[cobaltmute]

As promised, here is a picture of the first error portion on the proto boards. The issue here was that I had D+ and D- reversed on my inital footprint for the USB connector

To make the board work, you need to install the resistors as shown. R1 = Red, R2 = Yellow and R3 = Cyan.  The through hole for R3 is large enough to take the leads for both R1 and R2.
 
 

 

[cobaltmute]

Second error portion on the board:
 

 
The issue here is that this layout is for a positive regulator, when it should be a negative one.
 
The fix is to install the regulator at an angle, as my wonderful graphics shows.  Place pin 1 of the regulator on the pin 2 pad, and pin 2 of the regulator on the pin 3 pad.  Pins 4 and 5 on the other side of the regulator stay on their pads.  And most importantly, bridge pins 2 and 3 of the regulator.  Pin 3 of the regulator needs to be tied to pin 2 to enable it.
 

 

[c12mech]

Those look to be pretty easy fixes.  Should be no trouble at all.

 

[Gotez]

Yes, That should be doable.
 
Looking forward to the build!!
 
DigiKey tells me that P1.00MCACT-ND (RES METAL FILM 1.00M OHM 1/4W 1% ) is obsolete. Any tips for replacements?

 

[tomb]

Quote:

Yes, That should be doable.
 
Looking forward to the build!!
 
DigiKey tells me that P1.00MCACT-ND (RES METAL FILM 1.00M OHM 1/4W 1% ) is obsolete. Any tips for replacements?

My DigiKey says NRND, but they have 34,086 available.  I would not hesitate to go ahead and order it on that basis.  If those get sold before you need to order, pick another 1M, 1/4W 1% resistor.  There are several:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RNF14FTD1M00CT-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PPCQF1.0MCT-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=1.00MXBK-ND
 
I haven't checked each one of those for physical dimensions, but you get the idea: there are others available.  I'm not sure of this, also, but perhaps cobaltmute can confirm: typically, a 1M resistor is not usually in a critical part of a circuit.  It may be that the 1% spec could be relaxed a bit for that resistor and that would open up a lot more resistors to pick from.

 
 

 

[cobaltmute]

At quick check, the ones that tomb has listed are all too large.  There is a Xircon from Mouser that is compatible.
 
But the with 34,000 in stock we should be good for a little bit.

 

[Gotez]

You're right.
 
I should have looked better

 

[c12mech]

I was looking at the original post and saw that both PCM1794A and PCM1798 dacs can be used.  What is the major difference between the 2 besides the $16 price difference.  I have the data sheets for both and don't see a whole lot of difference.

 

[00940]

The PCM1794 has a stronger analog output (twice as much ma) and a better digital filter.
 
The only practical implication is that you have to adapt the I/V resistors accordingly (not to exceed 0.6V or so because the internal protection diodes would mess up your signal).

 

[tomb]

Yes, cobaltmute and I agree that the 1794 is the better chip.  My understanding is that's the chip he will focus on in refining the design based on the prototypers' experience.  That is the chip I'm supplying along with the PCM2707 to most of the prototypers.

 

[c12mech]

I figured there was a big difference just was not sure what it was, thanks 00940.  In the bom that was posted the 1798 was what came up under the digi-key p/n given.  I was one of the latecomers to ask for a board and so will not be getting the chips.  I have them ordered as samples from TI but they seem to be on perpetual back-order.  I'm really looking forward to building this just to see the difference out of both my pc and Macbook pro.   

 

[tomb]

Quote:

I figured there was a big difference just was not sure what it was, thanks 00940.  In the bom that was posted the 1798 was what came up under the digi-key p/n given.  I was one of the latecomers to ask for a board and so will not be getting the chips.  I have them ordered as samples from TI but they seem to be on perpetual back-order.  I'm really looking forward to building this just to see the difference out of both my pc and Macbook pro.   

PM me when you receive your PCB.  I may be able to supply you one by that time.  TI indicated an availability date of 3/20, if I remember correctly.  I'd be surprised if cobaltmute gets the chips and is able to deliver those and the PCBs well before that time.  He's not in the states, btw, so it's not like 3 days delivery, after all.

 
 

 

[c12mech]

Thanks tomb.
 
I'm not in the states either.  I live on Guantanamo Bay Naval Station.  The US mail is unreliable at best, 42 days once for a package.  I have all my important stuff sent to an address in Fort Lauderdale to be picked up by the planes I work on.  Sometimes I get it pretty quick and sometime it can take a week or so for them to get up there.  Just depends on scheduling.  If I have not received my chips by the time the board gets here I will send you a pm.

 

[cobaltmute]

The chips are in US mail from tomb to myself.  Let's all hope for faster than slower delivery.  Shortest I've seem from tomb is 5 days and longest has been 28 days.  We'll see what happens.

 

[forsakenrider]

Very excited for this!