FIrst Big Project: The Pi Media Center Dac - diyAudio
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Old 24th September 2015, 09:36 PM   #1
AnimeAi is offline AnimeAi  United Kingdom
diyAudio Member
Join Date: Sep 2015
Default FIrst Big Project: The Pi Media Center Dac

The idea behind this project is to combine a Raspberry Pi with a BluRay drive, touch screen control, high quality audio DAC (Digital to Analogue Convertor) and make use of the DAC circuit so a windows PC can also use it as a sound card.

This is the flow of digital/analogue data from inputs to outputs. You may notice I'm concentrating a lot on the audio parts and mostly ignoring the Pi and you'd be right! High quality audio at a fraction of the cost of an AV reciever for playing BluRays, DVDs and Cds is the priority. WIth the SPDIF input consoles such as XBox One can also take advantage. With the windows/mac usb PC input your main desktop can also take great advantage of the increase in sound quality you'll get by using decent speakers and audio processing

Click the image to open in full size.

Parts List:
1 x SPDif socket
1 x Micro USB socket
1 x HDMI socket (unsolder and extend raspberry pi hdmi)
1 x Ethernet socket (unsolder and extend raspberry pi ethernet port)
3 x 3.5mm jack sockets
8 x RCA socket
2 x dial switches (3 way, 5 way)
4 x On/Off switches (Raspberry Pi, USB BluRay, Amp, Main Switch)
1 x 47k/50k log pot (volume)
1 x SPDIF/USB IC PCB Module (XMOS or CM6610A)
1 x DAC PCB Module (IC TBA)
1 x Raspberry Pi 2
1 x 32GB microSD card (for Raspberry Pi OS and file storage - could be smaller but 32GB isn't much more expensive than 8GB these days)
1 x 7" Touch Screen
1 x USB Bluray Drive
4 x OpAmp PCB Modules (Must have 8PDIP socket to allow changing of OpAmps and integrate BUF634)
1 x OPA2604
1 x OPA2228
1 x AD8066
2 x OPA637 (in dual IC to 8PDIP convertor)
1 x TPA3116 PCB Module
12 x LED (display selected opamp, selected input and power status of parts)
Wires and solder to connect PCBs, LEDs, Switches, Dials and Power

Undecided Parts List:
-An enclosure that will fit 7" tft and usb bluray drive.
-Power supply of some sort. Will need ~200W output to drive 100W amp, raspberry pi, dac, opamp and usb bluray drive.

-BluRay drive will also play audio CDs via the DAC as well as DVD Movies and BluRay Movies.
-Raspberry Pi will handle most video files
-Raspberry Pi could be used to manage audio files negating the usb dac input, however normal PC audio would not function via the Pi. The Pi can only natively handle audio/video files, not streaming audio from games or videos/sound files viewed on the PC.
-I won't be designing any circuit boards myself - this is FAR beyond my skill levels. I've recently purchased several DAC modules, an XMOS usb interface and my first Raspberry Pi 2 to play with and experiment on LONG before I build this project. At time of writing I'm still awaiting delivery.
-The touch screen tft adds 60 to the build - twice the price of the Pi, however without it native playback of CDs would require a PC or phone/tablet. Using a PC would make the onboard bluray redundant - I want this to be as functional as possible!
-8PDIP sockets on the OpAmp boards will allow users to test many OpAmps easily with a single device until they find a favorite

Thoughts, Issues:
-Licences for MPEG-2 and VC-1 decode need to be bought from the Raspberry Pi shop
-How well does the Raspberry Pi 2 cope with BluRay playback from disc?
-Lots of different voltages are required - how much noise do step up convertors and voltage regulators add, do their power efficiencies mean more than 200W is needed for a PSU?
-Should use of headphone (3.5mm line out jack) disable the amp?
-Is soft start and speaker protection required and/or easy to implement?
-Custom coding... This will be my nightmare! I'm praying that nothing more than setting up the universal input/output pins and basic work with the linux based OS of the raspberry pi will be needed! Anybody done a similar project?
-Stipped down versions with a single OpAmp board, no TFT and no Amplifier could easily be produced. Potentially the raspberry pi and bluray drive could be omitted as well - this is the beauty of using modular PCBs
-Quality control will be a pain... It's hard to determine in advance how well made a prefabricated PCB is. Are the caps good or cheap and nasty? Is the soldering terrible? Is the board tuned for optimum performance or has it been made as cheaply as possible?
-Potentially if successful and worthwhile a single PCB could be designed to encompass all these compenents
-How could a snubbed 300-500W PC power supply handle this design? Would noise from a switching power supply kill the quality produced by the DAC, OpAmps and Amp? The Pi can handle dirty power fine but Amps are sensitive... Should a custom liniar torroid based PSU be designed or will this drive the project price up immensly?
-Lots of ICs on a single power source could cause ground loops, noise and other undesirable effects. Should seperate power supplies be considered?
-How to ground everything properly to avoid ground loops and noise!

