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Old 26th December 2012, 07:18 PM   #621
acko is offline acko  Australia
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Default USB isolation

Thank you Bunpei for the link.
I did look into usb opto before but costing more than 1K! but this product is well priced. Would have grabbed one but unfortunately have no desktop PC at the moment. Is there any USB-USB opto version?
Also, very interesting to hear that this opto isolation has improved the SQ given that the EXA itself has isolation after the FPGA. So it indicates that isolating the FPGA from PC has benefits.
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Old 26th December 2012, 11:54 PM   #622
Bunpei is offline Bunpei  Japan
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You may find something useful regarding USB isolaters on this page;
The Well-Tempered Computer
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Old 27th December 2012, 01:34 AM   #623
acko is offline acko  Australia
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Hi Bunpei,

Both the listed products: USB-GT and USB2ISO are only full speed devices (12Mb/s). I think the EXA2UI and other similar products require High Speed (480MB/s) versions, like what is capable with the Adnaco-S3B product from your earlier post.
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Old 27th December 2012, 01:05 PM   #624
Bunpei is offline Bunpei  Japan
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You must have discarded Icron USB Ranger on the page because the cost 900 USD might not meet your requirement.
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Old 27th December 2012, 01:12 PM   #625
qusp is offline qusp  Australia
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I think single stage isolation before reclocking is sufficient, I certainly wouldnt consider isolating the USB previous to that at $900 for only a very theoretical improvement (not sure if there is even a theory to explain a further improvement?)
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Old 27th December 2012, 02:42 PM   #626
Bunpei is offline Bunpei  Japan
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In my case, I hate to connect a ground line of my audio device to that of a dirty PC. It's not a theory. It's a kind of sense.
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Old 27th December 2012, 03:34 PM   #627
qusp is offline qusp  Australia
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you misunderstand me, isolating the dac and clock from USB ground is all well and good, I agree with that and do it myself, but isolating the digital FPGA logic areas from USB and then isolating it again after them...is only theoretical improvement, one I cannot think of a theory for. doing it this way (once directly before reclock stage) does not cost $900 either

data is verified as bit-perfect coming out of fifo main board and clock board with the isolation in place between fifo and clock board, with the only jitter at the output being that of the clock and clock buffer, where is the room for the $900 improvement?

it would be a similar situation with EXA, though with EXA the buffer is not as advanced and the isolation is after the reclock stage? used to be anyway, that may not still be the case.

Last edited by qusp; 27th December 2012 at 03:42 PM.
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Old 27th December 2012, 10:29 PM   #628
acko is offline acko  Australia
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Default USb Isolator

Bunpei, Price is a factor. Local distributor asking ~$1400 for the Icron USB Ranger!

I will drop the usb isolator in priority for the time being. The Turbo Reclocker should take care the 'limitations' of the EXA2UI and then see if any usb isolator will improve on this.
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Old 27th December 2012, 11:20 PM   #629
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It's worth noting that Ian recommended that if using the WaveIO with FIFO and the FIFO isolator he still recommended using the WaveIO nve isolator chip to isolate the usb from the FIFO FPGA, then FIFO isolator is only isolating FPGA noise from the reclocking stage.

Acko, it might be worth emailing Ian about.

Here is the link to his recommendations for using FIFO and usb audio source via WaveIO - Asynchronous I2S FIFO project, an ultimate weapon to fight the jitter
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Old 28th December 2012, 12:20 AM   #630
acko is offline acko  Australia
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Yes, I agree. WaveIO and other transports that has no on-board FIFO would benefit greatly from Ian's FIFO-Clock modules. If there is pre-isolation already it is best to leave it as is. I would also take the isolated outputs from WaveIO to isolate the FPGA of Ian's FIFO from PC ground. Lorien mentions jitter this way but hey, we have Ian's FIFO and reclock to clean things up again

On the other hand the EXA2UI has already got its own FIFO and isolators so there is no need to add further duplication of similar functions (and bulk). So I what I am proposing is just to re-clock the outputs of the EXA2UI using the clean DAC Master Clock (100M). On the AKL boards there are also isolators for the divided Slave clocks (from AKX701) replace the XOs of the EXA. The end result is a compact add-on to the EXA unit that has similar benefits as that of Ian's design.

Also from Ian's own comment, the FIFO buffer action does not exactly eliminate jitter (other than reducing latencies in data transfer). It is the isolation and re-clocking with low jitter XOs that gives benefits and if you look closely these drive the way the entire design has evolved.
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