# pupDAC Step-by-Step Build Thread



## tomb

The pupDAC is the newest DAC design from cobaltmute, the designer of the grubDAC and SkeletonDAC.  The pupDAC is a design primarily intended for the finest possible sound from a USB-only-powered DAC.  While DIY-friendly with a now forgiving layout, it is very compact and designed for the tiny Hammond 1455C801 metal case.  We think you'll find the sound from the pupDAC worth the work.
   
  Parts types are no different than what you have found on the AlienDAC, BantamDAC, grubDAC, and SkeletonDAC - TQFP-32, SSOP-28, SOIC-8, SOT-23-5, 1206 and 805 series parts.  It's just that there's so many of them.
	

	
	
		
		

		
			





  Still, go slow and keep track of the parts and you should have no problem.  The techniques are no different than on any of the DACs mentioned, with a small exception.
   
  Because there are so many parts on the pupDAC, trouble-shooting the PCM chips later on can be a real issue as access quickly becomes limited as the rest of the parts are installed.  Plus, if you botch those two PCM chips and are unable to fix them, then you've potentially ruined a significant investment in all the other parts you've installed afterwards. * IMHO, the most important thing you can do to ensure a successful build with the pupDAC is stopping, cleaning, inspecting, and testing the installation of the two PCM chips - U1 (PCM2706/7) and U3 (PCM1794).  Get these two chips right before moving on to soldering the rest of the parts and your build should be successful.*
   
  To many of you, SMD soldering is something new and perhaps a little bit scary.
  However, with the right preparation and strategy, you may find it easier in some
  respects than through-hole soldering. Like any Do-It-Yourself exercise, success
  depends a great deal on proper preparation and tools. SMD has some special traits that make a few tools (one in particular) absolutely necessary.
  Here's a list of things you need, with the first one an absolute necessity:

 *tweezers*
 flux pen
 helping hands
 small-diameter eutectic solder
 small-tip soldering iron
   
*Tweezers cannot be over-emphasized.* Without a good pair, I have trouble imagining how manual SMD-soldering can even be accomplished. Get a good pair! I use a pair of ESD-safe, bent tip tweezers that I bought at Fry's, but all the good DIY-suppliers have them in stock - Mouser, DigiKey, Allied, Newark, etc. Here's a pic that's similar to the pair that I use (I bought mine at Frys):



  Another device that you may find useful is the flux pen. The flux goes down as a
  thin liquid and gets sticky very quickly - almost sticky enough to hold a part in
  place. The pen form lets you apply the flux where you want it, even on a very small
  SMD PCB. I like Kester and stick with their products. The one I use is the Kester
  #186. It contains regular activating flux that works great (no water-soluable or
  no-clean flux for me).
   
  This varies with the individual, but I use a Hakko 936 soldering station, set
  at *375 deg.C.  *Yes, I've turned up the heat with the pupDAC. It has a rather large ground plane to the grubDAC or SkeletonDAC. I also use a 0.8D chisel tip for the Hakko: 900M-T-0.8D. This is a half-size chisel tip of the standard tip that comes with the Hakko 936 (900M-T-1.6D).  Keep in mind that the temperature setting and my tip selection go hand-in-hand.  If you use a larger tip at that same temperature, it could be that it transmits enough heat to burn.  So be aware of this if you choose to use different stuff - this is only a suggestion/guide and what works for me.
   
  Finally, solder is the same solder that I use for all my DIY stuff: Kester 44 eutectic, 63/37, 0.025" diameter.  (As a matter of fact, I bought a 1/2 pound in 2006 and have been using it ever since - _on every DIY project, not just DACs_.) Larger diameter solder is too big for SMD IMHO, and smaller stuff breaks all the time. Again, I cannot emphasize too much the need for using _*eutectic solder at 63/37*_. I have repaired a number of individuals' DIY projects over the years now, and I always shudder when seeing projects that used old 60-40 solder. It makes a real difference in the quality of the joints and there's no excuse - even Radio Shack sells 63/37 eutectic solder.
   
  Be sure to review the GrubDAC and SkeletonDAC websites and please check out Tangent's excellent tutorial on SMD soldering: Tangent's Tutorial 3 - SMD Soldering Techniques . I learned how to do SMD soldering with Tangent's methods and with a few exceptions (use of the flux pen), I've been using them ever since.  There are a couple of other excellent tutorials that exist on the web:
The Curious Inventor - Surface Mount Soldering
SMD Soldering Guide by Infidigm


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## tomb

Enough of text!!  This is supposed to be _photo_ step-by-step thread, so here goes:



  Above you can see my setup before starting to populate the pupDAC PCB.  Again, preparation is all-important.  Make certain that you have plenty of time, you're comfortable, and you're not rushed and nervous.  Good preparation helps to calm the nerves in handling those tiny parts.
	

	
	
		
		

		
		
	


	



   
  A closer look to the left at my stuff:



  From left to right at bottom: wire strippers (not needed, but just in case), a Leatherman knife (for those odds and ends that come up), quality flush cutters, detail scissors, _smooth-jaw_ pliers ($1.99 Harbor Freight special), curved-tip detail tweezers (see post above), and the pupDAC parts kit as it comes *mass-produced and packaged from Mouser*.
	

	
	
		
		

		
		
	


	



   
  A closer look from the right at my stuff:



  From left to right at bottom: the pupDAC kit as packaged from Mouser
	

	
	
		
		

		
		
	


	




, my building board (1x10 finish-pine) on a non-skid foam mouse pad, the pupDAC PCB held in a set of helping hands ($1.99 Harbor Freight special), on the building board - the Mouser-pupDAC kit package for the PCM2707, and finally - my Hakko 936 (now 6 years old and still going strong).
   
  From left to right at top: electrical tape (used to protect the corners of the PCB from the helping hands' alligator clips), my 6-year old 1/2 pound roll of Kester rosin-core eutectic solder (0.025" dia), de-soldering braid with a flux pen, brass wool for soldering iron cleaning (I quit using the water sponge years ago), and a high-intensity lamp.
   
  We each have our own working environment.  I'm not saying you have to have all of these things, but they really help me.


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## tomb

The first chip that needs to be installed is U1, the PCM2706/7 (both the PCM2706 or PCM2707 will work.  Why this chip first?  Because its pins are on all four sides (TQFP-32).  You need clear access to all four sides to solder it properly.  Once you add a single other part to the PCB, this will become harder.
   
  We hope you use the Mouser-produced kit, but keep in mind that the parts are not labeled according to the BOM and the PCB.  They are all individually-labeled, but with the Mouser's part number, not the pupDAC's:



  Above is shown the bag for U1 - Mouser has labeled it as their part#, which is a combination of the actual manufacturer's part# along with a Mouser prefix.  For the PCM chips, this is easy.  It's not so easy later on, so be sure to have the pupDAC BOM printed out and handy, so that you can check and verify each part before installing it on the PCB.
   
  Here we see the pupDAC PCB again (smudges notwithstanding).  It's held in the helping hands with alligator clips and electrical tape on all four corners for protection.  Note the "T3" stamp.  The pupDAC PCB's have been electrically tested at the manufacturer (Imagineering).  No shorted trace defects to confound your build trouble-shooting.
	

	
	
		
		

		
		
	


	






   
  The first thing we need to do is prepare an anchor point for U1:



  Note the arrows.  One is pointing to the alignment dot on the PCB.  Make certain the alignment dot on the PCM chip is in the same position!  The other arrow is pointing to the bottom pad on the right side.  I've applied a bit of solder to this pad.  I'm right-handed, so what I'll do is hold the soldering iron to this pad with my right hand, while my left hand is holding the PCM chip with tweezers.  While the solder on the pad is melted, I'll move the PCM chip into place so that the bottom right pin is positioned into the melted solder.  While still holding the iron and the chip, I'll make certain that the pins line up with all four rows of pads on the PCB.  I'll also make sure that the extended pads leave a bit of room on the outside of all of the pins (the PCM chip will be centered).
   
  If you get tired doing this, that's OK.  Remove the tweezers and the soldering iron.  Take a deep breath and relax.  Try again by getting a grip on the chip with the tweezers and then applying the soldering iron to melt the pad again.  Try to position the chip as good as you can - it will make the soldering much easier later on.  Plus, you only have one bit of solder and pad to worry about in this step, so you can keep re-trying as much as you want.  Even then, if the chip is a little rotated, you can actually twist it slightly on the PCB when the solder is cooled.  Just work with it as long as you need to get it in the right position.
   
  Here we see U1 in place.  One arrow is pointing to the soldered pad (the only one right now).  The other is pointing to the alignment dot on U1.  It's in the same position as in the pic above on the PCB silkscreen.



   
  If you're happy with the positioning of U1, then what we need to do next is to solder an opposite pad, locking U1 into place: 



   
  Now that we have two pins soldered, locking U1 into place, we'll proceed with soldering all the rest of the pins:



  Here I've fturned the helping hands and PCB at ninety degrees to the building board.  I'll solder the two rows indicated by the arrows.  The two anchor pins we soldered in the previous steps are in the other rows, so we won't be lifting the chip after all of our trouble getting it perfectly aligned.  You can also see that I've applied the flux pen to make the soldering go easier.
   
  Bottom line, with the tools I've outlined above, you can actually solder each pin of U1 individually if you'd like.  There's enough space to do this if your solder is on the order of 0.025" dia. and you use the small chisel point that I specified above.  If not, you can use the drag and wipe method (my preference) or the method that you prefer.  I like the drag and wipe because with the extended pads, you can literally solder every pin on the edge, removing the chances of bridges except at the very tip of the pins, where they're easy to access.
   
  Here I've turned the PCB around again, applied flux to the other two rows, and soldered them in place.



  We're now done with soldering U1!


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## tomb

Take a break and use the time to fully inspect your handiwork.  We're going to all of this trouble, remember, because if you get U1 and U3 (the two PCM chips) messed up, your experience with building the pupDAC will not be a fun one.
   
  I'm holding the PCB up to a very bright light to check for soldering bridges:



   
  My hand got tired, so I decided to tape it up there.  That way, I could check for bridges at my leisure.  A good way to do this is to reference the PCB photos on the pupDAC website.  Note that the arrow is pointing to a "bridge" that's actually a connection of the traces on the PCB.  It is not a soldering bridge.



   
  BTW, this lamp is LED-based, so it's bright but not very hot.  You may not want to tape up the PCB like this if you're using an incandescent lamp - damage may result!
   
  Anyway, I couldn't find any bridges at this point, so I proceeded on with the rest.


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## Avro_Arrow

If you want to get really good closeups of your board, don't forget my trick with the scanner...


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## tomb

Next up is U3, the DAC chip itself (PCM1794).  This chip is SSOP-28 and relatively expensive (almost half the price of an entire grubDAC kit!).  Nevertheless, it is exactly the same chip form as the PCM2702 that was used in the Alien and BantamDACs, and the PCM2704/5 chip used in the SkeletonDAC.  So all techniques and methods you may have used for those chips apply exactly!!
   
  Just as with U1, the first thing we want to do is apply solder to a corner pad and use that to position and anchor U3 into place on the PCB.



  The bottom arrow is pointing to the bottom right pad where I've applied solder.  This will be the first anchor point.  At top left, the two arrows point out the alignment dots for U3.  Make certain that U3's alignment dot matches these when you position the DAC chip.
   
  As with U1 above, grab the U3 chip with your tweezers.  When you got a good grip on it with your left hand, grab the soldering iron with your right and hold it to the bottom right pad on the PCB.  While the solder on the pad is melted and holding the soldering iron in place to keep it melted, move the U3 chip into position so that its bottom right pin is applied to the pad with the melted solder.  Try to align the chip so that the pins match up exactly with both rows of pads.  Try to also position the chip so that there's a bit of clearance on both sides and portions of pads to the outside of the pins on both sides.  As with U1 above, you only have a single pad with solder on it to worry about.  So take your time, get the chip anchored so that it's aligned.  As with U1, even after the solder has cooled on the anchor pad, you may be able to twist the chip slightly on the PCB to give a final alignment.  Use a combination of both so that you have it aligned as good as you can get it.
   
  I didn't show it, but I flipped the PCB around to get better access to the top left pad as the second anchor point.



  While I had the PCB flipped around, I also proceeded to apply the flux pen to both rows of pins/pads and then soldered the left side.  Which side you get to first doesn't matter as long as you have those opposite anchor pins soldered.
   
  Again, I use the drag and wipe method, but I throw some of the other soldering rules out the window.
	

	
	
		
		

		
		
	


	




  The pins are too small and too close together to solder individually, but maybe some of you will be capable of doing that.  For me, after doing a number of these through the years, I CHEAT.  Aligning the soldering iron parallel to the row of pins I'm going to solder, I apply a small (very small) bit of solder to the tip of the iron.  Then I apply it to the pins - on the outside tips and pads.  I may solder two or three pins at a time this way, finishing up with a drag and wipe to clean the excess solder that may result ("rinsing the iron in the brass wool each time before a drag and wipe).  So in effect, I'm applying solder to the outside of the pins, starting at top, and moving down 2 or 3 pins at a time.  Trying to heat the pads/pins with the soldering iron and then to apply the solder to the heated pins, just doesn't work for me.  Instead, apply solder directly to the iron, and then carefully to the pins (on the outside tips), while moving the iron down to the next set of pins at the same time.  I guess that's redundant, but I hope I'm getting the idea across.
   
  Once you've made it to the bottom of a row, then finish it off with another couple of drag and wipes.  If you see some pins that look "dry," apply a tiny bit of more solder to the tip of the iron and try again.  Finish up with another drag and wipe.  If you use the brass wool each time before you drag and wipe, the iron will be clean and will actually pick up some extra solder that could form bridges.  So not only does it give a better appearance to the soldered pins, it also serves to clean up excess solder.
   
  Here we see both rows of pins soldered:


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## tomb

Quote: 





avro_arrow said:


> If you want to get really good closeups of your board, don't forget my trick with the scanner...


 
  Yep! Great idea!
   
  Unfortunately, I need to buy a new scanner.  Seems they never update the drivers on those things and so I have to go back to an old laptop to use mine.


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## tomb

Take another break to inspect your handiwork.  Make certain that these chips are soldered correctly before proceeding with the rest.  So, if you don't have access to the scanner, use the light trick again:



  Note the arrows.  There are PCB-trace bridges in both places, so don't confuse these with solder bridges that you may have created.
   
  Another method of checking for bridges is to use your DMM.  Place a probe on one of the pins as it exits the chip (not on the solder or pad).  Follow the trace connected to that pin to some other place on the PCB.  Place the other probe, there.  If you read -0- resistance, then you have a good connection.  Similarly, follow the trace from an adjacent pin and place the other probe, there while still using the first probe at the pin's exist from the chip.  If you read something other than -0- resistance, then you should not have a cross connection/bridge.  Refer to the schematic for the pins that are grounded and simply place a probe at GND.  Also refer to the schematic for pins that may be connected to each other purposefully as with the arrows above.
   
  You can also use this time to re-check the U1 chip.
   
  When you are satisfied that you've got these chips soldered OK, then proceed on with the rest of the build.


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## tomb

At this point, you have a lot of tiny SMD parts left to solder.  As mentioned previously, the Beezar/Mouser kit has been packaged from Mouser with their part numbers on the bags.  So, you need the BOM to reference the part numbers with the pupDAC part #'s used on the PCB:



   
  Next up are the rest of the "U" chips.  All the remaining "U" chips on the top side of the PCB are TPS regulator chips, except for two.  One is a supervisory controller, U6, and the other one is the charge pump, U7.  Except for the supervisory controller which is SOT-23-3, all the other "U" parts are SOT-23-5. The five-pin chips have 3 pins on one side and 2 pins on the other.  I've found it's easiest to anchor and place the chip using the middle pin on the 3-pin side.
   
  Note that the single remaining "U" chip is the U9 opamp that gets soldered on the back side.
   



  Here the arrows are pointing out the solder that I've placed on the middle pins of all the remaining "U" parts, except for one outside pin on U6.  These pads will be used to place the U chips on the PCB.  The method is the same as that of the PCM chips: while grasping the part with tweezers using your left hand, use your right hand to melt the solder on the pad with the soldering iron.  Holding the soldering iron in place to keep the solder melted, move the part's pin in position onto the pad with the melted solder.  Check the alignment, then remove the soldering iron and let cool.  Then remove the tweezers.
   
  Using the middle pin on the 3-pin rows like this gives you maximum accessibility to solder all of the other pins.
   
  Since almost all of the 3-pin rows are on the left side, I've flipped the PCB and helping hands around so that I can access the soldered pad with the soldering iron in my right hand.  Working from right to left across the PCB, the first chip has been placed and soldered into position:



   
  The rest of the chips follow.  Move the PCB and helping hands around as needed to access and solder all the remaining pins:



   
  Next up is the oscillator, X1.



  The arrows point to one pad as the anchor pad (same old method) and the other arrow is pointing at the locating dot.  Be certain you align X1 accordingly.
   
  Here we see X1 soldered in place.  Note the locating dot on top of the part.  One important item to remember: the solder should wick up the sides of the oscillator, but do not use so much solder that it bridges over to the metal top.  If so, you will have shorted the oscillator and you'll need to clean it up:



   
  Here we have the 805 capacitors, next:



   
  The 1206 resistors - try to be organized and have the printing oriented in one direction:



   
  Finally, there are three 1206 ferrites on the top side.  Note that all the ferrite "L" chips are the same, so no confusion possible, here: 



   
  You've now finished all the SMD parts on the top side of the PCB!


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## tomb

Hmm ... I've always wondered when posting one of these, what does it take to start a 2nd page?  This seems awfully long for one page - oh, well.
   
  Next up is the backside of the PCB - the opamp, lots of little 805 capacitors, a couple of ferrites, and one 1206 resistor.
   
  Here we see the reverse side of the PCB:



  The arrows indicate the anchor pad I'm going to use for the opamp.  Also, pay close attention to the locating dots ont he silkscreen.  TI is being a little tricky these days - the OPA2835 comes with a line drawn across the width of the opamp on the locating side.  If you use this opamp, solder with the line on the end where the locating dot is on the PCB.  The LMH opamp has a circular dent in the top of the opamp that forms a permanent "dot."
   



  The arrow indicates the circular dent in the LMH opamp.  The anchor pin is soldered and the opamp is aligned.
   
  IMHO, an SOIC-8 opamp such as the ones the pupDAC use are just about the easiest SMD part to solder.  There is plenty of clearance between the pins to individually solder each pin. 



  I've soldered an opposite anchor pin to the first one and then soldered the rest of the pins, one at a time.  Finish off with a drag and wipe on each side, if desired.
   
  I kind of jumped ahead at this point with my photos, but no matter.  This is about 3/4 of the way through with soldering all the 805 capacitors on the reverse side of the PCB.  Same old method is used - I actually prime all the pads (one each) of the rest of the parts, then start with the smallest (805 capacitors).  Melt the pad you've applied solder on, and while holding the soldering iron to keep the solder melted, position the part in place with your tweezers.  When you have the part properly positioned, release the soldering, let the solder cool/harden, and then release the tweezers.  Go back and solder the remaining pad at your convenience.



  Note the arrows indicating the remaining pads that I've "primed" all at once, including the single 1206 resistor pad and the two remaining ferrite pads.
   
  Here we see all of the capacitors finished:



   
  Next up is the resistor:



   
  And the remaining two ferrites:



   
  Whoa!!  We've finished every SMD part on the board.  Take a short break at this point to inspect all of the SMD parts on the reverse side.  Make certain that you haven't forgotten to solder a remaining pad somewhere.  Also, take this time to fully rinse the PCB as shown in the next post.
   
  The easy through-hole stuff is next!


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## tomb

I like to clean everything up at this point.  Why?  Because the SMD parts can be immersed completely, whereas through-hole electrolytics are not completely sealed and could be hurt by doing this.  At any rate, it gets things very clean among all those tiny pins.  Wait till later and you may have all sorts of trouble getting things cleaned.
   
  I use 91% isopropyl alcohol from Walmart for cleaning all my projects.  It leaves no residue once the board is completely rinsed and it readily dissolves flux.  The use of an old toothbrush can help to get those troublesome flux patches off where the simple soaking does not.
   



   
  One thing to be aware of - the latest chips from TI use a different case material and is actually hygroscopic.  The pins are sealed at the case body, but the body itself may absorb moisture.  This is nothing to worry about except when you've rinsed at the end and you're ready to plug it in - don't.  Wait for a few hours, use a hair dryer, put the PCB out in the sun, etc. to make certain that things are dry under and inside the chips.  Otherwise, you'll drive yourself crazy trying to figure out why your DAC doesn't work or seems to de-activate itself every few minutes.
	

	
	
		
		

		
		
	


	



   
  More later ...


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## Avro_Arrow

Great job so far Tom!


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## mosshorn

Excellent job Tom, this is a great tutorial of not only the Pupdac, but of SMD soldering as well!


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## tomb

Thanks for the compliments, guys!
   
  On to the through-hole parts!
   



  The small precision resistors are first, since they're the lowest in height except for the SMD parts.  I like to solder in the resistors on the back, first.  Then we're done with everything on the reverse side of the PCB.  Why are there through-hole resistors on the reverse side?  Cobaltmute's design minimizes the offset from the opamp by making the lead-length and traces from these particular resistors as short as possible.
   
  As always, ensure that the rating is visible from the top when you install them.  Precision resistors such as these are not color-coded.  Therefore, if you don't ensure that the rating is on top and visible, you'll have a hard time confirming the proper values if you need to troubleshoot.  (DMM resistance measurements are often inconclusive on a populated PCB - the resistors are often in parallel with other resistors or devices, making it difficult to get a one-to-one reading on the resistor's value.)
   
*Warning!  Ensure that you pull the leads all the way through and get these resistors as flush as possible.*  The pupDAC PCB will be placed in the lowest slot of the Beezar/Hammond custom case.  *There is less than 2mm clearance between the bottom surface of the PCB and the inside-bottom of the case!*  You will also need to trim all the leads from the bottom of the PCB to guard against shorting.  More about that later when we finish the through-hole parts.
   
  Trim the leads and continue on with the resistors on the top side:



  Don't forget R12 over there in the middle by itself!
   
  Next up is the LED.  Since we're building this for the custom Beezar/Hammond case, we need to know how to install the LED so that it lines up with the machined hole in the endplate.



  Bend the leads at right angles as shown - just behind the point where the leads "neck-down" to entire the LED housing.  This is clearer in the next pics, but bottom line, you want to install the LED so that the LED is horizontal and parallel to the PCB, with the flange resting flush and at the edge of the PCB.
   
  I guess it's a Canadian thing 
	

	
	
		
		

		
		
	


	







, but cobaltmute labels the "Cathode" lead of the LED instead of the long "+" lead.
	

