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Custom linux DAP build - am I crazy?

tokyovigilante

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Hi All,

I would really like a dedicated DAP to replace my phone, however I use a Subsonic-API music streamer (Navidrome) primarily. I have used the various iOS apps, but none really work well particularly regarding sync and shuffle play.

I have built my own desktop player using the Subsonic API in Swift, and have had the crazy idea of building a DAP based on this software running Linux. I could use something like the Pimoroni Pirate Audio board, but would rather have everything in a single board with a 4-5" display and larger battery.

I have made some initial research, and have asked an electronic engineer to create a prototype PCB based on the ESS ES9218 DAC/Amp and an ARM Cortex processor. An SD card slot or WiFi could be used to load the OS/music, and a 3.5" output would be included. If a WiFi/BT chip is included, there is no reason BT streaming to/from the device could not be included also, or USB audio out etc... The sky is the limit when a general-purpose OS is running and the hardware is open.

Has anyone done anything like this or would be interested in such a device? Any thoughts on the DAC/Amp combo? The ESS chip is relatively expensive, but does have a Linux driver as released by LG



 

maverickronin

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I keep dreading the fact that I will need to do this eventually as Rockbox ports get fewer and farther between.
 

Vict0r

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The only Linux DAP I know is the Dethonray DTR1, so I'm curious to see where your project goes!
 

Jmudrick

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I think it's crazy. Buy a $250 LG V60 and uninstall or hide the stuff you don't want. That being said sounds like fun.
 
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tokyovigilante

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Ok, this is what I've got so far (schematic, PCB in progress)
  • Based on RPi CM4 compute module
  • TI PCM5242 DAC (connected via I2S for audio and I2C/SPI for control) and TI TPA1620 headphone amp
  • 4.3" 800x480 display (planned from Waveshare) and an aluminium CNC-milled case (pending final board dimensions)
  • 3.5" headphone jack
  • 2x USB 2, USB-C charge/EEPROM flash with battery charging/UPS while in use.
  • SD card slot
  • micro-HDMI port
  • BT/WiFi (on CM4 module).

Pros:
  • RPi board means much easier and easier support than a full custom SBC
  • TI combo easier to integrate and more easily sourced than the ESS chips
  • Can actually be used as a full desktop computer with networking as well as a portable DAP, plus all the bidirectional USB and BT support of the Pi.
  • LVGL is a near perfect tool for building a touchscreen UI for the player.
  • I'm hoping for 8-12hrs of battery life with sensible power management.
Cons:
  • CM4 potentially overpowered for this application
  • SNR/THD of TI DAC slightly lower than the ESS (~94dB THD at best)
  • Potential inability to use eMMC variants of the CM4 with an SD card (this is an issue with the SDIO pins being disabled, but there is a second SD (storage only) set of pins on the GPIO.
  • Will end up being bulkier than a single board solution once battery taken into account.
  • My crap EE skills and absolute state of the world/chip supply chain mean it may never be built. (Good luck actually getting a CM4...)
Thoughts? (Schematic licenced under CC BY-NC-SA 4.0)
 

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TheBatsEar

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Ok, this is what I've got so far (schematic, PCB in progress)
  • Based on RPi CM4 compute module
  • TI PCM5242 DAC (connected via I2S for audio and I2C/SPI for control) and TI TPA1620 headphone amp
  • 4.3" 800x480 display (planned from Waveshare) and an aluminium CNC-milled case (pending final board dimensions)
  • 3.5" headphone jack
  • 2x USB 2, USB-C charge/EEPROM flash with battery charging/UPS while in use.
  • SD card slot
  • micro-HDMI port
  • BT/WiFi (on CM4 module).

Pros:
  • RPi board means much easier and easier support than a full custom SBC
  • TI combo easier to integrate and more easily sourced than the ESS chips
  • Can actually be used as a full desktop computer with networking as well as a portable DAP, plus all the bidirectional USB and BT support of the Pi.
  • LVGL is a near perfect tool for building a touchscreen UI for the player.
  • I'm hoping for 8-12hrs of battery life with sensible power management.
Cons:
  • CM4 potentially overpowered for this application
  • SNR/THD of TI DAC slightly lower than the ESS (~94dB THD at best)
  • Potential inability to use eMMC variants of the CM4 with an SD card (this is an issue with the SDIO pins being disabled, but there is a second SD (storage only) set of pins on the GPIO.
  • Will end up being bulkier than a single board solution once battery taken into account.
  • My crap EE skills and absolute state of the world/chip supply chain mean it may never be built. (Good luck actually getting a CM4...)
Thoughts? (Schematic licenced under CC BY-NC-SA 4.0)
Some random thoughts:
  • I would consider dropping the RPi4 CM for a RPi Zero 2, it can be compared to the RPi3 in terms of computing power and has potentially lower power draw.
  • BT is a problem with metal enclosures.
  • Drop the "Can actually be used as a full desktop computer", either you build an appliance or a general purpose computer. Just because i can transport wet cement with my bike doesn't mean i work with it on a construction site.
  • If you stick to the RPi4 CM you will never reach 12h battery life or you need a comically large battery.
  • A dap only needs one USB out/in. I would drop the exposed SD card for internal storage.
 
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