?

In addition if we are going to help we need more than distant pic of the setup. We would need to see a schematic or wiring diagram that shows every single connection in detail. Also, close up hi-res pics can help to verify if connections are correct.

Usually loud hum is related to AC line frequency. Could be an open ground, could be a ground loop, could be AC where there is supposed to be DC due to miswiring or bad components, etc.
 
HI Mark and thanks for replying!

I did end up getting this solved and it was an AC miswiring on the transformer secondarys. Ian sent me a nice little diagram that helped me suss it out. Quiet as a mouse now and does sound so nice it does deserve a case which I am fabricating now. Thanks again,.
 
  • Like
Reactions: 1 user