	
	
		
		

		
		
	


	




  That's the "-" lead or the SHORT one.  *So be certain: The short lead goes into the "C" hole.*
   
  Here you can see more clearly exactly where to make the bend.  If for some reason, you end up with an LED that doesn't have leads shaped like this, then just be certain that you bend the leads so that the flange is flush to the PCB and at the edge of the board:



   
  Another view to make sure:



  Done this way, it lines up perfectly with the machined hole in the endplate.
   
  Next up in the lowest-to-tallest part hierarchy is the mini-USB jack:



  Remember here, too, that you're installing this to line up with a pre-machined endplate.  Make certain that the mini-USB jack is absolutely flush to the PCB (note that only the front half is actually flush to the PCB - check the drawing of the part if you're uncertain) and square (not turned at an angle).  Also, the mini-USB is a mechanical connection.  It will undergo a lot of stress with plugging and un-plugging a USB cable.  If you use the case bezels, there is no other support except for the solder connections at the PCB.  The arrow is pointing to the snap tabs that provide the greatest structural support to the jack.  Ensure that the pad hole is fully filled with solder from the bottom and that when you make the solder connection, you get good wicking to the top side as is shown here.
   
  Another view showing the "structural" solder wicking to the top side:



   
  Next are the Mica capacitors, C3 and C18:



  These things seem to have the worst quality control when it comes to sizing tolerances of any type of capacitor.  You will find different sizes between almost any two in a bag.  That's OK - just try to make sure that you pull the leads through as far as you can.  (You may see some through-hole plating chips popping out of the pads as if you're re-drilling the holes.)  This minimizes the lead length and ensures that you haven't exceeded your height clearances.  You may still need to bend them like wings to fit in the the electrolytic capacitor, C10, but more on that later.
   
  Here's another view illustrating how the caps are pulled through so that no bare leads are showing.  You may even slightly crack some of the epoxy coating on the high-part of the leads, but that's OK as long as you don't damage the capacitor's main body overall.



   
  Time to install the electrolytic capacitors!  It's a judgment call as to which is taller - the electrolytic capacitors or the RCA jacks.  The drawings will tell you that the RCA jacks are a tad shorter, but I haven't found that to be the case in real practice.  I think when you get electrolytics of this size, the variance in the rubber plug exposed at the bottom of the cap is fairly high.  Regardless, it's quite easy to hang the PCB over the building board so that you can get the RCA jacks flush to the PCB later on.
   
  My method in installing electrolytic capacitors is to place them all in the holes on the PCB.  Take my pine piece building board, turn it over and hold it on top of the capacitors while holding the PCB in my other hand.  Then while holding PCB on bottom and pine board on top with both hands, I turn over the entire assembly so that the pine board is back on the bottom and the bottom of the PCB with the capacitor leads are on top - ready for soldering.
   
  While pressing down on the bottom of the PCB to get the upside-down capacitors flush, I solder one lead each on each capacitor.  When that's done for all the capacitors, I flip the PCB over and check the caps for alignment and square them.  Them I flip the PCB back over and solder the remaining leads.
   
  C2, C9, C16, C19, C10, C26, and C27 are close enough in height to be soldered at the same time using the procedure described above.  C22 is just enough taller that you should probably solder that one in after all the others.
   
  As mentioned before, the Mica caps (as packaged in the Beezar/Mouser kit packaging) are too big to allow enough clearance for C10.  I simply bend the Mica caps like "wings" to either side of C19 as show below: 



   
  Another view of the electrolytic capacitors installed and the Mica caps bent to either side of C10:



   
  The RCA jacks are straight forward.  Install them before the 3.5mm/1/8" stereo jack.  (The 1/8" stereo mini-jack is the tallest part on the pupDAC.).  Note that the solder joints for these are also structural in nature.  However, they have real, bent-spring snap tabs at the ground connections, so the pad holes are actually too big to fill-in completely with solder.  You will end up melting all the plastic housing if you attempt to do that.  Instead, ensure that there's ample solder around the tab and fill-in completely the signal connection pads (the ones in back), so that they proved some structural support.  Note that the plastic tabs on the bottom in the front fit over the thin cutouts at the edge of the PCB.  This helps to lock them into proper position and ensures that the jacks are flush against the PCB at the top surface and front edge.



  Install the remaining 3.5mm/1/8" stereo mini-jack so that it's flush and square with the PCB.  Be careful with these parts.  It may be best to let them cool somewhat inbetween soldering their tabs.  The entire housing for all three jacks is plastic and can be easily melted if exposed to too much heat for too long.
   
  FINISHED!!  Another view of our completed pupDAC:



   
  Prior to final clean and rinsing, be certain to trim all the leads underneath the PCB.  This includes the leads/tabs for all the output jacks.  As mentioned previously, there is less than 2mm clearance between the bottom surface of the PCB and the inside surface of the bottom of the case.
   
  Clean and rinse as with a normal PCB at this point.  I like to use a toothbrush with the same Walmart 91% ispropyl alcohol used before.  Get the bottom of the PCB completely wet with the alchohol, using the toothbrush to scrub around the joints where the flux may be particularly thick and hard.  Pat it up with a good paper towel.  It may take you 4-6 rinses like this to get most of the flux off.  Your PCB should be very shiny and with very little dried, white flux around the solder joints.  Be sure you use a clean paper towel each time, or the alcohol will simply re-dissolve the flux in the paper towel.
   
  After you've done this, inevitably you've had flux bleed through the test point holes back to the top surface of the PCB.  Plus, you have those four resistors underneath whose leads and solder (therefore, flux) are on the top side of the PCB.  Use a toothbrush where it will fit, but I find several q-tips work well.  You can use them both to apply the alcohol and to dry it up.  This works fairly well, because the iamount of flux on the top side should be fairly small.
   
  Once you have the PCB clean, rinsed and all the leads neatly trimmed, let it dry for an hour or two (remember that new hygroscopic chip material).  After that, installing into the case is a snap!


----------



## tomb

I apologize, this must be Head-Fi's world's longest single-page posting.  I guess the forum software works on post count rather than number of character/lines or record size.


----------



## tomb

Once again, here are a couple of pics of the finished, trimmed, cleaned, and rinsed PCB.
   
  Top:



   
  And bottom:



  Note that the tabs are neatly trimmed for the RCA jacks and stereo mini-jack.  The PCB will not fit into the case with these tabs remaining in place!  The mini-USB jack's tabs/leads are already short enough - they barely fit all the way through the PCB holes.  So, no trimming needed there.  The rest of the trimming was the capacitor leads, the LED leads, and the resistor leads.
   
   
  Casework is next!
   
  As mentioned, the pupDAC is designed specifically for the Hammond 1455C801 case (or 1455C802 with plastic endplates).  We have designed a special machined version from Hammond with Beezar-anodized blue and laser-etching.  Four screws are all that's needed for final assembly!



  Those are special blue-anodized aluminum socket-head cap screws.  If you build your own, remember that the Hammond case does not come tapped.  Aluminum screws such as these will strip in short order if you haven't tapped the case.  Hammond uses 6-32 screw sizes as a standard with their 1455 series cases.  The ones shown here from Fastener Express are 1/2" long and work quite well on the tiny pupDAC case, but it must be tapped.  Hammond supplies some inexpensive self-threading phillips head screws, but in silver, they're not nearly as pretty as these.
	

	
	
		
		

		
			




   
  Here is the finished pupDAC completely assembled.  It's your choice on whether to use the transparent-blue bezels.  The endplates will fit either way.  The tip of the mini-USB jack and the tip of the LED are flush with the outside surface of the endplate if you don't use the bezels - that's the only difference.






   
  Yay!! I made it create a 2nd page!


----------



## Angelbelow

Thanks.


----------



## Angelbelow

Quick question, would swapping the op-amps from this list to the AD797BRZ be possible or would the entire system have to be redesigned?
   
   http://www.diyforums.org/PupDAC/bom/pupDAC-BOM.htm


----------



## tomb

Quote: 





angelbelow said:


> Quick question, would swapping the op-amps from this list to the AD797BRZ be possible or would the entire system have to be redesigned?
> 
> http://www.diyforums.org/PupDAC/bom/pupDAC-BOM.htm


 
  1. The specs are better with the OPA2836 and at a quick glance, I think they may be better with the OPA2835, too - bandwidth, distortion, current output and slew rate are all better.  The LM6643 may be a bit worse, but that's only 1 out of 3 that all work well in the pupDAC.
  2. The AD797 is not a low voltage opamp.  It can go down to +or- 5V, but you're not going to get that with any kind of quality using USB power.  The pupDAC works on a totally linear-regulated +or- 2.5V supply on the output opamp and it burns a volt or two of the USB power to get that.
  3. The AD797 is a single.  The pupDAC uses dual opamps.  You could probably rig up a two-single-to-dual adapter, but you wouldn't want to do that on a DAC.  The trace lengths and layouts are way too sensitive.
  EDIT: I think that's three strikes.
	

	
	
		
		

		
		
	


	



   
  Yes, you're looking at a different DAC altogether if you want to use that opamp.


----------



## kyoshiro

being the SMD soldering noob i am, how does 1 ensure U1 is properly soldered? can i also run across each leg with a knife and make sure they dont connect?


----------



## tomb

Quote: 





kyoshiro said:


> being the SMD soldering noob i am, how does 1 ensure U1 is properly soldered? can i also run across each leg with a knife and make sure they dont connect?


 
  Yes, I often use an X-acto knife to clear the pins.  It's hard sometimes to tell whether you've got a real bridge, or whether it's just some excess flux reflecting in the light.
   
  That said - short of an actual test by plugging it in, which really can't be done until the DAC is finished - there are two methods:
   
  1. Visual inspection.
  This needs to be very rigorous.  Hold it up to the light as I've shown in this thread, use a magnifying glass, take a macro photo and blow it up, or scan it and blow it up.  If some methods are un-revealing (glare, no contrast in a photo), then use another.  I can't remember if I mentioned it in this build thread, but I also do a preliminary cleaning after doing the two PCM chips in this DAC.  That removes the excess flux and lets you see the joints better - try not to proceed unless you are confident the pins are clean and soldered well!  Even so, you can still re-flow the chips on a completed pupDAC if you remove one or more electrolytics.  I just did that on one last night, re-flowed one side of the DAC chip and re-installed the electrolytic cap that was in the way - not too difficult if you find you have to do it.
   
  2. DMM trace continuity checks.
  With this method, you place one probe of a DMM at pin right at the exit out of the chip's plastic - above the solder joint, IOW.  Follow the trace that the pin is connected to until you're well away from the solder joint and place the other probe at that spot.  You should read zero resistance.  A good thing to do at this point is move one probe to the next pin/trace to also check to see if it's bridged.  This is obviously much more tedious than #1, but is a good fall-back if you're really having trouble pin-pointing a problem.


----------



## cobaltmute

angelbelow said:


> Quick question, would swapping the op-amps from this list to the AD797BRZ be possible or would the entire system have to be redesigned?
> 
> http://www.diyforums.org/PupDAC/bom/pupDAC-BOM.htm



The AD797 isn't spec'ed to run at +-2.5V, which is what the output opamp is running at in the pupDAC.

With some careful looking at the schematic and board, you may figure out a way to get +-5V, but I'm not going to say anything about how it would actually work.


----------



## kyoshiro

my opa2835 bag only contains a card and dehydrate packet lulz


----------



## kyoshiro

woops nvm, it was somewhere unexpected


----------



## tomb

Quote: 





kyoshiro said:


> woops nvm, it was somewhere unexpected


 
  Yep - it's hard to find that tiny little opamp amongst all of that anti-moisture business. 
	

	
	
		
		

		
		
	


	



   
  If Mouser hadn't packaged this stuff, there's no way I'd package one of those opamps like that.


----------



## kyoshiro

Quote: 





tomb said:


> Yep - it's hard to find that tiny little opamp amongst all of that anti-moisture business.
> 
> 
> 
> ...


 
  yea no kidding. I also figured out something during the soldering of the many leg SMDs. Good flux is a must to even solder it properly with swipe method. The cheap pen flux i was using didnt do the job so I ordered some BGA gel flux and it all came together very quickly lol


----------



## scootsit

Tomb,
  I've been super busy, but I'm finally getting around to working on this now. Is there any reason to swap the PCM2706 for PCM2707, or is this just to add some variety?
  Similar performance out of both?


----------



## cobaltmute

For our purposes they are exactly the same. The choice of part for the kit is based upon availability. 

IIRC, the difference is based upon the PCM2706 being programmable by an EEPROM.


----------



## scootsit

Quote: 





cobaltmute said:


> For our purposes they are exactly the same. The choice of part for the kit is based upon availability.
> 
> IIRC, the difference is based upon the PCM2706 being programmable by an EEPROM.


 

 Got it, thanks. I just updated my BOM last night, changed a few parts. You used some nicer caps than I speced, so I switched to yours.
   
  Anyway, I need to figure out another project (a pedal for a friend) before I place the order. But, soon! I'm very excited still.


----------



## kyoshiro

argghh LED not lighting up : (


----------



## scootsit

Does the LED need to be high efficiency, as speced or will any LED work?


----------



## tomb

Quote: 





scootsit said:


> Does the LED need to be high efficiency, as speced or will any LED work?


 
  Physically, any through-hole 3mm should work.
   
  Cobaltmute would need to confirm if a super-brightness, high-current LED would adversely affect the current draw and the USB connection.  The one that's spec'd is plenty bright, so I personally wouldn't go brighter than that.


----------



## kyoshiro

to be more correct, led doesnt light up and driver installation didnt start odears


----------



## tomb

Quote: 





kyoshiro said:


> to be more correct, led doesnt light up and driver installation didnt start odears


 
  Sorry I didn't see your first post, kyoshiro.  The LED pretty much takes its power directly from the USB connector.  There's not much else in the string except a single resistor and a ferrite.  If that indicates you're not getting proper power to the PCB, then nothing else is going to work, either.
   
  Can you supply some pics?


----------



## KimLaroux

I realize this will sound like at obvious question but I feel like the problem may be the PC itself. Have you tried connecting it to another computer?


----------



## kyoshiro

welp  got the LED to light up but computer recognizes it as unknown device ffffffffff
  I'll post some pics tmr after work as I had a long day


----------



## kyoshiro

https://www.dropbox.com/sh/3qkqeso6wbktmpy/B6mp5Dd6y0
   
  should have them pics there.


----------



## kyoshiro

ahh failed and shared my whole camera upload folder (oops)
   
  here is only the PCBs
  https://www.dropbox.com/sh/8kbkzzmkqtpp2hd/WS56Y4JZnY


----------



## tomb

Quote: 





kyoshiro said:


> ahh failed and shared my whole camera upload folder (oops)
> 
> here is only the PCBs
> https://www.dropbox.com/sh/8kbkzzmkqtpp2hd/WS56Y4JZnY


 
  Have you measured the voltages at the test points and can you share those with us?
   
  I am particularly interested in the 3.3V test points at U4 and U1 (the PCM2707 chip).  If the computer powers the LED but does not recognize the rest of the device, something is wrong in the PCM2707 portion of the circuit - that's what negotiates all the communication with the PC and the USB connection.  If those voltages are off, the PCM2707 may not be operating properly.  U4 looks a bit suspect in its connections and there may be some bridging on U1.
   
  If you can confirm those voltages, that may help to pinpoint the problem.


----------



## KimLaroux

Quote: 





kyoshiro said:


> ahh failed and shared my whole camera upload folder (oops)
> 
> here is only the PCBs
> https://www.dropbox.com/sh/8kbkzzmkqtpp2hd/WS56Y4JZnY


 
   
  C25 seems shorted. C27 may have a cold joint.
   
  If I were you, I'd reflow everything on the bottom. You seem to have had trouble soldering all that, did you use lead free solder?


----------



## H22

looks like there may be a few cold joints there.
   
  Tomb, perhaps you might consider including a small roll of good solder, a small tube of flux and possibly a roll of solder wick with these kits?
   
  Personally I don't know how I ever did SMD work without good flux (I like the stuff that chip-quick sells, but it is not cheep).
   
  I know it would add to the cost of the kit, but i think in the long run it would be worth it.
   
  Kyoshiro, I don't know where you are located, but see if you can get some flux (i prefer a gel type for SMD work) and some small (1/8 to 3/32 inch) solder wick before you "re-flow" your board.
   
  I would coat every joint with a little flux, then heat it with the iron till it melts and turns shiny, then remove the heat. Use the solder wick to pull up excess solder if needed.


----------



## tomb

Quote: 





h22 said:


> looks like there may be a few cold joints there.
> 
> Tomb, perhaps you might consider including a small roll of good solder, a small tube of flux and possibly a roll of solder wick with these kits?
> 
> ...


 
   
  EDIT: Just a suggestion, but maybe you guys should think a bit and use some tact before you declare that a builder is a lousy solderer.  I can't tell you how many people contact me directly through e-mail, simply because they're too embarassed to post photos of their work.  It's like stripping themselves nude in front of a camera.  Give 'em a little encouragement first ... try not to mention that their work may not look so good when they're crying for help.


----------



## tomb

Don't get me wrong - your help is greatly appreciated.  I would rather 100 times over that someone post their problems here, instead of contact me directly through e-mail or PM.  Hell, I'm no expert ... and even if I was, it wouldn't compare to having dozens of eyes look at the problem.  It's always best to post here and have you guys help.
   
  Guess that comment about including more stuff with the kit set me off.  I apologize.


----------



## KimLaroux

Yeah well it's always touchy to give advice in those cases. The line between insulting someone and saying what needs to be said is blurry at best. And on the internet, it's even worse. It's not like you can use a different tone. Words are just words. You have to use a thousands words to say something that can be said in ten, just to make sure you're not insulting someone. And everybody takes criticism differently... which worsen things even more.
   
  And just to be clear, I did not say he was a "lousy solderer". That would be insulting, which is not helping anyone. Besides, I've never soldering SMT chips myself, so I'm probably no better than Kyoshiro. Everybody's got to start somewhere. Nothing to be ashamed of.
   
  The instructions you published for the pupDAC are amazing, the best I've ever seen. I even pass the link to people on IRC that have troubles with SMT. I think you did an exemplary work with the whole pupDAC kits, and nothing more should be asked. I agree with you that a kit should not include tools to build the kit. DIY audio is a hobby, and acquiring the tools needed for a hobby is, well, part of the hobby.
   
  My comment about solder was from personal experience. The forms in which the solder cooled on Kyoshiro's board reminds me of the way lead-free solder works. Lead-free is a serious pain to work with, and as a DIY'er, I think starting with lead-free is shooting yourself in the foot. So, if Kyoshiro does in fact use lead-free, I recommend he gets 63/37, just like you recommend on the pupDAC's webpage.


----------



## kyoshiro

I'm using some 60/40 solder that I had lying around that I bought for soldering the O2, thought it would do the trick nicely as my other roll is a WBT lead-free.  But yeah first time soldering SMDs so need a bit more work here n there. I still havent had time to take the steps suggested as I have caught a cold, should get to it soon enough. Thanks for all the suggestions tho!


----------



## tomb

Quote: 





kyoshiro said:


> I'm using some 60/40 solder that I had lying around that I bought for soldering the O2, thought it would do the trick nicely as my other roll is a WBT lead-free.  But yeah first time soldering SMDs so need a bit more work here n there. I still havent had time to take the steps suggested as I have caught a cold, should get to it soon enough. Thanks for all the suggestions tho!


 
  Well, we're here when you're ready.  They were all good suggestions and Kim has pointed out a couple of trouble points you may want to check when you're feeling better.


----------



## tomb

Got over the cold yet and had any chance to do those measurements, etc.?


----------



## kyoshiro

Quote: 





tomb said:


> Got over the cold yet and had any chance to do those measurements, etc.?


 
  Will get to it this weekend. Giving a training session tomorrow and have been hard at work preparing for that and other things for my current project. (I work in the IT Sector) But yes, may even get to it tomorrow night


----------



## kyoshiro

gnd to 3v3 next to oscilator is 3.28V
  gnd to pcm's 3v3 is 3.32v
  gnd to 4v5 is 0
  gnd to -5v is only .3v
  gnd to -2v5 is 0


----------



## kyoshiro

welll, reflowed u3's pins that arent obstructed and it installs lol


----------



## tomb

Quote: 





kyoshiro said:


> welll, reflowed u3's pins that arent obstructed and it installs lol


 
  Well, that's good news!
   
  Does it completely work?  You had several voltages messed up, but some shorting pins could cause some of that.


----------



## scootsit

Are the FMT0 and FMT1 pins supposed to be connected on the PCM1794?


----------



## scootsit

Nevermind, looked at the schematic and answered my own question.


----------



## kyoshiro

Quote: 





tomb said:


> Well, that's good news!
> 
> Does it completely work?  You had several voltages messed up, but some shorting pins could cause some of that.


 
   
  nope  
  Get hissing on LEFT channel and nothing on right channel. I probably gotta sort out those voltages


----------



## kyoshiro

partially tried to reflow the other side of u3
   
  only 4v5 is reading 0 now.... grrr


----------



## DingoSmuggler

What does the +5V test point read?
  If it's too much lower than 5V, this may be an issue with the 4.75V reg.


----------



## kyoshiro

Quote: 





dingosmuggler said:


> What does the +5V test point read?
> If it's too much lower than 5V, this may be an issue with the 4.75V reg.


 
  5.03V so don't think its this regulator


----------



## scootsit

I seem to be getting no power from the USB. I have no idea why.


----------



## tomb

Quote: 





scootsit said:


> I seem to be getting no power from the USB. I have no idea why.


 
  Sorry to hear it, scootsit - do you have some pics of the PCB you can share?  Just some info - the USB connection is fairly straightforward.  If the LED doesn't light, it's pretty much the USB connector pins or some soldering issues with L1 and R1.


----------



## scootsit

Quote: 





tomb said:


> Quote:
> 
> 
> 
> ...


 

 I really gobbed the solder onto the USB jack to be sure it doesn't pull off the board. There's definitely a short somewhere between V+ and ground, it's probably in there. I'm going to fix it tomorrow. If I can't, then I'll post pictures. A few of the USB pins seem to all be connected, so I'm assuming there's a clump of solder stuck under it. Thanks for the offer, though!


----------



## randytsuch

Quote: 





kyoshiro said:


> partially tried to reflow the other side of u3
> 
> only 4v5 is reading 0 now.... grrr


 
  Check U5 (it comes from there), then check L4


----------



## scootsit

I got my first problem sorted. Now, the computer recognizes it and powers the LED. I'm getting pretty close to the right voltages everywhere except where the 4V5, I'm getting 0, and at -2V5, I'm getting -.7
   
  Thoughts?


