I will explain, why we need a flexible cable. This will allow you to place the Board with the bottom of the main Board and will not interfere with the cooling (the fan that can be installed from the top of the Board).
You can see OLED word above, which means that Khadas Audio board will support OLED screen/display.
@balbes150 Here is a questions for your suggestion:
Do you think Audio Input like 3.5 Jack or SPDIF IN is necessary, which means that users can use external audio device like mobile phone as the audio input source.
Minimum option price to 10-20$ (maybe connected through the contacts for USB on 40-pineway the line). This option may have the minimum set of circuits and interfaces. For audio output (RCA\SPDIF) and connect the microphone jack of 3.5
Max. The price is determined by composition. In this embodiment, must be all the interfaces and outputs for high-quality sound reproduction. I’m not good at audio , you may want to ask a question about the structure and parameters of the experts (e.g. Volumio or similar).
I think that the all idea behind of this kind of HATs in general is to be at least “look like” an audiophile boards. If someone just want to get some analogue stereo he can do it for 3-8 USD with a numerous of USB to RCA/3.5" “DACs”.
Bad designed audio board will have the same audio quality but for much more money.
Allo Kalli design is what you have to consider going for direct I2S output of VIM GPIO or JLSound I2SoverUSB as a alternative USB based one. But in any case reclock is a must! It’s good to have isolation as well. Best interface scenario for such a board is:
stereo jack out.
RCA SPDIF in (for other audio equipment to use the DAC part of the board)
multichannel SPDIF passthrough (can be directly from the VIM board GPIO for example)
toslink is not needed at all! Toslink is a worst digital interface for audio. To much jitter! This will compromise the board
I have tested VIM with Kali and with I2SoverUSB as well. Kali use FIFO and buffer to make reclock and this is the only valid way when the signal com directly from I2S. I2SoverUSB using asynchronous XMOS based USB with isolation which is the best workaround for recklock in “slave” mode.
For dac chip itself, the newer is better
ESS9028 is not bad, but Pro is better.
The retail price for such a board with isolation, reclock and good dac can be 100-200 (even more with Crystek oscilators for example) depending from the quality of used components.
BTW the picture on your website is Allo Piano 2.1 DAC … not bad at all for the money, especially in combination with Kali
VIM have only 2 USB. External sound card USB is 1 USB on the VIM and remains only 1 USB connector for other purposes. No one except Khadas, will not produce cheap sound card connection via a proprietary 40-pin connector. I strongly doubt that most users want audiophile the sound output for 100-200$. Many of them lack a simple audio output for headphones or speakers, to use VIM for audio playback without HDMI adapter and the monitor.
External powered USB can do the magic for those wants more USB ports and simple audio for less than a 20 USD/EUR. From other hand, good audio board can drive more interest from a very strong community. VIM is the most powerful DIY ARM device at reasonable price. I think that Amlogic have analogue output by design, so it can’t be so hard to get interface out. I can’t judge from Khadas business point view what is best for their business or even from the point of view of Khadas users. This is my opinion based on my own interests
BTW, balbes, I sow you givit a try to Volumio for vim. What was the result? Is this possible at all? I think they use kind of MPD fork with own web based “GUI”. Is this possible to patch their interface only which is open source and to use for example on Armbian custom MPD installation?
Yes, Volumio works well on all TV boxes with chips S9xxx via external USB module for sound output. I tested with a simple sound card for$ 2 and with a USB DAC. I have not yet figured out with a built-in sound system AMLM8AUDIO, it only works partially. You can see all the details in these topics.
If You have any TV box with S9xxx you can try his work. This system runs as well as LE from SD card.