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RE: RPi-4B and Power ??

Posted by soundchekk (A) on January 14, 2021 at 01:31:12

In Reply to: RPi-4B and Power ?? posted by tvr2500m on January 13, 2021 at 11:42:54:

Any of the advise you've been given so far I consider highly questionable.

If you experience "hum" in the system it's usually bad grounding connection
or a broken device.
Check your cables and connectors and also introduce a proper grounding scheme,
such as a star grounding scheme. Keep your cables short.

Now there keeps the myth "SMPS is bad", "Linear is good" and "battery is better"
nonsense floating around. Well underlined by the other responses to this thread.

There are characteristics which clearly define the quality of a power supply, such as

* current capability
* ripple (periodic) and
* noise (random),
* transient response,
* impedance,
* accuracy,
* load regulation,
* temperature stability,
* and more

These characteristics will define the quality of a power supply.

You can achieve top quality results with any type of power supplies.
What matters is the implementation first of all. Usually designing
a high quality SMPS is more complex then designing a Linear supply though.
And that's the key factor. Complex = high cost and effort. That's why you'll find many low Q SMPS out there and SMPSes got a bad rep.


However. There's no reason why a well done (having a good spec according to above) SPMS with a
nice buffer on it's output shouldn't do as good or better as a high Q (according to above spec) linear supply or a high Q battery supply.

Again, what matters are the specs.

Unfortunately manufacturers do not tell you much about it.
Even if the "Noise" spec is shown, it won't tell you much.
Often you'll find noise specs shown for a 0-20kHz range.
That's simply not enough. Higher frequency noise can also very well impact attached devices.
And it's a noise spec produced in a lab environment. You wouldn't know how such a device would work in a real world setup. How much noise it generates on the mains etc in your home environment.


Manufacturers hiding these and most quality parameters IMO for a reason.
Not many people demand them! I once did demand them for the Allo devices.
The answer was like. "We provide what others are providing". All I can tell I didn't make friends by asking for it.

E.g. attaching a 5 foot cable and some el-cheapo connectors plus adapters to a PS will definitely kill every "transient response" characteristic.
That's IMO why manufacturers simply avoid showing it. iFi and Allo belong of course to the few companies who talk about the subject at all.

You might want to have look at quality Lab Power supply specs. Usually these offer more related info. I'd expect high quality (audio) power supply manufacturers to at least extend their datasheets on that lab supply level.

I also had to taken my choice, even without having plenty of specs around.


I've been running my RPis with modified iPower SMPS for years. My RPi 4 server with 2 USB SSDs attached still runs stable with one of these. This doesn't mean that a stable and rather clean $15 SMPS wouldn't be able do the same job.

Still. Nowadays I'd buy an Allo Nirvana SMPS. For that purpose. I can keep the cable short. That keeps the impedance low and betters the transient response all at a reasonable price tag.

Now the streamer.

I'd try to keep the RPi and audio interface PS separated. I'd use two Allo Nirvanas or one Allo Shanti - the Shanti only in my modded version (shorter cables, DC relays) though.



I did have iFi and other USB filters around. I still use one on my Khadas Toneboard.
On modern DACs like the D90 - according to Audio Science Review - these filters do not show any effect on their measurement equipment. This of course could differ from DAC 2 DAC.

The Allo devices also offer a nice starground point to cope with groundloop issues.

Bottom line.


Even this response can not be satisfactory. I know. It's because there's
simply not the one and only solution.



Good luck on your journey.

Enjoy.


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