----------



## scootsit

I reflowed virtually everything on the board. I've got the -2.5 now. Still ~0 at the 4.5 test point. Also, all of the 5V/-5V points are actually at ~4.8/~-4.8V. Is that close enough?
   
  The 4.5V point is killing me, I've reflowed everything!


----------



## tomb

Quote: 





scootsit said:


> I reflowed virtually everything on the board. I've got the -2.5 now. Still ~0 at the 4.5 test point. Also, all of the 5V/-5V points are actually at ~4.8/~-4.8V. Is that close enough?
> 
> The 4.5V point is killing me, I've reflowed everything!


 
  Yes - the 5V values depend on your PC's power supply.  However, if there's a short, the voltage could sag a bit.
   
  Check the schematic and the board layouts on the pupDAC website.  U5 only has L4 in its direct path.  The rest of the stuff are capacitors to ground: C20, C21, C23, C2, and C16 - alsot C6 and C17.
   
  I'd look carefully at U5 is soldered and L4, but it's only a guess without pics.


----------



## scootsit

Quote: 





tomb said:


> Quote:
> 
> 
> 
> ...


 

 I'm getting 4.7V there, but no sound...may be time for some pictures. I'm going to try to reflow the DAC again, then I'll post pics if that doesn't fix it.


----------



## scootsit

Thanks so much, guys!


----------



## tomb

Well, honestly -  U1 and U3 don't look too bad from the photo's perspective.  I can't tell about the right side of U3, though.  You know that you can remove C9 and C10 if you have to, to get at the pins on the right side of U3.  I've done that before.
   
  However, U5 looks suspect.  Try to refer to the "drag and wipe" method on the pupDAC website - http://www.diyforums.org/PupDAC/PupDACsolder.php
  With a clean soldering iron, see if you can clean up those pins.  That might help.  L4 looks pretty bad, too.  It's quite possible that you have a short there.  If need be, remove the ferrite entirely and re-solder it, starting fresh.  You can melt one end while holding an X-acto knife under the ferrite, pulling it up.  Once you get one end up away from its pad, then you can melt the other end and pull it off.  Clean up with some de-soldering braid, and you can start completely fresh.
   
  Good luck and let us know how it goes!


----------



## scootsit

Sorry for the mediocre pictures. I'll give it a try later tonight. iI think the issue is on the day chip, not the usb chip, because it's being recognized, and the voltages are close, it just won't play. I'll try all of your suggestions and report back.


----------



## tomb

Quote: 





kyoshiro said:


> 5.03V so don't think its this regulator


 
  Sounds like the USB voltage is OK.  Got some pics?


----------



## scootsit

In all my hacking, I cooked the end right off of C11. Oh well, it's just a bypass cap, it should work even without C11. We shall see.
   
  Thought the short was there, but nope, not there. I'm running out of ideas.


----------



## scootsit

There is about 25 ohms from the IOR+, IOR-, IOL+, IOL- to ground, is that right? It seems awfully low.
   
  Also, could it just be the copious amounts of wet flux on the board?
   
  I'm also getting 0V on one of the 3.3V pads now. SO FRUSTRATING!


----------



## kyoshiro

Quote: 





randytsuch said:


> Check U5 (it comes from there), then check L4


 
  aha! that was it. Now my only problem is left channel distortion and right channel not really sounding loud at all.


----------



## scootsit

I need to order some new caps. While I'm ordering, I want to take care of any other stuff I might need. Has anyone directly compared the OPA2835 and the OPA2836? Does the difference in bandwidth and output current really make any difference?


----------



## Stephonovich

So, I built mine tonight.  Although the LED lights, it won't install.  Using my keen troubleshooting skills and my increasingly poor soldering techniques (as it turns out, frustration is directly proportional to Gin & Tonics, which is aggravatingly inversely proportional to quality of work), I managed to fix a few cold joints, but I have one remaining problem:  U4 is outputting 1.3V vice 3.3V.  I re-flowed U4, C4/C5/C7, to no avail.  I also re-flowed C1 and X1.  
   
  Is it possible that I damaged U4 (or some other component) with too much heat?  I didn't use heatsinks.  I have a pretty damn good soldering unit (PACE MBT), and used good flux/solder (Kester liquid pen, and eutectic).  The only time I thought I maybe had heat on for too long was when a capacitor stuck itself to the iron, causing me to frantically shake it off onto the table.  
   
  Also, yes, the solder globs are horrendous, as is the board cleanliness.  I blame the macro lens for capturing entirely too much detail.
   
  Any help is appreciated, thanks!
   
https://plus.google.com/photos/111881888765532210244/albums/5880217591828488561


----------



## DingoSmuggler

Quote: 





scootsit said:


> In all my hacking, I cooked the end right off of C11. Oh well, it's just a bypass cap, it should work even without C11. We shall see.
> 
> Thought the short was there, but nope, not there. I'm running out of ideas.


 
  When using very fast opamps, correct bypassing is absolutely necessary, not optional.
   
   
   


> There is about 25 ohms from the IOR+, IOR-, IOL+, IOL- to ground, is that right? It seems awfully low.


 
  It's a passive I/V stage consisting of a 22 ohm resistor to ground. So it should read 22 ohms.
  Current output DACs want to see a 0-ohm load _ideally_.


----------



## tomb

Quote: 





stephonovich said:


> So, I built mine tonight.  Although the LED lights, it won't install.  Using my keen troubleshooting skills and my increasingly poor soldering techniques (as it turns out, frustration is directly proportional to Gin & Tonics, which is aggravatingly inversely proportional to quality of work), I managed to fix a few cold joints, but I have one remaining problem:  U4 is outputting 1.3V vice 3.3V.  I re-flowed U4, C4/C5/C7, to no avail.  I also re-flowed C1 and X1.
> 
> Is it possible that I damaged U4 (or some other component) with too much heat?  I didn't use heatsinks.  I have a pretty damn good soldering unit (PACE MBT), and used good flux/solder (Kester liquid pen, and eutectic).  The only time I thought I maybe had heat on for too long was when a capacitor stuck itself to the iron, causing me to frantically shake it off onto the table.
> 
> ...


 
  I apologize, I've been busy at my day job with a big project - just got it finished today.
   
  Just MHO, but looking at your pics, it seems the solder joints are still too cold.  It's sometimes better to have higher heat and less overall contact.  IOW, high heat may allow you to quickly heat the solder and secure the joint, then remove the iron much faster than if you were using a colder temp.  Of course, moderation is key: it's very easy to turn the temps up where the chips die a fast death.
   
  Still, I would turn the heat up some (50 degrees F.?) and see if you can reflow those joints around X1 and U4.  Can't tell from the pics, but keep in mind that the X1 crystal will be shorted out if you get an solder on the top metal cap.  Other than that and re-flowing U4 to ensure there are no bridges, you may need to check U1, the PCM2707 chip.  If you can't get a connection - once the U4 is measuring correctly - then you may need to look at the U1 and U3 chips. If those chips have issues, it can translate through the rest of the circuit to even make the regulators supply less voltage.  Things are inter-connected, IOW.
   
  Good luck and let us know what turns out from your troubleshooting!


----------



## wompy

Hi,

 I purchased a pubDAC and soldered everything. It seems to be recognized ( I attached some console output), but neither under windows nor under arch linux I get some sound out of the board. Neither headphone jack nor RCA jacks give me something. I measured the testpoints as suggested on the page. 4V5 gives a little bit too much, Also the RCA Jacks have a bit too much Voltage.

 Any suggestions where I should start? Thanks for your advice guys!

 Kind Regards,
 Jo
   

3V3 - 3.29V
 3V3 - 3.27V
 5V -  5.02V
 -5V - -5.01V
 2V5 - 2.47V
 -2V5- - -2.48V
 4V5 - 4.73V

 GND->OL 4.5mV
 GND->OR 3.2mV
   
Console Output: http://pastebin.com/aTEryZYg


----------



## tomb

Quote: 





wompy said:


> Hi,
> 
> I purchased a pubDAC and soldered everything. It seems to be recognized ( I attached some console output), but neither under windows nor under arch linux I get some sound out of the board. Neither headphone jack nor RCA jacks give me something. I measured the testpoints as suggested on the page. 4V5 gives a little bit too much, Also the RCA Jacks have a bit too much Voltage.
> 
> ...


 
  4.73 is fine for the 4V5 point.
   
  The rest obviously looks OK, too (except the output offset).  It could be in the DAC chip itself (on the output side) or the opamp on the bottom of the PCB.  So ... it sounds like we need some pics.


----------



## wompy

Hi,
   
  It was the first time I did some SMD soldering, so don't be upset with the results. I resoldered U9 on the backside, but it didn't help. I did't want to touch the chips on the front side without your advice, because I had a lot of trouble soldering them (which you can see on the right hand side of PCM1794). Therefore I used a minimum amount of solder on the left side, but I measured through the legs at the top to their corresponding contact point somewhere else on the board and they "seemed" to have contact. If you say I should solder them again I will do so, but I did not want to make a bigger mess than it already is. Hope the picture quality is good enough, I didn't get them "sharper".
   
  Thanks for you help guys!
   
   
  https://imageshack.us/a/img690/8963/img20130602121140.jpg
  https://imageshack.us/a/img208/6914/img20130602121204.jpg


----------



## tomb

Quote: 





wompy said:


> Hi,
> 
> It was the first time I did some SMD soldering, so don't be upset with the results. I resoldered U9 on the backside, but it didn't help. I did't want to touch the chips on the front side without your advice, because I had a lot of trouble soldering them (which you can see on the right hand side of PCM1794). Therefore I used a minimum amount of solder on the left side, but I measured through the legs at the top to their corresponding contact point somewhere else on the board and they "seemed" to have contact. If you say I should solder them again I will do so, but I did not want to make a bigger mess than it already is. Hope the picture quality is good enough, I didn't get them "sharper".
> 
> ...


 
  I can't find anything amiss, except around the bottom right of the DAC chip.  At least from these photos, it appears you did very well, indeed, for a first time soldering SMD!
   
  Here's the situation - if a PC recognizes the device, but no sound output occurs, and all the voltages check out, then there has to be an issue in three possible places:

 Connections between the PCM2707 and the PCM1794,
 Connections from the output (analog music) side of the PCM1794, or
 Connections from the analog (music) output of the pupDAC.
   
  Of these, I would ordinarily tend to discount #1.  The reason being, first - your solder work looks fine on the PCM2707 chip and on the left side of the PCM1794.  Second, chances are if there was some issue in the connection between the two DAC chips, the PCM2707 would show some sort of error, too, and not be fully recognized by a PC.
   
  That said, one might make the case there's a fundamental issue with the connections between the two PCM chips.  Otherwise, you might get partial sound, static, or some other indication of an incomplete connection.  If you can't hear anything anywhere, then the issue may be more fundamental and it could be the connections between the PCM chips.  There are four of those - one is quite obvious and is the trace from the 4th pin from top right on the PCM2707 to the 4th pin from top left on the PCM1794.  The other three pass through vias to the bottom of the PCB and then connect to the left side of the PCM1794.  These pins are the first 3 pins on the top left of the PCM2707 and they connect to the 5th, 6th, and 7th pins from top left of the PCM1794.  IOW, the 4th, 5th, 6th, and 7th pins from top left on the PCM1794 are all of the connections between the PCM2707 and PCM1794.  Check those pins with your DMM and see if you can measure -0- resistance between them and their corresponding connections to the PCM2707.  If not, then you may need to re-flow the PCM1794 pins and even the PCM2707 chip, even though it looks good from the photos.
   
  That leaves either #2 or #3.  I would ordinarily discount #3, because it appears the soldering you've done on the opamp looks fine.  Certainly, there's plenty of room around the pins to determine whether you've got good connections or not.  If you can verify the traces from the tops of the pins to the traces, then I don't think there's an issue.  Still, it would help to check every SMD part.  Remember that capacitors left unsoldered may affect performance, but I doubt seriously they would cause the device not to work.  Resistors and ferrites, on the other hand, have to be soldered on both sides or there is an actual break in the circuit.
   
  If nothing else checks out so far, then that leaves the right side of the PCM1794 chip.  It's hard to tell for sure, but there may be a bridge between the bottom two pins on the right side.  If that checks out OK (look for zero resistance between the two pins to confirm a bridge), then verify connection from the pins to the traces for the most important pins for the audio output - the 3rd and 4th pins from the top right, and the 3rd and 4th pins from the bottom right.  Those pins are the balanced current outputs for the Left and Right channels of the DAC.
   
  One thing to look for when you measure with the DMM - it may be that you're pressing down on the DAC pin and the force is enough to make the pin have contact with the trace beneath, but without that force, the pin is not really making contact with the pad.
   
  It will be difficult - but I would try re-flowing the pins on the right side.  Note that I said - re-flow - not add solder.  I don't think the addition of solder is going to help on the right side - it looks like the solder quantity is sufficient.  What you want to do instead is make sure you apply enough heat that the solder joints are "smoothed" compared to what they look like right now.  Extra flux will help with that, but not more solder.  In particular, you want to be certain that the tips of the pins have been heated next to the pads.  If there's any solder at all there, then that should establish the proper connections.  At the same time, ensure that your soldering iron is clean (and stays that way), and it should "suck up" any bridges between the pins.
   
  It can be tough to find the answer in a situation like this.  I have the same problem with one that I have at home - I've built about 10 right now and they all worked out of the chute, but one is a problem that I can't solve.  If you reach that point, it may be that the DAC chip needs replacement.


----------



## Avro_Arrow

That's great troubleshooting advice from Tom.
  I had a look at the board too and nothing jumped out at me either.
  I hope you can get it going yourself.
   
  If worse come to worse though and you don't want to damage the board,
  I fix things once in a while for just the postage and parts. It's really only
  open if you live in North America though...otherwise postage would be
  more than its worth.
   
  Good luck!


----------



## wompy

Indeed, tomb really wrote a premium troubleshooting guide, I am very thankful!
   
  I found a little short cut between the legs of the 2707. I am not sure if I produced it while resoldering everything. Anyways - now it works. I followed the guide step-by-step and it was worth it. The sound is magnificient. I tried to get it run with my raspberry pi, but the sound is still crackly (but that's a rasppi-specific problem due to some USB-trouble). On my laptop I enjoy listening some music
   
  Thank you Avro for your proposal regarding sending the board in. I really appreciate it, but I had already trouble bringing the board from the US to Germany, I wouldn't have send it back 
   
  So I guess the next project has to be some diy-headphones..


----------



## tomb

Quote: 





wompy said:


> Indeed, tomb really wrote a premium troubleshooting guide, I am very thankful!
> 
> I found a little short cut between the legs of the 2707. I am not sure if I produced it while resoldering everything. Anyways - *now it works*. I followed the guide step-by-step and it was worth it. The sound is magnificient. I tried to get it run with my raspberry pi, but the sound is still crackly (but that's a rasppi-specific problem due to some USB-trouble). On my laptop I enjoy listening some music
> 
> ...


 
  That's wonderful news!!  Way to go!


----------



## COOKIESnPIE

Post deleted by user.


----------



## Avro_Arrow

Yes, you can substitute parts within reason.
  There is never more than 5 volts present on
  the board, so a 6.3 volt cap is fine.
   
  You can use either the RCA or 3.5mm outputs...you
  don't need to install both.
  Please note that while the board has a 3.5mm output
  connector, it is not meant to drive headphones directly.


----------



## COOKIESnPIE

Post deleted by user.


----------



## Avro_Arrow

The part specs can be taken from the BOM.
  As parts that are available change over time,
  it's easier to update the BOM than to edit the
  schematic.
   
  I have used my Shure IEM plugged in directly when
  I was helping test the prototype.
  As long as you listened at a lower volume level,
  it sounded OK. It really does sound much better
  through an amp.


----------



## tomb

Thanks, Avro Arrow for those posts!
   
  Just to be clear - Mouser packaged the kits for Beezar, but unfortunately, they didn't use the pupDAC BOM/Schematic labels.  They used their own part #'s, instead.  However, the pupDAC BOM on the pupDAC website has been edited to reflect all of the Mouser part #'s contained in the kits.  So, there shouldn't be any discrepancy.
   
  As for different voltages and ratings if you substitute parts, you can take the pupDAC BOM as the _minimum _requirement.  Increasing voltage, capacitance on the electrolytics (watch out that they still fit!), replacing some of the electrolytics with organic polymers, etc. - it's all up to you
   
  As Avro says - the output RCA jacks are simply in parallel with the 3.5mm jack.  So, it's an either/or or even both - we've had some people do that (but watch out for drastically lowered ouput levels if you go both at the same time).  Finally, yes - you can plug in some IEM's, earbuds, etc., but ultimately -  it's only a USB-powered DAC.  There's very little amplification - only enough to serve as a line-level output, really.  (Technically speaking, the only reason the opamp is there is to combine the balanced outputs of the TI DAC chip (best one they have!) into a single Left and Right output signal.)  So, it's designed primarily for use with an amp.


----------



## KimLaroux

Quote: 





tomb said:


> ...
> Finally, as Avro says - the output RCA jacks are simply in parallel with the 3.5mm jack.  So, it's an either/or or even both - we've had some people do that (but watch out for drastically lowered ouput levels if you go both at the same time).  Finally, yes - you can plug in some IEM's, earbuds, etc., but ultimately -  it's only a USB-powered DAC.  There's very little amplification - only enough to serve as a line-level output, really.  *(Technically speaking, the only reason the opamp is there is to combine the balanced outputs of the TI DAC chip (best one they have!) into a single Left and Right output signal.)*  So, it's designed primarily for use with an amp.


 
   
  In other words, the pupDAC II will have both single-ended AND balanced outputs.


----------



## tomb

Quote: 





kimlaroux said:


> In other words, the pupDAC II will have both single-ended AND balanced outputs.


 
  You got me excited with that one - I thought perhaps cobaltmute had posted something.
	

	
	
		
		

		
		
	


	




  I know he has plans for a fully discrete output and independent power supply on his next DAC, but I'm not sure whether he plans balanced outputs.


----------



## COOKIESnPIE

Post deleted by user.


----------



## yawg3d

Can't comment on whether you _really_ need them to be micas, but they're $1.50-$2.00 each and you need two of them. Doesn't sound that expensive to me, considering that you're building a project that costs around $80 in parts alone (without an enclosure).


----------



## tomb

Quote: 





cookiesnpie said:


> Just wondering, but do you really need a MICA CAPICATOR (220pf 500V MICA 5.9mmLS), or will a normal radial capicator (with longer wires to stick up above the board) be fine? Those ones seem quite expensive... o_O


 
  Don't use longer wires - the inherent inductance in the lead length could cause problems.  Those Mica capacitors are there for a specific reason.  They are very stable and have excellent high-frequency and RF applicability.  Use something else like electrolytics and you'll throw the opamp into oscillation.  I think cobaltmute mentioned once that it might be OK to use film caps there, instead, but certainly not an electrolytic.


----------



## cobaltmute

kimlaroux said:


> In other words, the pupDAC II will have both single-ended AND balanced outputs.







tomb said:


> You got me excited with that one - I thought perhaps cobaltmute had posted something.
> 
> 
> 
> ...




I have a few ideas kicking around, but given that it's just ideas at the moment, there is no comments about anything either way......


----------



## SoundSnow

I can't seem to find this package @ Mouser.com
  Let alone a category for packages or similar.
   
  Can somebody please post the link?


----------



## yawg3d

Quote: 





soundsnow said:


> I can't seem to find this package @ Mouser.com
> Let alone a category for packages or similar.
> 
> Can somebody please post the link?


 
  Are you talking about the metal case? "Package" is the wrong word, so that's why you can't find it. They're called "enclosures", and the one listen in the pupDAC BOM is the *Hammond 546-1455C801BK, Mouser part no. 546-1455C801BK.*


----------



## tomb

Quote: 





soundsnow said:


> I can't seem to find this package @ Mouser.com
> Let alone a category for packages or similar.
> 
> Can somebody please post the link?


 
  Or, if you are looking for the complete parts package from Mouser - sorry, but they've made an agreement with me that it's proprietary to Beezar.  You are welcome to use the pupDAC BOM to make your own Mouser project/shopping cart.  It's only the price and packaging that's proprietary to Beezar.


----------



## SoundSnow

Ah, i see! 
   
  With all the mentionings of mouser, i thought the complete package was able through them.
  I can't order from the USA, i'd probably end up paying twice the price for shipping and taxes to Europe, sorry.


----------



## COOKIESnPIE

Post deleted by user.


----------



## tomb

Quote: 





cookiesnpie said:


> Does anyone know if the pupdac supports the ASIO4ALL driver or has another asio driver?


 
  Yes, there should not be any issue.  The USB interface on the pupDAC is the PCM2706/7 chip.  That's used in very many DACs as the USB interface, including the grubDAC and Twisted Pear's DAC offerings such as the OPUS.


----------



## COOKIESnPIE

Post deleted by user.


----------



## tomb

Quote: 





cookiesnpie said:


> Is there a subsitute for the Crystek oscillator (C3391-12.000) ? Digikey is sold out (http://www.digikey.com/scripts/dksearch/dksus.dll?vendor=0&keywords=c3391-12.000) and their staff said that most likely they won't restock it in quite a while.
> 
> I don't buy from Mouser since the shipping to Canada is really expensive (and I get free Digikey shipping if I do a mail order
> 
> ...


 
  This one should work:
http://www.digikey.com/product-detail/en/ASV-12.000MHZ-E-T/535-10069-1-ND/2060864
   
  It's the same one used on the GrubDAC (for DigiKey parts).  There are several oscillators that will work - it just takes making sure the size is OK and the frequency is 12.00MHz.


----------



## tomb

I've recently had some interesting experience with laptop-USB connections and the pupDAC - NOT!  Seriously, I have a standard Dell Latitude at work with a docking station.  I thought it made no difference, but it does ... big time.  Apparently, a docking station is still not enough to equate to a full-size PC power supply.  With keyboard, mouse, printer, etc., connected, there is not nearly enough juice to power the pupDAC.  Interestingly, when I first connected a powered hub without the power, the laptop gave USB critical failure notices - not enough power.  The hub (D-Link) has several LEDs to indicate power/non-power and connections to each of the 4 outlets.  It cycles through turning on all of the LEDs when first connected.  Apparently, that was enough to exceed the USB power supply on the docking station.
   
  There's a huge difference when power was connected to the USB hub.  The pupDAC sounded like it does at home (despite the hub's switcher supply).  So, just in case - I figure there may be a lot of pupDAC laptop users out there: be forewarned that the pupDAC may not perform up to snuff with the limits on USB power.


----------



## COOKIESnPIE

Post deleted by user.


----------



## Avro_Arrow

Desoldering braid


----------



## holland

Quote: 





cookiesnpie said:


> SO WHAT SHOULD I DO???


