# The SkeletonDAC



## cobaltmute

Back in the days when tomb and I were working on bringing the grubDAC to production, we were looking at the kitting process and lamenting the fact that the PCM2706/7 were in such short supply and that the PCM2704/5 had huge quantities in stock.  We discussed the fact that it would be convenient to have a DAC built on one of those chips.  Spring and Summer came and being outside mountain biking seemed like a much better idea than sitting inside designing a DAC.
   
  However, it has been winter.  I'm not as young as I used to be and riding in the snow is not quite my thing.  So I designed the SkeletonDAC:

   
  The idea was to build a "bare-bones" (i.e skeleton) DAC based upon the PCM2704/5.  No external regulator and low part count.  However it did morph a little bit due the fact that after laid the PCB out, I kept looking at the fact that there was this expanse of board with nothing on it.  With a little bit of part shoving and some choices of parts, I managed to incorporate the SPDIF output of the PCM2704 onto the board, complete with output transformer.  As well, given that the PCM2704 is spec'ed at being able to drive headphones, there is the option to put larger output caps - basically anything with 2.5mm or 5mm lead spacing.  2.5mm caps positions are offset so that it is possible to use larger size electrolytics and drive headphones right off the dac.
   
  The board dimensions are exactly the same size as the grubDAC.  The USB input and audio output are in exactly the same place.  The same Hammond case can be used (even with SPDIF), so it should be a great versatile little dac.  From a build perspective, the only challenge to this should be that most of the surface mount parts are 0805.  However, if you can get the PCM2704 down reasonable clean, you should have a very high chance of success building the DAC.
   
  Board layers top and bottom:

   
  Top Layer

   
  Bottom Layer

   
  Schematic:

   
  The BOM is to come.  I need to clean it up to show the three versions that can be built - full, audio out only, SPDIF out only.
   
  Since BatchPCB's shipping to Canada is really sucky, the boards took a detour through Beezar as it is a lot cheaper for me to have tomb ship them to me than to have BatchPCB ship them to me.  As a result tomb has built two already and has already provided me with some really useful feedback on what to do with future versions of the board.  He has reported to me quite reasonable results driving headphones direct, but I'll let him report on that.
   
  At the moment, I'm looking into the cost of running a bit larger prototype run and was curious if there was anyone out interested in building some of these.


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## Armaegis

I am intrigued and would love to try... but I've never done any chip soldering before.


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## nikongod

id be interested in building one.


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## c12mech

I would definately be interested in doing one.  My goal this year is to build a couple of different DACs and try to get the design in my head for one on paper.


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## tomb

As cobaltmute said, the PCM2704/5 has a built-in headphone amplifier.  So, unlike previous DACs that were similar (Alien, Bantam), this one does a pretty good job powering small headphones directly.  Here's mine cased up in the familiar GrubDAC case with a pair of 47uf Elna RFS Silmic II's.  One has to be a bit creative in installing the caps.  They're too tall for the case lid to sit up vertically, but a little creative bending of the leads lets them sit horizontally, albeit a little staggered.
	

	
	
		
		

		
			





  Here's one I built awhile back with a pair of KSC-75's.  It drives them fine and sounds very good - at least as good as an Alien/Bantam.


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## c12mech

Isn't being creative part of what DIY is all about?  That looks good in that case.
   
  Would I be correct in assuming that the full version would be audio out and SPDIF out?  Is there room to mount SPDIF connector on the opposite end of the case from the headphone jack?


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## onyu

I'm interested in building one or two.
   
  Ordered a few 2704's to much some time ago.


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## particleman14

Have you thought about mounting the spdif pads 90* so that a pcb mount rca jack might fit?  I was looking how to incorporate a spdif input into the small hammond case, but it seems all the pcb mount rca jacks have pins that are inline (or tri pin) which differs from the pad layout on the board.  Is there any rca/spdif input part that will fit neatly for the hammond case?  This build definitely looks cool for maybe a friend or family member.


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## holland

Quote: 





tomb said:


> <snipped>


 

  
  I must say....you've got a real thing for those blue cases, eh?


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## tomb

Quote: 





particleman14 said:


> Have you thought about mounting the spdif pads 90* so that a pcb mount rca jack might fit?  I was looking how to incorporate a spdif input into the small hammond case, but it seems all the pcb mount rca jacks have pins that are inline (or tri pin) which differs from the pad layout on the board.  Is there any rca/spdif input part that will fit neatly for the hammond case?  This build definitely looks cool for maybe a friend or family member.


 

 I'm not sure it's that much of an issue.  Granted, I haven't done it yet for real, but it seems to me that it would be easy enough to loop the wiring over the transformer (choke) to have it exit with an RCA jack on the left end of the case.  Top mounted might be another possibility, although not as aesthetic.


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## particleman14

ya , I was trying to go for minimum protrusion from the rca jack.  I guess I'll have to use a panel mount rca if I want spdif.


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## RedLeader

I'd be interested, I've actually never built a DAC before


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## c12mech

After looking at this some more I have another question concerning SPDIF out.  Exactly what is it meant to connect to?  I don't see a lot of SPDIF inputs on the amp circuits that I look at or have built. 
   
  I know that probably sounds like a dumb question but I have to ask.  What searching I've done has not given any answers.
   
  In any case can an SPDIF input be added to an amp with the proper circuit in place?


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## nikongod

Quote: 





c12mech said:


> After looking at this some more I have another question concerning SPDIF out.  Exactly what is it meant to connect to?  I don't see a lot of SPDIF inputs on the amp circuits that I look at or have built.


 

 I'm pretty sure its there so you can use this thing as an USB-spdif converter to feed a bigger and badder DAC. 
   
  We put a DAC in your DAC so you can convert your digital stream while convert your digital stream.


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## cobaltmute

Quote: 





nikongod said:


> We put a DAC in your DAC so you can convert your digital stream while convert your digital stream.


 
   
  ^ This is why we do it.  And for those of us who don't have SPDIF on our computers.
   
  There was also inquiries about doing it on the grubDAC and since there was room on the board, why not?
  
  As for mounting a SPDIF RCA jack on the board, I'll have to look, but I'm not seeing a lot of room right away.


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## c12mech

Thanks nikongod.  That was kind of what I thought but just wanted to make sure.  Makes a lot more sense now.


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## PretentiousFood

This is awesome! I made a GrubDAC that I installed internally on my EeePC to make up for the subpar onboard sound but I've obbously had to carry around an externa amp whenever I wanted to use my headphones. Not so practical. Since this board has the same footprint I'd definitely be interested in swapping it out.


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## BobSaysHi

Quote: 





nikongod said:


> We put a DAC in your DAC so you can convert your digital stream while convert your digital stream.


 

 I loled


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## cobaltmute

There is a few prototype boards on there way from the US up to me.
   
  When I get them, I will offer then out to interested parties.  One part that needs to be tested as I don't have the right stuff is the "DAC in your DAC so you can convert your digital stream while convert your digital stream" as nikongod put it.


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## c12mech

I'm looking forward to doing this one as well as the pup dac.  I will be curious to see what difference it makes as a converter to another dac.  Hopefully all goes well and it makes things better.  I'm planning to do a gamma2 in the next month or two and will be able to do a little comparison.


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## cobaltmute

Okay gentlemen, I have a BOM:
http://dl.dropbox.com/u/630887/SkeletonDAC-r1-bom-a.xls
   
  The BOM list multiple choices for the output caps, depending upon your preference.  I have not put the case on the BOM, but it fits the Hammond 1551H.  If you are using the Hammond case, you need to watch your output cap height - approx 10mm is max.
   
  And I have 6 boards to give away as prototypes.

 Rules are similar to what I did with the pupDAC:

 One board only per person
 $5 CDN shipping to anywhere in the world
    
  Looking back at the thread, the following 5 expressed interest, leaving one board
     Armaegis
     nikongod
     c12mech
     onyu
     RedLeader
   
  My only criteria is that I'm looking for a least one build of either a SPDIF or Full build, as I don't have the right stuff to test this myself.  That means until I hear what the people on the list intend on building, the last board available will go to someone who expresses that they will build and test the digital out.
   
  If those that have expressed interest can confirm continued interest and build type, either in the forum or PM, we can get this moving along.


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## Avro_Arrow

I would be willing to do a full build and have another SP/DIF input DAC (DIR9001,PCM1793,LT1364) I can test the output with.


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## Avro_Arrow

Any chance of a group buy for the BOM?


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## Spacehead

Oh It has a headphone amplifier too. I would have expressed my interest if I had noticed that before.


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## Avro_Arrow

I did a BOM for Digi-Key if anyone is interested.


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## RedLeader

I don't need the SPDIF out (I've got a udac2 kicking around) so I'll be doing a more barebones build.


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## c12mech

I just finished going through the bom and have some questions since the schematic does not have values for components. 
   
  C11 says 10uf, p/n listed is 22uf
  C6 says 100uf, p/n listed is 220uf
  R3,R4 says 22 ohm, p/n is 22.1 ohm
   
  Just want to know about these before I order.


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## Armaegis

I'd be willing to try the full build. That said, I'm still kinda new at all this, so if an experienced builder wants the spot I don't mind being bumped.


  Quote: 





avro_arrow said:


> Any chance of a group buy for the BOM?


 

 I'm in for this.
   
  p.s. interested in the digikey BOM as well.


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## cobaltmute

So Avro Arrow has offered to do the full build, so everyone else that was on the list need not worry.  If you are on the list in post #21, can you please confirm or deny participation to me?  Best way to confirm participation to me  is to PM me your mailing address (formatted so I can just print it out and tape it to the envelope) and the e-mail address I can send the Paypal request for the shipping.  Also let me know if you don't want to participate as there are others that are interested.


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## cobaltmute

Quote: 





c12mech said:


> I just finished going through the bom and have some questions since the schematic does not have values for components.
> 
> C11 says 10uf, p/n listed is 22uf
> C6 says 100uf, p/n listed is 220uf
> ...


 
   
  C6 is a bulk capacitor for the board.  Largest value that fits is a good choice.  100uF is a guideline, but the 220uF listed is chosen as biggest that fits the case.
  R3,R4 - termination resistors on the USB data lines.  There is a range of acceptable values
  C11 - decoupling for the common voltage in the DAC.  10uF is datasheet, IIRC, but I'd read that the large value helps improve performance, which is why the part is spec'ed as such.


