[tomb]

 

   
Unnecessary lead length?  Are the resistors flush to the PCB.  For the four you measured above, are they on the bottom of the PCB, next to the opamp?  What about the mica capacitors?  Those have to really be pressed into the PCB to keep from sticking way up over any other part.  The added lead length could be offsetting things.
 
Have you tested the voltage into the opamp?  These would be pins 8 and 4.  See if those are the same voltage.  Pin 8 should be the same as the 2.5V test point coming from U10.  Pin 4 should be the -2.5V test point coming from U8.  See what those voltages are at the pins on the opamp, though - relative to Ground.
 
I can't think of anything else.  I would suggest that 3.3mV is not that much offset in the scheme of things, but you are claiming to hear a sound level difference between channels.  How about the rest of the through-hole resistors?  Can you compare their resistances, left channel to right channel and see if there's something not matched?

Everything is flush to the board, the mica caps do stick up maybe 1-2mm since that was as far as I could get them. Voltage into pins 4 and 8 match up.
 
As for the other resistors, I actually edited my last post with those readings.

Well, some of those resistors are in parallel - so the absolute values are off.  Since the problem is offset, though, we'd be looking for an imbalance somewhere and you're not measuring any.  The only thing left are the rest of the through-hole resistors, R5, R7 & R16, R18.  Try measuring those for an imbalance.
 
You've checked the resistors that control the opamp and you've verified that the opamp is getting the same voltage between the channels.  The only other possibility is that the signal level feeding into the opamp is off before it gets to the opamp.  That would happen at the four resistors mentioned above.  They take the output directly from the DAC chip (IOLP, IOLN & IORP, IORN).
 
If none of that checks out, I don't have an explanation.

 

[Jawmare]

Did you solder those top pads for the oscillator (clock chip)? It doesn't show in your pics, but what c an be seen looks awfully bare. Also, one of the two joints showing looks awfully cold. If the clock chip is not working, there's no way to synchronize/hand-shake the USB connection and the PC will not recognize the device.

Added solder and reflowed the clock chip, now it is detected by my pc (for some reason only usb 2.0 ports, usb 3.0 ports shows unrecognized device.)
 
Listening with an iem... low volume as expected but quite noisy... havn't fixed my amp yet.

 

[tomb]

 

Did you solder those top pads for the oscillator (clock chip)? It doesn't show in your pics, but what c an be seen looks awfully bare. Also, one of the two joints showing looks awfully cold. If the clock chip is not working, there's no way to synchronize/hand-shake the USB connection and the PC will not recognize the device.

Added solder and reflowed the clock chip, now it is detected by my pc (for some reason only usb 2.0 ports, usb 3.0 ports shows unrecognized device.)
 
Listening with an iem... low volume as expected but quite noisy... havn't fixed my amp yet.

 
The USB chip (PCM2707) is not compatible with USB 3.0.

  That said, I have read and used USB 3.0 sockets that were backward compatible, so I'm not sure why it's doing that.  I'll try to o some testing when I get a chance.
 
The big thing is that you got it working.

 

[HarryOMalley]

Hi there, im thinking about building a pupDAC myself, the only question i have is, is it possible to output the analogue signal via 3.5mm, as opposed to RCA?

 

[Jawmare]

Hi there, im thinking about building a pupDAC myself, the only question i have is, is it possible to output the analogue signal via 3.5mm, as opposed to RCA?

Yes, you use the 3.5mm jack in the back instead of the RCA jacks

 

[HarryOMalley]

Ah ok great! Thanks

 

[lordearl]

Which resistors in the schematic (http://www.diyforums.org/PupDAC/schematic/pupDACschematic.pdf) control the gain of the PupDAC?

My amp and speakers are very sensitive and I can't really get past 9 o'clock on the volume dial, is it possible to reduce the vrms output of the Pup somehow?

 

[tomb]

Which resistors in the schematic (http://www.diyforums.org/PupDAC/schematic/pupDACschematic.pdf) control the gain of the PupDAC?