 
   
  Put some flux on it.  A hot iron, and wipe it, parallel to the pins, away from the chip.  It'll flow onto the pads.  Clean the iron and wipe again.  The excess should stick to the iron in bits and get cleaned off with each swipe.  Braid if you need to, as in there is lots of solder.
   
  I use a flat tip, not pointy, for this, to heat up 2 pins.  I use the same method to break bridges.


----------



## tomb

Yes - what they said.  Either a judicious use of the de-soldering braid, or wipe "down and away" with the soldering iron tip horizontal to the pins.  You must be sure the soldering iron tip is clean of any solder, or it will make the situation worse.
   
  I've been known to use a toothpick (with the solder melted), dental pick or even an X-acto knife to cut through a bridge.  The X-acto knife is a last resort, though, because it can easily cut through the ground plane and traces.  You could end up doing more damage than fixing it.  Try the stuff mentioned above first, before you do anything else.  It shouldn't be a big deal at the point you are at right now.


----------



## COOKIESnPIE

Post deleted by user.


----------



## tomb

Quote: 





cookiesnpie said:


> Did it with flux... no desoldering braid needed. Thx


 
  Great!


----------



## mvrk10256

So just finished building and guess what. Unrecognized. I checked all the pins,a nd I have built a few grubs now, so I am pretty sure all is right. Help me out here guys. 
  
 Starting with the top left corner (where LED is) here are the voltage vias
 Rated Voltage  -----  My voltage
 3.3V                         3.302V (next to U4)
*3.3V                         2.204V( next to r10)*
 5.0V                         5.006V (under U5)
 -5.0V                        -5.004V (next to u7)
 2.5V                         2.497V ( next to L4)
*4.5V                        4.701V (above C6)*
 -2.5V                     -2.501V( under L6)
  
 Whats wrong with it? I reflowed everything I could think of, LED is on. 
  
 It seems that U2 is pushing 2.2V instead of 3.3. I have tried reflowing it. It is getting 5V input. It seems to be the correct part. Maybe I got shipped a bad VR?


----------



## mvrk10256

Update: It was the LDO, removed it, jumped 3.3V to the location, works like a charm.Just super annoyed cause that LDO is gonna cost me like $8 including delivery.


----------



## tomb

mvrk10256 said:


> Update: It was the LDO, removed it, jumped 3.3V to the location, works like a charm.Just super annoyed cause that LDO is gonna cost me like $8 including delivery.


 
  
 Shoot me a PM and I'll send you another one.  I need to know who you are and your address.  I can look up customers one at a time to see who is from Austin, but that might take me a while.


----------



## adnc

I ordered a board and build pupDAC with the parts I had. I'm impressed how good the sound quality is. There is a slight distortion I think I hear when no audio is on the board. on headphone aswell as on chinch. Also this is not hearable everytime. Does anyone else know this problem? Voltage measurements are all fine.

I'm running it on a raspberry pi and the above problem also occurse on my notebook.

I use pupdac to output my mpd music, but I'm only able to use software driven volume. What about hardware volume controll with pupdac is this possible?


----------



## mvrk10256

@adnc - are you driving headphones directly from the DAC? This is not a good idea, you really need to feed the signal into an amp.
  
 @TomB  - you guys ever plan on doing a phono preamp?


----------



## tomb

adnc said:


> I ordered a board and build pupDAC with the parts I had. I'm impressed how good the sound quality is. There is a slight distortion I think I hear when no audio is on the board. on headphone aswell as on chinch. Also this is not hearable everytime. Does anyone else know this problem? Voltage measurements are all fine.
> 
> I'm running it on a raspberry pi and the above problem also occurse on my notebook.
> 
> I use pupdac to output my mpd music, but I'm only able to use software driven volume. What about hardware volume controll with pupdac is this possible?


 
  
 The pupDAC is not really designed to directly feed headphones.  If the headphones or earbuds are very efficient, then you may get pretty good results.
  
 The sound that you're hearing could be one of two or three things: 1) clipping while trying to power headphones, 2) the raspberry pi, or a grounding issue on the PCB.  I have seen a few threads and comments that indicate perhaps the raspberry pi is not quite up to streaming high-quality audio.  Further, the pupDAC has more than a trivial current drain relative to USB from a laptop.  (Maybe the raspberry pi has even less power capability, but I dont' know.) A few posts back in this thread, I recommended a powered-USB hub unless you are feeding it from a full size desktop that can handle multiple USB power feeds.  As for the ground, this can cause some really irritating and intermittent noise issues.  It's one of the reasons that all Beezar DACs use dual ground wires/connections on the output connections.*  Without an excellent solder joint, t's very easy to get a poor connection on only one single ground wire with the size of PCB pads that are involved.
  
 Lastly, hardware volume control is sort of self-evident: there is no stereo volume pot on the pupDAC PCB.  The pupDAC would be about twice as big if a quality stereo volume pot was included - that was not in the design criteria.  However, there's nothing to stop you from wiring a pot externally to the pupDAC outputs.  I think an amp would be better, though.
  
 * If you're connecting into the 3.5mm stereo output jack, it only has one pin connected to ground.  Try to make certain that the ground connection has a good solder joint.


----------



## tomb

mvrk10256 said:


> @adnc - are you driving headphones directly from the DAC? This is not a good idea, you really need to feed the signal into an amp.
> 
> *@TomB  - you guys ever plan on doing a phono preamp?*


 
  
 It's been discussed with both Dsavitsk and cobaltmute from time to time, but there's nothing so far.


----------



## mvrk10256

So I think we should give TomB a round of applause. Once I sent him my addy, he mailed me the part that was DOA in the original kit immediately. Got it in today, soldered it down, and boom. Everything works perfectly. 
  
 Now I just need to find time between classes and all these damn interviews to finish the enclosure.


----------



## tomb

mvrk10256 said:


> So I think we should give TomB a round of applause. Once I sent him my addy, he mailed me the part that was DOA in the original kit immediately. Got it in today, soldered it down, and boom. Everything works perfectly.
> 
> Now I just need to find time between classes and all these damn interviews to finish the enclosure.


 
  
 Many thanks!  Glad you got it working - enjoy!


----------



## mvrk10256

tomb said:


> Many thanks!  Glad you got it working - enjoy!


 
  
 Thanks, I will post some more good build/assembly/review stuff later.


----------



## COOKIESnPIE

Post deleted by user.


----------



## tomb

cookiesnpie said:


> Hi,
> 
> I just finished building my pupDAC and it can output sound through Windows, but there's a big problem. I've already set the pupDAC as the default device in Windows settings, but somehow the volume control on my taskbar does absolutely nothing to control the volume level. Pulling the slider all the way up or down makes no difference to the volume (all really loud), all while the grey bar keeps moving up and down (the green bar is not there since the volume is set to 0, but it's still extremely loud).
> 
> ...


 
  
 Try Left-clicking on the icon in the taskbar.  Select "Playback devices" from the pop-up context menu.  Select the pupDAC from the collection of playback devices in the pop-up window.  If you made the pupDAC the default device, it will have a big green check-mark beside it.  When selected, Right-click and select "Properties" from the pop-up context menu.  Select the "Levels" tab from the pop-up window.  Adjust it there and see if makes a difference.
  
 Honestly, there is a bug (sorry - different "Windows Feature") in Windows 7 that manifests itself with the PCM2704/5/6/7.  It causes a conflict with the taskbar volume control when you make the device the default.  Texas Instruments has come out with the PCM2707C to combat this, but it is not supplied with pupDAC kits by default.
  
 I've never had this problem with Foobar2000, which seems to be the standard for most folks.  It allows you to specify the source and there's never any issue.   I would search for other media players that allow you to do this, assuming you're not happy with Foobar2000.  The problem comes up when selecting a USB device as default in Windows 7 with a PCM2704/5/6/7.
  
 Remember though - if you are adjusting volume through the operating system in any configuration with an off-board DAC, the USB is re-interpolated causing bits to be lost.  It's absolutely the wrong thing to do.  Pure sources like the pupDAC are intended to be used with an amp.  That removes the issue in every single case and ensures the best quality signal from the source.


----------



## COOKIESnPIE

Post deleted by user.


----------



## tomb

cookiesnpie said:


> Nope, the Levels did nothing. I plan to use this card for audio editing and mixing, not listening to music, so foobar is out of the question.
> 
> And BTW I just connected it to a HIFI and played it though the system, which was much better than directly connecting headphones to the pupDAC. Somehow, there's very little bass if you just plug in headphones directly - why?
> 
> Guess I'll have to build an amp soon... o_O


 
  
 The pupDAC is not designed to output any significant power - no source-only DAC is.  Bass typically requires more power than any other frequency.
  
 I'm sorry, but I have no explanation for why you can't adjust volume.  At the very worst with other customers, it has required specifically selecting the source when adjusting volume in Windows 7, but there has _never_ been an instance where the volume can't be adjusted at all.


----------



## adnc

Can someone then suggest a DIY amp? Which maybe is organized and documented like pupDAC?
 Ideally one whichs volume can be controlled by an application like MPD.
  
 All those I found on diyforums are for headphones, but I would prefere an amp loudspeaker amp.


----------



## tomb

adnc said:


> Can someone then suggest a DIY amp? Which maybe is organized and documented like pupDAC?
> Ideally one whichs volume can be controlled by an application like MPD.
> 
> All those I found on diyforums are for headphones, but I would prefere an amp loudspeaker amp.


 
  
 If I understand what you mean by MPD, maybe you can find a different client interface that will select and manage sources independently of the OS.  Looks like a lot to pick from here:
http://en.wikipedia.org/wiki/Music_Player_Daemon
  
 P.S. Search for "gainclone" if you want a DIY speaker amp.  Keep in mind that you'd still probably need a pre-amp (or headphone amp) if you're going that route.


----------



## COOKIESnPIE

Post deleted by user.


----------



## tomb

cookiesnpie said:


> How about an amp that powers both headphones and speakers? (Around 20W should be enough) Obviously, it has to be DIY.


 
 a little off-topic at this point ...


----------



## Stephonovich

I believe U4 isn't functioning on my board.  All voltages check out except for both 3V3; they're at 0 VDC.  Vin receives 5V, as does ON/OFF.  GND is at 0 V.  Vout has 0 V, and BYP has about 0.9 V.  I've re-soldered the chip a couple different times, with no effect.  Can I get a new U4, or should I order it off Mouser?


----------



## tomb

stephonovich said:


> I believe U4 isn't functioning on my board.  All voltages check out except for both 3V3; they're at 0 VDC.  Vin receives 5V, as does ON/OFF.  GND is at 0 V.  Vout has 0 V, and BYP has about 0.9 V.  I've re-soldered the chip a couple different times, with no effect.  Can I get a new U4, or should I order it off Mouser?


 
 PM me with your address.  I may have a spare.


----------



## nini_knoxville

Hey,
  
 just finished mine. Soldering the SMD stuff was pretty easy. All voltages at the test points are good, but the right channel makes no sound at all. I can see no solderingbridges and all parts seem to be okay. Measured all resistors. Does anyone have an idea what to check next? The only voltage which isn't correct is the output voltage.. on the left channel, i get 0.9mV.. on the right.. nothing.. nc


----------



## tomb

nini_knoxville said:


> Hey,
> 
> just finished mine. Soldering the SMD stuff was pretty easy. All voltages at the test points are good, but the right channel makes no sound at all. I can see no solderingbridges and all parts seem to be okay. Measured all resistors. Does anyone have an idea what to check next? The only voltage which isn't correct is the output voltage.. on the left channel, i get 0.9mV.. on the right.. nothing.. nc


 
 If it connects correctly to the PC and is recognized, then output issues are either in the DAC chip or the opamp.  Can you measure the pins on the opamp?  If the left and right input - pins 2 & 3 for Left Input and pins 5 & 6 for Right Input - measure the same, then there's something wrong with the opamp.  If they measure differently, then something's wrong with the DAC chip.
  
 That's my guess, anyway - see if it indicates something and let us know.


----------



## nini_knoxville

tomb said:


> If it connects correctly to the PC and is recognized, then output issues are either in the DAC chip or the opamp.  Can you measure the pins on the opamp?  If the left and right input - pins 2 & 3 for Left Input and pins 5 & 6 for Right Input - measure the same, then there's something wrong with the opamp.  If they measure differently, then something's wrong with the DAC chip.
> 
> That's my guess, anyway - see if it indicates something and let us know.


 
 Hi tomb,
  
 thanks for the advice. After measuring the opamp, it looks like the DAC is the source of problem. I'll try to make some high def photos later so you guys may see an error which i don't.


----------



## tomb

nini_knoxville said:


> tomb said:
> 
> 
> > If it connects correctly to the PC and is recognized, then output issues are either in the DAC chip or the opamp.  Can you measure the pins on the opamp?  If the left and right input - pins 2 & 3 for Left Input and pins 5 & 6 for Right Input - measure the same, then there's something wrong with the opamp.  If they measure differently, then something's wrong with the DAC chip.
> ...


 
 OK - we'll take a look when you get the photos!


----------



## nini_knoxville

As promised the pictures:


----------



## tomb

Well, for the Right channel - the 3rd and 4th pins from the bottom-right of the DAC chip are the Right channel outputs (IORN and IORP).  I don't see anything wrong with those pins, but there does seem to be a "whisker" bridge starting from the 5th pin up from bottom right.  I don't know if that's really something and whether it would have an effect on just the right channel, but maybe.
  
 You've done an excellent job of soldering, especially on the two big chips.  It's a reflective-photographic effect, I think, but it almost looks like some of the opamp pins are dissolved. 
	

	
	
		
		

		
		
	


	




  I would not suspect the opamp at first guess, though, since it's fairly easy to solder compared to the rest of the PCB.
  
 See if you can clear that whisker on the DAC chip and them perhaps apply a bit more heat with a few strokes of the iron on those bottom 3rd and 4th pins.


----------



## nini_knoxville

tomb said:


> Well, for the Right channel - the 3rd and 4th pins from the bottom-right of the DAC chip are the Right channel outputs (IORN and IORP).  I don't see anything wrong with those pins, but there does seem to be a "whisker" bridge starting from the 5th pin up from bottom right.  I don't know if that's really something and whether it would have an effect on just the right channel, but maybe.
> 
> You've done an excellent job of soldering, especially on the two big chips.  It's a reflective-photographic effect, I think, but it almost looks like some of the opamp pins are dissolved.
> 
> ...


 
 Thanks. It was my second SMD soldering kit.. the first one i did 2 weeks ago was the gamma 1/2 which suffered from a hair of a Q-Tip...
  
 But the whisker at the DAC was doing nothing. After reapplying a little bit of solder to all of the DAC pins, the right channel stillt outputs nothing


----------



## tomb

nini_knoxville said:


> tomb said:
> 
> 
> > Well, for the Right channel - the 3rd and 4th pins from the bottom-right of the DAC chip are the Right channel outputs (IORN and IORP).  I don't see anything wrong with those pins, but there does seem to be a "whisker" bridge starting from the 5th pin up from bottom right.  I don't know if that's really something and whether it would have an effect on just the right channel, but maybe.
> ...


 
 OK - I'll keep looking at the pics.


----------



## nini_knoxville

tomb said:


> OK - I'll keep looking at the pics.


 
 Thank you very much. I really don't know how to troubleshoot it any further without ruining my board or removing those chips, which will be a pain in the a**.


----------



## tomb

Just a gut check, but can you check the R21 resistor?  In your PCB-bottom pic, it's the far right blue resistor beneath the opamp.  Check to confirm continuity on both ends and see if registers 10 ohms.


----------



## Avro_Arrow

tomb said:


> OK - I'll keep looking at the pics.


 

 I had a look too...I didn't see anything either


----------



## nini_knoxville

tomb said:


> Just a gut check, but can you check the R21 resistor?  In your PCB-bottom pic, it's the far right blue resistor beneath the opamp.  Check to confirm continuity on both ends and see if registers 10 ohms.


 
 10.1 ohms...


----------



## tomb

nini_knoxville said:


> tomb said:
> 
> 
> > Just a gut check, but can you check the R21 resistor?  In your PCB-bottom pic, it's the far right blue resistor beneath the opamp.  Check to confirm continuity on both ends and see if registers 10 ohms.
> ...


 
 Dang!  I'll keep looking.  I see no reason to even consider removing the big chips, though - the joints look great from here (assuming that whisker was nothing).  Maybe something else will pop out at us.


----------



## Avro_Arrow

What are the voltages around the op amp?
 There should be at least a little offset or
 voltage on every pin.


----------



## Avro_Arrow

I have 118mV offset on the op amp inputs.

 And something like 5mV on one output
 and 16 mV on the other.


----------



## tomb

avro_arrow said:


> I have 118mV offset on the op amp inputs.
> 
> And something like 5mV on one output
> and 16 mV on the other.


 
 Knoxville - you never told us the actual values you got from measuring the opamp inputs.  Is it close to what Avro is quoting?


----------



## nini_knoxville

tomb said:


> Knoxville - you never told us the actual values you got from measuring the opamp inputs.  Is it close to what Avro is quoting?


 
 It's running pretty late here in germany now, i will measure those tomorrow after work and let you guys know.


----------



## nini_knoxville

I hope my measurments are okay (i'm not used to measure opamps...)
 pin1 & pin2: 92mV
 pin1 & pin3: 123mV
  
 but for the output:
 pin7 & pin5: 1.1V
 pin7 & pin6: 2.1V
  
 So what does this mean? The input offset is somewhere in avro's range, but the output is like through the roof


----------



## tomb

nini_knoxville said:


> I hope my measurments are okay (i'm not used to measure opamps...)
> pin1 & pin2: 92mV
> pin1 & pin3: 123mV
> 
> ...


 
 Yep, you're right.  Let me look at the schematic and your pics some more and see if I can figure it out.  When you get a chance, you might take a close look at the through-hole resistors and see if maybe you got some mixed up.


----------



## tomb

Here are some suggestions:
  
 It's hard to tell - your photos are great - but some of the solder joints may be cold.  In particular, it appears that some of the resistor leads look like they've been poked through the solder.  I'm sure that's not the case, only that it's some indication the joint may be cold.  So, be methodical about it, but start with the through hole resistors and see if you can re-flow the solder on their joints.  For instance, R14 and R15 take the Right channel outputs from the DAC chip directly.  If there's something faulty in the connection there, that may explain the lack of audio output in the right channel.  Go through all the resistors this way, stop, then re-measure with the power off and check for good continuity throughout the circuit.  A way to do this is - with power off - touch one DMM probe to the output pin on the DAC chip, then touch the other probe to the far lead (toward the opamp) of the resistor.  If you can read zero ohms, then things are OK.  Do this for the C3 and C18 mica capacitors, too.  While you're at it - also check L5.  One of the capacitors is blocking it, but it looks a bit dodgy on the right side.
  
 Let us know what you find when you have a chance.


----------



## Avro_Arrow

nini_knoxville said:


> I hope my measurments are okay (i'm not used to measure opamps...)
> pin1 & pin2: 92mV
> pin1 & pin3: 123mV
> 
> ...


 

 My voltages are referenced to Gnd (at the RCA), not from one pin to another.
 On the + and - inputs, there was only a couple mV difference in the four pins.
 The lowest was 117mV and the high was 119mV. And of course, the +2.5 and
 -2.5 supply voltages. The output offset should be less than 10mV but a little
 higher is not uncommon in the pupDAC.


----------



## nini_knoxville

avro_arrow said:


> My voltages are referenced to Gnd (at the RCA), not from one pin to another.
> On the + and - inputs, there was only a couple mV difference in the four pins.
> The lowest was 117mV and the high was 119mV. And of course, the +2.5 and
> -2.5 supply voltages. The output offset should be less than 10mV but a little
> higher is not uncommon in the pupDAC.


 
 Okay, i did this first. Pin 1 & Pin 2 & Pin 5 are 120mV, Pin 6 307mV!!!
  


tomb said:


> Here are some suggestions:
> 
> It's hard to tell - your photos are great - but some of the solder joints may be cold.  In particular, it appears that some of the resistor leads look like they've been poked through the solder.  I'm sure that's not the case, only that it's some indication the joint may be cold.  So, be methodical about it, but start with the through hole resistors and see if you can re-flow the solder on their joints.  For instance, R14 and R15 take the Right channel outputs from the DAC chip directly.  If there's something faulty in the connection there, that may explain the lack of audio output in the right channel.  Go through all the resistors this way, stop, then re-measure with the power off and check for good continuity throughout the circuit.  A way to do this is - with power off - touch one DMM probe to the output pin on the DAC chip, then touch the other probe to the far lead (toward the opamp) of the resistor.  If you can read zero ohms, then things are OK.  Do this for the C3 and C18 mica capacitors, too.  While you're at it - also check L5.  One of the capacitors is blocking it, but it looks a bit dodgy on the right side.
> 
> Let us know what you find when you have a chance.


 
 After that, i reflowed almost every through-hole part, but they were all good. All continuity checks were successful. I re-measured all resistor values for correctness.. no error there. Still no audio on the right output. After getting a little bit upset, i wanted to swap the opamp with the other provided (thanks again tomb for the fast shipping and so on). But as i started to remove the solder, i noticed after heating a pin, the solder kind of flowed beneath the lead. So, i tought rinsing it again with flux and reflow all pins and yes, that somehow did the trick. From the visual perspective, the solder joints looked really good (as far as i can judge that). But now, everything works like a charm!!! Next step will be putting it inside my PPAv2 amp to be used at my workplace, because i'm not allowed to switch my sound card 
  
 Thank you very much avro and spacially tom for your help and dedication. I really appreciate that!


----------



## Avro_Arrow

Glad to hear you got it figured out!


----------



## tomb

YAYYY!!
  
 Me too - many thanks for your help, Avro!


----------



## OJNeg

I've only skimmed through this thread so excuse me if it has been asked before:
  
 Is there any way to use some sort of 8-pin socket for the opamp?
  
 Also, if I were to build my own chassis for this PCB, how hard would it be to get all the jacks on the same panel?


----------



## tomb

Answers below -
  
 Quote:


ojneg said:


> I've only skimmed through this thread so excuse me if it has been asked before:
> 
> Is there any way to use some sort of 8-pin socket for the opamp?
> 
> ...


----------



## OJNeg

Understood, thanks.
  
 I'm thinking I'll order the short kit + silver Hammond chassis in a few weeks and get it started over the holidays.


----------



## berserkir

Hey,
 Just finished mine but even LED won't light up. Reflowed all pins and SMD parts. Tried with two USB-cables and two laptops.
 Checked also for solder bridges under magnifying glass but couldn't spot any
  
 Voltages in board:
 5V: 1,1
 4V5: -0.01
 others 0.
  
 Guess something is pretty wrong in this...


