[Avro_Arrow]

Your lowest voltage is 127.5mV.
You want to adjust the value of the others to match this value.
The easiest way to figure out what value you need is to get
a 200k 20k trim pot and install it across the Riv resistors one at
a time. Adjust the trim pot until the voltage reads 127.5mV.
Unsolder the trim pot and measure the resistance. Find the
closest standard value and solder this on top of the Riv you
just measured. Repeat until all the Riv read 127.5mV.

 
This process will account for tolerance in the Riv resistors
and the tolerance of the PCM1794a.
 
Edit: changed trim pot value.
The expected values of the parallel trim resistor
will be in the 1k to 10k range.

 

[COOKIESnPIE]

Post deleted by user.
 
 

 

[skeptic]

After flirting with the idea for quite a while - I caved and ordered my pupdac kit this afternoon.  Really looking forward to giving this build a go!  I have at least one successful smd project under my belt at this point (agdr's booster) and a wire se-se in progress (presently on hold pending a decision as to an enclosure), so hopefully I'm adequately experienced to manage the oscillator and bb 1794.  I suppose we shall see!  Will make sure to report back with either requests for help or confirmation of success (fingers crossed for the latter).
 
Thanks for the wonderful thread and build guide!  I love my current bb 1793 based dac and am hopeful that this will be a similar flavor.  As an aside, is anyone else contemplating the possibility of dropping their pupdac and a doodlebug in a single chassis? 

 

[tomb]

  After flirting with the idea for quite a while - I caved and ordered my pupdac kit this afternoon.  Really looking forward to giving this build a go!  I have at least one successful smd project under my belt at this point (agdr's booster) and a wire se-se in progress (presently on hold pending a decision as to an enclosure), so hopefully I'm adequately experienced to manage the oscillator and bb 1794.  I suppose we shall see!  Will make sure to report back with either requests for help or confirmation of success (fingers crossed for the latter).
 
Thanks for the wonderful thread and build guide!  I love my current bb 1793 based dac and am hopeful that this will be a similar flavor.  As an aside, is anyone else contemplating the possibility of dropping their pupdac and a doodlebug in a single chassis? 

You won't have any issue with the oscillator.  It's only trouble when people use too much solder and get some on the top - that shorts it out. The bb1794 is a different story. It's no different than soldering a PCM2702 on the Alien DAC or BantamDAC.  Still, it can be a challenge.  Check all the methods used for SMD soldering for the AlienDAC, BantamDAC, etc.  Also check the temperature on your iron.  I've soldered one perfectly before and still had it fail because the iron was too hot and fried the chip on the inside. 

 

[skeptic]

You won't have any issue with the oscillator.  It's only trouble when people use too much solder and get some on the top - that shorts it out. The bb1794 is a different story. It's no different than soldering a PCM2702 on the Alien DAC or BantamDAC.  Still, it can be a challenge.  Check all the methods used for SMD soldering for the AlienDAC, BantamDAC, etc.  Also check the temperature on your iron.  I've soldered one perfectly before and still had it fail because the iron was too hot and fried the chip on the inside. 

Thanks for the info and advice tomb! I was somehow confusing the 2707 and oscillator, but having cleared that up, it is good to know that I should be careful to avoid getting any solder on the top of the oscillator. I will also be doubly careful to avoid cooking the 1794.

 

[mcandmar]

That was my experience too, oscillator was no problem at all, it was the 1794 that proved to be the most challenging.

 

[tomb]

 

You won't have any issue with the oscillator.  It's only trouble when people use too much solder and get some on the top - that shorts it out. The bb1794 is a different story. It's no different than soldering a PCM2702 on the Alien DAC or BantamDAC.  Still, it can be a challenge.  Check all the methods used for SMD soldering for the AlienDAC, BantamDAC, etc.  Also check the temperature on your iron.  I've soldered one perfectly before and still had it fail because the iron was too hot and fried the chip on the inside. 

Thanks for the info and advice tomb! I was somehow confusing the 2707 and oscillator, but having cleared that up, it is good to know that I should be careful to avoid getting any solder on the top of the oscillator. I will also be doubly careful to avoid cooking the 1794.

 
 

  That was my experience too, oscillator was no problem at all, it was the 1794 that proved to be the most challenging.

Yep.
 
The PCM2706/7 should not be an issue, either.  The issue with the PCM2707 is lining it up on all four sides with the pads.  If you get it wrong, you can re-position it.  Just make d*mn sure you don't solder a second pin until you're completely satisfied that all the pins on all four sides are lined up.

 

[lordearl]

Out of interest - what is the vrms output of the pupdac?

 

[tomb]

Out of interest - what is the vrms output of the pupdac?

Someone would have to measure it, I guess - I haven't.  Maybe I'll try tomorrow.

 

[lordearl]

I think it would be in the realm of 0.75 to 1.25 vrms, it appears to work quite well with a preamp giving 10dB of additional gain in my system. It will be interesting to see the results of your test.

