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Improve Raspberry 4 streamer

Gekel

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Reading links you have posted seems to be better to underclock Raspberry cpu to have less output noise? Correct?
no. And why should the CPU frequency affect the sound quality? Are you sure you are on the right board? I would ask ppl on audiophile if you believe in this here...
 

audio_tony

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I am considering building a Raspberry 4 streamer with a DAC hat or separate board of some kind. It would be nice to have a small combined streamer and DAC.

I believe one of the main issues with having a DAC in the same box is perhaps power supply noise coming from the wall USB switching power supply or the Raspberry microprocessor. I am thinking of powering the DAC separately using a rechargeable battery with a linear voltage regulator. There might be an off the shelf USB power pack that would work. Or maybe an LT3045, or similar ultra low Noise switching regulator that separately powers the DAC hat. Has anyone tried this separate power supply approach?

Off the shelf USB power packs use a switching regulator to make 5V from the battery voltage. Many of the DAC boards use multiple regulators, including a switching one to make the -ve voltage rail for the output opamps. You need to look at the specifics to see if a separate PSU will improve anything.

Good point,


Good point, "Off the shelf USB power packs use a switching regulator to make 5V from the battery voltage", which could reintroduce noise that you were trying to reduce. You would need the battery directly connected to a linear power supply and bypass the switching regulator.

I performed some tests on a Raspberry Pi4 and the 'official' Pi PSU and a linear PSU. There was little between the two in terms of noise.

The biggest issue as ever, is one of ground loops, which do create noise.

There are too many images to post here so take a look at my measurements on my site: https://gtkc.net/usb-noise-measurements
 
OP
officialsm

officialsm

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I performed some tests on a Raspberry Pi4 and the 'official' Pi PSU and a linear PSU. There was little between the two in terms of noise.

The biggest issue as ever, is one of ground loops, which do create noise.

There are too many images to post here so take a look at my measurements on my site: https://gtkc.net/usb-noise-measurements

Thank you, could you explain here results of your tests and which is better configuration?
 

audio_tony

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Thank you, could you explain here results of your tests and which is better configuration?

In summary:
The column with the highest SINAD figure is the one of interest and the 'best'.
When powered by the linear PSU, the Pi is 1.48dB quieter than running with the official PSU. (in other words - this is of ZERO consequence).
It's slightly quieter still on battery, by 1.77dB, again of no consequence.
The results of a ground loop are shown in the bottom row where it can be seen that SINAD is reduced by 32.4dB - this may be audible at very high volume (and I'm thinking full volume) but that depends on several factors, amp power and preamp gain etc.

Ultimately, it's highly unlikely that anybody would be able to hear any difference between the Pi running on battery, linear PSU or official PSU.
So as long as you buy a decent PSU (doesn't need to be linear, and ideally isolated from ground) you'll be fine.

The sound quality does not change.

1623249161149.png


*NOTE: the slightly inferior noise figure above when using the isolated ADC is a function of the ADC itself - and not the noise figure worsening.
 
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