----------



## tomb

berserkir said:


> Hey,
> Just finished mine but even LED won't light up. Reflowed all pins and SMD parts. Tried with two USB-cables and two laptops.
> Checked also for solder bridges under magnifying glass but couldn't spot any
> 
> ...


 

 Yep.  The LED is a direct connection off of the USB jack through L1 and R1, so only the soldering of the USB jack, getting the LED in backwards, or somehow messing up L1 or R1 are the only things to cause it.  I can't say for the rest until we can see the PCB, but almost anything is fixable.


----------



## berserkir

Led is OK, still not light up, did some testing and used new LED in case old was damaged somehow.
 I would suspect USB-jack to be damaged/faulty, but I don't know how to check/measure that. 
 Cleaned and resoldered R1 and L1, still nothing. I'll put some pictures but I'll get to USB-microscope tomorrow so more will follow hopefully..
 Board is bit messy, cleaned it bit more after pictures.


----------



## tomb

I can't tell a whole lot from the pics, except that maybe L1 looks suspect.  If you look on the back of the PCB, the USB jack pin carrying the 5V from the USB buss has a direct trace through L1 to the LED and R1.  There's not much to go wrong there unless L1 or R1 are shorting out or not connecting the trace.  See if you can measure zero resistance from that pin on the USB jack to the first lead of the LED.  If it's not zero, then something's wrong with the connections to L1.


----------



## berserkir

double post


----------



## berserkir

These two are zero resistance, others aren't.
  

  
 Can short in X1 cause these problems? I was inspecting this closer and it seems that some pads possibly had connection to the top of the oscillator..


----------



## tomb

berserkir said:


> These two are zero resistance, others aren't.
> 
> 
> 
> Can short in X1 cause these problems? I was inspecting this closer and it seems that some pads possibly had connection to the top of the oscillator..


 

 Wrong ones.  Look at the giant trace coming from the bottom left pin in your pic - the far left one in the row of three.  That's the power pin.  Notice the large trace coming off of it and bending all the way around to L1.  L1 connects it to the rest of the trace that then flips around to the other direction at the front edge of the PCB and to the first lead on the LED.  Measure the first lead of the LED to that bottom left pin on the USB jack and see if you get zero resistance.


----------



## berserkir

Got mine working. Had little troubles but managed to finish it.
 Sound is just amazing, first I was thinking if it can get better than GrubDAC but apparently it can.
 Will post picture once I get the case finished..
  
 Big thanks to TomB for the product and support.


----------



## tomb

berserkir said:


> Got mine working. Had little troubles but managed to finish it.
> Sound is just amazing, first I was thinking if it can get better than GrubDAC but apparently it can.
> Will post picture once I get the case finished..
> 
> Big thanks to TomB for the product and support.


 

 I'm so glad you got it going!!


----------



## willco007

Hi All,
 I've just completed by build of a Pup DAC but alas, I've got a problem. I have audio but I have a pulsating noise; like a da-tha-da-tha that sort-of comes and goes.  All my voltage test points are between .1 and .2 volts off of what they should be as well.  I've checked my ICs for bridging and I *think* they are fine, but you never can tell.   Any ideas what could be causing this?
  
 EDIT: Also, on my Mac when I adjust the volume it has no effect; it's always full blast.  I'm not sure if the volume buttons are supposed to effect the volume or not, but I thought I'd mention it.
  
 Thanks in advance.


----------



## willco007

AND....with a bunch of solder reflowing later, presto, it works. Time to try it out with my SOHA. 
	

	
	
		
		

		
			




  
 Cheers!
  
  
 Quote:


willco007 said:


> Hi All,
> I've just completed by build of a Pup DAC but alas, I've got a problem. I have audio but I have a pulsating noise; like a da-tha-da-tha that sort-of comes and goes.  All my voltage test points are between .1 and .2 volts off of what they should be as well.  I've checked my ICs for bridging and I *think* they are fine, but you never can tell.   Any ideas what could be causing this?
> 
> EDIT: Also, on my Mac when I adjust the volume it has no effect; it's always full blast.  I'm not sure if the volume buttons are supposed to effect the volume or not, but I thought I'd mention it.
> ...


----------



## adnc

willco007 said:


> I've just completed by build of a Pup DAC but alas, I've got a problem. I have audio but I have a pulsating noise; like a da-tha-da-tha that sort-of comes and goes.  All my voltage test points are between .1 and .2 volts off of what they should be as well.  I've checked my ICs for bridging and I *think* they are fine, but you never can tell.   Any ideas what could be causing this?


 

 Hi,
  
 I'm facing the same Problem since the build of my pupDAC. that da-tha-da-tha comes and goes. Sometimes I think it is an issue of pcb position on the desk, but most of the time I do not know what this causes. I've double checked my solderings and measured all possible points. It works great, but if volume is down you hear that particular alternating sound.
  
 If someone has any suggestions I also would be interested in any solution.


----------



## Avro_Arrow

Does the DAC make the same noise on different computers?

 Does the DAC work fine other than the intermittent noise?


----------



## willco007

Hi Adnc,
 I think my problem was a bridged pin on the DAC chip itself; specifically on the right side (the side without the orientation dot).  I would triple check they are all clear and check again.  I reflowed all the ICs several times before it started working correctly.
  
  
 Quote:


adnc said:


> Hi,
> 
> I'm facing the same Problem since the build of my pupDAC. that da-tha-da-tha comes and goes. Sometimes I think it is an issue of pcb position on the desk, but most of the time I do not know what this causes. I've double checked my solderings and measured all possible points. It works great, but if volume is down you hear that particular alternating sound.
> 
> If someone has any suggestions I also would be interested in any solution.


----------



## willco007

Now that I have mine up and running, could someone verify that the volume controls on a Mac have no effect; is that correct? Is it always outputting a line level volume?
  
 Thanks.


----------



## christsay

correct that is how mine behaves, same as the GrubDAC's I've built and a Headroom Micro DAC.
  
 -chris


----------



## willco007

Thanks for the confirmation.  My AlienDAC responds to the volume keys, thus the question. Thanks again. 
  
 Quote:


christsay said:


> correct that is how mine behaves, same as the GrubDAC's I've built and a Headroom Micro DAC.
> 
> -chris


----------



## adnc

avro_arrow said:


> Does the DAC make the same noise on different computers?
> 
> Does the DAC work fine other than the intermittent noise?


 
  
 Hi,
  
 yes, it does make the same noise on different computers and the DAC works really fine except those noises. If I do hear music these noises are not hearable.


----------



## Avro_Arrow

I find that mine tends to pick up some noise from the computer.

 The noise varies by computer, with my desktop being the quietest and
 my Dell laptop being the noisiest. The noise is only audible on the quietest
 passages or with no music playing.


----------



## tomb

Hmm ... I have not noticed this at all, neither have any of the ones I've measured shown this. It can be caused by a number of things, though. Regardless, you have something that can improve bad DAC environments quite a bit.* 
	

	
	
		
		

		
		
	


	



  
  
 * I have come to the conclusion that laptops are just not a good source for USB-powered DACs, period.


----------



## Avro_Arrow

> Originally Posted by *tomb* /img/forum/go_quote.gif
> Regardless, you have something that can improve bad DAC environments quite a bit.*
> 
> 
> ...


----------



## adnc

tomb said:


> Hmm ... I have not noticed this at all, neither have any of the ones I've measured shown this. It can be caused by a number of things, though. Regardless, you have something that can improve bad DAC environments quite a bit.*
> 
> 
> 
> ...


 

 Hi,
  
 I'm seeing this on the Raspberry Pi where I mainly use pupDAC and also on my Samsung notebook.


----------



## tomb

adnc said:


> tomb said:
> 
> 
> > Hmm ... I have not noticed this at all, neither have any of the ones I've measured shown this. It can be caused by a number of things, though. Regardless, you have something that can improve bad DAC environments quite a bit.*
> ...


 

 Everything I've read about the Raspberry Pi, unfortunately, is that it is problematic in supporting USB audio.  Again as I stated above, the PupDAC perhaps represents the maximum that one can go in USB-powered performance.  Because of that, a laptop/notebook USB connection is probably not going to be enough for a PupDAC in some scenarios.
  
 We converted to all laptops with docking stations where I work and frankly, I've been totally astonished at how bad the USB power is in that kind of arrangement.  Unfortunately, even a docking station still uses more or less the same power adapter as the laptop.  A powered USB hub will help, but the power on those is pretty cr*ppy, too.
  
 For some reason - I guess the enormous power available in the typical desktop power supply - a desktop PC does not seem to have these issues.
  
 P.S. It should be noted that if you follow many of the threads on the ODAC, similar issues have been noted - especially dropping on and off at the drop of a hat.  NWAVGUY put a humongous ferrite bead on the USB input to compensate.  I don't agree with that strategy, but still - more evidence of the issue.


----------



## lithoras

Hey guys,
  
 So I build my pupdac, and all the voltages are correct expect one. The 3.3 v at U4 is a 2.02. Now I am not sure wether the chip is damaged or some capacitor somewhere. I reflowed all the joints from J1 to the checkpoint so I think something is damaged. I just don't know what it is. Can someone pls give the correct voltages of the C13, L1, C4, C7, C5, C1 and the X1 output. 
  
  
  
 P.S. the chip is recognized by windows, however the right channel does not work, I get clean audio from the left channel though.
  
  
 O and it seems that my U5 is heating up like crazy, I burned my finger when I touched it, after it was on for a couple of secs.


----------



## tomb

lithoras said:


> Hey guys,
> 
> So I build my pupdac, and all the voltages are correct expect one. The 3.3 v at U4 is a 2.02. Now I am not sure wether the chip is damaged or some capacitor somewhere. I reflowed all the joints from J1 to the checkpoint so I think something is damaged. I just don't know what it is. Can someone pls give the correct voltages of the C13, L1, C4, C7, C5, C1 and the X1 output.
> 
> ...


 

 Pics.
  
 Your issue is really with U5, I suspect.  It may be drawing down the overall voltage of the USB bus.  U4 is low, but apparently there's enough there for the computer to recognize it.  U4 supplies the voltage for the PCM2707, which controls the USB connection.*  Are there any bridges on the U5 chip?
  
 Pics. 
	

	
	
		
		

		
			





 
  
 * EDIT: I don't think the PCB would recognize it, otherwise.


----------



## lithoras

The incoming voltages on U4 and U5 are both 4.99 V yet both their outputs are off, u might be right cause indeed the U5 voltage check is high, I checked if there are any bridges via backlight on the pcb and there are none. I can't take pictures sinse I am a student and don't own a proper camera XD. 
 What is also interesting is that if I apply a small torque on the pcb I get stereo sound but the voltages don't change. the torque is equall to holding the long sides of the pcb and pushing in the middle on the J1 half of the pcb. The applied pressure is minimal.... I honestly don't know what that means XD
  
 * EDIT: oke so my U4 just broke down, I know this to be very true, cause well, it doesn't let any current through any more


----------



## tomb

lithoras said:


> The incoming voltages on U4 and U5 are both 4.99 V yet both their outputs are off, u might be right cause indeed the U5 voltage check is high, I checked if there are any bridges via backlight on the pcb and there are none. I can't take pictures sinse I am a student and don't own a proper camera XD.
> What is also interesting is that if I apply a small torque on the pcb I get stereo sound but the voltages don't change. the torque is equall to holding the long sides of the pcb and pushing in the middle on the J1 half of the pcb. The applied pressure is minimal.... I honestly don't know what that means XD
> 
> * EDIT: oke so my U4 just broke down, I know this to be very true, cause well, it doesn't let any current through any more


 

 Torque and applied pressure are sure signs of inadequate solder joints, I'm sorry to say.  I can't speak to the rest of it unless you are able to supply pics.
  
 You might try re-flowing everything.  I had another builder misinterpret that, so please read carefully.
	

	
	
		
		

		
		
	


	




  Please don't think that I'm that I'm suggesting that you add more solder to everything.  No more solder - simply turn up the heat (slightly) on your iron and try to re-melt every joint until it is completely melted and is "perfectly mixed" when you remove the iron.  If you have an iron that is not temperature-adjustable, then perhaps wait a number of seconds (or a minute) between each joint before re-applying the heat from the soldering iron.  You must completely re-melt every joint and then ensure that the solder joint stays that way while you remove the iron.  That's what re-flowing solder joints means.
  
 Short of that, try to get some decent solder (63/37 eutectic) or a soldering iron that allows some heat adjustment.
  
 Lastly, try to get someone who can take some pics.


----------



## lithoras

all right so I did that.
 I used this iron, http://www.conrad.nl/ce/nl/product/588666/TOOLCRAFT-ST-50A-Toolcraft-analoog-soldeerstation-50-W-Vermogen-50-W 
     I turned it up from 280-300 degrees
 and a solder of Sn60Pb39Cu1
 I re heated all the joints and checked for bridges --> no bridges, I think it is solid.
 that was the point on which my U4 broke down, at least I think. Because well the 3.3V is went a 0 and the 4.5V is a 4.95. That was the time I edited my post  
 I'll try to fix some pictures today.


----------



## tomb

lithoras said:


> all right so I did that.
> I used this iron, http://www.conrad.nl/ce/nl/product/588666/TOOLCRAFT-ST-50A-Toolcraft-analoog-soldeerstation-50-W-Vermogen-50-W
> I turned it up from 280-300 degrees
> and a solder of Sn60Pb39Cu1
> ...


 

 OK - looks like we have a language difference as well, because I don't understand a few sections of your post.
  
 Pics will help, for sure.


----------



## Ikarios

Hi folks, quick question about the pupDAC - since this thread is relatively recent and cobaltmute's thread is from November, I'm posting here - is the volume controllable via Windows volume control, or is it locked at 100% volume no matter what Windows shows, a la GrubDAC? Thanks!


----------



## lithoras

oke so it took me a while (work and being sick and stuff), but I finally got some decent pic's to show u. 
 http://i125.photobucket.com/albums/p57/lithoras/DSC_00351_zps280cdc29.jpg
  
 due to a spot on the lens it seems as if there is a bridge on U2, this is not the case. 
 there is a bridge on the left side of U3 between pin 3&4, as wel as on U8. These bridges however match the scematics of the board (they should be connected) airgo I did not put any effort into removing them.
 I hope you can find a problem I can solve, otherwise I think I should order a new U4 since it's output voltage is 0


----------



## lithoras

So I finally managed to make a decent picture. 
  
 "http://i125.photobucket.com/albums/p57/lithoras/DSC_00351_zps280cdc29.jpg"
 (due to a particle on the lence, it seems as if U2 has a bridge. This is not the case!!)
  
 I hope you can find a problem which I can solve, otherwise I'm afraid I need to order a new U4 since it's output voltage is 0.
  
 P.S. u can see 2 bridges, one on U3 on the left side on pin 3&4 and one on U8. These however match the schematics of the board (meaning the pins should be directly connected) so I did not put any effort into removing them.


----------



## tomb

lithoras said:


> So I finally managed to make a decent picture.
> 
> "http://i125.photobucket.com/albums/p57/lithoras/DSC_00351_zps280cdc29.jpg"
> (due to a particle on the lence, it seems as if U2 has a bridge. This is not the case!!)
> ...


 

 Yes, U3 has those pins bridged, anyway.  U8 has a couple bridged, too, but U8 is out of the range of your photo.
  
 I'm a bit worried with U2 in its appearance in the photo.  The rest seems to look OK on first glance, although most of the solder joints appear to be cold.


----------



## lithoras

oke.... So what do u suggest I do, I reheated every joint (put the iron on the pin, waited like 2-3 seconds) and u say the'r still cond :/  oke could be, I'll turn up the iron even further..... And it appeared to be working except for the right channel, me reheating those joints did not help. Reheating them a second time, caused me to burn in U4 (I think) since it's output voltage is now 0....
 I really don't know what to do anymore :S
  
 (I'll try making another picture this afternoon, from which u can tell the state of U2... it actually looks similar to U5 on the eye)


----------



## christsay

ikarios said:


> Hi folks, quick question about the pupDAC - since this thread is relatively recent and cobaltmute's thread is from November, I'm posting here - is the volume controllable via Windows volume control, or is it locked at 100% volume no matter what Windows shows, a la GrubDAC? Thanks!


 
  
 It's like the GrubDAC.
  
 -chris


----------



## tomb

lithoras said:


> oke.... So what do u suggest I do, I reheated every joint (put the iron on the pin, waited like 2-3 seconds) and u say the'r still cond :/  oke could be, I'll turn up the iron even further..... And it appeared to be working except for the right channel, me reheating those joints did not help. Reheating them a second time, caused me to burn in U4 (I think) since it's output voltage is now 0....
> I really don't know what to do anymore :S
> 
> (I'll try making another picture this afternoon, from which u can tell the state of U2... it actually looks similar to U5 on the eye)


 

 Cold joints don't necessarily mean it was a cold iron.  Lack of flux, the wrong solder, or the wrong kind of tip on the soldering iron can all cause it.  In some cases, it may be that you need to use some de-soldering braid to clean between the pins.
  
 Yes, you're correct that the angle of the photo might've caused me to suspect U2.
  
 Try to clean the PCB as best you can, clean up those solder joints (not necessarily by turning the heat up), and use an X-acto knife between the PCM chip pins, if you can.  Then tell us again what you measure on all of the voltages.  However, don't do that if something gets hot - measuring the voltages aren't more important than preserving the parts.
  
 Just an FYI, but I typically adjust to 325 deg. C. or slightly higher for SMD work.  I'm using a very small tip (0.8mm chisel), though, so you have to weigh that against a larger tip size which will distribute the heat faster. 
  
 EDIT: 
	

	
	
		
		

		
		
	


	




 deg. C.!  not F! - dang it!


----------



## jboehle

How long can and or should the board be soaked in alcohol for to get the flux off?


----------



## Fred_fred2004

I don't soak boards, just lay into it with an old toothbrush and blot dry with a wad of tissues, do that twice and all the flux will be gone
  
 cheers
 FRED


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## lithoras

I would like to say that I replaced U4 with a new chip I ordered, and the board now works as it should. All the voltages are correct just as the stereo sound (I however have a bit of noise coming from my tweeter. I can hear it at about 10 cm away from it.... any ideas where it might come from? or is it inherited tot the pupdac??)


----------



## tomb

jboehle said:


> How long can and or should the board be soaked in alcohol for to get the flux off?


 
  
  


fred_fred2004 said:


> I don't soak boards, just lay into it with an old toothbrush and blot dry with a wad of tissues, do that twice and all the flux will be gone
> 
> cheers
> FRED


 

 Neither of these is really a contradiction and I agree with both.  Soaking a board is fine - as long as everything is truly a solid-state component.  Once you add electrolytic capacitors or other "physical" components, though, you have to use the toothbrush and blot dry with paper towels/equivalent.*  Electrolytics are an easy justification - they have a liquid electrolyte inside and are not necessarily completely water-proof.  At the same time, physical components such as switches and pots - volume and otherwise - may have grease in them to promote easy physical interaction.  This can be destroyed if you soak a PCB with those components on it.
  
 I am careful in my build instructions that a total immersion of a PCB is only possible at a certain stage in the construction - not any further.
	

	
	
		
		

		
			





 
  
  
  
 * One caveat - I've had many larger boards that may take as many as half-a-dozen rinses or more with a toothbrush and paper towel blot before the flux is significantly removed.  That may just be me and the type of soldering I do, though.


----------



## jboehle

Sorry, I should have been more specific with my question.  Your guide is excellent!  I am done soldering on all the SMD components, so I am at that point in your guide when you say to soak the board.  I went at it with a new toothbrush a couple of times and a few minute soak but still have some flux left on the board.  It's pretty clean but it didn't all come off.  I'm just going to let it dry out and continue on.
  
 By the way at the bottom of this page of the picture guide, above the last pic on the page, it says "Finally, there are three 1206 ferrites on the top side.", but there are four ferrites on the top, not three.  Also, the pic is a little misleading, since you just mentioned ferrites, I would think the arrows should be pointing to the ferrites, not some caps.  One more thing, the last text on that page says "You've now finished all the SMD parts on the top side of the PCB!", but the pic does not show all the SMD parts on the top soldered.  Again not a big deal just a bit misleading.  I'm not complaining, just offering some feedback on how to make it better!  Your guides are great and much better than most other DIY projects I've come across.


----------



## tomb

jboehle said:


> Sorry, I should have been more specific with my question.  Your guide is excellent!  I am done soldering on all the SMD components, so I am at that point in your guide when you say to soak the board.  I went at it with a new toothbrush a couple of times and a few minute soak but still have some flux left on the board.  It's pretty clean but it didn't all come off.  I'm just going to let it dry out and continue on.
> 
> By the way at the bottom of this page of the picture guide, above the last pic on the page, it says "Finally, there are three 1206 ferrites on the top side.", but there are four ferrites on the top, not three.  Also, the pic is a little misleading, since you just mentioned ferrites, I would think the arrows should be pointing to the ferrites, not some caps.  One more thing, the last text on that page says "You've now finished all the SMD parts on the top side of the PCB!", but the pic does not show all the SMD parts on the top soldered.  Again not a big deal just a bit misleading.  I'm not complaining, just offering some feedback on how to make it better!  Your guides are great and much better than most other DIY projects I've come across.


 

 1. You're fine on what you did with the soak.
  
 2. Yes, you're sharp in noticing that.  I noticed it myself awhile back, then forgot to correct it.  If memory serves, you might look back through this very thread and see that it's correct, but that I copied it incorrectly on the website.  The Step-By-Step guide on the website is probably more technically correct than the "Build-by-Photo."  I'll see if I can correct it this weekend.


----------



## elmoe

Cool thread, thank you tomb for taking the time and energy to make a step by step, it really gives the urge to newbies like myself to give this build a shot.


----------



## jboehle

Finished the board tonight.  The step-by-step guide w/ pics is amazing and makes this project easy.  Make sure you follow tomb's advice.
  
 Decent tweezers are a must for all of the SMD work, I used the curved tip ones from this set and they worked great.
  
 When soldering some of the chips with the drag-n-wipe method, you might swipe some solder into an adjacent through-hole (I did this when soldering the op-amp on the bottom side).  No big deal, just use some solder-wick to clean it up.
  
 Checking all of your solder joints (particularly the SMD work) with a high power magnifying glass is a MUST.  I used the 10x spot lens on this magnifying glass extensively to check my work (although something with 10x magnification that had a bigger lens would've been nice).  Checking the chip solder joints in the bright sun is a great way to identify any problems.  I soldered the top two chips one night and waited until the day after to check them in the sun.  I'm glad I did because I saw a couple more bridges that I didn't see the night before.
  
