PCM2706

nenad88

Member
2016-11-06 11:28 am
I need USB to I2S board and there are cheap ones on Ali like this one.

s-l300.jpg


HTB1boPXXdjvK1RjSspiq6AEqXXaM.jpg_q50.jpg


I want to connect this board to PCM5102. Are these 2 boards compatible I have never fidled around dacs but as I understand pcm2706 board can act as dac but also can be usb->i2s link for pcm5102? Thanks.

Other option is to use esp8266 or esp32 with pcm5102 board but it is probably more limited than green board.
 
Last edited:

nenad88

Member
2016-11-06 11:28 am
Thanks, do You think it is better to omit gnd and vcc from usb board and use separate psu?

Also can you explain me this.

1. PCM5102A accepts up to 32bit audio data but pcm2706 can only provide 16bit will this usb board be bottleneck for this dac, I am not really sure how all this works.

2. PCM5102A is 32-bit, 384kHz interface but pcm2706 max sampling rate is 48kHz, also does this means that pcm5102a will never use 384kHz sampling rate with this usb board?

Thanks :)

This guy combined these 2 boards.

PCM2706+PCM5102 完成基板組み合わせ USB-DAC : TYO.STDのおきらく写真生活

[IMGDEAD]https://pds.exblog.jp/pds/1/201709/16/66/c0139966_743569.jpg[/IMGDEAD]
[IMGDEAD]https://pds.exblog.jp/pds/1/201709/16/66/c0139966_7441312.jpg[/IMGDEAD]
c0139966_744496.jpg
 
Last edited:
If you want to get the best sound, I'd definitely not use the USB bus power to feed the DAC. I've never gotten DACs fed direct from USB power to sound very good.

1) Yes the PCM2706 only outputs 16bits and the DAC can accept more than that. I'd not fret too much about that, 16bit audio can sound very impressive when done right. I very much doubt the 16bit 'bottleneck' will be the subjectively limiting factor in your system.

2) Yes, you're limited to a max of 48kHz with the PCM2706. Again I doubt its going to be a problem. If you want to handle higher rates, look for a USB interface that uses CM6631A - it'll be more expensive but you can then go up to 192k. Perhaps XMOS-based interfaces can go even higher.
 
I'm fairly sure they're compatible, yes. You don't need to connect anything to SCK on the DAC board, it will generate that signal itself when not externally supplied.
It might be better to connect MCLK (that's the correct name for I2S), as its crystal-generated on the converter pcb, and should be low jitter.

Quick guide to I2S clocks (these are the names used in most datasheets)

MCLK - master clock (not SCK, that's the I2C clock name, far too much scope for confusion between I2S/I2C)
BCLK - bit clock
LRCLK - left/right clock (aka sample clock).
 
If you study the PCM2706 DS in detail you'll note that the 12MHz clock isn't used to generate the audio clocks directly. Its fed to an analog PLL and the PLL's rate is itself locked to a multiple of the USB packet repetition rate. The USB mode is adaptive-isochronous meaning the host gets to set the sample frequency and the PCM2706 slaves to the host.

Yes the 12MHz clock from an XTAL is going to be low jitter but it won't be locked to the BCK and hence won't be useful to the DAC (which requires them locked).