[hifix]

Hello...

I've just "completed"  a raspberry pi system with a USB DAC and i thought that i'd share it here for anyone who might be interested.  I will include links for all the hardware and from where i "borrowed" scripts for the power management for the Pi and well as config settings.

The Raspberry Pi 3B and a PCM2704 USB DAC make up the frame work of this project and the tweaks to the DAC have been covered in the "MUSE X5 PCM" thread.   The Pi on its own it plays my music files and it can function as a UPnP & Squeezelite renderer / Airplay receiver etc.  With the USB DAC, i was hoping to achieve the same but with a better sound.



1.  Getting the Raspberry Pi to turn off and restart with a pushbutton (without a keyboard).
The Pi runs Moode Audio (free) and not being able to shut the Pi down without a keyboard would be a deal breaker for me.
After getting an acrylic case, i installed a pushbutton and a LED (with a resistor) to signal the powered state of the Pi.  There is more than one script out there for power management but the one outlined on hackster.io did not have an effect on CPU load.
Pi Power Management Script & Config:
https://www.hackster.io/uladzislau-bayouski/blackout-the-power-button-87e276
http://archimago.blogspot.com/2017/01/measurements-raspberry-pi-3-as-usb.html



2.  Tweaking the PCM2704 USB DAC
There are a few versions of this DAC going around.  This USB DAC has an Analog out (RCA & Headphone) as well as a digital out (Toslink & Coax).  Given the price, the sound from the DAC was a plesant surprise.  With inspiration from other builds, i decided to follow suit.  All the components of the output filter were desoldered and replaced with rated items from Elna (Silmic II) and PRP.  The supply caps were replaced with Nichicon FGs'.  The hardware changes added refinement to the sound.  At this point, i was with the idea that this could be a genuine start of a 2nd system.
DAC and parts from:
ebay seller: 2011sunnychen,  item number:151453208441
https://www.hificollective.co.uk/

3.  DIY USB Cable
With this DAC being my 2nd USB DAC (i got rid of my first one pretty quickly), i wanted to hear what all the hoopla surrounding USB cables was about.  Being unwilling to fork out for a "HiFi" usb cable i decided to borrow the idea from a thread on head fi (DIY USB a-b cable) and make my own using shielded Cat6a network cable.  Compared to the generic 1m and 0.5m USB cables that i had on hand, the shorter (0.4m) and heavily shielded DIY cable was a step in the right direction.
Idea and instructions from:
https://www.head-fi.org/threads/diy-usb-a-b-cable.665635/

4.  Linear Power Supply
I was initally hesitant with this one.  Also dubious as to the benefits of clean power in this particular setup.  Due to not being able to source my regulator of choice, i decided to take the punt and try the the power supply for myself.  And i'm glad i did.  The build quality is far above what i would have DIY'd (most of my power supplies are all DIY).  This linear power provided a better defined sound.  It was also clear that it was fuller sounding in the lower frequencies.  Back to back, the switched mode supply had a harshness to it.  This was not the case with this linear supply.  For critical listening the upgrade in power supply is recommended.
The power supply retailer offered customised power supplies and aluminium housings (i wanted something clean looking with no brand names, no logos etc).  There was some to and fro in correspondence to get everything sorted.  This one worked out very well.
Power Supply from:
ebay seller : minishow0328, item number: 142458851433

I'm currently using a Raspberry Pi with an audiophonics i-sabre DAC as part of my main rig.  With an early comparison, this combo seems to be hitting pretty hard.  I will update this thread as this setup gets tweaked.

[Yaaaaaaaaaaaaaaa]

Wow, James, that's quite a setup, and a great write up!

I recall our initial conversations regarding RPi audio; you've travelled a fair way since...

[hifix]

Wow, James, that's quite a setup, and a great write up!

I recall our initial conversations regarding RPi audio; you've travelled a fair way since...

Hi Paul,

Cheers man, i remember our conversations.  Thank you for your help in getting me started with the Pi. 
I'm still using the audiophonics i-sabre dac that all this started with.

Next up for this setup.. is to circumvent USB power and run the DAC directly from the power supply.  I'm hoping it will work out.

[mcgsxr]

Cool project, thanks for sharing.

I am about to embark on my own first Pi journey.  A Hifiberry HAT equipped faux Squeezebox.  Should be pretty straightforward, but my first adventure so who knows!

Will feed my Bolder modded Grant Fidelity TubeDAC-11.

