Raspberry Power Supply

JMMF2019

Member
2020-01-20 1:53 pm
Hello all,

I'm considering a upgrade from the standard raspberry pi 4 switching-mode power supply (Buy a Raspberry Pi 15.3W USB-C Power Supply – Raspberry Pi) to a low noise power supply in order to take the most advantage of the HF SDR equipament connected to it.
I have a switching-mode power supply from my previous HF trasnceiver: 15V, 30AMP PS. Thus I thought of using a linear regulator connected to this power supply, setting the output voltage to 5.1V. I'm currently looking at LM138/LM338 regulators.


What are your advice?
Better to get a dedicated PS from the 230V mains for the raspberry pi to minimize the noise?


Thank you in advance
 
You want to build a low-noise power supply for your RPI. The RPI itself is digital and will pollute your 5.1V low-noise line with all kind of switching noise. What started as a low-noise supply will end up as having as much noise as an ordinary good power supply.
For a DAC board, you use a low-noise supply where you attempt separating the digital and analog power lines on the DAC board. A well constructed DAC board takes into account that the noisy digital power line (and even ground line) should not be mixed up with delicate analog supply. An RPI is constructed as a digital computer that, for the most recent versions, consumes quite some power (due to speed and complexity).
For analog or other noise sensitive circuits you connect to your RPI, you can see if you can feed only them from a separate low-noise power supply (with much less power needs). Feeding the RPI itself from a particular low-noise power supply makes no sense to me.
 
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JMMF2019

Member
2020-01-20 1:53 pm
That's very interesting. I really hadn't thought about the RPI itself polluting the line. Many thanks for the clear and detailed information here...

You want to build a low-noise power supply for your RPI. The RPI itself is digital and will pollute your 5.1V low-noise line with all kind of switching noise. What started as a low-noise supply will end up as having as much noise as an ordinary good power supply.
For a DAC board, you use a low-noise supply where you attempt separating the digital and analog power lines on the DAC board. A well constructed DAC board takes into account that the noisy digital power line (and even ground line) should not be mixed up with delicate analog supply. An RPI is constructed as a digital computer that, for the most recent versions, consumes quite some power (due to speed and complexity).
For analog or other noise sensitive circuits you connect to your RPI, you can see if you can feed only them from a separate low-noise power supply (with much less power needs). Feeding the RPI itself from a particular low-noise power supply makes no sense to me.
 

ranshdow

Member
Paid Member
2020-07-10 6:19 am
SF bay area
That's very interesting. I really hadn't thought about the RPI itself polluting the line. Many thanks for the clear and detailed information here...



A RPi will send mains noise that the standard 5.1V 3A RPi wall wart picks up straight through a DAC HAT, out the RCA jacks and into the preamp even when the RPi is off. Plugging the wall wart into the wall, or into a power strip in the off position, is sufficient to pick up this noise. All you need is a sensitive 'noise detector' - in my case, a passive preamp with 1:8 voltage gain cranked to full volume, feeding an ACA.


I've heard this with two different RPi's, each with different DAC HATs, and one of which had Mark Johnson's PO89ZB DC filter circuit between the wall wart and the DAC. They all give the buzz and about the same level. I can also get buzz from a phono stage or a Sony CD player under the same conditions but at ~1/2 the volume that the Pi gives.



I don't know how to solve this and not sure if I care at this point.