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This is a follow-up to my Ruizu X02 Unboxing and Initial Notes thread.
To recap, the Ruizu has a limit of a 1,200Kbs bitrate and 48kHz sample rate for FLAC. This is a pretty heavy limit that only became evident when I unboxed and read the manual. The test FLAC file I tend to use from the Sony website is 24bit at 92kHz with a bitrate of 3,329Kbs. Sure enough, it got an 'unsupported file' error. The eventual solution was to downsample. More specifically, I had to drop the Sony file to 16bit at 48kHz to obtain a bitrate of 994Kbs because even 24bit at 48kHz was showing a bitrate between 1,700 and 1,900Kbs depending on the FLAC file efficiency used (more on that below).
@amirm commented 'That is a strange limitation Flac data rate in this day and age..' So we decided to check out this limitation by trying to identify the DAC chip. Below is the full story. The first half is also contained in this video:
Proviso: this was done during my lunch break. Forgive the limited photos and the rather awful video. My Canon 7D has a nice USM L 24-105 lens..but the lens needs maintenance. It didn't like the downward tilt and self-zoomed itself during filming. We had one take. This is what we got.
Kicking off, we started from zero to ensure this was a realistic disassembly. If I can do it, you can do it.

The device itself has a nice, simple plastic case.

The case itself has a join going right around. This is promising. It indicates it was snapped together and therefore can be snapped apart.

The snag was that pressing and pulling the device revealed no play whatsoever beyond a distortion being possible around the SD card slot.

This lead to using a fine screwdriver to prise apart the edges to eventually locate the 'snap joints' holding the two sides of the case together. Metal being harder than plastic, and some degree of trial and error being required, this lead to some nasty scratching of the case.

Once we are inside we see a nice, simple setup. Battery on top of the screen. Circuit board below. Very minimal PCB, everything centered around one chip, with another tiny chip located adjacent to the 3.5mm analogue out socket.

The primary chip is identified as what appears to be a WP 29F64G08CBABA Revision B from a company with a swirly M logo. During my video I thought that might be the SoC. Nope. It is the flash memory. Incredibly this chip has 75% of the retail cost of this entire device. Chinese makers really do make things down to the bone on cost.

This leaves us with one other chip to think about, the little item near the 3.5mm analogue port. It is incredibly hard to read in this photo but in the real world I could just make it out as a 5807M TH994 chip. It is an Arduino FM Receiver.

This is where my video ends. Me content to wander off and identify these chips. My little Ruizu being content to be put back together, scars and all, though failing to turn on. A cliffhanger if ever there was one.
However, while the video was importing I did two things.
The first was to attach the Ruizu to power and see it immediately pop back to life. Fantastic! It was just a depleted battery.
The second thing I did was fiddle around with the PCB before I replaced the backplate again. The adventure continued with undoing two really cute little screws.

Two additional screws were located until the wrap providing extra protection for the PCB to screen mount, and the battery to screen attachment. Like I said, the engineers really did put some effort into this little thing.

Bingo! Side 2 of the PCB. Or should that be side one. The manufacturer brand, creation date and whatnot are all located here. We also have a promising chip to explore!

The ATJ2127 ZK60TEA 37B. ATJ2127 to its friends. We have it! The DAC is now known. More specifically, we are viewing the Actions ATJ212X family, with the ATJ2127 variant including embedded RAM and ROM, ADPCM record capabilities and a USB interface.