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## Avro_Arrow

For the Digi-Key BOM, the only inductor I could find in that footprint was 1uH, not 10uH.
  Will the 1uH be of any use or is the value too low?


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## cobaltmute

Quote: 





avro_arrow said:


> For the Digi-Key BOM, the only inductor I could find in that footprint was 1uH, not 10uH.
> Will the 1uH be of any use or is the value too low?


 
   
  1207 and 1210 should fit the board as well.  For these you're only talking a slightly wider part and 10uH parts are available.


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## Avro_Arrow

Done
  Quote: 





cobaltmute said:


> 1207 and 1210 should fit the board as well.  For these you're only talking a slightly wider part and 10uH parts are available.


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## c12mech

Thanks for the clarification.  As I do more of this stuff I find the circuits are starting to make a lot more sense.


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## Avro_Arrow

Here is the BOM on Digi-Key.
   
  I think you have to be logged in first to see it.
  Let me know if it works.


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## c12mech

I tried to see the bom and it just sends me to the BOM manager page.  Even if I'm logged in this still happens.  Any suggestions on how to see it?


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## Avro_Arrow

It might not work...check this wording in the BOM help:
   
  "Click the link in the "Public/Protected" column associated with a BOM you authored that you would like to change the access rights to. Access restrictions include public, where anyone in your company that has a Digi-Key Web Customer ID can access them, and protected, where the BOM creator can specify who in the company with a Digi-Key Web Customer ID can have access to the BOM."
   
  It sounds like you can only share a BOM within the same company name.
  Anyway, the BOM is listed as "public" and the BOM ID# is 28657.


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## cobaltmute

I can put the BOM in my DropBox with the Mouser BOM if it makes life easier.


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## Avro_Arrow

Thanks cobaltmute, that sounds like the best plan.


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## cobaltmute

Avro_Arrow's Digikey BOM:
http://dl.dropbox.com/u/630887/SkeletonDAC%20BOM%20from%20Digi-Key.xls


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## c12mech

I did a little cross referencing between Mouser and Digi-key and will stick with my Mouser BOM.  Digi-key seems to be out of some of the parts and for others requires a minimum of 10 pieces.


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## tomb

Quote: 





cobaltmute said:


> Okay gentlemen, I have a BOM:
> http://dl.dropbox.com/u/630887/SkeletonDAC-r1-bom-a.xls
> 
> The BOM list multiple choices for the output caps, depending upon your preference.  I have not put the case on the BOM, but it fits the Hammond 1551H.  If you are using the Hammond case, you need to watch your output cap height - approx 10mm is max.
> ...


 

 Hey guys - my understanding is that not many of you have responded to cobaltmute.  Please remember the PCB's are FREE.  Cobaltmute is only asking for postage.


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## nullstring

Quote: 





tomb said:


> Hey guys - my understanding is that not many of you have responded to cobaltmute.  Please remember the PCB's are FREE.  Cobaltmute is only asking for postage.


 


 I am also interesting in building cobaltmute's r1 power supply.
  If it works out for him, I wouldn't mind receiving both in the same parcel.
   
  I haven't looked at the BOM yet, but I assume it's pretty cheap, and I need more SMD practice anyway.
  I'll take a look at it when i get home from work.
  EDIT: I also wouldn't mind testing out SPDIF.


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## c12mech

I think I got all the stuff from Mouser for about $20.  Not including the dac chip, I got it from the TI sample program.


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## BK_856er

Quote: 





tomb said:


> Hey guys - my understanding is that not many of you have responded to cobaltmute.  Please remember the PCB's are FREE.  Cobaltmute is only asking for postage.


 

 PM sent to cobaltmute earlier today.  Would like to build one asap.
   
  BK


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## BK_856er

OK, I'm in.  Anyone have a mouser alternate for the (optional) X1 spacer/insulator pn 520-700-9001?
   
  BK


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## tomb

Quote: 





bk_856er said:


> OK, I'm in.  Anyone have a mouser alternate for the (optional) X1 spacer/insulator pn 520-700-9001?
> 
> BK


 

 I've never used that spacer for any DAC I've built that used the crystal.  That goes all the way back to AlienDACs.  It never caused a problem.


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## cobaltmute

I can include a spacer with the board.


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## BK_856er

Quote: 





cobaltmute said:


> I can include a spacer with the board.


 

 Thanks!  Anything that adds even a tiny amount of robustness/ruggedness will be potentially beneficial for this particular build.
   
  BK


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## cobaltmute

I still have three boards available...


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## forsakenrider

I'll take one, maybe I will have better luck with it then the PUP1. also I have a friend who I would like to give one (He's using the headphone out from his computer, silly guy)
   
  If thats cool, you should have my Paypal still


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## Armaegis

I don't think I've seen this anywhere, but what's the difference between the PCM2704 and 2705?


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## Avro_Arrow

PCM2705 has an SPI interface.
  
  Quote: 





armaegis said:


> I don't think I've seen this anywhere, but what's the difference between the PCM2704 and 2705?


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## cipe

I'm starting to get into DIY stuff.  I've just finished building the crack otl and I have the parts for a gamma 1 on order.  If you have any extra boards I'd be more than happy to build this.


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## cobaltmute

@cipe:  PM me your address (formatted so I can print and stick it on an envelope) and your Paypal address and I'll get it out to you in a day or two.
   
  @forsakenrider:  I'll get yours out in a day or so as well.


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## c12mech

I got my board yesterday and noticed that the pad for the 2704 seems a bit narrow.  Will the production boards have a wider area here.  It makes it really hard to get that chip in place.  I'm going to try again tonight Just had to leave it alone last night before I made a big mess of it.


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## cobaltmute

Yes the production boards will have longer pads for the PCM2704.


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## tomb

I had a bit of trouble with the shorter pads, too.  The good thing is that it's a lot harder to make bridges.  However, I had the trouble of not enough contact - not too much (bridges).  The "drag and wipe" method as described on the BantamDAC website helps a lot.  I repeated that technique a couple of times until the chip was recognized by the PC.  It was fairly straightforward, actually.  It made all the difference and was easy to do - no solder, just some extra motions with the soldering iron.
   
http://www.diyforums.org/BantamDAC/BantamDACsolder.php


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## Spacehead

I need some boards


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## c12mech

I go the chip soldered tonight.  It went on the first time tonight with no bridges that I can see.  I used a trick I saw on curiousinventor.com.  They have some really good tutorials for smd stuff over there.


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## Avro_Arrow

My parts should be in tomorrow.
  I'm planning on putting mine together Friday.
   
  I did some hi-res scans of the boards if anyone needs them.
   
  I'll take some pictures of the build in progress too.


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## c12mech

My parts showed up today. I'm sorting through them now. Hopefully I'll have it going tomorrow night.  I've been distracted tonight with the DT48 cans that got here today also.


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## Avro_Arrow

I think I got my PCM soldered on first try.
  I miss my stereo microscope for this work...


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## cobaltmute

I'd say that looks pretty clean.  The only thing I can see is the solder is extending past the pads on the bottom left pins.  Probably not an issue.
   
  Did you pin-by-pin it or drag and wipe?


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## Avro_Arrow

Thanks!
   
  I did it pin by pin.
  The little tails show I didn't use enough flux.
  It probably would not have been a problem if the
  pads were longer. I'll probably re-flow it to get rid
  of the tails.
   
  With the combination of flux, solder and iron I used
  to have at work, I could drag a little ball of solder along
  the ends of the pins and it would do a perfect job without
  leaving any bridges (and took about thirty second for a 
  chip this size). I can't seem to get this method to work
  at home, I get too many bridges. I just use the pin by pin
  method at home.


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## cobaltmute

The pads on the production board will be longer.
   
  I usually do the drag and wipe and then maybe a bit of braid to clean up the extra solder as my solder is a bit high gauge.


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## Avro_Arrow

Thats a good job too. Our soldering instructor would have been proud of you.


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## cobaltmute

Now I just need to get all my R and C to look that good.  I always end up with too much solder, even if I'm trying to be stingy.


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## c12mech

I am listening to this dac right now.  I finished it just  a few minutes ago and am so far impressed.  Right now I've just got it set up with the hp out.  I don't have an SPDIF dac finished yet to try that part out.  I've got it going into my ssmh and DT880's right now and it sounds good.  The detail in orchestral pieces is much clearer and it sounds like Alyson Krauss is standing right right in front of me.  Here is a pic of it as is sits right now.  I'll get it in the box this weekend.


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## c12mech

This worked fine with my pc but when I plug it into my Mac nothing happens.  Is it not compatible with OSX?  I hope it is since that is what I use as my source most all the time.
   
  As mentioned the detail is really good.  I can actually hear the keys clicking clearly on an oboe in one of the high res samples from HD Tracks.  I could hear it before but it was always just kind of a blur, now it is very pronounced.
   
  Just a little feed back on what I'm hearing so far.  I will spend a lot more time with it this weekend while I'm putting together the Pup1.


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## cobaltmute

Should work.  From the datasheet:
   
   
  Quote: 





> Operating System
>  Microsoft Windows 98SE/Windows Me Japanese/English edition (For Windows 98SE and Windows Me,
> the HID function is not fully functional with the default class driver.)
>  Microsoft Windows 2000 Professional Japanese/English edition
> ...


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## c12mech

I'll keep trying it with the Mac and see what happens.


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## Avro_Arrow

Well, it lives!
   
  If I was thinking before I started, I would have cut down the
  leads on the DAC a bit. The sort pads turned out to be more
  of a pain than I thought they would. At first pins 15 through 21 refused
  to make contact with the pads but in the end I won. Sound is good
  with the 220uF Silmic II on the output. I'll test out the SP/DIF when
  I find either an RCA connector or cable I can chop up in my junk box.
   
  Thanks Cobaltmute!


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## cobaltmute

The PCB program I use seems to have all its pads setup more for reflow than hand soldering.  Makes it a pain, as I usually have to go change all the footprints.
   
  Glad you like it.


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## BK_856er

Build seemed to go OK, plugged it into an XP box and got all the right device messages including "ready to use" but then 30sec later a "USB device not recognized" message.  Tried other ports, etc. and that error message pops up instantly.
   
  Anything to try short of re-flowing things?
   
  BK


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## c12mech

Forget what I said about it not working on the Mac.  It works fine from there also.  It just does not do the whole installing drivers kind of thing that the pc does. 
   
