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Old 15th November 2012, 04:34 AM   #771
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Quote:
Originally Posted by qusp View Post
then use mini coax or ribbon, its only important that there is a ground each signal, what you have there is a radio transmitter. you dont have enough connections there to have it twisted and grounded all the way to the dac, you have a single ground connected
You see single wire of ground but it's grounded to Pin 1, 2, 3, 5, 7 of RJ45, while Pin 4, 6, ,8 carrying Data, BCLK and FSCLK, only last inch not twisted, all pairs grounded.

Click the image to open in full size.

Last edited by Hercules; 15th November 2012 at 04:37 AM.
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Old 15th November 2012, 04:45 AM   #772
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Agree that in the cable the pairs are all twisted, but you do need to consider continuing those connections from the RJ45 to the PCB. qusp is correct in this case IMO.

Even if you don't twist them, run a gnd wire for each signal wire.
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Old 15th November 2012, 04:55 AM   #773
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Originally Posted by hochopeper View Post
Agree that in the cable the pairs are all twisted, but you do need to consider continuing those connections from the RJ45 to the PCB. qusp is correct in this case IMO.

Even if you don't twist them, run a gnd wire for each signal wire.
All twisted pair grounded, just use one wire instead of 5 wires, it's meaningless if not grounding them, at the very last inch
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Old 15th November 2012, 05:22 AM   #774
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Pin 1,2, 3, 5, 7 were grounded in this way, if you can't see from the photo, my bad.
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Old 15th November 2012, 05:28 AM   #775
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Some info here might help - Grounding of Mixes Signal Systems

Other pages on that site also are very informative.


The point is that for signals like i2s the return path should be very close to the signal conductor. I believe there are gnd connections adjacent the FS, BCK and DATA signal terminations on the pcb, my suggestion is to use those, gnd is not simply to provide a common reference potential in this case, the return path of the high freq signal is more complex and when handled poorly will act as a dipole antenna.
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Old 15th November 2012, 05:30 AM   #776
qusp is offline qusp  Australia
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what he said^^

additionally they put those ground pads and connections there for a reason, its part of the ethernet spec and ethernet has the advantage of being a differential signal thats buffered and error corrected, i2s does not, it needs all the help it can get to go on a cable

it may seem i'm picking on you, not the case, people look at the photos here to see how things are done, its better they know the correct way to do it. I get emails almost every day asking me about stuff like this, better that its all out there.

if you are using a buffalo dac then iuts probably set to 'best' DPLL, thats a pretty relaxed setting as well

Last edited by qusp; 15th November 2012 at 05:37 AM.
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Old 15th November 2012, 05:38 AM   #777
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It's okay for each ground run a single wire, as the doc from Amanero, pin 13 to 20 also ground terminal.
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Old 15th November 2012, 06:04 AM   #778
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It took me 15 mins to rewire them, as it's all solid core, need a tweezers to hold the wire, as the RJ45 socket is PCB type, quite hard to avoid short of wires.
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Old 15th November 2012, 06:13 AM   #779
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Just my laziness to work in that way in a small box, and want to put it sing ASAP, it's always room for better job beyond working condition.

Quote:
Originally Posted by qusp View Post
what he said^^

additionally they put those ground pads and connections there for a reason, its part of the ethernet spec and ethernet has the advantage of being a differential signal thats buffered and error corrected, i2s does not, it needs all the help it can get to go on a cable

it may seem i'm picking on you, not the case, people look at the photos here to see how things are done, its better they know the correct way to do it. I get emails almost every day asking me about stuff like this, better that its all out there.

if you are using a buffalo dac then iuts probably set to 'best' DPLL, thats a pretty relaxed setting as well
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Old 15th November 2012, 08:03 AM   #780
qusp is offline qusp  Australia
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Quote:
Originally Posted by Hercules View Post
It took me 15 mins to rewire them, as it's all solid core, need a tweezers to hold the wire, as the RJ45 socket is PCB type, quite hard to avoid short of wires.
cool, much better, but it would be a lot easier if you just used Ribbon cable instead of that 50mm of solid core silver...

the point is, when dealing with high frequencies, each signal needs its own return close to it as possible, or it radiates HF noise.... fact, its got nothing to do with just making sure the devices have a ground connection between them. thats why each of the signals in the ethernet cable and each of the signals on the PCB have a return/ground to go with them.

at these high frequencies, the air presents a low impedance (thats why radio signals can travel for billions of KM through air and space), it doesnt really care that much if it has a cable to travel on or not, if it doesnt have a nearby wire to travel on, it'll just go its own way through the air to the nearest point (of its choosing) if need be.

it is not OK to run a single ground, I dont care what Amanero says (if he does indeed say that, that would be strange considering hes given a return per signal on the PCB as there should be) it will work that way, but its not how it should be done.

Last edited by qusp; 15th November 2012 at 08:06 AM.
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