 Once past all the SMD work, the through-hole stuff goes quick.  I still need to do the final flux cleaning, but I went ahead and plugged it into my Mac and all the voltages checked out okay.  The DC offsets at the output jacks were 0mV and 1.1mV, so I'm good there.  I checked all the other voltages at the test points and every one was within 0.02V except for the 4.5V one, mine tested at 4.72V.  Is that okay?  The pupDAC was identified fine by my Mac.
  
 Would the DC offset at the output jacks be any different when playing music and/or when having the computer volume turned up all the way?  Meaning should I test under those conditions as well?  How about when using it with different computers?


----------



## tomb

jboehle said:


> Finished the board tonight.  The step-by-step guide w/ pics is amazing and makes this project easy.  Make sure you follow tomb's advice.
> 
> Decent tweezers are a must for all of the SMD work, I used the curved tip ones from this set and they worked great.
> 
> ...


 
  
 Thanks for the kind comments!

 4.72 is fine.  The regulator in that part of the circuit actually regulates to 4.75.  A few hundredths off can be attributed to the meter and other variances.  I think cobaltmute simply did want to take up the room on the PCB by using 3 digits with the silkscreen.
	

	
	
		
		

		
		
	


	




 
  
 As for your last question, no, the offset will not change under differing conditions.  One note, though - you should always have the volume turned up all the way on whatever media player you're using.  Otherwise, it will start interpolating bits to lower that volume and you'll actually lose some data integrity and quality.  That doesn't apply to the computer volume, unless the PupDAC becomes the default media device and you're using the OS volume control to reduce volume.  The only way you should be reducing volume through the PupDAC is with an amplifier.  An exception to that might be if you're using IEMs plugged directly into the PupDAC, but then that's a somewhat compromised scenario, anyway.  Still, I've gotten great results doing that, but it would probably still work better if you went through some sort of amplifier.
  
 I always recommend Foobar2000, because it lets you choose the music source separately from the computer's OS.  I'm not sure about a Mac, though, so YMMV.


----------



## yhbyhb4433

I just assembled my kit. The mac did recognize it as DAC, but when I connected it to a earbud, the music was played through earbud in maximum volume(at least it's loud) and I can't change the volume through mac. I checked the voltage as follows:
 3V3: 3.297V
 5V: 5V
 4V5: 4.76V
 -5V: 0.429V
 -2V5: 0.59V
 offset:0.588V
  
 Could anyone please give some insight on where to debug?


----------



## tomb

yhbyhb4433 said:


> I just assembled my kit. The mac did recognize it as DAC, but when I connected it to a earbud, the music was played through earbud in maximum volume(at least it's loud) and I can't change the volume through mac. I checked the voltage as follows:
> 3V3: 3.297V
> 5V: 5V
> 4V5: 4.76V
> ...


 
 Well, I would've said the MAC's OS, but you have an issue at the 2.5V test point.  If you're only measuring 0.59V, then something is wrong.  Check all the pins around U10.  Make sure they're clear of bridges and have good connections to the pads.


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## Avro_Arrow

yhbyhb4433 said:


> Could anyone please give some insight on where to debug?


 

 I'd check U7 for shorts and opens.
 Also C32, C33 and C34.
 Your whole negative rail is not functioning.
 Re-flow if necessary
  
 If all else fails, replace U7


----------



## tomb

avro_arrow said:


> yhbyhb4433 said:
> 
> 
> > Could anyone please give some insight on where to debug?
> ...


 

 Correct, as usual.  For some reason, I was reading his .429V as close to -5V.


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## yhbyhb4433

avro_arrow said:


> I'd check U7 for shorts and opens.
> Also C32, C33 and C34.
> Your whole negative rail is not functioning.
> Re-flow if necessary
> ...


 
 Thanks Avro! It turned out the output from U7 is not making contact with the board. I put a little bit solder on that leg and now every point gets the right value. Anyway, thank you!


----------



## KimLaroux

From what I'm seeing in this tutorial, the enclosure does not seem to be grounded to the USB shield. Any reason for this? Would there not be improvements from earthing the case?


----------



## tomb

kimlaroux said:


> From what I'm seeing in this tutorial, the enclosure does not seem to be grounded to the USB shield. Any reason for this? Would there not be improvements from earthing the case?


 

 The shield from the USB cable and the connector metal are grounded through the USB buss.  JMHO, but there's a heckuva lot more metal in a PC chassis than the little aluminum PupDAC case.  In comparison, the case is kind of trivial.


----------



## mcandmar

Another little Pup is born!
  
 Finished putting this together this afternoon and spent the evening, night, and wee hours listening to all sorts of music though it. I have to say i am deeply impressed, it handled everything i threw at it with aplomb.  I am running it through a USB Isolator/Linear regular i built for my ODAC, though the Doodlebug is my next project.
  
 Vs the ODAC i found a few differences, the high end is sweeter and more refined, and the mid to low end has a lovely energy to it. Where the ODAC can sometimes sound flat and lifeless this little Pup has a bigger pair of lungs and handles dynamic shifts much better.  I dont know how they compare on stats like THD, distortion, crosstalk etc and to be honest i don't really care, all i know is it sounds better to me.  Only downside i can see is the limitation of the USB interface, 24bit would be nice to have, not that i have much 24bit material anyway.
  
 I had intended to use this DAC with a portable valve amp as my music rig for work but i cant see myself unplugging it from my S.E.X. amp any time soon.  This really is an awesome little DAC, nice work Tomb!


----------



## TheLaw

Hey guys,
  
 I built a GrubDAC a while back and it sounds great. However, my one gripe with it was that Windows 7 didn't like it all too much. If I wanted to change the volume, I had to go into the advanced mixer and change the volume on each program separately. I could not simply pull the master volume up or down, which also made using an Fn+key volume shortcut useless. 
  
 Does the PupDAC suffer from the same problem? I'm planning on using it with Windows 8 in the even that I build one. I guess I should also ask, does the GrubDAC still have this problem on Windows 8?
  
 Thanks.


----------



## mcandmar

I'm going to go out on a limb here and say that shouldn't happen, the issue is more likely to be with the laptop itself and not the DAC.  I can confirm the PupDAC works perfectly with Windows 8.1, however its not best practice to be lowering the volume on a DAC, your better off doing that on the amplifier.


----------



## tomb

mcandmar said:


> I'm going to go out on a limb here and say that shouldn't happen, the issue is more likely to be with the laptop itself and not the DAC.  I can confirm the PupDAC works perfectly with Windows 8.1, however its not best practice to be lowering the volume on a DAC, your better off doing that on the amplifier.


 
 Agreed.  The OS starts interpolating bits to lower the volume and you'll lose ultimate quality doing that.  Granted, there are some circumstances where you may want to do that - I've done it myself when I wanted to try plugging IEMs directly into the DAC, etc.  However, those instances should not be the norm.  The pupDAC is designed to be used with an amplifier.
  
 All that said, there is an issue with Windows 7 and beyond and the way they enabled volume control through a USB device.  Texas Instruments actually came out with the PCM2706/7 "C" version to address the different methods used in Windows 7 and beyond.  I haven't tested this myself yet, though, so I don't know if simply replacing the chip in the pupDAC with a "C" version would fix the volume control limitation that you describe.


----------



## COOKIESnPIE

Post deleted by user.


----------



## tomb

cookiesnpie said:


> Hi,
> 
> Have any of you noticed a staticky noise with some ticking when you turn up the volume a LOT on your amp when hooked up to the PupDAC? I never noticed this at first, but even with a ferrite on the USB cable I can hear noise if nothing's playing and the volume's maxed out. I never play it that loud so I didn't notice it at first - but is it a limitation of the PupDAC?
> 
> BTW I'm using an O2 amp right now, which makes no noise if connected to another source (i.e. the pupdac is the culprit)...


 

 The noise on the PupDAC is generally down in the -120 to -130dB range when properly connected on a quality USB power supply.  You can see that using a DoodleBug makes a difference, but even without, there's nothing that could be amplified enough to cause audible noise:

  
 Now, that's not saying it isn't your PupDAC - just that something is wrong if it is. 
	

	
	
		
		

		
			





  I'd check your output connections, first - all the way back to the PCB.  A poor ground connection on the analog side can cause a multitude of issues with noise.  You might also check the proximity of any other devices that could be introducing noise.  With the wide variances in DAC design, grounding methods, and enclosure techniques, it's quite possible the PupDAC could be picking up noise from external devices when another source does not - or vice-versa.  Or, your cables could be picking it up, too.  If the PupDAC's output is higher than other sources or if there is any other difference in the way it is connected, this may make the extraneous noise more noticeable on the Pup compared to another source, even though it may be present all the time.
  
 Good luck and let us know what you find in your trouble-shooting!


----------



## Avro_Arrow

cookiesnpie said:


> Hi,
> 
> Have any of you noticed a staticky noise with some ticking


 
  
 Does the noise change/disappear if you use a different computer?


----------



## jboehle

I get the ticking as well. I will have to try a different computer. It's only in my left channel. I switched the cables from L->R and the ticking moved to the right channel. This was hooked up to a 2011 MacBook Pro that was not connected to a charger at the time. With Monoprice 8323 phones i could hear it as low as 50% volume. With DT880 600ohm I couldn't hear it even at full volume.


----------



## COOKIESnPIE

Post deleted by user.


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## COOKIESnPIE

Post deleted by user.


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## Avro_Arrow

I used to get noise from my laptop with the pupDAC. I didn't get the noise with the desktop.

 It was mostly on just one channel. That was the reason I designed the Doodlebug.
 The noise I got was different depending on which laptop I used. My HP was the quietest,
 the Dells were the worst. The noise was never very loud, mostly just between songs or
 very quiet passages.
  
 pupDACs do sometimes have more offset on one channel. I think mine has about the same
 offsets as yours. I have a prototype version.
  
 Other parts of my system are Shure SE535 and a PPA v1. with glassman buffers.


----------



## COOKIESnPIE

Post deleted by user.


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## COOKIESnPIE

Post deleted by user.


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## jboehle

I haven't been able to test mine with a different computer yet.  My one working amp (M3) is disassembled while the case is at the powder coater.  I have a Bottlehead Crack kit to build, but it's top plate is also at the powder coater.  And the KSA5 clone I'm building, I f'd up and shorted out the opamp on one of the channels and it seems to have damaged some/all of the output section.
  
 I will try to hook my pupDAC up tonight and at least measure voltages.
  


> 4V5: *4.74V* (I don't remember what the numbers were when I tested it right after it was built, but this seems a bit off...


 
  
 I think that is okay, check my posts from earlier in this thread, I think my measurement there was the same and tomb/Avro said that one was fine.


----------



## jboehle

COOKIESnPIE here is the post from tomb that says the ~4.75V is okay: http://www.head-fi.org/t/636683/pupdac-step-by-step-build-thread/195#post_10345285


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## COOKIESnPIE

Post deleted by user.


----------



## jboehle

Hah, I hadn't thought about that correlation 
  
 Yeah, I was just pointing out that the 4.75V was okay.  The DC offset of 8.1mV definitely is a little high.  Particularly going into an amp like the M3 which has no output offset protection.


----------



## tomb

cookiesnpie said:


> A "Bottlehead Crack" and a profile pic of Rob Ford? Beautiful.
> 
> Jokes aside, the 4.75V may not be problem but my DC offset is way off.


 

 I agree that offset is way too high.  I'm at a loss to really pick out anything in your pics, though - except the resistors.  Cobaltmute spec'd the resistors around the opamp at 1% tolerance.  Those aren't V-D RN50's that you've used, so I'm not sure if they're in the recommended tolerance.  Just an FYI, but even Tangent used to (still does?) have articles online about matching resistors around an opamp for ensuring the minimum in offset with his amps designs.  Matching resistors used to be de riguer when the CMoy, PIMETA, and PPA were first in vogue (not that they still aren't).  Cobaltmute even designed the very critical resistors to be installed on the PCB bottom - right next to the opamp - in an effort to reduce lead lengths and potential oscillation issues.  The pupDAC will definitely result in opamp oscillation (especially with the OPA2836) if everything is not just so-so with the resistors and lead lengths.
  
 I'm not saying for sure that's what's going on - *it's still only a guess*.  Perhaps the resistors could be causing the issue and maybe the opamp is oscillating.  Strange things can go on when that happens, including ticking sounds when the oscillating opamp causes regular/intermittent capacitor discharges.


----------



## COOKIESnPIE

Post deleted by user.


----------



## lordearl

Is anyone using the pupDAC with JRIVER and Windows 8?
 What is the optimal setting?  I'm finding WASAPI EVENT STYLE to be a little unreliable, so currently use the DIRECT SOUND with 0.10s buffer and everything upsampled to 96khz - any others using similar settings?


----------



## tomb

cookiesnpie said:


> They're 1% KOA metal films, not "military grade" though. I might be able to get some more accurate resistors near the opamp for a spin, but besides from that I don't know where to look either. I spoke to someone in the industry before building this and they said that rarely you need mil grade resistors unless you need high reliability - just the right tolerances are fine. He could be wrong though...
> 
> 
> 
> ...


 

 Well, "someone in the industry" may not know about mismatched resistors on a sensitive opamp.  It's not necessarily the precision of the resistors, although that buys you some consistency from resistor to resistor with the same rating.  It's the differences between two resistors of the same rating that can cause offset when applied to the two different Left and Right channels.  For instance, a 100R resistor at 1% precision may be 99 or 101 ohms, a 1K resistor might be 990 vs. 1010 at 1% and so forth ...  Differences of that magnitude can definitely cause offset.
  
 You might try measuring the resistors and see if you get a difference in the same rating resistor from one channel to the other channel.
  
 Actually, this can apply to solder joints, too.  A few sub-standard joints that may predominate in one channel over the other can combine to increase the resistance in that channel.  That might result in the offset, too.  It kind of explains why two people can build the same thing with the same parts and yet get two different performance results.  It's also why re-flowing solder joints over an entire PCB can sometimes result in fixing a problem. 
	

	
	
		
		

		
		
	


	



  
_Again, these are guesses ..._


----------



## jboehle

Hooked it up to my 17" MacBook Pro tonight and got some new measurements.
  
 5V = 4.989V
 -5V = -4.9702V
 -2V5 = -2.4890V
 2V5 = 2.4897V
 4V5 = 4.7235V
 3V3 = 3.308V
 R = 1.04mV offset
 L = 0.1mV offset
  
 All looking great!
  
 Hooked it up to my work 15" MacBook Pro which had a charger hooked up.  Fed it through my KSA5 clone amp.  With Monoprice 8323 'phones I can hear ticking in both channels from 50%+ volume.  With AT ESW9 'phones it starts about 65%+ volume.
  
 Looking forward to trying the Doodlebug!


----------



## lordearl

lordearl said:


> Is anyone using the pupDAC with JRIVER and Windows 8?
> What is the optimal setting?  I'm finding WASAPI EVENT STYLE to be a little unreliable, so currently use the DIRECT SOUND with 0.10s buffer and everything upsampled to 96khz - any others using similar settings?


 
  
 Actually I don't know that the upsampling is working correctly, as (according to the datasheet) the PCM2707 only takes up to 48kHz....anyone else tried this?


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## COOKIESnPIE

Post deleted by user.


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## tomb

cookiesnpie said:


> I removed and checked the resistors near the opamp... while the 1.5k ones were exact, the 10 ohm ones were at 10.8 - I'll probably replace them later. Anyways, I also resoldered everything else on the board (including the chips) and the ticking seems to have disappeared. However, the high DC offset and the noise at high volumes still remained....
> 
> Strange.


 

 Well, take satisfaction that something improved. 
	

	
	
		
		

		
		
	


	




 
  
 As for the resistors - maybe I wasn't clear before or perhaps I'm not understanding now: absolute values matter little.  What matters is whether you have 10.8 on one channel of the opamp and 9.2 on the other channel.  If they're both 10.8 even though they're supposed to be 10, it's OK - it's still a match.


----------



## tomb

BTW, I don't think I ever answered the question about lead length ...
  
 Leads are extraneous parts to a circuit.  However, being metal and being conductive, they have an inductance per unit length.  On very small circuits that operate at high frequencies, that little bit of inductance may be enough to upset the stability in the circuit.  That's why the critical resistors for the opamp on the pupDAC are designed to be installed on the bottom of the PCB - closest to the opamp.  It's to reduce any instability caused by the lead length.


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## COOKIESnPIE

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## tomb

cookiesnpie said:


> tomb said:
> 
> 
> > If they're both 10.8 even though they're supposed to be 10, it's OK - it's still a match.
> ...


 

 Well, after all of this - I have to come down on the side of Avro: it's probably the power supply in one way or another.  Your offset is still high, but that could be power related as well.*  I can't think of anything else it might be and your board pics look fine.  Some of the regulators may be a bit dodgy from their appearance, but if you're measuring all the proper voltages (you are), it should be OK.
  
 A couple of the chips that appear like regulators are actually not.  For instance, U6 controls the reset on the DAC chip.  I'm guessing and out of my element here, but without this, the DAC may fall completely offline if the voltage drops and then you would have to disconnect and re-connect to allow the PC to bring it back online.  Or, it  could be that very bad dropouts occur during the middle of the music stream - I'm not quite sure.  Regardless of which, this is a terrible nuisance, so U6 controls the reset to the DAC chip if the voltage drops below acceptable limits.  It could very well be that your voltage from the PC is marginal and the chip is continuously re-setting the DAC output.  That might cause the ticking.  Again, just a Wild Ass Guess (WAG).
  
 There's also U7.  This is the charge pump controller.  It essentially creates a zero-voltage reference, allowing a + and - analog output, which obviates the need for output coupling capacitors.  Again, if this chip is malfunctioning, it may seriously affect the signal.  It's quite possible that it could cause offset in one channel, too - especially since it's the thing that setting the zero voltage point of the output.  There again, a WAG.
  
 Maybe some others more knowledgeable than me can chime in and correct my guesses or elaborate. 
	

	
	
		
		

		
		
	


	




 
  
  
 * Plenty of power doesn't necessarily mean it's at the right voltage.


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## COOKIESnPIE

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## COOKIESnPIE

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## KimLaroux

Measuring an unloaded power rail is not a reliable way of learning what voltage a load is fed. The only way to know for sure is to connect the load, make sure its powered, and then measuring the voltage at the load.


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## mcandmar

USB can be anything from 4.5v to 5.2v with a nominal of ~5v.  In reality it fluctuates depending on supply load, for example plug in a USB memory key and copy some data to it while monitoring the voltage and it will jump all over the place.
  
 One thing i have found the PupDAC susceptible to is dropouts due to spikes in the output ground. I can fairly consistently make it drop off by power up my valve amp connected to it, or even turning on my cheap Chinese eBay soldering station can cause it to drop off, though interestingly the USB connection to my UPS drops off too when i use it.
  
 It doesn't seem to make any difference if i power it from the computers USB output, Doodlbug or a completely overkill power supply / Isolator box i previously built so it has to be small voltage spikes coming back into the RCA output grounds that is causing it, or a voltage differential between the input and output grounds.
  
 Whatever amp you are connecting to the PupDAC, make sure its powered from the same power point as the computer, other than that i haven't really got any solutions to avoid it.


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## tomb

mcandmar said:


> USB can be anything from 4.5v to 5.2v with a nominal of ~5v.  In reality it fluctuates depending on supply load, for example plug in a USB memory key and copy some data to it while monitoring the voltage and it will jump all over the place.
> 
> One thing i have found the PupDAC susceptible to is dropouts due to spikes in the output ground. I can fairly consistently make it drop off by power up my valve amp connected to it, or even turning on my cheap Chinese eBay soldering station can cause it to drop off, though interestingly the USB connection to my UPS drops off too when i use it.
> 
> ...


 

 I've experienced some of this, but seems like with the DoodleBug it comes back online without a manual disconnect-reconnect.  It sort of reminds me of why we went from BUF634's with headphone amps in the early days and went to discrete parts, instead.  The OPA2836 may provide ample protection against frying the DAC - a serious problem with the Starving Student and Alien/BantamDACs and Gamma 1's.  It's one reason I'm a whole lot more careful with any source when connecting/disconnecting to a powered-up amp (I simply do NOT do it anymore.).  Yet, what we're describing might be attributed to less output protection circuitry in the opamp.
  
 Of course, whenever comparisons were made - the less protection circuitry, the better something sounded.  So, I would rather accept the hassle of it knocking offline sometimes with the understanding that it will sound better  The BUF634 has a lot of protection circuitry on the output, but it always sounded kind of "tame."
	

	
	
		
		

		
			





  I don't get that impression with the OPA2836 (maybe a little with the OPA2835).  I'm not saying for sure that's what is happening with the Pup, but the DoodleBug seems to put it all in the context of either a trivial hassle at worst, or at best - it improves everything, especially sound quality.


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## mcandmar

That is interesting, i have found when its offline it emits static out of one channel so that would imply it is the output opamp that shuts down. If you unplug the DAC and wait for the capacitors to discharge it goes away, reconnect it again and away you go.  I've actually gotten used to powering up the amp before the DAC's power supply so its not an issue for me.
  
 I certainly wouldn't want to add anything that would alter the sound as i love this thing just the way it is, only bit of audio hardware i own that i haven't felt compeled to modify.


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## COOKIESnPIE

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## mcandmar

The noise i was referring to is only when the DAC gets knocked offline.  Are you saying you get a noise when the amp is connected and running?


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## COOKIESnPIE

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## tomb

Even my "official specs" are pretty poor compared to a PupDAC connected to a DoodleBug.  Still, your graphs are much worse than any I've seen on a PupDAC.  Unfortunately, it only confirms what we already know - something is wrong with your PupDAC.
  
 You did not build from a Beezar kit.  We haven't found anything amiss, necessarily, on your build's pics.  So, maybe there's an issue with the parts themselves.  We talked about the resistors and apparently you confirmed that they are of good quality.  However, what about the rest of the parts?  What kind of oscillator did you purchase?  Is there anything different about the onboard regulators you chose?  Could the ferrites be rated too low in amperage and introducing resistance into the circuit where they shouldn't?  Is there a particular reason you chose to use the OPA2835 instead of the OPA2836?  The difference in the two chips is extreme, to say the least.  That said, the OPA2836 would probably be less stable in this situation, being a much faster chip in MHz, slew rate, and current impulse.
  
 Anyway - look at those parts.  The charge pump might be a source of trouble, too.


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## mcandmar

cookiesnpie said:


> Oops - I thought you got the noise even if the DAC wasn't knocked offline. I've made several posts about the noise (it's from the DAC and occurs regardless of amp or computer), and the fact that I have high DC offset. Start here at this post and work your way down.


