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my DAC design - pup1 DAC - Page 30

post #436 of 674

The behavior I get is whenever there is proper communication with the computer, the pin is driven high.

If the DAC is not properly recognized, the pin stays low. The pin never goes low as a result of being idle.

I. too. thought it might only light when music is playing but that is not what happens.

Also, if I just supply power, the pin stays low.

If you use "disconnect" in the device menu, the pin will go low.

 

Quote:
Originally Posted by cobaltmute View Post


If I'm reading the datasheet right, it appears that this pin only get driven high during music playing. Is that what it does on your DAC?
I like the idea, but I'd have to move stuff around as pin 11 is "trapped" right now by traces on both sides of the board.
post #437 of 674

You could use the current limit resistor for the LED to escape from between the traces...

 

Edit:

You could also change R10 to PTH, that would give you the room to escape.

 

Another Edit:

On third thought...

It's probably much easier to just re-route the I2S lines under the chip.

That frees up the room to drop a via to the bottom to escape to the

LEDs current location.


Edited by Avro_Arrow - 7/18/12 at 6:34am
post #438 of 674
Thread Starter 
Quote:
Originally Posted by Avro_Arrow View Post

The behavior I get is whenever there is proper communication with the computer, the pin is driven high.
If the DAC is not properly recognized, the pin stays low. The pin never goes low as a result of being idle.
I. too. thought it might only light when music is playing but that is not what happens.
Also, if I just supply power, the pin stays low.
If you use "disconnect" in the device menu, the pin will go low.

It is interesting though that the datasheet says on page 27 that on an idle bus that it will drive suspend low.
post #439 of 674

Here is another suggestion:

 

Add some 22R to the I2S lines...

 

Edit:

 

And move the bypass caps for the op amp to the bottom.

They will fit at each end of the op amp.

Might solve some of the oscillation issues.


Edited by Avro_Arrow - 7/18/12 at 6:42am
post #440 of 674
Quote:
Originally Posted by tomb View Post

I think cobaltmute mentioned offline that he would just go without the 3.5mm output option.  I think that makes sense, too.  A DAC this good should really just be used with RCA's, anyway.

Please don't drop the 3.5mm option. I've been using both outputs simultaneously for two amps with no issue at all just like I do with the Gamma2. More options = moar betta!

post #441 of 674
Thread Starter 
At this moment the 3.5 is staying.

I think I have done all the revisions I'm going to do on the board at this point.
post #442 of 674

And truly, there isn't anything wrong with the current design. I know that others would love to have access to it :-) A co-worker borrowed it other day; I think I'm going to have to hunt him down to get it back.

post #443 of 674
Thread Starter 
The only thing left to be done is decide if I want to put all the resistors for the op-amp stage on the bottom or just some as is pictured here.



The big changes from the proto board all of you built are:
  • slightly larger pads for both the PCM2707 and PCM1794
  • removing the ground plane under the op-amp
  • moving the op-amp resistors around to shorten the loops around the op-amp
  • making cut-outs on the board so you don't have to trim the pins off the RCA jacks.
  • pushing some stuff around so there is room for the mica caps. The lead spacing is still a touch narrow, but that is to allow options for that part position.
post #444 of 674

I think what is happening is even with no music playing, the bus is still active, monitoring the HID pins.

 

Quote:
Originally Posted by cobaltmute View Post


It is interesting though that the datasheet says on page 27 that on an idle bus that it will drive suspend low.
post #445 of 674
Quote:
Originally Posted by cobaltmute View Post

The only thing left to be done is decide if I want to put all the resistors for the op-amp stage on the bottom or just some as is pictured here.
700
The big changes from the proto board all of you built are:
  • slightly larger pads for both the PCM2707 and PCM1794
  • removing the ground plane under the op-amp
  • moving the op-amp resistors around to shorten the loops around the op-amp
  • making cut-outs on the board so you don't have to trim the pins off the RCA jacks.
  • pushing some stuff around so there is room for the mica caps. The lead spacing is still a touch narrow, but that is to allow options for that part position.

I would prefer to leave all the through-hole resistors on top.

 

 

Looks GREAT!! biggrin.gif

post #446 of 674
Thread Starter 
Quote:
Originally Posted by tomb View Post

I would prefer to leave all the through-hole resistors on top.


Looks GREAT!! biggrin.gif

There are currently four resistors on the bottom of the board. These are the resistors at the output of the op-amp. The idea for having them on the bottom is to have the shortest trace possible to the resistor, to help with stability for the fast op-amp. It also reduces any capacitance effects from the PCB itself.

Nothing says you have to install them on the bottom....
post #447 of 674
Quote:
Originally Posted by cobaltmute View Post


Nothing says you have to install them on the bottom....

Wouldn't they be reversed in the circuit if they went on the top? blink.gif

 

It's still early and I woke up to a lot of thunderstorms ... my brain is obviously not working yet.

post #448 of 674
Thread Starter 
Quote:
Originally Posted by tomb View Post

Wouldn't they be reversed in the circuit if they went on the top? blink.gif

It's still early and I woke up to a lot of thunderstorms ... my brain is obviously not working yet.

Grab a PCB, and put a resistor into its proper position. Now pull out the resistor and put it into the board, in the same holes, from the other side.

Is there a difference?

From a physical mounting perspective, not really.

From a trace perspective yes. In the pupDAC, the trace would be on the bottom of the board from the op-amp. If the resistor is on the top of the board, the signal leaves the op-amp, travels to the through-hole, through the distance of the board, up the lead and into the resistor. If the resistor is on the bottom of the board, it travels to the through hole pad, up the lead and into the resistor.
post #449 of 674

I know I left my brain in bed earlier, but where's your sense of humor this morning?wink.gif  Everyone knows when you turn a resistor around, the current goes the other way.blink.gif

 

Seriously, it looks good - let's do it.


Edited by tomb - 7/20/12 at 6:52am
post #450 of 674
Thread Starter 
Well, I did forget to mention the difference in gravitational forces on the current..... biggrin.gif

For the truly geeky:
Total number of pins: 257
Pins in a net: 242
Not connected pins: 15
Total number of vias: 50
Total number of connections: 194
Unrouted connections: 0
Completion: 100%
Total number of parts: 88
Total number of nets: 48
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