Hey folks, newcomer here after being a reader for a few years š
Iām working on small DIY DAP (imagine if iPod Shuffle and Shanling M0 had a baby) and after 1st prototype Iām trying to squeeze the best possible performance from the limited PCB space / orientation and will appreciate your help
I did split design into multiple PCBs and arranged them into C-shape - you could see high freq. and audio parts + dimensions marked on the images attached:
I donāt have any experience designing top-notch audio PCBs (or low noise analog in general), so all extra opinions/thoughts are very welcome, but my main questions are:
In overall I want to create end game portable DAP with buttons š So any drops of wisdom from you folks will really help to make it happen! š
Iām working on small DIY DAP (imagine if iPod Shuffle and Shanling M0 had a baby) and after 1st prototype Iām trying to squeeze the best possible performance from the limited PCB space / orientation and will appreciate your help
I did split design into multiple PCBs and arranged them into C-shape - you could see high freq. and audio parts + dimensions marked on the images attached:
I donāt have any experience designing top-notch audio PCBs (or low noise analog in general), so all extra opinions/thoughts are very welcome, but my main questions are:
- Iāve used PCM5102A to just have I2S sound output - but does it make sense to use smth better? Iāve heard that biggest contributor to noise will be the rest of the design and getting better DAC with lower noise floor is not really worth it since the rest of the design wonāt be able to go that low.
- What is the best amplification option to squeeze in here considering it will be for headphones only? I donāt drive anything demanding, but having some margin for the future will be useful.
- Any recommendation on analog parts (i.e. using smth else than mlcc caps, any specific manufacturer e.t.c.)? Any examples of best in class PCBs of similar size to learn from?
- If I will route audio signal from amp to jack on another PCB via headers - could that introduce significant extra noise?
- Is common PCB stackup S-G-G-S is okay or I could get extra shielding by using G-S-S-G? Considering that on DAC PCB below analog signal it will be mostly G-G-S-G since I doubt I would need 2 layers for analog part and will just pour 2nd signal as well.
- Will making PCB 0.8mm introduce some extra coupling that will be critical compared to 1.2mm stackup?
- Should I put some shielding on PCB with MCU? Like the ones that could be usually seen on ESP32 modules or on XIAO boards - thin metal enclosure wrapping top layer components to limit noise coupling to DAC PCB. Or itās just way too far to influence another PCB?
- I plan to use connected ground planes - i.e. no separation between analog and digital. Or itās a good idea to split them and then connect using ferrite beads and other voodoo magic?
- LDOs are the best choice for portable analog power source, right? Since buck & switching will introduce more noise.
- Using same LDO for DAC and MCU DVDD is okay, right? Only AVDD should have separate LDO to decouple from digital noise.
- Should I do vias stitching if I don't have any wireless onboard? Could that help shield any external noise or it's not an issue unless I add bluetooth.
- I have another option of stackup where PCBs will be on top of each other (āParallel Stackupā image) - will that couple way too much noise from digital PCB?
In overall I want to create end game portable DAP with buttons š So any drops of wisdom from you folks will really help to make it happen! š
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Looks like you are going about this is maybe not such a good way. Seems like there are a lot of assumptions baked into the questions you are asking, but the questions you aren't asking are perhaps the more telling.
How about this instead, show us the just the dac board schematic, and the rough proposed layout of devices that will go on the dac board including the location where power comes in to the board? How would you propose to connect the dac board ground plane to the ground planes of the other boards? Why or why not use any power planes?
Then consider in more general terms how you will isolate the dac both electrically and mechanically from the MCU. How will you manage both radiated and conducted EMI/RFI coupling from the MCU/display/digital storage, etc., to the sensitive analog dac circuitry (also considering that in dacs, clocks are included as sensitive analog circuitry).
Also, please describe your plans for how this will be powered, batteries recharged how and how often (with a wall wart?), data transferred to/from a PC or any other external devices. That's just in case any external connections could introduce noise/interference into the sensitive dac circuitry.
Then once some of the more sensitive circuitry has been thought through sufficiently, the start working from the dac board needs towards more detailed planning of coupling/interaction with the digital circuitry.
Just some thoughts for your consideration, is all.
How about this instead, show us the just the dac board schematic, and the rough proposed layout of devices that will go on the dac board including the location where power comes in to the board? How would you propose to connect the dac board ground plane to the ground planes of the other boards? Why or why not use any power planes?
Then consider in more general terms how you will isolate the dac both electrically and mechanically from the MCU. How will you manage both radiated and conducted EMI/RFI coupling from the MCU/display/digital storage, etc., to the sensitive analog dac circuitry (also considering that in dacs, clocks are included as sensitive analog circuitry).
Also, please describe your plans for how this will be powered, batteries recharged how and how often (with a wall wart?), data transferred to/from a PC or any other external devices. That's just in case any external connections could introduce noise/interference into the sensitive dac circuitry.
Then once some of the more sensitive circuitry has been thought through sufficiently, the start working from the dac board needs towards more detailed planning of coupling/interaction with the digital circuitry.
Just some thoughts for your consideration, is all.
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