 
  
 Sorry missed that.  I agree with Tomb its most likely something to do with the output opamp, since the DAC doesn't use any DC blocking caps in the signal path it either the chip or the half a dozen resistors in the signal path.  Personally i don't like those resistors, i certainly wouldn't use them in a signal path so for the sake of a few $'s bin them and fit some decent low noise vishay's as per the BOM sheet.  I would also try measuring for DC around resistors 5,7,16, and 18 to verify the DC is being generated from the opamp or further upstream in the main PCM1794.


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## COOKIESnPIE

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## tomb

cookiesnpie said:


> I'll look at replacing U6 and U7 when I'm shipping in parts for my next project, and maybe pickup some mil grade Vishays as well. My oscillator is not the one stated in the BOM, as that (like the OPA2836) was sold out at Digikey at the time. I used the subsitute recommended by tomb (ASV-12.000) instead. The ferrites and regulators are the official ones on the BOM.
> 
> How would you measure the DC around the resistors?


 

 Stick one probe of your DMM in Ground, then use the other probe to touch the resistor leads of each resistor and note the measurement.  It would probably help if you measured the "output" lead in each case, since that would represent the voltage _after_ the resistor.
  
 FYI, if the DC measurements are way off prior to the opamp, something else is wrong.  If the DC is equal, same resistor on left vs. right channel, then the opamp is the culprit.  At least in terms of offset ...


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## COOKIESnPIE

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## mcandmar

That didn't look bad so i measured mine out of interest and the figures are very close, though mine is silent.
  
 R5 130mv/122mv
 R7 130mv/122mv
 R16 129mv/121mv
 R18 129mv/121mv
  
 Right -1mv
 Left -5mv
  
 P.S. I started expiermenting with RMAA, how did you guys get the noise floor so low?  I tried two mic inputs my machine has, onboard Realtek, and a Sound Blaster X-Fi and both are ~100db when i have the mic level set for ~ -1db level?


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## COOKIESnPIE

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## mcandmar

/face palm moment. Good point sir, don't know what i was thinking there...doh!
  
 I'm wondering if repeating the same tests but measuring for AC would tell us anything, i.e. is the noise measurable, and is it measurable before the opamp. I think the DC offset is a red herring and not related to the noise issue you are having as its not much higher than my readings.


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## COOKIESnPIE

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## mcandmar

Now were getting somewhere...
  

  

  
@COOKIESnPIE I'm all out of ideas


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## tomb

mcandmar said:


> <snip>
> 
> @COOKIESnPIE I'm all out of ideas


 
 Me, too.  I greatly appreciate your effort in trying, though!
  
 COOKIESnPIE,
 It may be as mcandmar says - one of the chips somewhere may be bad, perhaps too much heat in soldering, etc.  I confess that out of over a dozen PupDAC's I've built, there's one that baffles me - but it was one of four that I was building at the same time and I realized about midway through that I had the iron turned up way too high.  Plus, it was the first one in the lot and I spent a lot of time re-positioning the PCM chips - it turned out to be practice for the other three, but I think all that time exposed the primary chips to too much heat.  I later on replaced the PCM2707 chip, but it still doesn't work, which makes me think it has to be the DAC chip, now.  All voltages are correct and there's no offset to speak of on the output.  The PC just won't recognize it, however, and continues to give a USB connection error (why I thought it was the PCM2707 chip).
  
 Anyway, I hope you can figure it out on yours.  I'm at a loss to give you any constructive guesses at this point - that's all they'd be: guesses.


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## mcandmar

LOL, oh what fun i could have trolling the ODAC thread with that one


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## tomb

mcandmar said:


> LOL, oh what fun i could have trolling the ODAC thread with that one


 







  
 I may frame it.


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## COOKIESnPIE

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## Avro_Arrow

If we do the math, assuming R3, R4,R14 and R15 (Riv) are 22 ohms and the center current of the PCM1794a is -6.2mA...

  
 Actually, the resistance seen by the output of the DAC is 21.7 ohms, we will use that figure.

  
 The voltage at Riv should be 134.54mV. There is a 2% tolerance giving us a range of 137.2308mV to 131.8492mV.

  
 R7 and R8 form a voltage divider yielding 126.131 at the non-inverting input of the op amp.
  
 This does not take into account resistor tolerances or op amp bias current/voltages.


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## bada bing

mcandmar said:


> LOL, oh what fun i could have trolling the ODAC thread with that one


 
  
 Now that is interesting 
	

	
	
		
		

		
		
	


	



 I've seen your results in the doodlebug thread for the PuPdac without the doodlebug.
 Did you happen to run the ODAC without the doodlebug? I had made an assumption
 that the ODAC might benefit from the doodlebug more than the PuPdac in a typical
 setup because the ODAC seems to be light on power rail filtering at first glance. 
  
 I wouldn't want to stir up a hornet's nest, but that is interesting.


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## COOKIESnPIE

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## Avro_Arrow

Perhaps the voltage being lower than expected is due to the PCM expecting to get 5 volts but
 only getting 4.75 due to regulation and filtering.
  
 I will measure mine and see what I get.


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## Avro_Arrow

Here are the results I got from mine.
  
 Mine is a prototype version but close enough.
  
 Riv
 1. 127.0
 2. 127.1
 3. 125.3
 4. 125.5
  
 Offset
  
 Right: 2.2mV
 Left: 0.6mV
  
 2835
  
 1. 0.6mV
 2. 119.1mV
 3. 119.1mV
 4. -2.49V
 5. 117.1mV
 6. 117.6mV
 7. 2.2mV
 8. 2.5V


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## mcandmar

bada bing said:


> Now that is interesting
> 
> 
> 
> ...


 
  
 I wanted to but my machine is refusing to install it, its something with Windows 8.1 as i'm having trouble getting it to install a bunch of different USB DACS.  The ODAC will only work through the Isolator in one port, and the rest of the DAC's wont work at all.   Oddly though the PupDAC will work in any port, i dont really know whats going on yet..


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## COOKIESnPIE

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## COOKIESnPIE

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## SilverEars

Interesting measurements mcandmar.  You should bring up the measurements to the ODAC section.
  
 Kinda off topic, but any of you guys know of a simple ESS9018 implementation like the ODAC(9023) that is powered by USB?  I want to try it, and possibly add doodlebug if the PS noise is prominent.


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## Avro_Arrow

cookiesnpie said:


> I've been comparing your numbers to mine, as I'm not an engineer I can't really tell is the slight variances in our numbers make a difference.


 
  
 The PCM1794a has a 2% tollerance on it's output current and all the resistors have 1% each.
 I think all the voltages are within tolerance.
 With all the components involved, 5% is probably not an unreasonable expectation.
 If you were to match components, the best you could expect would still probably be
 only about 3%.
 It would be possible to add a high value resistor in parallel with Riv to trim the voltage to
 closer tolerance. At least you would get your offsets down to almost nothing.


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## COOKIESnPIE

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## 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.


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## COOKIESnPIE

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## 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?


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## tomb

skeptic said:


> 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

tomb said:


> 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.


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## mcandmar

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


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## tomb

skeptic said:


> tomb said:
> 
> 
> > 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.
> ...


 
  
  


mcandmar said:


> 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.


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## lordearl

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


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## tomb

lordearl said:


> 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.


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## 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.


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## mcandmar

From memory its ~1.5v rms


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## 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

juswyq said:


> 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.
> 
> ...


 

 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.


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## juswyq

tomb said:


> 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!


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## tomb

juswyq said:


> tomb said:
> 
> 
> > Good luck on finding the fix with that pin.
> ...


 

 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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## lordearl

It's actually best not to use the slider in windows anyway, it's not the most accurate (in terms of bits) means of attenuating the signal. JRIVER is one great piece of software that gives volume control without loss of digital signal quality, and it works perfectly with the Pupdac. As Tom says, Foobar works fine too.


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## hitman47

I finished the first of my two pupDAC kits yesterday. Had an easily fixed short at first (2 pins on the PCM2707 had a tiny bridge that shorted out the 4.75V regulator) and then it seemed to work for a while, but started cutting out after a few minutes. I noticed the 3.3V supply shared by the 2707 and the 1794 was shorted out so I started looking for the bridge. It turned out to be a tiny little speck of solder (presumably) way behind the adjacent VDD and DGND pins on the 1794 that was a pain in the behind to get out - I ended up scratching pretty hard between the pins with a blade until it consistently measured as open. It was behaving really strange before, sometimes it would work for a while after I reflowed the joints or scratched a bit and then short out again after 10s-2min of being powerd on. It appears to be fixed completely now though, I'll take it to the university tomorrow and have a closer look under the microscope to be sure.
  
 The moral of the story I guess is to be REALLY careful soldering those SSOP28 packages - the long pads can lead to almost un-fixable bridges way behind the actual joints. I really have to invest in a paste+microscope (+hot air, although that's not exactly optimal for ICs) setup one of these days, soldering close-pitch chips is a cakewalk with that equipment.
  
 The DAC sounds really nice, by the way - thanks to cobaltmute for the design and tomB for supplying the (excellently packaged) kits at such a reasonable price! When using it together with my "The Wire" headphone amp there are no caps in the signal path whatsoever and the bass really comes through nicely.
  
 Edit: Well, it just happened again. I'm going to have to remove the PCM1794 to fix this.


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## tomb

Sorry to hear of your troubles ...  SSOP-28 has always been challenging.  Nevertheless, previous experience with the AlienDAC, the BantamDAC, and now the SkeletonDAC made us think it wouldn't be such an issue.  Yet, for some reason on the PupDAC, it's been a recurring problem.  I think a lot of it has to do with the fact that the PCM1794 is not an inexpensive chip.  Plus, once you get a PupDAC populated, you have $75 invested in the parts and the PCB.  That makes mistakes hurt a lot more. 
	

	
	
		
		

		
			




  
 We're going to try to address this in the future.


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## hitman47

Yeah, it's my own fault for not being careful enough while soldering it. I've soldered SSOP28 chips before and it was fine, I just screwed up and the narrow pitch makes shorts behind the pins (that don't actually touch them but are only between the pads) almost impossible to fix without removing the chip - maybe you could make the PCM1794's solder pads a bit shorter on the next redesign?
 Anyway, thankfully I have access to equipment that will make desoldering and replacing the chip pretty comfortable at university. For my second DAC I'm gonna get a flux pen instead of the liquid flux I've got now, that stuff doesn't strike me as too great in comparison to the nice thick flux from the pens. Or I might just cave in and solder the 1794 with solder paste and a microscope (although it would hurt my hand soldering pride a bit, that's better than having to spend yet another $15 for a new chip) at the university.


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## tomb

hitman47 said:


> Yeah, it's my own fault for not being careful enough while soldering it. I've soldered SSOP28 chips before and it was fine, I just screwed up and the narrow pitch makes shorts behind the pins (that don't actually touch them but are only between the pads) almost impossible to fix without removing the chip - maybe you could make the PCM1794's solder pads a bit shorter on the next redesign?
> Anyway, thankfully I have access to equipment that will make desoldering and replacing the chip pretty comfortable at university. For my second DAC I'm gonna get a flux pen instead of the liquid flux I've got now, that stuff doesn't strike me as too great in comparison to the nice thick flux from the pens. Or I might just cave in and solder the 1794 with solder paste and a microscope (although it would hurt my hand soldering pride a bit, that's better than having to spend yet another $15 for a new chip) at the university.


 

 I'm sold on flux pens for IC chips.
  
 As for shorter solder pads, the production version you're using actually had the pads lengthened from the prototypes.  Believe me, it was _harder_ with shorter pads.
  
 The potential fix is that we're going to soon offer PupDAC PCB's with the PCM2707 and PCM1794 already "picked and placed" and soldered on the PCB.  The first manufacturing batch has been ordered from Imagineering.


----------



## mcandmar

I had similar fun doing mine but i found delsoldering braid was invaluable to suck out any excess causing shorts. I did also use a flex pen which helped.


----------



## hitman47

mcandmar said:


> I had similar fun doing mine but i found delsoldering braid was invaluable to suck out any excess causing shorts. I did also use a flex pen which helped.



Yeah, I tried that but the short wasn't even visible under the microscope with the chip installed so it was a pretty hopeless endeavour.




tomb said:


> (...)
> The potential fix is that we're going to soon offer PupDAC PCB's with the PCM2707 and PCM1794 already "picked and placed" and soldered on the PCB.  The first manufacturing batch has been ordered from Imagineering.




That's nice, although I don't think I'd buy it like that if I had the chance - I'm a bit stubborn when it comes to soldering my own components. 
In any case, the soldering guru in the lab removed the 1794 for me (I was a bit shy about heating it up for too long with the hot air), I cleaned up the pads and soldered in a new chip with solder paste under the microscope. The board worked fine in a quick test, I'm gonna leave it plugged in longer to see if it's definitely working for good when I get home. Here's how it looks now:






Edit: I've had it plugged in for about 5 hours uninterrupted now, and it seems I managed to fix it permanently! I'm definitely not gonna solder the second one at home, the microscope just makes everything soo much easier. I definitely recommend using one when soldering the PCM1794 to everyone who has access to one.


----------



## wjxkk

I finished my pupdac few days ago, but my computer can't recognized it, and then I measure the voltage for each test point, I found the voltage is low (0.01v) at 3v3 (the one beside the U1), other voltages looks fine.
  
 I reflowed some parts and checked there is no bridge for each chips. I'm afraid I may damaged pcb at this point? or may be the LDO?


----------



## tomb

wjxkk said:


> I finished my pupdac few days ago, but my computer can't recognized it, and then I measure the voltage for each test point, I found the voltage is low (0.01v) at 3v3 (the one beside the U1), other voltages looks fine.
> 
> I reflowed some parts and checked there is no bridge for each chips. I'm afraid I may damaged pcb at this point? or may be the LDO?


 

 The LDO could be damaged, or there could be a short/bridge somewhere in the 3.3V circuit that's pulling the voltage down.  See if you can measure (power off) resistance to Ground at various points along the 3.3V traces to see if you have a zero resistance somewhere - that would be a short.  That's the trace that goes from U2 to L3, C19, and then branches off to U1 and U6.  If you can't determine a short/bridge (zero resistance), then most likely U2 has been fried or is not properly connected.  You're at least in the right area, for sure, because the PC will recognize the device even if U3 (the DAC chip) is not operating correctly.  The device that makes the USB connection is U1 and it needs the 3.3.V supply to make that happen.


----------



## wjxkk

tomb said:


> The LDO could be damaged, or there could be a short/bridge somewhere in the 3.3V circuit that's pulling the voltage down.  See if you can measure (power off) resistance to Ground at various points along the 3.3V traces to see if you have a zero resistance somewhere - that would be a short.  That's the trace that goes from U2 to L3, C19, and then branches off to U1 and U6.  If you can't determine a short/bridge (zero resistance), then most likely U2 has been fried or is not properly connected.  You're at least in the right area, for sure, because the PC will recognize the device even if U3 (the DAC chip) is not operating correctly.  The device that makes the USB connection is U1 and it needs the 3.3.V supply to make that happen.




I measured the output voltage of U2, nearly 0, and input voltage seems ok, 4.9v. And there was once I try to debug, but I plug it in for 3 mins and u2 became very hot. Is that may indicate some problems? I also will check the resistance later.


----------



## tomb

wjxkk said:


> tomb said:
> 
> 
> > The LDO could be damaged, or there could be a short/bridge somewhere in the 3.3V circuit that's pulling the voltage down.  See if you can measure (power off) resistance to Ground at various points along the 3.3V traces to see if you have a zero resistance somewhere - that would be a short.  That's the trace that goes from U2 to L3, C19, and then branches off to U1 and U6.  If you can't determine a short/bridge (zero resistance), then most likely U2 has been fried or is not properly connected.  You're at least in the right area, for sure, because the PC will recognize the device even if U3 (the DAC chip) is not operating correctly.  The device that makes the USB connection is U1 and it needs the 3.3.V supply to make that happen.
> ...


 
  
 Sounds like you should've checked that resistance, first. 
	

	
	
		
		

		
		
	


	




  If U2 is getting hot, there's a short somewhere.


----------



## wjxkk

I found the resistance between ground and output of U2 is nearly zero, and L3 as well. I couldn't find any bridge for U1 U6, so probably I burned U2?


----------



## hitman47

I had the exact same issue - 0V at U2's 3.3V test point and U2 getting hot as hell. It turned out to be a short behind two pins on the 1794. And I mean aaaall the way back there - no chance of getting at it with a soldering iron. I had to remove the 1794, clean everything up, which I doubt I would have managed without a microscope, as I'd been trying to scratch out the bridge between the culpable 1794 pins which resulted in a still non-working DAC along with an almost ruined PCB with little solder blobs invisible to the naked eye stuck in very problematic places- can't recommend going that way, just remove the 1794 straight away once you're certain that's where the short is. I recommend first double-checking your PCM2707 pins for shorts and if you're certain that's not where the problem lies, remove the 1794 - preferrably with hot air or a pair of hot tweezers with the right tips, or if that's not an option, chip-quik or something equivalent. Clean the pads really well (you don't wanna end up lifting one off though, so be careful), get a new 1794 and install it as carefully as you can - be especially conservative on the amount of solder you use when soldering the new pin (you could try reusing the old chip, not sure whether anything could have happened to it due to these issues - I decided to play it safe and use a new one). Soldering tight-pitch ICs by hand and with traditional solder wire is always a bit of a gamble and the long pads on the pupDAC board open the possibility for shorts in places where you can't reach them with an iron. For me the short was between (or rather behind) the VDD (which is supplied by U2) and AGND pin, I think. 

At the risk of repeating myself, if you have the opportunity of working under a microscope for this kind of job, do it. It's sooo much easier to see where the little solder balls are sticking and causing shorts. Also, using solder paste to solder the new IC makes a world of difference too.

By the way, I think frying the regulators isn't possible by shorting them as they have over-current protection so I'm rather sure you've got a mean little solder bridge somewhere.


----------



## tomb

This has happened too often for my tastes and we are doing something about it.  We normally expect that an SOP-28 should be solderable by DIY-er's (as in AlienDAC, BantamDAC, and SkeletonDAC).  However, the inability to electrically confirm prior to installing the total investment in parts and the overall combination of placement/surrounding parts makes trouble-shooting extremely difficult.  The high investment in parts only makes a failure hurt more.  I've experienced this myself, having an un-workable PCB where I've removed the PCM chips (electrolytic caps, too!) a couple of times with no success.
  
 Beginning sometime this weekend, ordering the PupDAC kit will have the option of selecting a machine-pick&place PCB for U1 and U3 (the PCM2706/7 and PCM1794).  These are extremely high-quality soldering jobs that were machine-made, not by some little person toiling away in a sweatshop somewhere.
	

	
	
		
		

		
		
	


	




 The only difference is that the PCB edges are saw-cut instead of routed, but every single spec is still the same.


----------



## Avro_Arrow

Looks good Tom.
 I think that will be a popular option.


----------



## hitman47

I finished my second pupDAC today - I soldered the integrated circuits at the university lab and it was a breeze. Solder paste makes it sooo much easier, just dispense that stuff and wipe the edges of the pins with the soldering iron to get almost machine-quality joints - the hardest thing about the whole process is to get the amount of paste exactly right so it looks perfect.
  
 I did have a bit of a scare at first, as the supply voltages were all a bit too low (3.1V instead of 3.3 and stuff like that) and the DAC stopped working after playing for about half a minute. I did some multimetering and noticed the resistance between the 2.5V and ground pads was a constant 280 ohms. I guessed correctly (a rare occurrence in situations like this one) that C11 was to blame. I just KNEW it couldn't have been an IC as I'd inspected everything closely under the microscope and didn't have to apply excessive heat to any of the chips. I desoldered C11 and it was indeed blown, I measured a rather low resistance across the desoldered cap. I didn't have any 100nF caps laying around so I substituted two 1uF X7R MLCCs for C11 and C12, they seem to be doing their job fine. This is actually the first time I've managed to kill an MLCC, and I've definitely abused many of them rather badly.
  
 Here are my two "puppies" next to each other - the one I built today is connected in the picture:


----------



## lordearl

How are you guys downsampling hi-rez files with the PupDac?
 I'm using JRIVER and just today have tried downsampling 96khz to 48khz and find it has a more natural feel than when the 96khz is downsampled to 44.1khz.  I think the 24 bits are simply 'chopped' to 16 bits and I can't notice any degradation in sound from when I use a hi-rez.
  
 The PupDac has such a clean, studio-like sound to it without being fatiguing that I really don't mind having hi-rez files downsampled to 48khz (from 96khz or 192khz) or 44.1khz (from 88.2khz).  Just goes to show, it's not about the specs of the DAC, it's the implementation that matters most.  I'd be interested to hear other peoples' impressions....


----------



## tomb

lordearl said:


> How are you guys downsampling hi-rez files with the PupDac?
> I'm using JRIVER and just today have tried downsampling 96khz to 48khz and find it has a more natural feel than when the 96khz is downsampled to 44.1khz.  I think the 24 bits are simply 'chopped' to 16 bits and I can't notice any degradation in sound from when I use a hi-rez.
> 
> The PupDac has such a clean, studio-like sound to it without being fatiguing that I really don't mind having hi-rez files downsampled to 48khz (from 96khz or 192khz) or 44.1khz (from 88.2khz).  Just goes to show, it's not about the specs of the DAC, it's the implementation that matters most.  I'd be interested to hear other peoples' impressions....


 

 Sometimes I feel awfully ignorant.  I don't know exactly how this process takes place, but what you describe is accurate.
  
 I have many SACD and DVD-A FLAC files that I've downloaded.  They range from 24-bit 88kHz all the way to 24-bit 192KHz.  The biggest apparent difference in my Foobar is the Bitrate column, which I always use in the playlist.  Normal CD FLAC files range from about 700 kbps to 1000 kbps.  However, the SACD and DVD-A files range from 2000 kbps to over 8000 kbps!  In some cases, these are even 6-channel audio and show up as such in the Foobar visualization windows with 6 distinct bars/lines per channel (VU meters, peak meters, oscilloscope, etc.).
  
 All I'm doing is playing these files over USB using the PupDAC, a DoodleBug, my Torpedo and Windows 7 (64-bit now, but 32-bit worked just as well).  I have no idea how all of this works.  I've even bought a DVD-A of a Porcupine Tree album and I've read how to convert the files to FLAC, but haven't done it myself, yet.
  
 Regardless - as you say - the PupDAC (and my DoodleBug) and Foobar2000 seem to handle all of it in stride.  I would've guessed there would've been some artifacts or other noticeable audio degradation.  Instead, the audio is definitely superior to Redbook-FLAC files and sounds glorious (for lack of a technical term 
	

	
	
		
		

		
			





).
  
 So as you've experienced, one doesn't need a 24-bit, 192 kHz DAC to enjoy such files.  _It's definitely possible to improve upon Redbook-CD quality simply using 16-bit USB._


----------



## mcandmar

All the re sampling is done by the Windows Mixer.  Buried inside control panel / sound / playback tab / your device / advanced tab, you can set the default sample rate and bitrate.   Every sound played through windows mixer then gets up sampled or down sampled to that setting.
  