Any thoughts, susggestions and/or constructive criticism are very welcome. I'm hoping this will teach me a lot and eventually build me up to designing my own PCBs with the knowledge I gain.

NOTE: This project has also been posted to the Raspberry Pi forum as they will be much better at helping me work out speficies with the Pi!
Attached Images
File Type: gif Pi Media Center Dac.gif (46.6 KB, 372 views)
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Old 26th September 2015, 05:45 PM   #2
JZatopa is offline JZatopa  United States
diyAudio Member
Join Date: May 2003
Location: Chicago
It sounds like you are going to use this for both stereo and surround sound. So I am guessing the Dac is for 2.0 and the HDMI is for 5.1. You could do this but its going to be way simpler using X64 and windows. I don't see the benefit to using the RPI in this environment. Yeah it saves you a few bucks but the added work of getting everything functional is disproportionate. Have you considered building a more HTPC type system, possibly with XBMC or something similar as the frontend?
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Old 28th September 2015, 12:32 AM   #3
AnimeAi is offline AnimeAi  United Kingdom
diyAudio Member
Join Date: Sep 2015
To be honest, I've had issues with windows and audio dropouts for a long time. My DPC latency is to blame but it's a pain in the rear end to trace down to a single fault. I'm actually not planning on having 5.1 or 7.1 sound built into the first design as that would require a very different approch with the DAC since the majority of "good" ones seem to be stereo only.

The HDMI is simply the transport mechanism for video data and will plug directly into a TV/Monitor with the PCM sound from the BluRay/DVD being diverted to the DAC. I'm not 100% sure if this is possible without custom drivers yet and won't know for certain until I've had time to play with both the Pi and the various circuits.

The aim of this project is to build something for under 200 that will connect to a set of nice speakers (Most likely my spare Celestion Dittons with the crossovers I rebuilt that for 50 second hand and 20 in parts outperform some of the 500+ speakers I've tested - to my ears at least!) Once finished it should in theory outperform a 300+ AV reciever and BluRay player combination (since I've yet to find a BluRay with a decent integrated amp) for a fraction of the price and access all my digital video and audio files to boot. If the first version works well I'll look into ways to get 5.1 and 7.1 sound without immensly complex circuitry and multiple DACs.

As for added work... Sure, I could buy something off the shelf but where is the fun in that? I'm rather looking forward to tinkering with all this and getting my hands dirty. The rewards at the end will surely be worth it as will the knowledge I gain.
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Old 28th September 2015, 01:25 AM   #4
dangus is offline dangus  Canada
diyAudio Member
Join Date: May 2004
Location: Vancouver Island
Just playing blu-rays will be a challenge, since it may be a crime to decrypt them without a license. There's a lot to be said for a thrift store bluray deck and a sale-priced AVR. I'd concentrate on just making a pi play music in a convenient way, using a cheap alphanumeric LCD. That would be useful in a car as well as at home.
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Old 28th September 2015, 01:55 AM   #5
AnimeAi is offline AnimeAi  United Kingdom
diyAudio Member
Join Date: Sep 2015
For the nominal fee of 1.20 (for bluray) and 2.40 (for DVD) the licences you can buy in the Pi store should cover it from what I understand.

To be honest though, DVD and BluRay is an afterthoght. My main priority is going to be the audio side and building something that functions both as a USB/SPDIF DAC, play audio CDs as well as a mid-high end player and something that can access a NAS drive directly. Getting films too is nice but not a proprity.
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