Here are all the published details:
• MIPS32 processor Core with 5-stage pipeline
• Memory Management Unit
• Simple SRAM-Style Interface
• Multiply/Divide Unit (high-performance configuration)
• Power Control
• MPEG1/2/2.5 Audio Layer 1,2,3 decoder，bit rate 8-448Kbps, 8-48KHz, CBR/VBR
• WMA Decoder, bit rate 32-384Kbps, 8-48KHz
• FLAC decoder
• APE decoder
• 7 or 5 bands equalizer with user-defined 64-step-gain from -12 to 12 dB
• Fast Forward and Fast Reverse
• Fade in and Fade Out
• Digital global gain control
• Integrated Motion JPEG Video Decoder, up to [email protected] resolution
• Support up to 4(pcs) Nand Flash, including SLC, MLC and TLC with 8/24/40/60 bit ECC
• Support following memory card interface
- Multi Media Card Specification Version 4.3(1/4 bit mode)
- Secure Digital Card Specification Version 3.0(1/4-bit mode)
• Support Booting up directly from NAND FLASH/ eMMC/SPI Nor Flash.
• Support 24MHz OSC with on-chip PLL
• Support generating 24MHz and other PLL from Externel 32.768KHz OSC
• Internal 32KHz RC oscillator
• Energy saving with dynamic power management, supporting Li-on only
• USB 2.0 device and host controllers with HOST support
• A variety of serial controllers supporting I2S, I2C, SPI, UART
• Support LCM with 8bit CPU Interface.
• Support FM Radio input and 41 levels volume control
• D/A+PA SNR :without A weight>91dB
• Build in Stereo 16-bit Sigma-Delta D/A
• A/D SNR >90dB
• Headphone driver output 2x20mW @16ohm
• Operating voltage: I/O 3.1V, Core 1.2V
• Standby Leakage Current: <50uA(Whole System)
• Low Power Consumption (No LCD) : <[email protected] (128kbps)
<[email protected] bat (96kbps WMA)
<[email protected] bat (20fps AMV video)
Do you notice something missing? I notice something missing. Let's rewind a little. The Ruizu X02 is great! Cheap enough to be bought as a tiny treat, highly functional and with support for lots of formats like FLAC. But the FLAC support is marginal because it has a limit of a 1,200Kbs bitrate and 48kHz sample rate. This limitation is not contained in the DAC published specifications above, which just refer to a 'FLAC decoder.' It is not reflected in the advertising around the Ruizu X02 either, which also cheerfully just mentions FLAC as a supported file format. It was not until I opened the package, opened the manual and read it that I saw the FLAC limitation recorded.
Let's be fair. Ruizu did mention the limitation, something the chipmaker does not on their public material, and that is worthy of bonus points. However, it would be far, far better if that limitation was made explicit in the general marketing material. It is hard to get FLAC files limited to 16 bit at 48kHz these days. Any download from something like HDTracks will be 24bit 92kHz. As such, the device is not fit for my originally intended purpose.
Out of curiosity I went searching for the datasheet from Actions related to the ATJ2127. It is a remarkably hard thing to find. Most links returned overviews but no PDF. Instead, datasheet sites kept popping up with information for the Actions ATJ2135 or the ATJ2115C. Perhaps Actions preferred to just supply it to customers on inquiry.
And that is it. I have my little media player back, a little battered on one side, but after providing a substantial amount of fun. We have an ID on the DAC. We have an idea of the ultra-thin margins of the device (see comment about regarding the cost of the Flash memory chip alone). We also have a hint to how the limitations around FLAC did not make it into general marketing.
It is hard to get cranky with Ruizu. They did mention the limitation in the manual and - astonishingly - they even have a 2019 firmware update for this device. Check out the PCB shots above: this is a consumer electronics device manufactured in 2015. That level of support would be great for a far more expensive product. Finally, after cracking it open, I have tremendous respect for their engineering team. Again, as with the support, the build details and care would also be great for a far more expensive product.
Conclusion: Ruizu do a great job but before buying a product it probably would pay to message them explicitly to check feature support unless that support is explicitly outlined - including limitations - on their site. I am keeping this player and will give it to someone with apologies for messing up the case, something that is entirely on me. And finally, I will attempt to hone my skills to produce more accuracy and less comedic effects in future teardowns.
Parting note: want to do measurements on the player? Let me know and I’ll send it along.