 If you want a bit perfect playback you need to use a plugin like WASAPI for Foobar, that will bypass the Windows mixer and pipe the data to the DAC in whatever sample/bit rate the recording is in. Only problem is if you try and play a 24bit recording through a PupDAC all you will get is silence as it can only handle 16bit.
  
 If your a purist like me its preferable so nothing is re sampling or modifying the audio source in any way, but a PupDAC 2.0 would be nice


----------



## Avro_Arrow

I use the resampler in Foobar2k with wasapi.


  
 My signal chain:


  
 Laptop, Doodlebug, PupDAC, Steve McCormack DNA.5, Martin Logan Sequel II.


----------



## FJJB

I dont know if this is the right place to ask these troubleshooting questions, however my recent build of the pupdac, although it sounds great and works, doesnt light its LED indicator. My guess is, that ive used the wrong Red LED. Instead of using the one recomended by the pupdac, ive used the one recomended for the doodlebug. Does the subtle change between the two LEDs (10ma forward current vs 20ma forward current) be making this LED malfunction? Every checking spot has good readings except the 4.5v one which in displaying 4.8v!! My supicion is that this is because of the LED not forwarding the current.
  
 Sorry for my ignorance. And thanks in advance.


----------



## tomb

fjjb said:


> I dont know if this is the right place to ask these troubleshooting questions, however my recent build of the pupdac, although it sounds great and works, doesnt light its LED indicator. My guess is, that ive used the wrong Red LED. Instead of using the one recomended by the pupdac, ive used the one recomended for the doodlebug. Does the subtle change between the two LEDs (10ma forward current vs 20ma forward current) be making this LED malfunction? Every checking spot has good readings except the 4.5v one which in displaying 4.8v!! My supicion is that this is because of the LED not forwarding the current.
> 
> Sorry for my ignorance. And thanks in advance.


 

 An LED will light at 1ma current or less.  I'm probably exaggerating, but the point is, many LED's have a fairly linear performance with current - especially red ones.  In any event, there is no way your LED would not light at 10ma.  10ma is simply a conservative selection to keep the LED lasting longer.
  
 I suspect you simply soldered it in backwards.  Take it out, reverse the leads and solder it in again.  It'll probably light right up.  Note that soldering it in backwards should not have damaged it unless you melted it with the soldering iron.


----------



## lordearl

avro_arrow said:


> I use the resampler in Foobar2k with wasapi.


 
  
 Ok as I didn't listen with Foobar (only JRIVER), i downloaded the program and tested it.
 Indeed, to get bitperfect playback you *must* use the resampler with wasapi.
 If you don't, then the hi-rez files go through the windows filter.
 Tom - test it out and see what you think.  It's a revelation and a great result for the PupDac that it is not noticeable (at least to my ears) when hi-rez files are resampled!
 I guess we would need a PCM1794 that operates > 48khz to know for sure, but when I compare AK4399 @ 192khz and PCM1794 @ 48khz, I know which DAC I prefer (the latter!).


----------



## FJJB

thanks for the reply tomb! however i tested the led both ways and still doesnt light up. I know this is a cosmetic thing and besides that the sound is pretty amazing and clear, however Im not sure if this will damage or affect some of the other parts in the long run (Im still getting 4.8-4.9v on the 4.5v spot, although in the other spots its alright). Another thing I noticed is that I cannot control the volume of the dac or mute it in the windows volume manager. Is this normal?


----------



## mcandmar

Has to be either a bad connection on resistor R1, or the LED is bad.  What i would do is,
  
 -Remove the LED and test it, almost all multimeters have a diode test function.
 -Measure the voltage across the pads for the LED to confirm power is there, if not measure resistance across R1.


----------



## FJJB

Ok, so i tested the resistance of r1 (by desoldering it) and it just works and after putting it back i test the traces and they work. I also tested the traces from the usb connection-L1 to the anode part of the Led everything seems alright. However I changed the diffused Led for a transparent one and it lights very dimly. Then to test if it was the R1, I bypased the R1 by placing a very bright white led (since bypasing the resistor would burn a normal Led in a second because of the current) from the anode through-hole to the first pad of the R1 resistor (bypasing the cathode through-hole and the pad connected to this). The Led turned on very bright. So probably this means that the R1 is or either to resistant for the Led or I just dont know.
  
 sorry if it gets confusing to read...


----------



## mcandmar

Ahh ok, i missed that part. Those LEDs have a very low output so i agree a higher value resistor for R1 is probably needed.  They were used to setup the voltage regulator instead of being used as an actual visual indicator so personally i would just replace it with something more suitable.


----------



## nivz

Hi Guys, I just finished building a pupdac and a doodlebug. I'm having some issues with the pupdac, and was hoping someone could point me in the right direction to fix it.
  
 The dac gets detected by windows and audio plays through it, but there's a quite loud ticking or clicking noise with some static noise in the background. It's not related to the output level of the audio I'm playing, as in if I play something loud enough. I can't hear the noise. The test point voltages are all fine apart from the 4.5v, which reads 4.7. But I saw on this thread that it is normal for it to be ~4.7v.
  
 The dc offsets are 1.2mv on the right channel, -2.0mv on the left channel.
  
 Powering the dac through the doodlebug still has the same static and clicking noise (even when not connected to a PC).
  
 Any help would be appreciated. Thanks!
  
 Edit:
 This was tested using IEMs plugged in directly to the 3.5mm out. The noise is on both channels, it's not a random clicking noise, as in the timing of the clicking stays constant (10clicks a second perhaps). The noise levels keeps going up and down..


----------



## tomb

nivz said:


> Hi Guys, I just finished building a pupdac and a doodlebug. I'm having some issues with the pupdac, and was hoping someone could point me in the right direction to fix it.
> 
> The dac gets detected by windows and audio plays through it, but there's a quite loud ticking or clicking noise with some static noise in the background. It's not related to the output level of the audio I'm playing, as in if I play something loud enough. I can't hear the noise. The test point voltages are all fine apart from the 4.5v, which reads 4.7. But I saw on this thread that it is normal for it to be ~4.7v.
> 
> ...


 

 My guess is that you have a bridge or intermittent short somewhere.  There's a capacitor somewhere that's constantly charging/discharging. The discharges are the clicks you hear.  It may need nothing more than a thorough cleaning ... and most important, a thorough drying.  I've had this happen from residual cleaning alcohol retained in or under one of the chips.  Maybe try setting it beneath an incandescent light bulb for awhile?


----------



## nivz

Thanks for the advice TomB.. I cleaned the board with flux cleaner and deionised water, let it dry under a bulb for about 12hrs.. the problem is still there.. On the PCM1794, There's a bridge on pins 11 and 12, I've scratched the soldermask on the via next to these pads so it's impossible to remove that bridge now, on the schematic these two pins are grounded (FMT0 and FMT1), So I left the bridge as it is.. I didn't think this could be the problem as those two pins are connected to the same via (one I managed to scrape the soldermask off) that goes to C8 on the other side anyway...
  
 I'm very new at this so I don't know how I should go about checking if a cap is shorting, can I just check the voltage across every cap? I'll try to post some photos if I can get something to focus close enough to see the details of the board.. Thanks again!
  
 Edit:
  
 Pics:
 1794




  
 2707




  
 Board top




  
 Board bottom


----------



## nivz

Previous post needed moderator approval for links..


----------



## tomb

nivz said:


> Thanks for the advice TomB.. I cleaned the board with flux cleaner and deionised water, let it dry under a bulb for about 12hrs.. the problem is still there.. On the PCM1794, There's a bridge on pins 11 and 12, I've scratched the soldermask on the via next to these pads so it's impossible to remove that bridge now, on the schematic these two pins are grounded (FMT0 and FMT1), So I left the bridge as it is.. I didn't think this could be the problem as those two pins are connected to the same via (one I managed to scrape the soldermask off) that goes to C8 on the other side anyway...
> 
> I'm very new at this so I don't know how I should go about checking if a cap is shorting, can I just check the voltage across every cap? I'll try to post some photos if I can get something to focus close enough to see the details of the board.. Thanks again!
> 
> ...


 

 To tell the truth, I don't see any issue with the PCM chips.  Another thing that can cause the symptoms you describe is the opamp.  Are you certain everything is clean and dry around it?  The fact that you haven't trimmed any leads is suspect.  Conceivably, those could be touching something and arcing when you're trying to operate the DAC.  Also look for anything that might be shorting right around the opamp.  It looks like you used the OPA2835.  The 2836 is much, much better.


----------



## nivz

tomb said:


> To tell the truth, I don't see any issue with the PCM chips.  Another thing that can cause the symptoms you describe is the opamp.  Are you certain everything is clean and dry around it?  The fact that you haven't trimmed any leads is suspect.  Conceivably, those could be touching something and arcing when you're trying to operate the DAC.  Also look for anything that might be shorting right around the opamp.  It looks like you used the OPA2835.  The 2836 is much, much better.


 

 I've checked around the opamp and I can't see anything that might be shorting.. I'll trim the leads a bit closer to the joints. Could you please tell me if there should be a voltage across the mica caps? they both have 130mV on both sides of the cap, reference to ground. (and 0V across the caps). I can't think why I used the 2835 :s.. maybe mouser didn't have it instock at the time, but I will replace it with a 2836..
  
 Thank you so much for taking the time to assist me .


----------



## tomb

nivz said:


> tomb said:
> 
> 
> > To tell the truth, I don't see any issue with the PCM chips.  Another thing that can cause the symptoms you describe is the opamp.  Are you certain everything is clean and dry around it?  The fact that you haven't trimmed any leads is suspect.  Conceivably, those could be touching something and arcing when you're trying to operate the DAC.  Also look for anything that might be shorting right around the opamp.  It looks like you used the OPA2835.  The 2836 is much, much better.
> ...


 

 I don't have one apart to measure right now, but any capacitor in a live circuit should read zero DC volts.  That's the purpose in many instances - they block DC, but allow AC current to flow.
  
 The 2836 is very much superior, but maybe you should try to get rid of the ticking and noise before changing out the opamp.  The reason I mentioned the opamp is that if it is oscillating, it can also cause the ticking and noise that you describe.  I couldn't see the resistor pads very clearly in your photo and thought you might have some shorting in that area.  You might check to see if the opamp is getting hot?
  
 If that doesn't work, I would suggest trying to re-flow the solder on the simpler parts - don't mess with the PCM chips or the TPS regulators.  See if that helps, first.


----------



## nivz

tomb said:


> I don't have one apart to measure right now, but any capacitor in a live circuit should read zero DC volts.  That's the purpose in many instances - they block DC, but allow AC current to flow.
> 
> The 2836 is very much superior, but maybe you should try to get rid of the ticking and noise before changing out the opamp.  The reason I mentioned the opamp is that if it is oscillating, it can also cause the ticking and noise that you describe.  I couldn't see the resistor pads very clearly in your photo and thought you might have some shorting in that area.  You might check to see if the opamp is getting hot?
> 
> If that doesn't work, I would suggest trying to re-flow the solder on the simpler parts - don't mess with the PCM chips or the TPS regulators.  See if that helps, first.


 
  
 Hi tomb,
  
 Apologies for not replying for a long time, I only got around to looking at the pupdac again today. And I figured out what it was. The noise comes from my wifi signal.. As soon as I dropped the output power of the router, the noise from the pupdac was completely gone. If I increase the power, noise comes back, so it definitely is the wifi signal.
  
 I don't have the case for the pupdac, but I'm guessing when inside the metal enclosure this won't be an issue. I will try and mount it inside a metal housing to make sure that solves the issue before I order the custom made ones from yourself.  I really appreciate you taking the time to reply to my earlier posts. Hopefully this might help someone with a similar issue down the line.
  
 It also picks up noise from a wireless keyboard and a mouse to lesser extent, moving the receivers well away from the dac got rid of a screeching noise it makes when the mouse was moved and a very low ticking noise from the keyboard. It is pretty much dead silent at this point.
  
 I've also got the 2836, can't wait to swap it on and see what the difference will be. Even as it is I'm amazed at the sound quality!
  
 Best regards,
  
 Nivz.


----------



## tomb

nivz said:


> tomb said:
> 
> 
> > I don't have one apart to measure right now, but any capacitor in a live circuit should read zero DC volts.  That's the purpose in many instances - they block DC, but allow AC current to flow.
> ...


 
  
 Thanks for your kind comments.  I'm glad you found out what's wrong.
  
 Just and FYI, but here's what is next to mine (or within 3 feet):

PC
Two LCD monitors
Wireless home phone
LAN wireless router
Cable modem, also with wireless router
Wireless keyboard
Wireless mouse
 I don't have a problem with the PupDAC in its case.


----------



## Jawmare

LED on, pupdac not recognized by pc, the following voltage check fails
  
 4V5 = 4.7V
 -5V = 0V
 -2V5 = 0V
  
 Any idea?
  
 PS: going to check U7/C32-34 Tomorrow, but visual inspection looks fine


----------



## tomb

jawmare said:


> LED on, pupdac not recognized by pc, the following voltage check fails
> 
> 4V5 = 4.7V
> -5V = 0V
> ...


 

 The 4.7V is fine.  The 5 and 2.5 are not.  Check for shorts around U7 and U8.


----------



## UnsatisfactoryR

Hi, I recently built my pupDAC and it's great. I have one issue though, the voltage offset between channels is too much, and one channel is noticeably louder than the other. All of the voltage test points are within .05 volts of stated value, except for the 4.5v one that reads 4.749v. The big issue though is that one channel reads .5mv and the other reads 3.3 mv. I have tested the barrel of the rca connectors, the pads where they mount, and the unpopulated 1/8" output pads. They all read the same values.
  
 I'm not sure what I should be checking to troubleshoot this, so any help is much appreciated.


----------



## tomb

unsatisfactoryr said:


> Hi, I recently built my pupDAC and it's great. I have one issue though, the voltage offset between channels is too much, and one channel is noticeably louder than the other. All of the voltage test points are within .05 volts of stated value, except for the 4.5v one that reads 4.749v. The big issue though is that one channel reads .5mv and the other reads 3.3 mv. I have tested the barrel of the rca connectors, the pads where they mount, and the unpopulated 1/8" output pads. They all read the same values.
> 
> I'm not sure what I should be checking to troubleshoot this, so any help is much appreciated.


 

 First, 4.79V is pretty much where it should be for the 4.5V test point.  The 4.5V is a theoretical number, but in practice, it's always worked out to about 4.75V, depending on scatter in the various parts.
  
 As for the offset, it's possible that you had some bad luck in the resistor tolerances.  I haven't sold a kit in awhile, so I'm curious - did you purchase and install the 1% V-D RN50 series resistors?  If not, that could be the problem.  The OPA2836 is a very aggressive opamp and if the resistors are not very, very close in value, you could end up with more offset than desired.  It's the reason we chose the 1% resistors, because that lessens the chance for unmatched resistors between the channels.
  
 Anyway, look closely at the resistors on the back side of the PCB.  Those are the ones that were so critical they were located on the bottom of the PCB - in order to reduce the lead length.  These are R6, R9, R17, and R21.
  
 By the way - just in case, the silkscreen was messed up on the R6 resistor.  It looks more like an "R5," but R5 is clearly labeled on the top.  The resistor on the bottom is "R6."  I would think if you got these two mixed up, it might explain a lot.
  
 Anyway, let us know ...


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## Jawmare

tomb said:


> The 4.7V is fine.  The 5 and 2.5 are not.  Check for shorts around U7 and U8.


 
 C34/35 was dead, replaced the cap, now all voltage check is fine, windows still doesn't recognize the device, but gnd to jack are showing 1.85V. here are some pic of the board itself: http://imgur.com/2vOeYD4,02UIKKL,Vldscce
  
 on linux, dmesg gives device descriptor read/64, error -62


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## tomb

jawmare said:


> tomb said:
> 
> 
> > The 4.7V is fine.  The 5 and 2.5 are not.  Check for shorts around U7 and U8.
> ...




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.


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## UnsatisfactoryR

tomb said:


> First, 4.79V is pretty much where it should be for the 4.5V test point.  The 4.5V is a theoretical number, but in practice, it's always worked out to about 4.75V, depending on scatter in the various parts.
> 
> As for the offset, it's possible that you had some bad luck in the resistor tolerances.  I haven't sold a kit in awhile, so I'm curious - did you purchase and install the 1% V-D RN50 series resistors?  If not, that could be the problem.  The OPA2836 is a very aggressive opamp and if the resistors are not very, very close in value, you could end up with more offset than desired.  It's the reason we chose the 1% resistors, because that lessens the chance for unmatched resistors between the channels.
> 
> ...


 
 So I finally had some time to mess about with this. I tested these 4 resistors and they're all spot on. Tested with a Fluke 87V 
  
 R6 - 1.499k
 R9 - 10.2
 R17 - 1.499k
 R21 - 10.2
  
 I reflowed the OPA 2836 for sanity's sake even though the joints looked nice. I looked over the rest of the joints using a 100mm macro lense and zooming in, which really helps show those chip leg joints, and everything looks nice. After putting the resistors back in, I'm still getting the a high offset.
  
 Any other ideas?
  
 Edit: To add a bit more, I tested the other resistors, but in circuit cause I didn't feel like pulling them all. Obviously some are going to read different than their values in circuit, but I figured it would let me compare both channels to each other. Everything matched up with it's respective pair. The only deviations from the listed values were R7 and R18 read 94 instead of 100 ohms, and R8 and R19 read 113 instead of 1.5k.


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## tomb

unsatisfactoryr said:


> tomb said:
> 
> 
> > First, 4.79V is pretty much where it should be for the 4.5V test point.  The 4.5V is a theoretical number, but in practice, it's always worked out to about 4.75V, depending on scatter in the various parts.
> ...


 
  
 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?


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## UnsatisfactoryR

tomb said:


> 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.


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## tomb

unsatisfactoryr said:


> tomb said:
> 
> 
> > 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.
> ...


 

 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.


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## Jawmare

tomb said:


> 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.


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## tomb

jawmare said:


> tomb said:
> 
> 
> > 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.
> ...


 
  
 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.


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## 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?


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## Jawmare

harryomalley said:


> 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


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## HarryOMalley

Ah ok great! Thanks


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## 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?


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## tomb

lordearl said:


> 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.


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## 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.


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## 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 ?


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## 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.


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## TheLaw

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


----------



## tomb

thelaw said:


> 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.


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## 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


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## tomb

snapper96 said:


> 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.


----------



## snapper96

Yikes, rereading my post makes me wonder what I was doing when I typed that mess out.  Anyway, I don't know why I didn't actually check voltages, I'll do so tonight and report back.  Thanks!


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## snapper96

tomb said:


> 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.


 
  
 I finally got a chance to take a look and a few of the voltages were completely messed up.  I replaced the various parts to get the voltages reading as expected and everything is working as it should.  I appreciate your help, I had been away from working on this stuff awhile and I completely spaced checking the voltages.  Thanks for the assist!


----------



## tomb

snapper96 said:


> tomb said:
> 
> 
> > 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?
> ...


 
  
 Glad it all turned out OK.


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## webbofconfusion

I just completed mine... Just a few minor issues... and after two hours of checking voltages and soldering a few components again, I am up and running. Easy build... Would suggest this for anyone.


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## Blimmy (Feb 9, 2021)

Hello Everyone,

I just finished soldering my Pupdac! It sounds great! There's only one problem... The volume cannot be adjusted. I read earlier in this thread that someone had the same issue, but it wasn't clear to me how they fixed it.

The problem:

Windows volume control does not have any effect on volume output to my HD599s
Volume is very loud.
Some diagnostic info:

The board is detected as: "3- USB AUDIO    DAC"
Windows volume bar can be adjusted but has no effect.
Volume can be reduced through applications such as Spotify and YouTube.
Music sounds great with reduced volume from applications with internal volume control.
No noise can be heard when nothing is playing.
Test Pad voltages
Test Pad 3.3V-1 =  3.294V
Test Pad 3.3V-2 =  3.287V
Test Pad 5V =  4.940V
Test Pad -5V = -4.923V
Test Pad 4V5 = 4.746V
Test Pad 2V5 = 2.496V
Test Pad -2V5 = -2.499V


After some reading of the PCM2706C datasheet, it seems as though it is operating in its default control interface. In which, the spdif output to the PCM1794A is not volume controlled? Is my reading of that correct?
" The master volume control is not supported. A request to the master volume is stalled and ignored. " (Section 9.5.1.2 - Ti PCM2706C datasheet).

Where should I look next for fixing this issue?

Thanks in advance for the help


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## tomb

Blimmy said:


> Hello Everyone,
> 
> I just finished soldering my Pupdac! It sounds great! There's only one problem... The volume cannot be adjusted. I read earlier in this thread that someone had the same issue, but it wasn't clear to me how they fixed it.
> 
> ...


Just to be clear, this was resolved off-line.

We thought a few years ago that the PCM2706/7C was a solution, but a software control is necessary that is not included in the PupDAC design.

The PupDAC is just like most sources in the high-fidelity headphone world (or speakers, too).  It isn't intended to be connected directly to a headphone, nor do we recommend that as a regular practice.  Connecting to a headphone amplifier makes the need for a software volume control moot.

Also, any software volume control is going to lower the music stream resolution.  There are some technical calculations that can be done with the ENOB headroom of the DAC vs. the digital stream that argue against this as a real worry, but again, better to use a headphone amplifier with am analog volume control and remove all doubt of damaging the music resolution.


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## mcandmar (Jul 7, 2021)

Curious if anyone has any thoughts on this as i keep blowing the arse out of the voltage regulators.  PupDAC has worked perfectly for years, until recently when i got a second hand Schiit Vali headphone amp, the original model with two sub miniature 6088 tubes.  The unit is powered with a 15v AC adapter.

Problem is if the PupDAC is connected to the Vali, and i then connect the USB to the computer there is a chance it will blow the voltage regulators in the PupDAC.   First time it happened it took out the two (3.3v) regulators U2+U4, and the 4.5v regulator U5.  I have just done it again by accidentally unplugging the USB and plugging it in again, this time U2 went bye bye.

I am assuming its to do with the Vali not being ground referenced and letting its ground plane float, as i dont have a problem if i connect the PupDAC USB first, then connect power the Vali.

I am wondering if any clamping diodes across the input of the PupDAC would help cure this issue, or any other ideas anyone has?   ....i know the obvious answer is to not use the Vali and go back to my old amplifier, but i kind of like it, and pairs well with my headphones.

P.S. As a backup i am using a Skeleton DAC and not having the same issue, seems to be a little more resilient.


----------

