Linear power supplies for RPi DACs

[Datun Walnut]

Hi All.
I'm running a raspberry pi 3b with a hifiberry DAC plus pro hat. I've isolated the DAC from the power of the RPi and am now running it from a linear power supply fed through a mains conditioner. I'm now really happy with the sound for its price (not sure if the mains conditioner does much tbh). Is there any mileage in feeding the RPi from a linear psu or can I leave that dirty? Also, I'm assuming there's an opamp on the DAC. Is it any good or could I bypass it and run it into my Lampizator buffer?

 

[edbarx]

Hi, I have a Raspberry Pi 3B+ which I power from its stock switch-mode power supply. Till now, it does not seem to degrade playback quality, but I am also using an IQaudIO DAC PRO hat as my sound card. The installed operating system is Raspbian with systemd and pulseaudio disabled or uninstalled.

 

[jrocker]

Your assumption on there being an opamp on the output of the DAC chip is incorrect. There isn't one.

 

[Mark Tillotson]

Is there any mileage in feeding the RPi from a linear psu or can I leave that dirty?

The RaspPi itself is all digital, there's no point whatsoever giving it a clean PSU, as it spits all manner of hash all over it (its far dirtier than any SMPS for instance). A well designed DAC has completely separate analog and digital supplies/grounds going into the DAC chip and lots of filtering on the analog supplies to keep it clean.

Powering the DAC module separately from the Pi is potentially with benefit by adding to the analog/digital separation.

Waving some of these (with spectrum analyzer) over such circuitry is an eye opener: Beehive Electronic
(you can make your own probe sets cheaply BTW, the RF spectrum analyzer is a different matter though! - but it does show the immense amount of EMI around digital circuitry - perhaps the best advice is keep the DAC at some distance from any digital PCB, or else shield between them. I've probed around the keyboard keys in my laptop and each one leaks lots of near-field EMI a cm or two - stacking a DAC as a Pi hat is not the ideal placement!)

 

[Bare]

Was interesting.. up until the 'Lampizator' bit.

 

[alwaysHiFi]

I have Linear psu into my Pi 2. I was surprised how much current Pi requires, when it does stuff, like start playing ect. I see peaks of around 3A, norm running around 400 to 500mA. So you need pretty beefy linear for this sort of load. Having large psu does make Pi very stable, never drops out, hangs or needs rebooting

Does it help sound quality? I feel better about it. It removes a switch mode psu from close to the rest of my HiFi power.

My Pi drives a digione which is not supplied from the Pi. Digione is powered from another linear supply. Together with these power supplies, sound quality is good to me. Moode and Chord 2qute dac.

 

[phofman]

Reality check RPi2

https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_2b_1p2_reduced.pdf


NCP6343 - 3MHz step down DC/DC
https://www.onsemi.com/pub/Collateral/NCP6343-D.PDF

PAM2306 - 1.5MHz step down DC/DC
https://www.diodes.com/assets/Datasheets/PAM2306.pdf

 

[edbarx]

The RaspPi itself is all digital, there's no point whatsoever giving it a clean PSU, as it spits all manner of hash all over it (its far dirtier than any SMPS for instance).

I've probed around the keyboard keys in my laptop and each one leaks lots of near-field EMI a cm or two - stacking a DAC as a Pi hat is not the ideal placement!)

So, you are stating a Pi Hat like IQaudIO DAC Pro is improperly designed. The IQaudIO hat has costed me more than the Raspberry Pi 3B+ itself!

 

[jjasniew]

So, you are stating a Pi Hat like IQaudIO DAC Pro is improperly designed.

Well, everyone's got themselves wrapped around the axle of the "hat" or "shield" concept; probably just what you want for robotics, sprinkler systems, household measurement and control - stuff that doesnt need the same level of "woo" that is necessary due to the extraordinary sensitivity of the human ear in so many dimensions, i.e. what people say they can hear.

While I see USB isolators being used for the purpose of ground loop breaking while using USB DACs, the convenience of just "hatting" the DAC is perhaps too ubiquitous to break.

I'm pretty sure a galvanic isolated I2S connection could be designed (if not done already/long ago) and the Pi and its DAC "hat" put in separate, isolated spaces within an enclosure - or fully separate boxes with separate power sources. Only depends on how far you want to go attempting to rectify what I see as a legitimate concern.

That said, I just bought the HiFiBerry I2S power amplifier "hat", which I'm planning on attaching to my Pi 3B (running Moode) in the usual way. Hope it works and sounds as good as I expect in my little FR 2.1 bedroom system Certainly OK simply using a Dayton APA-102 D amp with the Aune T1 DAC. (I want full digital bit transport right up to the speaker terminals)