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Old 7th January 2013, 08:51 AM   #921
PET-240 is offline PET-240  Australia
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Ian has an isolator for the FIFO boards already, ask him if he has one about, WILL be MUCH better than the NVE IL715 option.
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Old 7th January 2013, 09:03 AM   #922
qusp is offline qusp  Australia
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yep, and dont bother isolating the fifo input IMO, just use that single isolation stage just between the fifo main board and clock board, that then isolates everything that comes before it. you could isolate the fifo itself as well, but that doesnt really seem necessary to me.
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Old 7th January 2013, 09:26 AM   #923
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Hi Ian,

I received GBIII55 order in a good condition. Thank you for professional product. :-)

Daniel
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Old 7th January 2013, 09:30 AM   #924
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While I can see the logic of my fellow Brisbane residents it should be noted that Ian posted a guide here on using the xmos based WaveIO usb source with the FIFO.

In that post it was his recommendation that if using i2s out of the WaveIO to feed the FIFO it is best to use the isolated i2s output of the WaveIO (it has both iso and non-iso outputs as well as spdif, lest just consider the i2s options for this as it is what is relevant to the Amanero board). He suggests using this isolator chip in addition to his isolator between FIFO buffer and reclocking stage. The WaveIO uses the same NVE IL715 chip for its isolated output.

Also note, at the input of the FIFO there are 5V tolerant i2s pins, the isolated side of the NVE IL715 chip can be supplied with 5V from the FIFO board J5 and then you do not need to worry about an additional power supply (if the FIFO i2s input were only 3.3V tolerant you would need to find a 3.3V regulator somewhere or add one to your system).

The jitter from the isolator is negated by the FIFO+reclocking, so the additive jitter from the NVE isolator is no longer relevant to your DAC performance.

While it may not appear to give much logical advantage at first glance there appears to be no significant downside to having it there and not terribly expensive or complex to add.

It also means that you able to supply the Amanero (or other usb source) from usb power with confidence that you're not missing anything.

So in the end what we are weighing up is the extra cost of the NVE chip + a few caps + adapter pcb against the advantage of what could be in a way considered a two stage filter on the PC noise. Any PC noise that remains after the NVE isolator will be further attenuated by the FIFO isolator as well as it will no longer have any significant bearing on the operation of the FIFO buffer.


Cheers,
Chris

Last edited by hochopeper; 7th January 2013 at 09:37 AM. Reason: edited for clarity
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Old 7th January 2013, 10:10 AM   #925
qusp is offline qusp  Australia
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yes, but he (much like yourself) gave no reason for the recommendation, simply that it was there as an option, the added jitter would be taken care of, so why not, was what I took out of it. I would agree with that recommendation, there is no penalty at all. he was only able to give an assumption that the fifo may operate better that way, but I have not seen any recommendation to buy 2 isolator boards for sources that do not by default have an optional isolated output

Last edited by qusp; 7th January 2013 at 10:14 AM.
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Old 7th January 2013, 10:19 AM   #926
qusp is offline qusp  Australia
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I do not accept somewhat vague assumptions as reasons, you know that.
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Old 7th January 2013, 10:31 AM   #927
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Quote:
Originally Posted by qusp View Post
I do not accept somewhat vague assumptions as reasons, you know that.
Of course and for good reason. I do that agree my 'two stage filter' approximation is particularly vague!!

I actually just came back to say that the isolator between FIFO buffer and re-clock stages should be a higher priority (IMO it is essential) than this isolator.

While the cost is (comparatively) small and the downsides are practically non-existent, I would just do it (if you can get an adapter PCB easily) and not think twice. I wanted to write it out for others who had missed Ian's post and to ensure that anyone choosing to build/not build the additional isolator did so with more consideration than 'qusp said don't worry'. If they do go ahead and build the isolator it is also important that they know what voltage they're connecting to the supply on each side of the isolator chip, so its still important to note that the FIFO input is TTL tolerant.



(I know qusp knows this, but for others, I have a WaveIO so I will be doing this anyway as the cost for me to implement the IL715 is effectively $0)

Last edited by hochopeper; 7th January 2013 at 10:36 AM.
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Old 7th January 2013, 10:47 AM   #928
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To be fair to Ian I think he also has pointed out somewhere in the R&D thread that there is a potential ground loop created between the PC power supply and the FIFO/DAC power supplies, so the isolator breaks that potential loop also. If it is a problem in another user's system or not, we cannot know.