  BK,
   
  Try reflowing the chip.  Mine did not work the first time.  I got the unknown usb device message.  I hit all the pins again and it has worked great ever since. 
   
  Compared to my other projects this weekend this was a breeze.  If I'm going to do much more smd stuff or IEM repairs I may have to invest in a stereo microscope.


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## BK_856er

OK, just reflowed the chip after flooding with liquid flux.  Quite a challenge with the taller components installed.  That fixed it!
   
  It's now properly recognized in XP and also on a Mac.
   
  Now to wire up the output and give a listen...
   
  BK


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## c12mech

Glad you got it working.  I agree it is tough to reflow with the tall stuff there.  I hit the corner of one of the output caps with my iron.  Still works fine though.


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## BK_856er

It's up and running, but no sound from the R channel.  Will need to track down the problem.
   
  BK


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## Avro_Arrow

Check for 1.something volts DC at the DAC side of the output cap.
  If there is no DC voltage there then keep re-flowing until there is...
  
  Quote: 





bk_856er said:


> It's up and running, but no sound from the R channel.  Will need to track down the problem.
> 
> BK


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## BK_856er

Quote: 





avro_arrow said:


> Check for 1.something volts DC at the DAC side of the output cap.
> If there is no DC voltage there then keep re-flowing until there is...


 

 Good call.  Getting 1.6V on the working L channel, and 0V on the non-working R channel.  I'll reflow the chip pins associated with the R channel and try again.  Those short board pads are a real bear to deal with and inspect.
  
  BK
   
   
  ** edit **
   
  Mission accomplished!  Two channels are way better than one.  Reflowed several R channel DAC pins and fixed a solder bridge I introduced with the reflow (doh!).  Now getting 1.69V at both caps and it makes really beautiful music.  Very impressive, actually.  I think this one is ready to go to Afghanistan.


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## Avro_Arrow

You should check the filter caps too to make sure they have continuity back
  to the chip. I had problems with several pins that looked good but had
  no continuity. Check the voltage at the pin and make sure the same voltage
  shows up at the filter caps.
   
  Quote: 





bk_856er said:


> Good call.  Getting 1.6V on the working L channel, and 0V on the non-working R channel.  I'll reflow the chip pins associated with the R channel and try again.  Those short board pads are a real bear to deal with and inspect.
> 
> BK
> 
> ...


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## forsakenrider

It seems digikey is out of L1, is there an alternate? I found this, although 600mA and 420 mOhm:  http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=445-3654-1-ND


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## cobaltmute

That should work.


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## forsakenrider

Thanks for the quick reply! order placed so I should be able to build this little guy tomorrow night!


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## Avro_Arrow

This is the L1 I used from Digi-Key.
   
  Quote: 





forsakenrider said:


> Thanks for the quick reply! order placed so I should be able to build this little guy tomorrow night!


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## forsakenrider

well mines up and running! playing tunes right now! I used Wima 1uf on the output since I dont plan on using it to drive head phones. This is such a simple little guy it only took me about 1.5 hours to assemble! case work not done yet as I will save that for another day, I just needed to get it done so I could unplug my pup1 and add the 2.5v reg i got with my digikey order! now both are running full tilt, I think I will have an Erik DAC showdown this weekend!


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## cobaltmute

Well part of the point of the SkeletonDAC was to have it easy to build. 
   
  Enjoy.


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## Teal

I'm currently using a Bantam DAC with a Mini^3 amp on my laptop driving Grado SR80 and I've been meaning to finish building a Carry Amp/GrubDAC combo. It certainly would be easier to just build a SkeletonDAC and would less to carry around. How does the sound quality of it compare to other DAC/Amp combos. Can it drive low impedence headphones as well as a standalone amp?


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## c12mech

Here it is all cased up.  It was a very tight fit and I had to change the output caps to the 100uf's.  I think it actually sounds better now.  I've been using it for for a little over a week now and I'm right now listening to Leonard Cohen Live In London which I've listened to constantly since I bought it and I now here little details in the songs that never noticed before.  I have stopped what I was doing a couple of times just to listen because I heard something new.  The more I listen the more I like it.


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## cobaltmute

@c12mech:  Glad you are enjoying it
   
  @everyone else who has built a board:  Anyone try the SPDIF out yet?


----------



## Avro_Arrow

Yes, it does. Sounds the same as if I set my digital output to 16 bit.
  Doesn't sound quite as good as the same thing at 24 bits.
  Good design, works well, sounds good. I know the next version
  will be easier to solder.
   
  Thanks again!
   

  
  Quote: 





cobaltmute said:


> @c12mech:  Glad you are enjoying it
> 
> @everyone else who has built a board:  Anyone try the SPDIF out yet?


----------



## torndorff

Is it still possible to get one of these boards?  I am looking for exactly this device!


----------



## cobaltmute

More boards will be available in the very near future.


----------



## tomb

Quote: 





cobaltmute said:


> More boards will be available in the very near future.


 

 Cobaltmute is being nice and is trying to keep the pressure off of me. 
	

	
	
		
		

		
			





  I have the production SkeletonDAC boards in hand and am working on the website and kits as we speak.  Maybe another week ... two at the absolute worst.


----------



## Undisclosed

any word on this? id love to build one!


----------



## tomb

Still working on the kits and the website, but it will be soon.  They'll go for $20, complete with mini-USB (case and output connectors extra).


----------



## ElectroGeek007

I would like to try my hand at building this as well, especially for that price.


----------



## kchapdaily

very interested in building this. 
	

	
	
		
		

		
		
	


	



   
  would it work to build this with regular through hole components if i use the same values?


----------



## tomb

Quote: 





kchapdaily said:


> very interested in building this.
> 
> 
> 
> ...


 


 No, the DAC chip will not respond well to the inductance/capacitance/resistance from the leads of through-hole components.  What may seem to be trivial values from the leads at through-hole size can end up being monumental to the tiny currents and voltages present in the DAC chip.


----------



## kchapdaily

Quote: 





tomb said:


> No, the DAC chip will not respond well to the inductance/capacitance/resistance from the leads of through-hole components.  What may seem to be trivial values from the leads at through-hole size can end up being monumental to the tiny currents and voltages present in the DAC chip.


 

 thats what i was afraid of. kind of figured. any news on the kits or schematics/bom? id love to build one


----------



## tomb

Quote: 





kchapdaily said:


> thats what i was afraid of. kind of figured. any news on the kits or schematics/bom? id love to build one


 

 Well, I'm taking some time off around the 4th of July, so maybe it will give me a chance to get everything finalized.


----------



## kchapdaily

Quote: 





tomb said:


> Well, I'm taking some time off around the 4th of July, so maybe it will give me a chance to get everything finalized.


 


  sounds good ill keep my eyes peeled!


----------



## ryssen

Me to.


----------



## tomb

These are finally available.  Price is a couple of dollars more than mentioned previously - I didn't realize it would take over 1100 ziplocks to make up 100 kits.


----------



## kchapdaily

cant wait to build this!


----------



## cobaltmute

Quote: 





tomb said:


> These are finally available.  Price is a couple of dollars more than mentioned previously - I didn't realize it would take over 1100 ziplocks to make up 100 kits.


 

 And that is why I let other people do kits.


----------



## akgfan

Price is good, but I would need a DAC with headphone amp for AKG K242HD headphones. We are waiting for notebook for my mother to arrive, so I'm thinking about building DAC for her. But potentiometer is needed.
   
  What about sound quality in comparison with grubDAC? Or should I build grubDAC with a small opamp headphone amp instead?


----------



## tomb

Quote: 





akgfan said:


> Price is good, but I would need a DAC with headphone amp for AKG K242HD headphones. We are waiting for notebook for my mother to arrive, so I'm thinking about building DAC for her. But potentiometer is needed.
> 
> What about sound quality in comparison with grubDAC? Or should I build grubDAC with a small opamp headphone amp instead?


 

 Well, I hate to state the obvious, but if Beezar sells both products (and will continue to do so) and one costs almost 75% more than the other ... which one do you think is better in sound quality?
   
  I think we've said this before, but the SkeletonDAC is essentially a replacement for the BantamDAC: a small, inexpensive, and relatively easily-constructible (given the SMD required) Do-It-Yourself DAC.  We quit the BantamDAC specifically because *the PCM2702's price has risen to almost $20 (!) *- that's basically the price of the entire SkeletonDAC by itself!  (It would've been equal before the 1100 ziplocks. 
	

	
	
		
		

		
		
	


	




)  Now, the reason the PCM2702 has risen to that price is because TI declared it NRND (Not Recommended for New Designs) a couple of years ago.  That's simply another reason to go in a different direction than the BantamDAC: at some point, the PCM2702 will simply become unavailable.
   
  Unfortunately, TI's listed replacements for the PCM2702 - the PCM2704/5/6/7 are not drop-in replacements.  They are their own unique chips, all with different pinouts, and their own unique features.  Thus, cobaltmute and Mute Audio came up with a different design entirely, the SkeletonDAC.  It has some extra features beyond the original Bantam - the built-in headphone amplifier of the PCM2704/5 chip and the ability to use a SPDIF output.  However, the price-performance is still focused at the BantamDAC level.
   
  BTW, that built-in headphone amplifier in the PCM2704/5 chip is capable of about 12mW into a 32ohm load.  So, I'm not sure you would want to go plugging in full-size headphones on a regular basis and expecting top-of-the-line performance.  We are saying that it can yield good results with earbuds and smaller phones such as KSC-75's.  Even so, the output coupling caps should be selected with care to ensure a reasonable bass response.  We would also anticipate that someone would use the volume control of the PC's media player and would not recommend a potentiometer, per se.  For a full-featured, USB-powered, DAC-Amplifier combination, we would recommend something like Joneeboi's Carrie.
   
  EDIT: Of course, used as a DAC source with a separate amplifier, the SkeletonDAC is fully capable of supplying a flat frequency response from 20 - 20KHz.  With the 1uf coupling capacitors we supply with the kits, the frequency response would look something like this, depending on the impedance of a separate amplifier's pot:
   





 Use of optional audio-quality 47uf 6.3v electrolytics (BG's, ES's, Cerafines, Silmic II's, etc. ) would bring the 10K pot frequency response down to -0.5dB at 1Hz!


----------



## tomb

I'm still working on the HeadphoneDAC webpage, but the rest of the site should be good to go:
SkeletonDAC


----------



## tomb

Anyone built one yet, that's willing to share?  I've shipped quite a few over the last few weeks.


