ProtoDAC TDA1387 X8 project

[wolf7250]

For my current setup, it would go between the SMPS and the Kali. These DC filters attenuate noise, but they don't eliminate it. People have used multiple filters in series. But then you are affecting the transient response of the power supply. It would be best to filter, then go into a capacitor or ultracapacitor reservoir.

There is still noise generated by the Raspberry Pi CPU and also the switching regulators of the RPi. Only the original RPi 1 had linear regulators. Some people would actually do microsurgery on RPis with switching regulators, and replace with linear regulators.

That noise from the SMPS gets everywhere. Not only on the positive line, but in the grounds and radiates back onto the AC line. Some EMI as well, but much less significant. Electronics need to pass EMI standards set by the FCC and European regulators.

Until I heard the 5V ultracap supply of the PurePi, I didn't fully appreciate the haze of noise that the Allo basic 5V SMPS was casting, even with the built-in filter of the Kali. I knew there was some noise, but didn't realize it was that much. For some reason, the Allo SMPS creates a larger soundstage, so it has that benefit in its corner. The LifePO4 battery and/or ultracap supplies plus isolation (to deal with the noise from the RPi) seem to be the best solutions.

Thanks! This is all really great information. And has prompted me to investigate further into the products available on the Ian Canada website...
I found these (which you may already be aware of):

1. Isolator Pi which seems to handle the issues of noise on the Raspberry Pi GPIO etc - think that the FiFoPi Q7 has this built in??
   
2. Shield Pi Pro which seems to fulfil two functions:
   a) Act as an EMI shield (less interesting based on your observations of EMI not impacting performance as much) and
   b) Power Supply noise filter
   

If I was to go with a FiFoPi MA (and any Pi other than a Zero W) then I think the Isolator Pi could be useful.
The shield Pi Pro looks like it could be a really good alternative to the Power Supply noise filters we've already been discussing.
What do you think? Were you already aware of these products?