Hackaday Prize Entry: A Modular Open-Source AV Receiver

Hi-Fi hasn’t changed much in decades. OK, we’ll concede that’s something of a controversial statement to make in that of course your home hi-fi has changed immensely over the years. Where once you might have had a turntable and a cassette deck you probably now have a streaming media player, and a surround sound processor, for example.

But it’s still safe to say that hi-fi reproduction hasn’t changed much in decades. You can still hook up the latest audio source to an amplifier and speakers made decades ago, and you’ll still enjoy great sound.

Not so though, if instead of a traditional amplifier you bought an AV receiver with built-in amplifier and processing. This is a fast-moving corner of the consumer electronics world, and the lifetime of a device before its interfaces and functionality becomes obsolete can often be measured in only a few years.

To [Andrew Bolin], this makes little sense. His solution has some merit, he’s produced a modular open-source AV processor in which the emphasis is on upgradeability to keep up with future developments rather than on presenting a black box to the user which will one day be rendered useless by the passage of time.

His design revolves around a backplane which accepts daughter cards for individual functions, and a Raspberry Pi to do the computational heavy lifting. So far he has made a proof-of-concept which takes in HDMI audio and outputs S/PDIF audio to his DAC, but plans are in hand for further modules. We can see that this could become the hub of a very useful open-source home entertainment system.

If you make one, please remember to enhance it with our own sound-improving accessory.

24 thoughts on “Hackaday Prize Entry: A Modular Open-Source AV Receiver

  1. This claims to be an A/V Receiver, but I see no video components, video switching abilities, or plans for that functionality. Nonetheless, this is definitely a neat project that I could see myself making use of.

    1. Video will come later. I have no plans to do any video processing, but I will be eventually adding a HDMI switcher at least. It’s a low priority for me, as my TV has enough inputs for all my devices…

    1. Mine is a Sony component System with Mission speakers from the early 90ies I bought as a student, quite expensive at that time. Only that some components are not much used any more: Tape, MiniDisc and Tuner and even the CD player. The tape deck is not even working. I play most stuff from the PC

  2. I wonder if a set of standards could be developed for this? Then we could have the AV equipment of a desktop PC. Buy a case, a motherboard, and whatever daughter boards are significant to your use..

  3. If it doesn’t have HDMI 2.0a and HDCP 2.2, as well as Dolby Atmos and so on decoding, what’s the point? You can pick up a used HDMI 1.x era AV receiver for cheap and just use that … and if you don’t need any of these functions, then you don’t need an upgradable open AV receiver either.

    1. Old receivers still don’t have a lot of the feature set that I’m envisaging. They aren’t hackable. They don’t automatically activate night mode when your kids go to bed, they don’t adjust the volume when a bus drives past.

      Chips to handle Atmos are expensive (can you get them in qty 1? I haven’t looked yet) … I want to get a good handle on the basics first.

  4. Video input/switching would be an awesome addition to enable Ambilight capabilities. Even without this, I have been thinking about a device as this, though maybe more focused on the audio pre-amplifier capabilities. My NAD C370 supports bypassing the pre-amp and feeding a direct signal to the power amp.

  5. I’m not sure about others but I’m finding my AV receiver less and less critical.

    Currently my TV has a large number of HDMI & legacy inputs, and then outputs the audio stream as SPDIF/Dolby/DTS over optical. The AV receiver then takes this optical and decodes/amplifies it. Im hoping that any TV I buy in the future will do similar, including the provision of new video inputs as standards evolve. Between the TV switching capabilities and a Logitech Harmony remote, it’s all automated and seamless.

    Out of my 6 sources, 4 are basically switched via my TV. The remaining two are the radio built into the AV receiver and a standalone CD player, but they are hardly getting any use these days as I prefer streaming internet radio and mp3s via XBMC.

    1. The only issue I find with a setup like this is that bitstream audio can’t be passed through optical. I suppose the TV could encode the bitstream into DD/DTS, but it seems unlikely that any would do so. I suppose if you use HDMI ARC this issue could be mitigated.

  6. I still use my AV receiver (Denon) to switch all inputs, and my TV is relegated to being a large screen HDMI monitor.

    Before I got the Denon, I was hacking a Sony receiver (STR-DB930) which didn’t have HDMI inputs at all. I used a cheap Chinese HDMI switcher box, and drove the IR RC input with a micro controller – that was watching two inputs inside the receiver which fed the multiplex that chose the right audio input. When the receiver switched audio input, the mux input would change, the Atmel 8051 sent an RC stream out to the video switch which tracked it.

    Then the cheap Chinese HDMI switch broke one day after about six months, so I ordered up another from that auction site; but when it arrived the RC protocol had changed! Nothing more boring than returning to a hack to have to re-encode the remote control stream.

    I reverted to buying receivers from that auction site which were faulty in some way and I could fix instead. I ended up buying about four, selling two of them back again once repaired which paid for the other two.

  7. “hook up latest audio source to an amplifier and speakers made decades ago” – Yes, and that’s the reason I would not accept a phone without the 3,5mm audio (not only headphone) jack.

  8. The PCI modular idea for a AV unit is cool, but the issue that always plagued me was the case becomes the major hurdle unless you want to try and be compatible with ATX. PCI brackets are a little tight – xlr is out.

    Work around might be to use the cutout where the motherboard back plane is.

    It’s all compromises and results in a less than ideal solution.

    The best solution I thought of is to use PCI connectors (cheap, common, only need one of them since you use edge connectors) but scrap the whole ATX idea and make line card style with wider back. Could do laser cut acrylic for the panels, could do the inserts/mounting stuff with acrylic too which would let you easily adapt it all to rackmount case, or whatever. (later folks who wanted could easily adapt it to metal)

    It’s a cool project, i’ll be following with interest!

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