----------



## torndorff

Shoot, I sat down to assemble the DAC and may have swapped C11 and L1, but can't tell because they lack markings (that I can see, at least).  Any way I can tell them apart? 
	

	
	
		
		

		
		
	


	




  This is my first attempt at SMD and didn't really anticipate this problem.


----------



## akgfan

Capacitors on GrubDAC have olive color and coils grey/black.


----------



## torndorff

Thanks for the color reference akgfan!  I was worried I would make the problem worse by taking them out of the package, so I never noticed they were different colors.  Do the Skeleton DAC kit contents match the Mouser or Digikey BOM?  From Digikey, C11 should be about 40% taller than L1 -- can someone confirm that for me?  
  
  Quote: 





akgfan said:


> Capacitors on GrubDAC have olive color and coils grey/black.


----------



## Magedark

Oh my, why haven't I seen this project yet? This looks to be a future project, seeing how it's very cheap, and I could use a DAC around.


----------



## tomb

Quote: 





torndorff said:


> Thanks for the color reference akgfan!  I was worried I would make the problem worse by taking them out of the package, so I never noticed they were different colors.  Do the Skeleton DAC kit contents match the Mouser or Digikey BOM?  From Digikey, C11 should be about 40% taller than L1 -- can someone confirm that for me?


 

 Mouser.


----------



## Madebynick

Following my order of a SkeletonDAC, I have a couple of questions for you guys if one of you could help?
   
  I made my own IEM's with great success a few months ago and have been contemplating a DAC to complement them for a while. They are not difficult to drive and as such, I think that there is a great possibility that the SkeletonDAC should do a sterling job without the need for a separate amp. Unfortunately, the SkeletonDAC page is not working at the moment (perhaps this is not intentional?) and despite the reading I do, my electronic skills are not quite the same as my DIY superpowers. 
   

   
  My questions relate to the caps used in the SkeletonDAC design, particularly C6 (which I believe is the main power cap) and C13 and C14, which I understand are responsible for filtering sound before being output to my desired cable/connectors. 
   
_Before I continue, I should mention that physical size is not a problem for me as I will not be using the blue casing as suggested by others and could accomodate physically larger components. _
   
  With regards to my intended use of the DAC, should I consider replacing any of these 3 capacitors? Would I see any benefit to this at all? I currently run my IEMS from my computer directly. Sound isn't bad but there is a lot of hiss (sibilance??) and I sometimes resort to an equaliser to increase bass and warmth a little. Do any of you think this would still be necessary if I were to use and/or tweak the SkeletonDAC?
   
  I would be very grateful for any thoughts from those with experience and technical knowledge regarding the above. Perhaps one of you has wanted to achieve the same result as me and has had some success? I will be following this forum and wait with baited breath.
   
  Nick


----------



## tomb

Quote: 





madebynick said:


> Following my order of a SkeletonDAC, I have a couple of questions for you guys if one of you could help?
> 
> I made my own IEM's with great success a few months ago and have been contemplating a DAC to complement them for a while. They are not difficult to drive and as such, I think that there is a great possibility that the SkeletonDAC should do a sterling job without the need for a separate amp. Unfortunately, the SkeletonDAC page is not working at the moment (perhaps this is not intentional?) and despite the reading I do, my electronic skills are not quite the same as my DIY superpowers.
> 
> ...


 

 If you're referring to the "SkeletonHeadphoneDAC" page, yes - it's not available right now.  I've been working on some curves to give everyone an idea of the cutoff frequency with various headphones.  Unfortunately, IEMs usually have a very low impedance - I would strongly recommend something like a 75 ohm adapter if you're wanting to get a lot of bass out of them on a SkeletonDAC.  If we assume a total load of 91 ohms for the SkeletonDAC, then a value of 82uf for C13 and C14 will give you a -3dB at 20Hz, while response is down only 0.5dB at 60 Hz.  If you went all the way to 220uf (still relatively small electrolytics at 6.3V rating), you'd only have a -0.5dB loss at 20Hz.  You could try a Muse ES cap at 220uf 16V (higher voltage ratings are OK - 6.3V may not be available in some audiophile capacitors) and you could keep the Wima's that come in the kit as bypasses for a good all-around frequency response.  That's if, as you say, size is not an issue.  Another option is the Elna Silmic RFS II at 220uf 6.3V.  You probably won't need any film cap bypasses on those, because they're so good.  Handmade sells them for $0.60 each.*
   
  C6 is not a concern if you purchased the kit.  It's a 560uf organic-poly with super-low ESR and will do just fine.
   
   
  * Besides the spreadsheet graphs and curves, there's the whole issue of the different variants of output caps when feeding headphones of varying impedance.  Right now, I sell the 47uf Elna Silmics and have used them in my own SkeletonHeadphoneDAC build, but they're a compromise and assume that you will give up some bass (-3dB cutoff is about 55Hz with KSC-75's) in order to fit everything into the standard plastic case.  Anyway, that's why the web page has been delayed - lots to ponder and work out on this particular score.  However, please keep in mind that we're attempting all of this with a $20 DAC.


----------



## torndorff

Finish populating the PCB yesterday, and it's running great!  Sounds really nice running from PC to SkeletonDAC to Roger Gomez NP-100v12 12AU7 headphone amp.  Next up is to populate the R1 power supply prototype and run the power for the NP-100v12 through there to clean it up.  I'll post photos when it's complete and encased.  Worked under Ubuntu 11, OS X and Windows 7 on plugin.


----------



## tomb

Quote: 





torndorff said:


> Finish populating the PCB yesterday, and it's running great!  Sounds really nice running from PC to SkeletonDAC to Roger Gomez NP-100v12 12AU7 headphone amp.  Next up is to populate the R1 power supply prototype and run the power for the NP-100v12 through there to clean it up.  I'll post photos when it's complete and encased.  Worked under Ubuntu 11, OS X and Windows 7 on plugin.


 

 Great!  Can't wait for the photos!


----------



## tomb

*Madebynick*,
   
  Here's an example of what I was talking about up there with the cutoff frequency.  These are from a spreadsheet I developed where I modeled the actual RC high-pass circuit governing equation (not just the cutoff frequency) made by the SkeletonDAC if you attach it directly to headphones.  The first is using 47uf output capacitors, which will fit if in the standard Hammond case if mounted horizontally (bending the leads).  The second graph is using 220uf output capacitors, which I think is a good choice if the standard case is not used.  The "91 ohms" curve was sandwiched in there based on your question, assuming a 75 ohm adapter with 16 ohm IEMs.  There's a 16 ohm curve, too, but I think the capacitor size required gets a little bit unreasonable, whiich is why I was suggesting the 75 ohm adapter.
   
   












 EDIT: In case someone gets the wrong idea, hooking the SkeletonDAC directly up to an amplifier will give a virtually flat response all the way down below 20Hz.  The load represented by most of our headphone amps is somewhere in the range of 10,000 ohms to 100,000 ohms (typically the volume pot).  That makes a huge difference.  The graphs above are intended only in the special instance of connecting the SkeletonDAC directly to headphones.


----------



## torndorff

Almost forgot!  I noticed yesterday that the link of 'Step 2' of the construction pages has C5 listed twice.  The silkscreen on the PCB is correct, it's just the image 
	

	
	
		
		

		
		
	


	




  http://diyforums.org/SkeletonDAC/SkeletonDACstep2.php


----------



## tomb

Quote: 





torndorff said:


> Almost forgot!  I noticed yesterday that the link of 'Step 2' of the construction pages has C5 listed twice.  The silkscreen on the PCB is correct, it's just the image
> 
> 
> 
> ...


 

 Good catch!  That's supposed to be C2 down lower by the bottom.  I'll work on getting that fixed and report back when it is. Thanks!


----------



## Madebynick

*Tomb*
   
  Many thanks for the reply sir. You have set a few things straight in my head which is a big help. On your advice, I took delivery of some 75ohm resistors and will integrate them into the new cable I'm building. I do think I need to do some reading around this subject however as there are many terms thrown around which are still somewhat confusing to me! 
   
  Perhaps you could clear up a couple of other things for me too if thats ok? 
   
  You mention that the new TI chip you're using in the SkeletonDAC can now be used as a headphone amp and as I understand it, the headphones would simply be connected to the same output one would use when connecting the DAC to an amp (assuming standard setup with flat frequency response). With this in mind, what makes the new TI chip more suitable for driving headphones from this output compared to the original chip? If the answer is outside the scope of this forum, please tell me. I won't mind. 
   
  Secondly, and this is probably basic knowledge that I should have already accrued before I venture to these forums, is to do with those frequency response curves you posted. It's taken a lot of web reading to try to explain to myself exactly what these graphs mean and now I think I understand. Please feel free to send a rolling eye emoji and point me towards electrical engineering nursery school if I'm wrong. 
   
  If I'm correct, those graphs are showing (very simply put) the volume of the frequency range indicated by the graph. These curves are the direct result of altering the combination of resistor and capacitor values and suggest that with a larger capacitance value, the volume of lower frequencies will be higher and therefore sound output will appear more bassy? (Apologies if I sound like a bass head here. I don't mean to!) What makes me think that I may be wrong however is the shape of the frequency curve around 1300Hz. Is this curvature due to a filter built into the circuits design that ensure higher frequencies cannot be heard? I may guess that the effect of increasing the load applied to the DAC as a result of the 75ohm resistor is the controlling factor dictating where this curve plateaus? Am I correct in thinking that if this flat response was no seen at 1300Hz and above, that the higher frequencies would be clearly heard as a background hiss as I have experienced in the past? 
   
  I do hope these questions won't cement my reputation for being an audio electronic novice to the point where my head will be permanently hung in shame.
   
  Thanks in advance,
   
  Nick


----------



## tomb

Quote: 





madebynick said:


> *Tomb*
> 
> Many thanks for the reply sir. You have set a few things straight in my head which is a big help. On your advice, I took delivery of some 75ohm resistors and will integrate them into the new cable I'm building. I do think I need to do some reading around this subject however as there are many terms thrown around which are still somewhat confusing to me!
> 
> ...


