Is it possible for end users to program the CS4398 chip via XMOS to enable direct DSD?
https://www.diyaudio.com/forums/digital-line-level/252266-cs4398-dsd-format.html
Also somebody asked 'Does the cs4398 support DSD256?' Most implementations only do 5.6 MHz.
Audio Precision APx525
http://archive.siliconchip.com.au/cms/A_112766/article.html
A very nice review of DIY CS4398 for beginners
http://wwenze.blogspot.com/2012/03/cheap-and-good-or-just-cheap-ljm.html
It seems CYBERDRIVE SEIUN JR-2 was an attempt to copy Sony's early 2010s walkman design.
Back in 2016 they could rely on audio fairs, crowdfunding and the DSD logo to drive sales. They included the CAEE technology, a clear copy of Sony's DSEE. They used ESS9018Q2C and xmos.
Worth noting for Feather/Aura that some earphones exhibit noise and the default volume is always loudest, whereas SHDP remembers the volume setting for next use.
This is probably setting records for '
cheapest DSD capable DAC':
https://www.makkyon.com/2019/08/27/cyberdrive-clarity-feather-dac/
So in Japan, Feather was 1480 yen and Aura was 1280 yen shipped in Aug 2019. In the history of DSD audio and online shopping there has never been nor can there ever be such a low price for a CS4398 DAC! Of course in China the regular price is around the same on taobao. If this is the true cost of the device, it is not bad at all.
Specs for Feather/Aura are stated to be 112 dB SNR, 0.0085% THD+N, headphone amp is
DirectDrive 40 mW at 16 ohms. Feather/Aura is likely to rank quite low. The CS4398 used to be a high-end chip, but over the years the price per chip has probably come down so much that it can now be used in very cheap DACs. It's no exaggeration to say that this chip is the whole package you get (although the XMOS is more conspicuous in terms of area).
By the way, the headphone amplifier part is a chip called "AIF BDM", which is probably the same as "MAX97220", based on the photos of other teardowns. How it works is explained:
https://www.maximintegrated.com/en/design/technical-documents/tutorials/3/3979.html
The combination of CS4398 and
MAX97220 is used in Vivo x5 pro. Unfortunately little is known about Vivo x5 pro except that its CS4398 is a custom version. Clearly phones nowadays can't use such an old bulky chip!
Maxim Integrated's DirectDrive tech is fairly old. But it must have contributed to making portable audio possible. These days people might still prefer more attention to the amp section instead of eliminating capacitors. But it's not that simple. It is not clear how the amp creates a doubled supply voltage to output 2V from 5V supply. Meanwhile, amps are explained here:
https://www.maximintegrated.com/en/design/technical-documents/tutorials/5/5590.html
They say the
MAX97220A headphone amp uses a Class AB topology in a bridge-tied-load configuration with low THD+N and delivering up to 125mW of power and that it 'is one of the most widely used Class AB headphone amps in the world today'.
So is "AIF BDM" really a
MAX97220A? See the
datasheet for MAX97220A. It says the 'top mark' is '+AIF' for MAX97220AETE. It's a 3mm x 3mm x 0.8mm, 16-pin TQFN. Yes, check the pic, it is 16 pins. A 3D model is
here. Price is $0.59/unit. Also, Cyberdrive seems to have copied from this datasheet the value of '112 dB SNR'. So that really helps! But THD+N is quoted higher by Cyberdrive.
All in all, this small CYBERDRIVE drives well. The overall performance is definitely above the price. Because of the size of the unit, there is no room for analogue processing using operational amplifiers, so you could say that the sound comes from the DAC chip as it is. On the other hand, ultra-high frequency sound can feel a little uncomfortable or a bit painful. The CYBERDRIVE has a 'muddier sound' and feels noisier overall compared to other modern dongles. It's perhaps not even the headphone amp's fault. As you can see, the CYBERDRIVE is not a replacement for a good measuring USB DAC but it may be the perfect introduction for those who want to buy a DSD compatible DAC.
Regarding XMOS, D30 (not all iterations)/Feather/Aura uses 6U6C5 which is also called
XS1-U6A-64-FB96-C5. It provides a lot of info. CAD is
here. Its price for one is quite high. Perhaps CYBERDRIVE does cost more to manufacture than its current low price. So it's still not known whether XMOS XS1 can be accessed via USB on a PC. The USB controller XMOS XS1, which is referred to as a "controller" rather than an interface because it has a powerful multi-core microcontroller inside. The core processor is a 32-bit, 6-core processor with a processing speed of 500 MIPS and supports USB Audio Class 2. The XS1 can be programmed by the manufacturer to be used not only as a USB interface, but also as an embedded device in a wide range of consumer electronics, automotive, industrial and robotic applications.
The Cirrus Logic CS4398 is a 24-bit/192kHz multi-bit delta-sigma D/A converter. It has a dynamic range of 120dB. The music signal (PCM) is processed through a fast and slow roll-off digital interpolation filter (digital filter) and then through a multi-bit delta-sigma modulator. It then passes through a multi-element switched capacitor and a low-pass filter to the analogue output.
The analogue output is a voltage output in a differential configuration. The DSD mode can be processed either directly or via a Direct Stream Digital (DSD) processor. The DSD processor has a 50kHz filter to prevent damage to the speaker's tweeter, and an adjustment function to match the output levels of PCM and DSD. Other internal features include digital de-emphasis, volume control and ATAPI channel mixing.
Now that I'm an expert in the surface useless pieces of knowledge on CYBERDRIVE Feather/Aura, I'd like to move on to XMOS programming for newbies.