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Linear PSU for Raspberry Pi 3, which one? Confused.
Linear PSU for Raspberry Pi 3, which one? Confused.
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Old 18th October 2017, 09:00 PM   #1
drtebi is offline drtebi  United States
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Question Linear PSU for Raspberry Pi 3, which one? Confused.

I am having trouble to figure out which PSU (kit or assembled) to choose for my raspberry-based network transport project.

The plan so far is:

- Filtered Power Inlet module with fuse
- R-Core transformer with two 110V primaries
- Linear PSU
- Powerblock
- Raspberry Pi 3 with Allo DigiOne
- S/PDIF output jack
- Ethernet input jack

The PSU is where I am stuck. I have searched all over the internet for a PSU kit with instructions etc., and initially settled on building the sigma 11 PSU from amb.org, but now the site is down!

There appear to be suitable Chinese PSUs offered on eBay, but with vague or confusing instructions (if there are any).

I am looking for something like the PSU-2448 from FiveFish Audio but that particular one is rather for mic-preamps.

I am new to this, but from what I have learned, this appears to be what I need:

-> A transformer with two 110V primaries and a secondary of about 6V output
I want to be able to switch it to 220V later on, so two 110V primaries running either in series or parallel should work for that(?).

-> A low noise PSU that can handle at least 1.5 amps.
The raspberry in the proposed configuration shouldn't need more than ~700mA, although I don't know the power consumption of the Allo DigiOne; but 1.5A would be safe, also considering the occasional USB connection to a keyboard/mouse etc.

I would really appreciate any pointers. You can also tell me that I am completely wrong with my approach... convince me of something better
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Old 18th October 2017, 11:16 PM   #2
Mark Johnson is offline Mark Johnson  United States
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Linear PSU for Raspberry Pi 3, which one? Confused.
If the raspberry pi 3 is a digital circuit board, the benefits of supplying its DC power from a linear PSU, will be small.
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Old 18th October 2017, 11:37 PM   #3
jplesset is offline jplesset  United States
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Rasberry Pi is indeed digital. It's a small computer. Unless you end up with an extremely noisy power supply, liner is not a requirement for excellent sound.
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Old 18th October 2017, 11:48 PM   #4
drtebi is offline drtebi  United States
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Quote:
Originally Posted by Mark Johnson View Post
If the raspberry pi 3 is a digital circuit board, the benefits of supplying its DC power from a linear PSU, will be small.
Quote:
Originally Posted by jplesset View Post
Rasberry Pi is indeed digital. It's a small computer. Unless you end up with an extremely noisy power supply, liner is not a requirement for excellent sound.
I have heard that a few times, but I have also heard the opposite a few times, so I guess it is debatable.

So let's just say I want to do it anyway... any suggestions on a good kit?
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Old 18th October 2017, 11:53 PM   #5
Andrewbee is offline Andrewbee  Jamaica
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May I suggest you read this article, based on measurements and not "subjective science"

If you still want a linear supply after that then I would suggest one of those USB power banks - a big battery, maybe one of the 20K mAh units. Whats more linear than a battery afterall.

Archimago's Musings: MEASUREMENTS: Raspberry Pi 3 as USB Audio Streamer (with recommended CRAAP config & TIDAL/MQA arrives)


Andrew
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Last edited by Andrewbee; 18th October 2017 at 11:57 PM.
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Old 19th October 2017, 12:33 AM   #6
drtebi is offline drtebi  United States
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Quote:
Originally Posted by Andrewbee View Post
May I suggest you read this article, based on measurements and not "subjective science"

If you still want a linear supply after that then I would suggest one of those USB power banks - a big battery, maybe one of the 20K mAh units. Whats more linear than a battery afterall.

Archimago's Musings: MEASUREMENTS: Raspberry Pi 3 as USB Audio Streamer (with recommended CRAAP config & TIDAL/MQA arrives)


Andrew
But the article clearly says:
It just sounds much better now that I have tweaked the parameters. Bass is deeper. Treble even more trebly. Soundstage goes back a mile with 360 envelopment.
!!

OK, just kidding. Although the test was not between a switching and linear power supply, I must assume that the difference of these two is rather inaudible, and I may just kill the idea of a linear power supply.

Well then, any other suggestions to get the best out of a raspberry pi 3 based transport?