 

 1. The PCM2704/5/6/7/ chips all have a built-in headphone amplifier.  The chip that it replaced was the PCM2702.  It had no amplifier and the output was taken directly from the Digital-Analog converted output.  In the case of the PCM2702, it was a voltage output, but very small with practically no current output.  IOW, you could actually damage the PCM2702 chip if you attempted to feed headphones directly from the DAC.  With the built-in headphone amplifier of the PCM2704/5 used in the SkeletonDAC, you can actually hook headphones up and generally speaking - not worry about blowing up the DAC chip.
   
  All that said, the quality in driving ability of the DAC's amp is not super.  So, the types of headphones, their efficiency, and the resulting high-pass filter circuit resulting from your parts choice will dictate how well it drives a pair of headphones.
   
  2. You have this backwards, actually.  The "0 dB" line on those graphs (the X-axis) is the point of _normal_ volume, all things being equal. So, what the curves are telling you is how much the bass is _decreased_ by the resulting RC-circuit high-pass filter.  The RC-circuit high-pass filter is a natural phenomenon of the electronic circuits and loads in play.  You have no choice in the matter on whether it will occur - only that you have a choice in selecting parts that will minimize the bass loss.  With low-impedance phones, a very large value capacitorr (470uf to 1000uf) will result in almost no bass reduction at all.  However, the caps will be very, very big (in most instances).  So, what I'm trying to portray is that you can come up with a compromise between bass lost and inconvenient capacitor size.  That's all.
   
  I'm not sure what you mean by the 1300 Hz.  I suppose if you looked with a magnifying glass at the first graph up there that's based on 47uf output capacitors, one might say that the bass attenuation begins at about 1300 Hz with a 16 ohm impedence headphone load - and bass attenuation begins at about 1100Hz with 32 ohm headphones, 1000 Hz with 60 ohm headphones and so on and so forth.  But - that's all you can say about it.  The whole point is that is the theoretical result with 47uf output coupling caps.  As you can see in the second graph, the frequencies at which bass begins to be attenuated is quite a bit lower with 220uf output coupling caps.
   
  The 75 ohm resistors were suggested to raise the "R" value in the fundamental relationship of the RC circuit.  R is multiplied times C (and also modified by other factors).  So, if we increase R or increase C - the result is that bass attenuation begins at a much lower frequency.  The difference is that big resistors are much cheaper and easier to obtain and install in the circuit than big capacitors.  At some point, higher value resistors will have a noticeable impact on the audio sound themselves, but if given a choice between increasing impedance at 16 ohms or selecting some outrageously large and expensive capacitors, the 75 ohm resistor is a no-brainer.  This has a long history of precedence, because that's exactly what a 75 ohm adapter is intended to do with IEMs and small PDP's.  Small PDP's cannot afford to include physically large output capacitors, so the resistor adapter was developed, instead (R times C exists with PDP's and their headphone connections).  Output coupling capacitors may not exist with all PDP's, but usually a line-out adapter bypasses everything that was intended to cut down on the DC offset.  So, to protect your headphones, DIY line-out adapters usually involve output coupling capacitors of some type.  This would also occur in the SkeletonDAC (and the Bantam/Alien before it): if output coupling capacitors were not used, your headphones would see 2.5V on output at zero volume.  That's why the capacitors are used, but the physics of the resulting electrical circuit has some drawbacks - mainly that an RC circuit is formed with the "R" of the headphones.  This means that if you are not careful in parts selection with the capacitors (or some resistor adapter), then you will lose bass in the audible frequency band (what the curves in the graphs above show).
   
  EDIT/PS - After posting the first response above, I realized that one neat solution is to simply use the 560uf organic polymer caps - used in the GrubDAC and SkeletonDAC as power caps - as the output coupling caps on the Skeleton DAC [for direct-connected headphones].  I haven't tested how they sound, but others seem to think that OsCons (another organic polymer type of capacitor) sounded pretty good in the signal path. The nice thing is that those 560 uf's are very little bigger than the pads already on the PCB - and height is not an issue, even with the little Hammond plastic case (1551HTBU).


----------



## tomb

torndorff (above) pointed out an error in the construction graphics on the SkeletonDAC website here:
http://www.diyforums.org/SkeletonDAC/SkeletonDACstep2.php
   
  The PCB was showing two "C5's". That's now been corrected - one was C2.  The Layout and Board pages were always correct.  For some reason, I just pulled an older background on those construction graphics pages.
   
  Anyone built one yet that can share some pics?


----------



## tomb

OK - here's another correction.  I just got a PM awhile ago asking about parts for the USB-to-SPDIF convertor option.  In searching to remember the answer, I noticed that the part was not documented on the website in the BOM.  I've since made that correction so that the part number at Mouser and DigiKey for the transformer (Pulse PE-65612) is shown on the BOM.
   
  Please note that this transformer is not included in the Beezar kit, but it is the only part that isn't.  So, if you desire to use the USB-to-SPDIF option, all you need to do is add the transformer.


----------



## Madebynick

Thanks for all your clarification with this Tomb. Following your recommendations I've finished my Headphone DAC with 1200uf caps (as I happened to have some that I could salvage from an old mixer) and housed everything in a little extruded aluminium case from Hammond. I soldered my USB cable to the board as the pins on the connector was sadly damaged in the post. The DAC powers my homemade cans and IEMS well with as good an example of bass response that I've heard from these headphones. 
   
  I'll be sure to upload some pics when the lighting is better.
   
  Postage to the UK was fast and the surface mount soldering is surprisingly straight forward (although a flux pen is essential). I would certainly recommend the kit to anyone thinking of building a DAC and I'd be very interested to hear it next to some of these expensive branded units available. 
   
  Thanks again to everyone involved in the development of this kit. I don't think I'll buy another piece of ready-assembled audio equipment again!


----------



## tomb

Quote: 





madebynick said:


> Thanks for all your clarification with this Tomb. Following your recommendations I've finished my Headphone DAC with 1200uf caps (as I happened to have some that I could salvage from an old mixer) and housed everything in a little extruded aluminium case from Hammond. I soldered my USB cable to the board as the pins on the connector was sadly damaged in the post. The DAC powers my homemade cans and IEMS well with as good an example of bass response that I've heard from these headphones.
> 
> I'll be sure to upload some pics when the lighting is better.
> 
> ...


 

 Glad to hear it!!


----------



## Galesden

Im having trouble with the PCM2704 chip. I decided to go with the flood and suck method as the drag and wipe method just wasnt working for me. However, my suction device isnt working that well. I have some solder wick, but it is radioshack stuff and it doesnt wick very well. What should I do? Should I get some higher quality wick?


----------



## tomb

Quote: 





galesden said:


> Im having trouble with the PCM2704 chip. I decided to go with the flood and suck method as the drag and wipe method just wasnt working for me. However, my suction device isnt working that well. I have some solder wick, but it is radioshack stuff and it doesnt wick very well. What should I do? Should I get some higher quality wick?


 

 Do you have some separate flux?  If the wick is not working properly, more flux usually does the trick.  You have to be absolutely certain that the wick is free of solder, too.  Cut it down to where it's only clean and un-contaminated copper wick, then start with that.  Dip the wick into some flux and apply heat with the soldering iron by pressing the wick between the solder joint and the soldering iron tip.
   
  Flux should be the non-corrosive type - rosin is best. Or, if you bought a flux pen, use that.  Wicking is somewhat of an art.  With the right heat and flux, it will literally suck up the solder.  A cold iron, no flux, or a wick whose tip is already saturated with solder will all inhibit this process.  You should be continually cutting off the wick with each new application so that only clean wick remains.


----------



## nickosha

Hello,
   
  This project looks very interesting to me. I'm just getting done with finals so I'll be going home for a few weeks, but I hope to order a kit and build it when I start next semester. I'm keeping an eye on how that headphone feature turns out. Anyways, I noticed that on the project website, the text in the browser tab (and probably the window, depending on what browser you use) on the page for the "Tweaks" section says "GrubDAC Tweaks" instead of SkeletonDAC tweaks. It's just a little, insignificant thing that I noticed. I think that that is the only page affected. 
   
  Thank you, tomb, for all of your work on all of this. I've been pretty quiet on this forum, but I think all of these projects are really cool.


----------



## tomb

Quote: 





nickosha said:


> Hello,
> 
> This project looks very interesting to me. I'm just getting done with finals so I'll be going home for a few weeks, but I hope to order a kit and build it when I start next semester. I'm keeping an eye on how that headphone feature turns out. Anyways, I noticed that on the project website, the text in the browser tab (and probably the window, depending on what browser you use) on the page for the "Tweaks" section says "GrubDAC Tweaks" instead of SkeletonDAC tweaks. It's just a little, insignificant thing that I noticed. I think that that is the only page affected.
> 
> Thank you, tomb, for all of your work on all of this. I've been pretty quiet on this forum, but I think all of these projects are really cool.


 

 Thanks for the kind comment, but remember that cobaltmute is the genius designer.
	

	
	
		
		

		
		
	


	




  I wouldn't have anything to do if it wasn't for the wonderfully gifted designers around here that let me support and market their designs.
   
  Anyway, I'll get that corrected on the web site when I get a chance.  I'm off for the holidays, so maybe I can get some of this done.


----------



## Galesden

My computer does not want to recognize the DAC. Im trying to use it as a USB to SPDIF converter. I plugged it in and the led lights up, but there are not messages showing up recognizing the dac. Also, I have connected the SkeletonDAC to an external dac, which is connected to an amp. If I play music off my computer, sound should come out of my headphones, yes? All that happens right now is sound comes from my laptop speakers. Should I reflow the pins on the dac chip? I soldered one side pretty cleanly, but the other side is slightly off and Im concerned that it is the problem. I hope I am just using it incorrectly and I dont have to reflow the pins.


----------



## tomb

Quote: 





galesden said:


> My computer does not want to recognize the DAC. Im trying to use it as a USB to SPDIF converter. I plugged it in and the led lights up, but there are not messages showing up recognizing the dac. Also, I have connected the SkeletonDAC to an external dac, which is connected to an amp. If I play music off my computer, sound should come out of my headphones, yes? All that happens right now is sound comes from my laptop speakers. Should I reflow the pins on the dac chip? I soldered one side pretty cleanly, but the other side is slightly off and Im concerned that it is the problem. I hope I am just using it incorrectly and I dont have to reflow the pins.


 

 Unfortunately, your mis-alignment is a lot worse than you led me to believe in your PM's.  I see several bridges.  Some of the pins are actually in the absolute worst-case position: they are straddling the space between pads and making connections to both.  This is obvious simply by taking a look at your photo.
   
