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Old 4th January 2013, 10:02 PM   #461
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OK, here is where I am now. I have made some changes to the circuit. I am now using a 74hc4040 to divide bclk by 8 which should give 4fs to 8fs in most situations. This is optional however, as one could, I suppose, bridge across the 4040 without installing it. I have to admit I have a very basic understanding of the logic chips.

As another option, one could forgo the logic chips and instead use R17, C25, C26, and D1 on the bottom of the board and perform a grundig style DEM connection. I have read recently how some prefer that style.

As far as the size of the board. As it is now it is 3.2 x 2.9 inches.

Terminating the u.fl with resistors is no problem, just need to determine the proper placement. Is there any situation where terminating it could cause a problem?

Sorry about the messy schematic, it has been through many revisions. Will clean it up when boards get made.

As always critique is welcomed.

Thanks,
Chris
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File Type: png dac-1-simple-v4-sch.png (41.4 KB, 357 views)
File Type: png dac-1-simple-v4-sch-ps.png (15.2 KB, 345 views)
File Type: png dac-1-simple-v4-top.png (791.0 KB, 308 views)
File Type: png dac-1-simple-v4-bot.png (554.2 KB, 271 views)
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Old 5th January 2013, 02:26 PM   #462
regal is offline regal  United States
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Quote:
Originally Posted by vanofmonks View Post
OK, here is where I am now. I have made some changes to the circuit. I am now using a 74hc4040 to divide bclk by 8 which should give 4fs to 8fs in most situations. This is optional however, as one could, I suppose, bridge across the 4040 without installing it. I have to admit I have a very basic understanding of the logic chips.

As another option, one could forgo the logic chips and instead use R17, C25, C26, and D1 on the bottom of the board and perform a grundig style DEM connection. I have read recently how some prefer that style.

As far as the size of the board. As it is now it is 3.2 x 2.9 inches.

Terminating the u.fl with resistors is no problem, just need to determine the proper placement. Is there any situation where terminating it could cause a problem?

Sorry about the messy schematic, it has been through many revisions. Will clean it up when boards get made.

As always critique is welcomed.

Thanks,
Chris
As far as terminating the ufl, from an rf perspective I just don't see how you wouldn't terminate them unless whats driving them isn't set at the right output impedance, this is all to minimize reflections.

But also are you 100% sure you want to make PCB's with the thru-hole logic chips? Really the potato chips are the way to go as some measurements in another thread recently showed. With digital smaller footprint is always better.

Also I believe now I see what 3setup was refering to with the cut ground plane, its the VR's. You want as much groud plain retuning currents as possible, this is where a 4 layer board comes in handy, but at at some point it just becomes easier to build PTP on a pored copper ground plain in 3 dimensions.

I guess if I had the patience to work with PCB software I would do 4 layers and use better regs than the TL431's but I uderstand the time involved, what you have is a big improvement over the red baron boards as is. But if you want to go that direction (4 layer pcb) I have some snippets saved that explain the current flows around the TDA and the better 4-layer practice I could email you, shoot me a PM if you want.
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Old 5th January 2013, 04:10 PM   #463
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Here is a version with expanded unsplit bottom ground plane.

I'm not sure what you mean by thru-hole logic as I changed to smt already. If the the potato chips are better, I have no problem changing. Which chip would be better for the 74hc4040 divider, or is that good as it is?
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Old 5th January 2013, 05:02 PM   #464
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Some reason I can't edit my last post, but I forgot to ask which VR would be recommended over the tl431? Is there is a consensus?

Also, aren't the potato po74g02 pin compatable with the smt 74hc02?

And for terminating the u.fl I would just use a 50 ohm from signal to ground right?

Thanks,
Chris

Last edited by vanofmonks; 5th January 2013 at 05:06 PM.
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Old 6th January 2013, 01:11 AM   #465
erin is offline erin  Australia
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Quote:
Originally Posted by regal View Post
Is the TL431 really a good choice? If you went smt with potado logic and dropped the TL431's you could have a really small board that could butt right next to salas regs.
I know that TL431 with TDA1541 sounds much better than a board without TL431.
Tried both. No contest.

Is there better? Not sure. You tell me..
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Old 7th January 2013, 07:23 PM   #466
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OK, here we are with the latest. I have added 2pin headers for each supply. This, I think, is the best compromise as it should allow the use of the Salas regulators voltage sense function and just use the normal headers for the supply. From what I can tell, one of the primary benefits of the Salas regs is the remote sense function which allows for the regulator to be some distance from the load. Or, one could use ccs supplied tl431, or a combination. I don't want to go only Salas regulators as I don't have any currently

As far as terminating the i2s signals, from what I have found that is done on the source side with 22 ohm resistors usually, so barring other info I will leave it off.

So, I think I will move forward with this one, unless some other errors are found. I guess post if interested in the board though I'm not sure what kind of initial run to do. I think it will depend on how many people are interested. I would like if a few people with test equipment and the desire to test would be involved.

Thanks,
Chris
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File Type: png dac-1-simple-v8-top.png (976.5 KB, 57 views)
File Type: png dac-1-simple-v8-bot.png (683.1 KB, 43 views)
File Type: png dac-1-simple-v8-sch.png (41.4 KB, 75 views)
File Type: png dac-1-simple-v8-sch-ps.png (17.0 KB, 70 views)
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Old 7th January 2013, 10:31 PM   #467
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Decided to use a 74hc4024 instead of 4040 since only dividing by 8. Board is a little smaller.
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Old 8th January 2013, 10:33 AM   #468
erin is offline erin  Australia
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I don't understand why you are routing the current output pins inside the chip and then between the pins? And seriously, you should increase their thickness.
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Old 8th January 2013, 03:33 PM   #469
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Well they started there from an earlier version of the board which had more ps components at the end of the chip, but I'm not sure it would matter greatly. I could run them out the end of the chip now, but that would disrupt the ground plane from pin 14 to the supply. So either way I think it is a trade off, and I think disrupting the ground plane may be worse. Not sure why the trace thickness need increasing. They are significantly larger than the signal requires. How many mills do you think they should be?
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Old 8th January 2013, 04:11 PM   #470
qusp is offline qusp  Australia
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I must admit to still being a bit confused as to why the pinheader is after the ufls, why not before and have the u.fl facing the other direction? particularly if anyone ever populates both, having a big-*** pinheader directly in the way of what is supposed to be at least somewhat impedance controlled signal when it should he easy for that to not be the case, seems odd to me. I presume you have a reasoning for it though?
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