[hifix]

With quite a few hours on the setup i've gone back to try an earlier DIY USB cable.  Compared to the DIY Cat6a USB cable, this one is even shorter @ 35cm.  The 5v and GND connections are seperated from the noisy D+, D- connections.  The D+, D- twisted pair are wrapped in aluminium foil.  The shield which was floating (left pic) - is now grounded at the source.  The ferrite bead underneath the al foil has been removed.



Both the data and power wires are from a solid core Cat6a data cable.  To the ear, this is the best one yet.  From the hacks / tests, it appears that shielded power lines do not reward audio reproduction.  This one has a better grip on the lower frequencies.

Update:

USB Connections using the 2nd DC output of the power supply.  No longer using any of the power connections from the USB port.
Note that the ground potential for the DAC and the Pi must be the same.



The voltage rail is buffered by a 2200uF low esr cap (the sanyo wg in the picture has been replaced).

To my ears, this setup sounds pretty good.  I think i'll leave it alone for now.

[Yaaaaaaaaaaaaaaa]

I think i'll leave it alone for now.

Famous last words...

[hifix]

Famous last words...

I know ... 

[JohnR]

Cool 

[8T_BoCO]

I'm using  a Pi 3 & USB DAC as well, but with a monitor & BT keyboard/mouse combo.
VLC (native on Raspberian OS) lets me see & configure the USB output device for sample-rate fidelity (software resampling disabled).

The major bonus of a Pi for audio, beyond its size & power requirements, is the absence of a noisy fan (like the 10 y.o. nettop it is replacing)!
Audio streaming hardly taxes the Pi hardware, so it stays cool in its AL case.  Highly recommended as a cheap & cheerful solution.

[audioengr]

I tried a Pi using a DIGIONE HAT board so I could drive my DAC with S/PDIF.  Jitter from it was higher than my products, but not bad for the price.  I had problems playing 192 and 176.4 files however.  I modded the Pi board to improve the power, but it didn't fix that.

Compared DLNA using Linn Kinsky to Roon using Roon Bridge using this platform.  Linn Kinsky was much better.  This is what prompted me to back away from Roon.

Steve N.

[mcgsxr]

I am happy running the Pi with the Digione HAT running Picore player and feeding my DAC by COAX.  No issues with up to 24/192 in my setup.

I have not compared it to any other server/streamer setup since trying the Pi, so I cannot comment on how it sounds compared to other options.

[JohnR]

The latest version of the Pi has issues at 192k if you connect by Ethernet and use USB at the same time. With a HAT, USB is not in use and so there should be no issue at all. The other problem area can be Wifi interference at 2.4 GHz. So use 5 GHz, it works really well.

[mcgsxr]

Ahh.  I am an Ethernet user so I guess I ducked one potential issue.

[audioengr]

I had 192 problems with Ethernet, not USB.

[zacster]

I'm up to 3 different RPi configurations in my house.  One uses an Allo Boss hat, one the Hifiberry, and the third uses either an AQ Dragonfly Black or an iFi Nano iDSD.  I run them over wifi using Audirvana to feed them from my iMac.  I've never had any issue with any bitrate up to 24/384.  As for the sound, the Boss is the best and I see no reason to use anything else, including a high-end separate DAC.  The others are all perfectly fine for feeding the other systems.  The Boss is powered by battery, and I have yet to use up the battery supply during a listening session, and sometimes it is playing all day. 

I've tried other configurations, running over wired ethernet and/or wallwart power but I couldn't tell the difference, so wifi and battery was the easiest choice.  There are no electrical issues this way.  One thing that made a huge difference was building a silver interconnect and using that between the Boss and my pre-amp.  But I mean a huge difference.  It was a total eye opener.  And this got me to thinking, since my pre-amp is a DIY Aikido tube pre, I can build the RPI/Boss into the pre-amp chassis and hard wire it in with a much shorter length of that same silver wire. 

[hifix]

In my testing with a GPIO connected audiophonics i-sabre dac, i did find a difference with the use of wifi (Pi 3B).  All my pi setups are connected with a network filter (similar to the sotm cat6 item).  In my main rig the network filter was critical. 

[Update]
After a bit more testing... i have got the thing dialed in with the system settings in Moode Audio 3.81
Linux Kernel : Advanced-RT (Real Time).
MPD Scheduler Policy : Real-time fixed-priority Round Robin scheduling policy