  Ordinarily, I'd suggest an X-acto knife to get in there and cut the bridges.  However, with the pins straddling the pads in most cases, you really need to move the chip.  Get some de-soldering wick and try to remove every bit of solder on that side.  Then bend the chip so that the pins are aligned with the pads.  It's OK - the pins on the other side will be fine, but you need to be sure that all solder is removed from this side before you do that.  If we had caught it when you had just soldered the anchor pins on either side, it would be an easy matter.  I do it myself quite oten.  All you need do is melt the solder on one side and the pins on the other side will bend enough to let you align it.
   
  In this case, be sure you can lift the PCM chip up off the PCB on this side (very carefully).  If you can do that, then you know you've removed enough solder.  Then, making certain the chip is flat agains the PCB, rotate it so that it's aligned.  The pins on the other side, by virtue of being soldered, will bend to meet the new alignment.  Then solder the pins on this side again.
   
  You can't do anything with the SkeletonDAC - either audio output or SPDIF convertor - until you get the PC to recognize the DAC.  The LED is not consequential - it only indicates power from the USB buss.


----------



## Galesden

Yeah, thats what I was worried about. Oh, well, I guess I will try to fix it.


----------



## akgfan

You could make a special tip for soldering gun, if you have one. I did one in the past and desoldering chips was a piece of cake.


----------



## Netdewt

I bought a couple of PCBs today. I'm doing a Cmoy first, then I'll get to this. I hope it's good (and I don't screw it up)!


----------



## tomb

Quote: 





netdewt said:


> I bought a couple of PCBs today. I'm doing a Cmoy first, then I'll get to this. I hope it's good (and I don't screw it up)!


 

 Take it slow.  Make sure you're properly organized before you start with all the right tools, etc.  That way, all you have to focus on is the handling and soldering of the very small parts.  The SkeletonDAC website can clue you in to all the tools and setup you need.


----------



## cobaltmute

tomb is correct - building a DAC is about taking your time and not getting frustrated.


----------



## BK_856er

Netdewt, I don't know what your experience level is, but I successfully built a gamma-2, prototype skeleton-dac and grub-dac in that order with zero background in surface mount soldering.  In each case I had to reflow a connection or two and remove one or two solder bridges.  Use really good lighting, and some type of magnification can be a huge plus (for me it's essential).  I learned a lot from watching a few technique videos, for example from curious inventor.  Good luck and don't hit the redbull too hard before you start!
   
  BK


----------



## Netdewt

Thank you for the tips.
   
  I have a Weller solder station, flux pen, and desolder braid stuff. So far I have mostly made cables and done small projects like adding an AUX in to my car stereo.
   
  I already have a Shigaclone in my queue and I've been afraid to start because of my experience. I ordered a bunch of free sample ICs last year and I've been searching for projects to use them with (two were OPA2132PA and PCM2704). Every January I get a DIY itch, so I decided to so the Cmoy, then ran across the SkeletonDAC. After all that I'd like to re-cap my speakers and maybe my amp.


----------



## Netdewt

Any chance you guys can fix the Excel version of the BOM on the website?
   
  http://www.diyforums.org/SkeletonDAC/SkeletonDAC-bom.php


----------



## tomb

Quote: 





netdewt said:


> Any chance you guys can fix the Excel version of the BOM on the website?
> 
> http://www.diyforums.org/SkeletonDAC/SkeletonDAC-bom.php


 

 Fixed!  Sorry about that!


----------



## Netdewt

Thank you.
   
  I know LEDs do not matter, but I was thinking of using the same one I use in my Cmoy. The one you have suggested is 3.5V, and the one I want to use is 2V. Is this possible? Is there a resistor value that can be changed?


----------



## tomb

Quote: 





netdewt said:


> Thank you.
> 
> I know LEDs do not matter, but I was thinking of using the same one I use in my Cmoy. The one you have suggested is 3.5V, and the one I want to use is 2V. Is this possible? Is there a resistor value that can be changed?


 

 My guess is that it won't really be an issue - current is more important, but let's see if cobaltmute will reply with the authoritative answer.


----------



## cobaltmute

netdewt said:


> Thank you.
> 
> I know LEDs do not matter, but I was thinking of using the same one I use in my Cmoy. The one you have suggested is 3.5V, and the one I want to use is 2V. Is this possible? Is there a resistor value that can be changed?




Since you've built a cmoy, you likely know tangents tutorial and how to find the right resistor value  Rail voltage is 5v (straight from USB) You would adjust R6 to get your desired current. I prefer no more than 1mA in the LED, but that choice is yours. I dislike overly bright LEDs


----------



## lehtinel

Built one succesfully! Had a previous GrubDAC experience and the SkeletonDAC was very similar so had the routine down. Proper light, helping hands, keeping the parts in bags until they get out on the board and everything went nicely. First startup - no identification / light on LED, turns out one of the pads on L1 was not soldered so fixed that. Light on LED but malfunction recognition on PC - some reflowing on the U1 and one final test for the evening and everything worked great!
   
  Will attach it to a PCI bracket and stuff it in my HTPC, will hopefully beat the Realtek ACL850 sound quality wise.


----------



## lehtinel

...that said, I thought I had it working . It seems to go mute / non mute / mute / non mute / mute / non mute as I hook it up. The USB connection is ok, tried on two computers with a mini-b and direct contacts. Any ideas?


----------



## cobaltmute

What exactly do you mean by mute/non-mute?
   
  Does the DAC "detach" for the PC?
   
  Is it just the sound that stops playing?
   
  If it is just the sound, what player are you using?


----------



## lehtinel

It does not detach, it is recognized and stays in the system as it should, the sound is good also, only problem is it drags the audio slider down in Windows 7 and on my Macbook it mutes the audio or drags the audio. Very strage.
   
  The source does not matter, Spotify, Foobar, iTunes all do the same. 
   
  Could post pictures later on.


----------



## lehtinel

Hmm, hmm, I might have solved the problem, at work though, so can't try solving it now. I have the C14 cap shorted it seems, as i placed it level with C13 and soldered the holes two holes that are further apart together (which I shouldn't have done, of course).


----------



## lehtinel

...naah, fixing that didn't solve the problem, still goes to mute.


----------



## Avro_Arrow

Look for a short between pin 21 and 22 on the PCM2704


----------



## lehtinel

Seems I got it working now, soaking it in alcohol for cleaning seems to have done the trick. Checken pins 21 and 22 too, no short there, thanks for the tip Awro!
   
  Nice, now to install it in the machine it belogs...


----------



## KimLaroux

Quote: 





lehtinel said:


> Seems I got it working now, soaking it in alcohol for cleaning seems to have done the trick. Checken pins 21 and 22 too, no short there, thanks for the tip Awro!
> 
> *Nice, now to install it in the machine it belogs...*


 
   
  Please report if inserting it inside a computer case introduces EMI in the audio out. I would still enclose it in a metal shield, just to be safe.


----------



## particleman14

I guess I should post my finished skeletonDAC.  Finished it a couple months ago..everything works like a charm..headphone and spdif out.  
   
  here are some pics..http://imgur.com/a/58cEf#q6wbG


----------



## lehtinel

Quote: 





kimlaroux said:


> Please report if inserting it inside a computer case introduces EMI in the audio out. I would still enclose it in a metal shield, just to be safe.


 
   
  Yeah, will see how it sounds once inside the case. I've got small metal shields from a Cambridge Audio amp Im trying to salvage, might just cover the IC & chip part of the SkeletonDAC.


----------



## lehtinel

Okay, so far I've watched a couple of movies and listened to music through the DAC, clear and crisp sound, no EMI noise that I can pick up, works great. I would say that the output is better than on the built-in chip of my motherboard, but, thats how it should be 
   
  Thanks for the desing cobaltmute and for the delivery TomB!


----------



## cobaltmute

Great to hear that you have had success.


----------



## civilmonkey

+1 thanks for Cobalmute for the design and TomB for the kit.  I received the kit today and built the DAC during my kids nap (a long one thankfully).  For the PCM I used the wipe technique, created a few solder bridges and used wick to clean them up.  I used the Elna RFS Simmic II 47uf caps and it sounds really great to me. I love hearing new detail in song, in one song I can hear the guys chair creaking as he moves around near the end of the track.
   
  I used the space where the transformer would have gone to put in RCA connectors.


----------



## tomb

Quote: 





civilmonkey said:


> +1 thanks for Cobalmute for the design and TomB for the kit.  I received the kit today and built the DAC during my kids nap (a long one thankfully).  For the PCM I used the wipe technique, created a few solder bridges and used wick to clean them up.  I used the Elna RFS Simmic II 47uf caps and it sounds really great to me. I love hearing new detail in song, in one song I can hear the guys chair creaking as he moves around near the end of the track.
> 
> I used the space where the transformer would have gone to put in RCA connectors.


 
  Hey - looking good!  You did a really great job on those RCA jacks and the Elna's, too.  The bass is a bit clipped feeding headphones directly with those Elna's, but connecting to an amp gives you all the bass that exists anywhere, period.  (-3db at 0.34Hz with a 10K pot)  They sound about as good as a film cap, too.
   
  Another SkeletonDAC lives!


----------



## civilmonkey

Quote: 





tomb said:


> Hey - looking good!  You did a really great job on those RCA jacks and the Elna's, too.  The bass is a bit clipped feeding headphones directly with those Elna's, but connecting to an amp gives you all the bass that exists anywhere, period.  (-3db at 0.34Hz with a 10K pot)  They sound about as good as a film cap, too.
> 
> Another SkeletonDAC lives!


 
   
  Thanks, the DAC is feeding a CTH amp and lots of bass, punch and detail.  To be honest, I put the Elna's in based on faith, that one line on your site saying 'Some people have expressed a preference for these caps over any other on the AlienDAC'.  I might have to build another just to see how the Elna's compare to film caps.  
   
  I forgot to mention in my first post, and should mention for the benefit of others that to get the RCA jacks in I had to sand the PCB around 2 mm shorter lengthwise as the nut on the back of the jack stops the PCB from seating properly.  Also, the nuts stopped the lid from closing fully, so the ridge on the top lid was also sanded slightly where the RCA jacks are.  The jacks were tight fit, but if you're willing to sand a bit and take your time, not a problem.