My amp and speakers are very sensitive and I can't really get past 9 o'clock on the volume dial, is it possible to reduce the vrms output of the Pup somehow?

 
The gain is set from the quotient of R6/R5 (Left) and R17/R16 (Right).  Along with R7 and R18, R5 and R16 establish the voltage reference for the diffierential output of the PCM1794 DAC.  So, you don't want to mess with the four resistors R5, R7, R16, and R18:

 
The gain is actually set by R6 (Left) and R17 (Right).  The BOM specs them at 1.5K.  You might try anything down to 1K and see how things work.  You do not want to use less than 1K or the opamp may lose stability. 

 

[tomb]

I am highly embarrassed that this took so long, but PupDAC kits are available again, with the option of Pick & Place, machine-soldered PCM chips available.  I think this option is incredibly important.  It potentially turns the PupDAC into an SMD beginner's kit (with caution advised).  If you look at the price of the PCM1794 and PCM2707, they approach $25 for the two, plus shipping.  That's equal to the option of pre-soldered itself.  The potential loss is even more serious than that, though, because there's really no practical way to test and troubleshoot the chips until the entire PupDAC is completed, potentially wasting even more parts in the process.
 
Needless to say, picking the option is highly recommended.  When I run out of stock on separate PCM2707's and PCM1794's, I won't even sell the kit without the Pick & Place option in the future. 

 
 

 

 

 

 

[Wisor]

Hey,

I finally started to work on my pupDAC Project

I ordered almost everything except chips. I was looking for them on Mouser and there is like 6 different PCM 1794 chips from Texas Instruments.

Here is the link:
http://eu.mouser.com/Search/Refine.aspx?Keyword=Pcm+1794

I noticed the difference in SNR, but is there any other difference?

Which one should I get ?

 

[tomb]

I'm not sure I've ever seen the S/N specs vary. In any event, the DAC chip's noise performance is not the limiting factor in this design - it isn't in almost any overall DAC design. Almost any of the other circuit components will have more noise.

Buy the cheapest one - but be certain the form factor is identical to the PCB. I don't think TI makes them any other way, but then I would've never guessed the noise specs could be different, either.

 

[TheLaw]

Hey all,
 
Does anyone know the hole diameter for the four PCB mounting holes?
 
Thank you very much in advance.

 

[tomb]

Hey all,

Does anyone know the hole diameter for the four PCB mounting holes?

Thank you very much in advance.

1/8", give or take a bit. They're intended for 4-40 screws.

 

[snapper96]

Greetings,
 
I'm hoping someone can point me in the right direction to solve an issue with my pupdac.  I built it last winter and it ran great for 3-4 months and I really enjoyed the sound.  However, one day it stopped outputting sound (still shows up as USB DAC) and I started to investigate.  My investigation discovered no immediate short or any sort.  However, if I check 5v to -5v testpoints and THEN check -5v tp or 5v tp to ground they will both be shorted to ground(not a blip, but shorted as long as I hold it).  Based on that behavior my first thought was a cap issue of some sort but I'm a bit at a loss as to where to start.  Anyone have any pointers on where to go?  Any help is appreciated, thanks!
 
-Tony

 

[tomb]

Greetings,

I'm hoping someone can point me in the right direction to solve an issue with my pupdac.  I built it last winter and it ran great for 3-4 months and I really enjoyed the sound.  However, one day it stopped outputting sound (still shows up as USB DAC) and I started to investigate.  My investigation discovered no immediate short or any sort.  However, if I check 5v to -5v testpoints and THEN check -5v tp or 5v tp to ground they will both be shorted to ground(not a blip, but shorted as long as I hold it).  Based on that behavior my first thought was a cap issue of some sort but I'm a bit at a loss as to where to start.  Anyone have any pointers on where to go?  Any help is appreciated, thanks!

-Tony

I'm not understanding how you worded your post. What is the difference between "5v" and "5v tp?" Aren't they both the same test point? Forget about "shorted," what is the actual voltage to ground that you measure at those points?

If the "-5V" test point does not measure -5V referenced to ground, then something is wrong with U7, the voltage-inverting charge pump.