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pupDAC Step-by-Step Build Thread - Page 19

post #271 of 286

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.


Edited by Avro_Arrow - 5/11/14 at 4:26pm
post #272 of 286

As a test, I placed a 10K resistor (in parallel) on R14 and brought down the DC offset to around 3 mV. The noise was still there, and when I ran RMAA it reported way lower specs that what I'd originally measured. The dynamic range was around 70, noise around 70, crosstalk in the 60s, etc. Am I doing something wrong?

post #273 of 286

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? 

post #274 of 286
Thread Starter 
Quote:
Originally Posted by skeptic View Post
 

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. 

post #275 of 286
Quote:
Originally Posted by tomb View Post


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.
post #276 of 286

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

post #277 of 286
Thread Starter 
Quote:
Originally Posted by skeptic View Post
 
Quote:
Originally Posted by tomb View Post


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.

 

 

Quote:
Originally Posted by mcandmar View Post
 

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.

post #278 of 286
Out of interest - what is the vrms output of the pupdac?
post #279 of 286
Thread Starter 
Quote:
Originally Posted by lordearl View Post

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.

post #280 of 286
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.
post #281 of 286

From memory its ~1.5v rms

post #282 of 286

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. 


Edited by juswyq - 9/23/14 at 9:38pm
post #283 of 286
Thread Starter 
Quote:
Originally Posted by juswyq View Post
 

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.

post #284 of 286
Quote:
Originally Posted by tomb View Post
 


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!

post #285 of 286
Thread Starter 
Quote:
Originally Posted by juswyq View Post
 
Quote:
Originally Posted by tomb View Post
 


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.).

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