----------



## scootsit

I've been really keen on using those small step-down transformers with IEMs lately in my portable rig, they sound great, and really ensure that the IEMs get enough current. I'm not sure the skeletonDAC swings enough voltage, but I think on the next skeleton I build, I may try throwing the step-down transformers on it. The transformers will block any DC, so I should be fine without any output caps, right?
   
  I will of course report back on the results.


----------



## Frodo

Hi, I just wondered, is the Skeleton DAC safe to use with the Millet Starving Student Hybrid? I read that the SSMH had destroyed a few Bantam / Alien DACs.
   
  http://www.head-fi.org/t/445851/starving-student-blows-up-dacs


----------



## Avro_Arrow

I can't see any reason why it would not be safe.
  The output is capacitor coupled so no DC can make
  it in or out.
   
  Cheers!
  Quote: 





frodo said:


> Hi, I just wondered, is the Skeleton DAC safe to use with the Millet Starving Student Hybrid? I read that the SSMH had destroyed a few Bantam / Alien DACs.
> 
> http://www.head-fi.org/t/445851/starving-student-blows-up-dacs


----------



## tomb

Quote: 





frodo said:


> Hi, I just wondered, is the Skeleton DAC safe to use with the Millet Starving Student Hybrid? I read that the SSMH had destroyed a few Bantam / Alien DACs.
> 
> http://www.head-fi.org/t/445851/starving-student-blows-up-dacs


 
  Use with caution.  All of those other DACs had output capacitors, too.  The common symptom was a DAC that had the chip directly output (through capacitors) to the SSMH.  IOW, there is no buffer, opamp, or other active device between the DAC chip's output pins and connection to the SSMH.  Since the SkeletonDAC falls into that category, caution is advised.  It's possible that since the PCM2704/5 has a built-in headphone amplifier, that it offers more protection than the PCM2702, which formed the basis for the Alien and Bantam.  We don't know that for sure, though.
   
  You should also be aware that the issue was really traced to the CISCO switching power supply used in the original Starving Student.  The CISCO power supply seems to have a floating ground and a different potential voltage can develop around the RCA jacks.  If you happen to plug in one of the DAC's mentioned and touch the outside of the jacks with the center pin of the RCA interconnects, a discharge will occur that will fry the DAC chip - output capacitors or not.
   
  If you don't use that power supply, then you shouldn't have a problem.


----------



## scootsit

Would it be okay to use transformers instead of capacitors on the SkeletonDAC?


----------



## tomb

Quote: 





scootsit said:


> Would it be okay to use transformers instead of capacitors on the SkeletonDAC?


 
  Maybe - but just keep in mind that this a phenomena limited to that CISCO switching power supply on the SSMH.  It got more than one of AMB's Gamma 1 DACs, too.


----------



## scootsit

Quote: 





tomb said:


> Quote:
> 
> 
> 
> ...


 

 Oh, I was referring more generally. I want to use some step down transformers, I've been using them (from Radio Shack) instead of an amp with IEMs, to boost the current, and I've had good results. I want to drive some IEMs directly off of the SkeletonDAC, could I replace the caps with transformers, since both should block DC, right?


----------



## cobaltmute

scootsit said:


> Would it be okay to use transformers instead of capacitors on the SkeletonDAC?




I can't see it would be an issue. The only thing I can think of would be size of the transformers that you could find.


----------



## scootsit

Quote: 





cobaltmute said:


> Quote:
> 
> 
> 
> ...


 
  http://www.head-fi.org/t/553094/continued-sidetrack-discussion-from-tiniest-portable-amp-i-can-build-nikongod-microtransformer-based-impedance-step-down-box


----------



## scootsit

Quote: 





scootsit said:


> Quote:
> 
> 
> 
> ...


 

 Given the 1k+ impedance of the input side of transformer (the output side is ~8z), there should be no roll-off on the bottom end, right?


----------



## Frodo

Quote: 





tomb said:


> Use with caution.  All of those other DACs had output capacitors, too.  The common symptom was a DAC that had the chip directly output (through capacitors) to the SSMH.  IOW, there is no buffer, opamp, or other active device between the DAC chip's output pins and connection to the SSMH.  Since the SkeletonDAC falls into that category, caution is advised.  It's possible that since the PCM2704/5 has a built-in headphone amplifier, that it offers more protection than the PCM2702, which formed the basis for the Alien and Bantam.  We don't know that for sure, though.
> 
> You should also be aware that the issue was really traced to the CISCO switching power supply used in the original Starving Student.  The CISCO power supply seems to have a floating ground and a different potential voltage can develop around the RCA jacks.  If you happen to plug in one of the DAC's mentioned and touch the outside of the jacks with the center pin of the RCA interconnects, a discharge will occur that will fry the DAC chip - output capacitors or not.
> 
> If you don't use that power supply, then you shouldn't have a problem.


 

 Thanks, I will be using the FSP025-DYAA6 from *http://tinyurl.com/b55uhgp* when I build the SSMS it was just $8.50 on eBay, if there are any problems I will post.


----------



## Frodo

Hi, finished my DAC last night, the 2704 went down well, I flooded the pins and the wicked off the excess solder. I tried the wipe method first but I just couldn't get it to work.
  In fact the most difficult (and time consuming) thing was getting the surface mount components out of those tiny packets, is there an easy method? I couldn't find information on the internet. 
	

	
	
		
		

		
			




   
  I was a bit shocked at first when I plugged in my HD 595s and then ATH-M50s directly and noticed the lack of bass. However after I actually read though the website and forums and realised I would need to change the caps it sounds great. Currently using some 220uf 100v KMG caps that I had laying around, but I will order some better quality ones later today, I have quite a large case so I welcome any suggestions.
   
  I have one question, I want to use The Skeleton as a desktop DAC with my Starving Student amp (I'm going to leave it permanently connected, to hopefully reduce the risk of blowing the chip), I want to use an on/off switch. I use one with the Alien DAC I previously built and it is very useful with the Mac, flick the switch and you go from headphones to built in computer speakers immediately and back again without having to change any settings.
   
  Is it possible to add an on/off switch and if so, where can I connect it?
   
  Many thanks, Andy


----------



## tomb

I think an on-off switch will involve cutting a trace on the PCB - probably the one between the USB pin that leads to the +5V pad just ahead of the mini-USB jack.  Then you'd wire an SPST switch to the mini-USB jack pad and the +5V pad on both sides of where you'd cut the trace.
   
  Just a guess - maybe cobaltmute has another suggestion.
   
  As for removing SMD parts from the packaging: tweezers.  Use the same ones you use for placing the parts.  The pointed ends are very handy for pulling back the film covering of the SMD parts packages.  Then you just flip the parts out on your building board.


----------



## cobaltmute

If you insert the switch in the 5V line that would be the best bet. 

Take the 5V lime from the cable, run it to the switch and then to the board.


----------



## tomb

Duh!  Make the split in the wire, not the trace.


----------



## Frodo

Hi, Thanks for such fast responses, probably not the most elegant solution, but in the end I just removed the Mini USB connector bent pin 5 out horizontally (so it was sticking out the back of the connector) and wired the switch between that and the 5v pad, then soldered the connector back onto the board.  A blob of hot glue should stop the wires pulling on the pin until I get it all safely back in the case.


----------



## Frodo

I just wondered if anyone is using bypass caps, and is there any particular value in it?
   
  It's going to be a while before I get new output caps and wondered if using the Wima caps that came with the Skeleton DAC kit  in parallel with the Nicon 220uf caps I am using at the moment would be a worthwhile mod. I've read that bypass caps can improve high frequency response.


----------



## cobaltmute

The only recommendation that I can suggest is to try and decide what you like.


----------



## scootsit

Quote: 





tomb said:


> Quote:
> 
> 
> 
> ...


 

 Wouldn't that floating ground be a possible issue for nearly any source?


----------



## tomb

Quote: 





frodo said:


> I just wondered if anyone is using bypass caps, and is there any particular value in it?
> 
> It's going to be a while before I get new output caps and wondered if using the Wima caps that came with the Skeleton DAC kit  in parallel with the Nicon 220uf caps I am using at the moment would be a worthwhile mod. I've read that bypass caps can improve high frequency response.


 
  Actually, I tried a bypass combination once based on Dsavitsk's recommendations in his excellent "Notes on Output Coupling Capacitors."  It was back a few years ago and the DAC was the AlienDAC, but the same principles apply.  If memory serves, I used a couple of Muse ES's at 4.7uf, and bypassed them with a couple of 0.22uf Sonicap Gen II's.  It sounded very good ... until I blew it up with a Starving Student amp.
	

	
	
		
		

		
			





  Sorry - I guess that's too close to home in this situation.
   
  IOW, yes - I think the right combination of bypassing might yield excellent results if you have the room.  However, what I used was definitely one of the specific combinations that Dsavitsk mentioned in his articles.  The ES's are known for excellent bass, while the Sonicap Gen II's were known for sparkle.  Unfortunately, I think Soniccraft quit making the Gen II's.  Anyway, it's worth experimenting and Wima's are usually a great bypass caps in most situations  Roederstein box film caps are also a great bypassing cap.  Just remember that combinations may vary widely.  Bypassing is almost witchcraft and voodoo in terms of predicting the results of various combinations.


----------



## tomb

Quote: 





scootsit said:


> Wouldn't that floating ground be a possible issue for nearly any source?


 
  There seems to be some benefit of protection when a DAC has an output buffer or opamp.  IMHO.  I don't keep up with some of the latest FIO/UDAC/Nuforce stuff, but a few years ago, DIY was about the only place where you had output signals taken directly off of the DAC chip.  That's what the original AlienDAC did and the BantamDAC after it.  Some famous mods to CD and DVD players did the same thing.  Someone would identify where the DAC chip was on the DVD player and solder some boutique film caps between the DAC chip output pins and the RCA jacks of the DVD player.  Then they'd claim the modded sound was more "pure" and better.  (Maybe it was?)  The SkeletonDAC does the same thing, it's just that the new chips actually have a rudimentary headphone amplifier encapsulated in the PCM DAC chip (PCM2704, PCM2705).  So, that may provide some additional protection because we never noticed frying DACs when the DAC had some additional circuitry beyond the DAC's outputs.
   
