Open-source USB interface: Audio Widget - Page 137

qusp · 15th March 2012, 03:37 PM

yes the divider is awesome i forgot to comment, i was going to be stuck trying to deal with this myself

TheShaman · 03:50 PM

Quote:

Originally Posted by RayCtech

I2S and I2C (SPI) need galvanic isolation.
The remaining can as you indicate be moved to the USB power domain or a separate power domain.

I'm with Ray on this one.
A small board with I2S (e.g. IL715) and I2C (e.g. ADUM1250) isolation would be great and all that's needed.
Not to mention it'll be usable by all USB-I2S-DAC projects most of which nowadays feature an arduino or something.

RayCtech · 04:18 PM

zinsula · 15th March 2012, 04:10 PM

Quote:

Originally Posted by borges

Yes, after AB-1.12 the next prototype(s) could be an insulating go-between for the USB-I2S module.

I suggest optos on I2S (from module) and MCLK (to module). Note that this would require external power for the analog parts, and that IO functionality would be reduced to a minimum. Let me know if you have thoughts on this.[...]

Just a pointer on this subject here...from gmarsh

UnixMan · 15th March 2012, 08:06 PM

Hi Børge,

wow, great news that of the AB112+1.13 "Easter Egg"!

Quote:

Originally Posted by borges

Today the module supports I2C, SPI, display, UART, GPIO, buttons etc. Forwarding all those through galvanic isolators would take up a lot of board area and possibly power.

although it may be annoying to change that now, I believe that some of what currently is on the AB (such as buttons, display port, etc) actually belongs to the USB board.

IMHO, on the AB board(s) there should be only the DAC, the clocks and whatever else is strictly required to be on "the clean side" and/or may be required to control DAC (or digital output) operation such as I2C, etc. Anything else should be moved to the USB board.

UnixMan · 11:44 PM

Quote:

Originally Posted by UnixMan

It would be very useful to try to identify and list here suitable clocks ...

could those NDK be an option also for the widget?

"Synchronous MCLKing scheme for ES9018", from thread "ESS Sabre Reference DAC (8-channel)", post #1883.

1audio · 16th March 2012, 03:18 AM

Finding quality audio crystal oscillators is not easy. Most are custom (or surplus from someone's custom run). The Golledge oscillators Borge has seem pretty good. On my AB1.1 the 48K has less jitter and is pretty free of deterministic sidebands. The 44.1 chain is not as pretty. It may be the oscillator.

Crystek has very good oscillators that are now available from Digikey and Mouser in 22,24,44,48 MHz for audio. At $30 they are not cheap but very high performance. The next step in performance is much more and much longer lead times.

Phase noise gets worse as the frequency goes up. 100 MHz is near the highest for oscillators. Above that you use multipliers etc. The performance degradation come from the Q being less on higher frequency crystals. They get really thin at those higher frequencies. The lowest phase noise is 4-5 MHz.

The NDK oscillators look interesting but not available here easily. Tent Labs has an assortment but is missing the higher frequency oscillators.

I could make a simple doubler circuit to get 2X 44&48 with low phase noise. It will be analog/rf stuff plus digital stuff. It may be the best option, although multiplying the 22/24 up may be even better.

qusp · 16th March 2012, 05:39 AM

any thoughts on doing something like from AN67 for a XO? that is if its useful at correct speeds

1audio · 16th March 2012, 06:12 AM

Quote:

Originally Posted by qusp

any thoughts on doing something like from AN67 for a XO? that is if its useful at correct speeds

Please provide more details, AN67?

qusp · 16th March 2012, 08:20 AM

ahh sorry i figured you would know it, probably you have seen it. it will require very high quality layout and its not cheap, but would be tweakable for frequency output, in fact multiple frequency output should not be too difficult provided it can be gotten up to useful speed and you will know that better than I

Linear Tech Application Note 67. from Dale Eagar a composite opamp Wein Bridge type oscillator. i have all the opamps it needs funnily enough

15th March 2012, 03:58 PM	#1363
RayCtech diyAudio Member Join Date: Sep 2007 Location: Multiple...	Last edited by RayCtech; 15th March 2012 at 04:18 PM. Reason: I had written a reply and some attached documents that for some reason disappeared..

16th March 2012, 03:18 AM	#1367
1audio diyAudio Member Join Date: Mar 2004 Location: SF Bay Area Blog Entries: 2	Finding quality audio crystal oscillators is not easy. Most are custom (or surplus from someone's custom run). The Golledge oscillators Borge has seem pretty good. On my AB1.1 the 48K has less jitter and is pretty free of deterministic sidebands. The 44.1 chain is not as pretty. It may be the oscillator. Crystek has very good oscillators that are now available from Digikey and Mouser in 22,24,44,48 MHz for audio. At $30 they are not cheap but very high performance. The next step in performance is much more and much longer lead times. Phase noise gets worse as the frequency goes up. 100 MHz is near the highest for oscillators. Above that you use multipliers etc. The performance degradation come from the Q being less on higher frequency crystals. They get really thin at those higher frequencies. The lowest phase noise is 4-5 MHz. The NDK oscillators look interesting but not available here easily. Tent Labs has an assortment but is missing the higher frequency oscillators. I could make a simple doubler circuit to get 2X 44&48 with low phase noise. It will be analog/rf stuff plus digital stuff. It may be the best option, although multiplying the 22/24 up may be even better. __________________ Demian Martin Product Design Services

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15th March 2012, 03:37 PM	#1361
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	yes the divider is awesome i forgot to comment, i was going to be stuck trying to deal with this myself

16th March 2012, 05:39 AM	#1368
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	any thoughts on doing something like from AN67 for a XO? that is if its useful at correct speeds

16th March 2012, 08:20 AM	#1370
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	ahh sorry i figured you would know it, probably you have seen it. it will require very high quality layout and its not cheap, but would be tweakable for frequency output, in fact multiple frequency output should not be too difficult provided it can be gotten up to useful speed and you will know that better than I Linear Tech Application Note 67. from Dale Eagar a composite opamp Wein Bridge type oscillator. i have all the opamps it needs funnily enough