20260409 - not sweetPotet but i am declaring war on daps

Introduction

The Arcturus Project is a portable digital audio player that is designed to play CD-ripped FLAC lossless audio files from a SD card. It is an attempt to de-slop modern DAPs and modernize ultra-portable digital audio players.

Why Arcturus?

i thought it sounded cool and thats the star i saw tn thats it nothing fancy no symbolism でぇす☆ヾ（´∀`）

Philosophy

This is a direct challenge to the idea of modern Hi-Fi bricks. They are marketed as portable but somehow always end up being deadweight. The selling point for these unstable Android slops is that they offer Hi-Fi audio at 192KHz 32-bits, or direct DSD256 playback. They are also usually capable of driving monstrous magnetic planar headphones which is very impressive. However, if you are wearing your magnetic planar headphones on the train, you deserve to be bullied.
Most of the time, people just want a small music player that you can carry around. It doesn’t need the fanciest topology; it doesn’t need to be able to drive your studio headphones, it doesn’t need to run Android. All it needs to be is well-engineered, light, small and portable. It should be able to playback your audio library through your headphones without you having to lug around a giant brick. It’s the way things has always been.
Recently, I find myself reaching for my iPod Touch 4G and iPod Nano 7. However, I have a hard time using them for a long time because of the limited flash memory. Both of the devices are filled to the brim with MP3s and that’s still a small fraction of my library. Wouldn’t it be so nice if I could just put an 1TB SD card in there? That’s a thing now. Also not to mention the 30-pin and lightning cables… They are completely unusable (`３´)ﾌﾞｰﾌﾞｰ. Everything should be on USB-C PD. It is honestly a shame that a well-built modern device like this hardly exists.

Engineering (the boring stuff)

Due to the selection of parts in this thing, it will probably unintentionally end up being “Hi-Fi.” This, however, is not the point here. It just happened that I picked the nice parts. Also, these are just the parts I have worked with so I am gonna stick with what I know.

Power

To make this dingus portable, the power topology is quite complicated.

• BQ25895 Switching Charger
  • This is used to generate the SYS voltage and act as a charger for the battery. This also enables high power charging with the help of PD negotiation from the STM32.
• TPS63000 Buck-Boost
  • Switching supply for 3.3V digital rail, as shrimple as that.
• TPS61022 Boost
  • Boost the battery voltage to 5.5V so it can be used as a stable input for our dual rail charge pump.
• LM27762 Dual Rail
  • This black magic of a chip let’s you generate dual rail 5V. Will be used to power the DAC VREF, opamps and the headphone drivers

DAC Selection

• AK4493SEQ (honestly I can probably cheap out on this)
  • It’s a nice DAC and because I have worked with this chip before. Too lazy to use something new.
    

Analog Frontend

• OPA1612 (expensive)
  • MFB Low-Pass Filter for filtering out AK4493 high frequency switching noise and single-ended conversion
• OPA1622 (aight)
  • Amplification and driving the stink buds

MCU

• STM32H735VGH6
  • BGA is a pain in the butt to design but it saves a ton of space. We are trying to minaturize the device here so this is prob the best option.

Audio Master Clock Generation

• ASDLJ-E-49.152MHZ-L-R-T & ASDLJ-E-45.1584MHZ-L-R-T
  • True 44.1KHz and 48KHz family clock generation. I will sacrifice a little board space so I don’t have to resample.

Summary

All in all, this is just a goofy project I am working on the side to procrastinate from more important responsibilities teehee (ﾉ∇≦*) ｷｬﾊｯｯｯｯ♪