 

[mcandmar]

From memory its ~1.5v rms

 

[juswyq]

my pupdac has a problem - sometimes the volume will go down to very low levels. Fiddling around with the components on the pcb will sometimes bring it up to the original, much higher, volume levels. I suppose there is a broken contact somewhere but I can't find it.
 
Does anyone know what the problem could possibly be? The sound plays perfectly fine, just that the volume is much softer.
 
Thank you.
 
edit: I have a feeling it's the IREF pin on the PCM1794. Will try fixing it tomorrow to see if it works.
 
Another question:
The output of the pupdac is a bit too loud for my audioengine a5. turning it just a bit above minimum volume and it's already too loud. is there any way to make the output softer? I used to use a fixed value potentiometer but that has its own problems. The windows master volume control doesn't work for me. 

 

[tomb]

  my pupdac has a problem - sometimes the volume will go down to very low levels. Fiddling around with the components on the pcb will sometimes bring it up to the original, much higher, volume levels. I suppose there is a broken contact somewhere but I can't find it.
 
Does anyone know what the problem could possibly be? The sound plays perfectly fine, just that the volume is much softer.
 
Thank you.
 
edit: I have a feeling it's the IREF pin on the PCM1794. Will try fixing it tomorrow to see if it works.
 
Another question:
The output of the pupdac is a bit too loud for my audioengine a5. turning it just a bit above minimum volume and it's already too loud. is there any way to make the output softer? I used to use a fixed value potentiometer but that has its own problems. The windows master volume control doesn't work for me. 

Good luck on finding the fix with that pin.
 
As for making the volume output softer, I'm not sure there's a problem ... at least with the PupDAC.  It adheres to industry standards at the output and is no stronger than most sources.  The volume in Windows is not compatible with the PCM2707 USB chip.  Microsoft started this with Windows 7, I believe.  Supposedly the version "C" of the PCM2707 is supposed to address this, but I haven't seen anyone actually achieving the results desired.
 
You might look toward your media player.  I use Foobar 2000 all the time and it has its own volume control that can easily adjust the PupDAC output.

 

[juswyq]

 
Good luck on finding the fix with that pin.
 
As for making the volume output softer, I'm not sure there's a problem ... at least with the PupDAC.  It adheres to industry standards at the output and is no stronger than most sources.  The volume in Windows is not compatible with the PCM2707 USB chip.  Microsoft started this with Windows 7, I believe.  Supposedly the version "C" of the PCM2707 is supposed to address this, but I haven't seen anyone actually achieving the results desired.
 
You might look toward your media player.  I use Foobar 2000 all the time and it has its own volume control that can easily adjust the PupDAC output.

I am using the PCM2707C chip and I can confirm that the volume control doesn't work on windows 7. Any idea if it works on windows 8? Might be time to upgrade.
 
Also, I am using the individual application volume controls, but any new program that is opened will be turned on to the default 100% volume. For acceptable volumes, my foobar is turned to 10% volume so there is a huge difference in volume. I guess it's just not suited to the high amplification of the audioengine a5s.
 
I also tried using a fixed value potentiometer before the input to the speakers, but it results in a high pitched noise. This high pitched whine is also present if the potentiometer in my audioengine a5 is turned down to very low volumes, so I can't go too low there either. Not sure why this problem exists.
 
Thanks for your help!

 

[tomb]

 

 
Good luck on finding the fix with that pin.
 
As for making the volume output softer, I'm not sure there's a problem ... at least with the PupDAC.  It adheres to industry standards at the output and is no stronger than most sources.  The volume in Windows is not compatible with the PCM2707 USB chip.  Microsoft started this with Windows 7, I believe.  Supposedly the version "C" of the PCM2707 is supposed to address this, but I haven't seen anyone actually achieving the results desired.
 
You might look toward your media player.  I use Foobar 2000 all the time and it has its own volume control that can easily adjust the PupDAC output.

I am using the PCM2707C chip and I can confirm that the volume control doesn't work on windows 7. Any idea if it works on windows 8? Might be time to upgrade.
 
Also, I am using the individual application volume controls, but any new program that is opened will be turned on to the default 100% volume. For acceptable volumes, my foobar is turned to 10% volume so there is a huge difference in volume. I guess it's just not suited to the high amplification of the audioengine a5s.
 
I also tried using a fixed value potentiometer before the input to the speakers, but it results in a high pitched noise. This high pitched whine is also present if the potentiometer in my audioengine a5 is turned down to very low volumes, so I can't go too low there either. Not sure why this problem exists.
 
Thanks for your help!

Well, I didn't give much help.  I'm sorry to hear that the "C" version chip doesn't make a difference.  It may be that a couple of pins need to be activated or connected to something to enable the volume control and the PupDAC doesn't have a provision for that.
 
All that said, it sounds like the audioengine is the culprit.  I would have to believe that if you just connected a CD player or something similar, the same thing would result, because the PupDAC is perfectly comfortable as simply another component in an audio-hi-fi collection of sources (as in connected to a receiver, pre-amp, etc.).