So that gives us 3 possible reasons:

- ground loops
- some remnant of the PC noise making it through to the 'clean' side of the isolator
- removing PC noise allowing the FPGA to operate with less noise at its input may allow it to better ensure bit perfect operation of the FIFO.

After I set up my FIFO I am hoping to play with different arrangements of isolation and see if there are any subjective differences between each. I am also waiting on my copy of this book - http://www.hottconsultants.com/EMCE_..._contents.html to arrive, hopefully in there I will have some reading on the subject

Last edited by hochopeper; 7th January 2013 at 10:52 AM.
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Old 7th January 2013, 11:08 AM   #929
qusp is offline qusp  Australia
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of course there is a potential ground loop, I consider the effects of all of that a bit vague too, so I included Ian in that comment lol I read that post basically as providing potential reasons why you might use something that is there. quite different to presenting rationalised reasons why something should be bought and built

Even if there is a potential ground loop, there is nothing to illustrate what the effect of some small loop currents would have on the FPGA, given that the stage directly after it has an isolator and then a reclock stage that has been proven resets jitter to essentially zero. so it would have to be a ground current capable of changing bits from 1 to 0 and we both know how unlikely that is.

adding another isolator for a high speed interface, to do properly you might want to use u.fl on the output if you plan on 384khz just in case (not really but you might), take the power for the output of the isolator from? if you use something other than the fifo supply, thats an opportunity for ground loop currents too, but regardless its probably another supply, another board, another cable and all for? I mean really what actual reason?

anyway best not continue this convo here in the GB thread.

no problems with another perspective other than mine... all good in the name of discourse.

Last edited by qusp; 7th January 2013 at 11:14 AM.
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Old 8th January 2013, 07:12 PM   #930
aos is offline aos  Canada
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5. AR2 2 x Si570 clock board - definitely!
6. wktk_smile
7. hirez69 1 x Si570 clock board, 2 x Isolator board, 4 x TPS7A4700 reg board, 2 x Battery management board
8. CeeVee - you bet!
9. number9 Si570 Clock Board
10. analog_sa - GB maniac
11. edbk
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14. NicMac - as usual!
15. Zoran
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32. palmito
33. crazikid
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37. rsotirov 1x Si570 clock board
38. kvl 1 x Si570 clock board, 1 x Isolator board, 1 x TPS7A4700 reg board, 1 x Battery management board, 1 x back door kit.
39. bkdog
40. necplusultra
41. Nikola Krivorov X2
42. nvduybom
43. Popolvar
44. TNT
45. sidiropa 1x Si570 clock board, 1x isolator 1x 1.0mm FFC/FPC cables combo, 1x battery management pcb
46. leejh
47. Alcaudon
48. sernikus (all + 2xSi570 )
49. enantra
50. Giordano, FIFO kit + a dual osc.
51. oyvind I2S FIFO KIT, Si570 clock board, S/PDIF Interface Board, I2S backdoor KIT for S/PDIF board, BIII adapter PCB, SMT connector package for BIII adapters, FIFO isolator board V1.5 MINI KIT, battery management pcb
52. duster1 1x Si570 clock board, 1x isolator
53. Blitz Si570 clock for dual osc. (two needed ?), 1x isolator, 1 x TPS7A4700 reg board, 1 x Battery management board, 1 x back door kit.
54. Josoeff 1 x FIFO kit and 1 x S/PDIF interface board
55. crobbins5421 1 x FIFO kit, 1 x S/PDIF board, 1 x Si570 Clock Board
56. Regal 2 x Si570 clock for dual osc, 1x isolator, 1 x TPS7A4700 reg board, 1 x Battery management board, 1 x back door kit.
57. aos FIFO kit, dual xo clock, S/PDIF board, 1 x Si570 clock, 5 x U.FL socket, 3 X 6" U.FL cable, 1 X I2S backdoor kit, 1 X SMT XO adapter, 1 X BIII adapter, 1 X SMT conn for BIII, 1 X FIFO isolator, 1 X cables combo
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