Should I also assume that the difference between USB -> DAC vs. Allo DigiOne S/PDIF -> DAC should be indistinguishable? What is the advantage of the Allo DigiOne then? Longer cables?
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Old 19th October 2017, 12:55 AM   #7
Andrewbee is offline Andrewbee  Jamaica
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In a nutshell, a digi output HAT gives you a digital output which you then plug into your DAC. Think of the Digi HAT and RPI3 as a transport. S/PDIF is the recommended connection vs e.g. USB (quieter).

The other version is as a DAC where you have a DAC HAT as the output e.g. Hifiberry DAC + on the RPI so you now have a DAC output.

So for instance in my particular situation I have a digital amp so only need a transport. I use the optical output from my CD player straight into the optical input of my digital amp, no DAC needed but next for me is a second RPI3 and a DIGi HAT so I can use my HDD with FLAC files on the digital amp.

For my analogue amps I use a HDD with FLAC files connected to a RPI3 with a Hifiberry DAC + Pro so that would be like a transport and DAC.

Hope that helps.

Andrew
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Old 19th October 2017, 01:05 AM   #8
drtebi is offline drtebi  United States
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Quote:
Originally Posted by Andrewbee View Post
In a nutshell, a digi output HAT gives you a digital output which you then plug into your DAC. Think of the Digi HAT and RPI3 as a transport. S/PDIF is the recommended connection vs e.g. USB (quieter).

The other version is as a DAC where you have a DAC HAT as the output e.g. Hifiberry DAC + on the RPI so you now have a DAC output.

So for instance in my particular situation I have a digital amp so only need a transport. I use the optical output from my CD player straight into the optical input of my digital amp, no DAC needed but next for me is a second RPI3 and a DIGi HAT so I can use my HDD with FLAC files on the digital amp.

For my analogue amps I use a HDD with FLAC files connected to a RPI3 with a Hifiberry DAC + Pro so that would be like a transport and DAC.

Hope that helps.

Andrew
Thanks Andrew. I think I have understood that much already. I do have a DAC that can accept S/PDIF as well as USB. It's a pretty good DAC (RME ADI-2 Pro), so I wanted to just use the Raspberry as a transport only (e.g. no DAC within the Raspberry).

But since I could use either
1) Raspberry USB -> external DAC, or
2) Raspberry with Allo DigiOne S/PDIF -> external DAC
I was wondering if there would be any advantage in 2).

The Allo DigiOne is very similar to the Digi HAT by the way.
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Old 19th October 2017, 01:57 AM   #9
Andrewbee is offline Andrewbee  Jamaica
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IMO, generally its 6 of one, half dozen of the other. They are all pretty similar, more alike than different. I think once you get to the e.g Hifiberry DAC + Pro stage where you have a transformer for isolation and separate clocks for jitter reduction (another somewhat controversial subject) I don't see it getting much better. There is a the ability to power the analog section separately which you were contemplating, I really don't see the necessity, its really all "fluff". If the power to the RPI3 is "clean" (tests show it is) why power the DAC or part of it separately unless to satisfy the audiophile tweakers addiction.

Even switching power supplies have their fans, a switching frequency for a linear power supply is 50 / 60 cycles depending where in the world you are vs a switching power supply which could be as much as 1MHz or more, which one would likely be more audible? If properly done none would be. The switching power supply however will be smaller, cooler and cheaper.

If its "Bit Perfect" then it can't get any better, different sounding maybe but technically its as good as it gets.

Once here its like seasoning a meal, some may like a lot of Garlic and others not, it does not make it better or worse, just different.
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Last edited by Andrewbee; 19th October 2017 at 01:59 AM.
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Old 19th October 2017, 02:08 AM   #10
drtebi is offline drtebi  United States
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Quote:
Originally Posted by Andrewbee View Post
Once here its like seasoning a meal, some may like a lot of Garlic and others not, it does not make it better or worse, just different.
You clearly haven't tried my cooking yet

One thing just occurred to me: The external DAC I am using is actually also my Pre-Amp. So it would make little sense to use a DAC on the Raspberry, go into the external DAC where the analog signal is again converted to digital etc. In other words, I would have unnecessary D/A - A/D - D/A conversion.

Well, I think I will just get the Raspberry for now, and then play around with it...
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