  Frying the DACs in the scenarios that were mentioned is a very illustrative comparison betwen "theoretical infallibility" and the real world.  There's probably not a person on Head-Fi who would admit that a capacitor would pass DC current, but nevertheless, it does - under the right conditions.  After all, a lethal transient could simply be "interpreted" as the first part of a low frequency sine wave.  I don't know - maybe that explanation is invalid, but frying the DAC through a DC discharge at the outputs is a fact and was repeatable (for many people unfortunately).  I actually heard the static discharge through my headphones on a couple of occasions when a DAC was fried.


----------



## DingoSmuggler

Quote: 





tomb said:


> There's probably not a person on Head-Fi who would admit that a capacitor would pass DC current


 
  That's a funny way to say it. As you know, a coupling capacitor passes "dc current" while its charging to the potential difference of the 2 points being coupled.


----------



## tomb

Quote: 





dingosmuggler said:


> That's a funny way to say it. As you know, a coupling capacitor passes "dc current" while its charging to the potential difference of the 2 points being coupled.


 
  Yes of course, but I'm talking about well-charged caps - _I think_.   One might say the film caps could've discharged in the length of time it took to connect/disconnect to a Starving Student, but this happened with electrolytics, too.  You would hope they'd hold a charge a little longer.  I suppose as another possible explanation, the zapping could've happened while the caps were in a discharge state.  It was so intermittent/unpredictable, however, it was hard to test - expensive, too.


----------



## KimLaroux

Quote: 





tomb said:


> [...] There's probably not a person on Head-Fi who would admit that a capacitor would pass DC current, but nevertheless, it does - under the right conditions.  After all, *a lethal transient could simply be "interpreted" as the first part of a low frequency sine wave.*  I don't know - maybe that explanation is invalid, but frying the DAC through a DC discharge at the outputs is a fact and was repeatable (for many people unfortunately).  I actually heard the static discharge through my headphones on a couple of occasions when a DAC was fried.


 
   
  DC voltage is simply dV/dt = 0. Any transient would, by definition, not have dV/dt = 0. So a transient is not DC.
   
  The decoupling capacitors block DC, but the moment dV/dt != 0, it will allow current trough. We use this to filter audio signal out of DC bias, since audio signal is everything but dV/dt = 0. The thing is, capacitors work both ways. If there's a change in voltage at the output of the circuit, the capacitor will allow this difference in voltage to flow back trough the circuit. Since the other side of the cap is the DAC chip, this transient discharges trough the chip. If it's not built to handle such current, it fries.
   
  In this case, the static discharge when connecting the DAC to the amplifier causes the voltage at the output of the capacitor to rise (dV/dt > 0). This causes the capacitor to conduct in the opposite direction it's intended to, which applies a voltage to the output of the DAC chip. The reason it fries the chip is probably as simple as it not being tough enough to handle voltages being applied to it's output.
   
  The damage occurs on the rising edge of the transient, as this is when the capacitor conducts.


----------



## Frodo

Quote: 





tomb said:


> Actually, I tried a bypass combination once based on Dsavitsk's recommendations in his excellent "Notes on Output Coupling Capacitors."  It was back a few years ago and the DAC was the AlienDAC, but the same principles apply.  If memory serves, I used a couple of Muse ES's at 4.7uf, and bypassed them with a couple of 0.22uf Sonicap Gen II's.  It sounded very good ... until I blew it up with a Starving Student amp.
> 
> 
> 
> ...


 
   
  Thanks for the info, as you recommended I'm now using the Wilma's as bypasses and I'm pleased to report that it does seem to be a nice improvement , highs are much brighter and clearer (it also makes me happy that the Wilmas' are being put to good use). I have to make a trip into Tokyo after Christmas so will look out some of the caps you've mentioned. The shipping from Mouser is very expensive here.
   
  Really sorry to hear about your Alien, I hope it was repairable. I've got my Skeleton plugged into my Starving student and it sounds excellent with thankfully no problems yet, I'm really really hoping it stays that way. I'm probably going to leave it more or less permanently connected.
   
  I've also built an Alien, I'm going to pair that up with an Objective 2 eventually, so the link to Dasvitsk's article is very useful.


----------



## tomb

Quote: 





kimlaroux said:


> DC voltage is simply dV/dt = 0. Any transient would, by definition, not have dV/dt = 0. So a transient is not DC.
> 
> The decoupling capacitors block DC, but the moment dV/dt != 0, it will allow current trough. We use this to filter audio signal out of DC bias, since audio signal is everything but dV/dt = 0. The thing is, capacitors work both ways. If there's a change in voltage at the output of the circuit, the capacitor will allow this difference in voltage to flow back trough the circuit. Since the other side of the cap is the DAC chip, this transient discharges trough the chip. If it's not built to handle such current, it fries.
> 
> ...


 
  Well, yes - I think this is an accurate explanation of what happens.  I didn't want to digress into diffierential calculus in my post, but you've got it.  It doesn't happen on more sophisticated DACs because there's enough circuitry on the output to dissipate/absorb that transient before it hits the DAC chip's output pins.
   
  Regardless, some people tend to think that DC is DC, period, and just re-gurgitate the principle that capacitors block DC and that's supposed to cover it.  I just meant to convey the idea that not everyone's opinion of what constitutes DC is absolute.
   
  It's probably the difference between a calculus-based Physics curriculum and one that's not calculus-based.


----------



## vaugi

Hi Guys,
   
  Is the PCB available in the UK?  I've looked at Beezar and it looks like it's $10 shipping to the UK, a bit expensive for me.
   
  Due to that I thought I'd have a go at trying to proto-type it on a protoboard with through-hole components - but now I've read the whole thread I can see why I've not got it to to be detected and just spent two frustrating days trying it to no avail.  Wish I'd noticed that earlier!
   
  I'm assuming it's due to the through hole components being the problem as stated.  I've put the PCM2704 on a SSOP-DIP converter board - is it easy to fry the chip in mounting/reflowing? I was a bit worried about the heat from keep dragging and reflowing to get it right.  I'm pretty new to DIYing.
   
  Anyway, looks like I'll have to start properly and try to get the board somehow, if anyone knows a better route than paying $10 for postage please let me know!


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## tomb

Quote: 





vaugi said:


> Hi Guys,
> 
> Is the PCB available in the UK?  I've looked at Beezar and it looks like it's $10 shipping to the UK, a bit expensive for me.
> 
> ...


 
  That's been corrected.  True shipping to the UK is $7.30.  That's with 75 cents of Beezar handling.  I've been having some trouble with the shipping module at Beezar because of the new USPS pricing.  First Class International really took a hit - things almost doubled.  However, there were another couple of dollars that were not supposed to be in that calculation because the weights were off.
   
  Not counting my packaging, printing and gas costs to the Post Office (the 75 cents), the basic rate is still $6.55.  You are not going to find cheaper than that ... anywhere.
   
  I refunded $2 to another customer who ordered some light weight stuff a couple of days ago. 
	

	
	
		
		

		
		
	


	



   
  P.S. This goes without saying, but even at that cheapest shipping rate, the full SkeletonDAC kit is your best value.  The shipping is still $7.30.


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## vaugi

Many thanks for the reply TomB, and it's fine I fully understand the pricing, in fact I should have bought when I first looked a few months ago when it was about $5-6 delivered. Postal prices in the UK have shot up too over the past year.
   
  I'll have another play with the protoboard and if I can't find a problem I'll bite the bullet and purchase.


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## berserkir

Experimental SkeletonDAC with 3.5mm jack for driving medium size headphones is alive!
 Sounds quite good actually and doesn't lack bass. Drives Koss Porta pros and AKG 404s with ease.
 Will add potentiometer in the future..
  
 C6 : Nichicon UHN 1500uf
 C13 and 14: Elna Silmic II 220uf bypassed with *Vishay ERO MKT1817 1uF*


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## dhp

So I just built a SkeletonDAC and it's working to great success with 470uF Nichicon KWs as my output caps.  I was planning on using earphones directly out of this DAC, but damn, it is really really really loud.  I have to lower teh volume down to 1, and then halve the volume in foobar to get to listening volume.  How do I reduce the volume on this so I don't risk blowing out my ears?  Just put a resistor in the output?


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## tomb

dhp said:


> So I just built a SkeletonDAC and it's working to great success with 470uF Nichicon KWs as my output caps.  I was planning on using earphones directly out of this DAC, but damn, it is really really really loud.  I have to lower teh volume down to 1, and then halve the volume in foobar to get to listening volume.  How do I reduce the volume on this so I don't risk blowing out my ears?  Just put a resistor in the output?


 

 That's a good question and I'm not sure I know the best way to go about it.  Maybe someone else will see this and offer a suggestion.  I've used KSC75's with mine and the Foobar volume control was more than sufficient.  You must have some highly efficient earbuds/iems.


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## dhp

tomb said:


> That's a good question and I'm not sure I know the best way to go about it.  Maybe someone else will see this and offer a suggestion.  I've used KSC75's with mine and the Foobar volume control was more than sufficient.  You must have some highly efficient earbuds/iems.


 
  
 Yeah I was using some SE530s.  I tested this on some Grados and it was not as bad, although I can get my HD650s to listenable levels at 25%, which is still way too much volume considering I never want to drive 650s with this.


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## mcandmar

Hi all,
  
 Just finished building a SkeletonDAC, it should really be called a CuteDAC 
	

	
	
		
		

		
			




  
 I do have one issue, on my main machine (Windows 8.1 x64) and it detects a USB DAC but fails to install, tried removing it and re detecting but it doesn't seem to be able to install a driver for it.  Tried it on a Windows 7 machine and it worked perfectly first time.  Any ideas?
  
 Cheers,
  
 Mark


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## tomb

I'm sorry to say that I have no experience with Windows 8.  Maybe someone else can confirm/deny whether the TI PCM270X chips work with Windows 8.
  
 I know that there was a volume control issue with Windows 7 and TI's PCM270X chips, where the volume could not be controlled separately with software but only through the OS.*  So they came out with "C" versions of the PCM2704/5/6/7..  However, TI doesn't appear to have any additional info about operating system compatibility on these chips since 2007.
  
 * We always recommend full volume on the DACs in any PC OS or software - the bits get interpolated/re-sampled if the volume is lowered.  It's best to only use the amplifier volume control.  Granted, in the SkeletonDAC we talk about a scenario where it is used for direct listening, but those kind of quality considerations have to be balanced against the purpose of a $22 DAC.


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## mcandmar

Thanks Tomb, i was reading through the datasheets and they dont mention anything newer than Vista with exception of the C version being fully Windows 7 compatible.  The chip i got is the older version as its all Mouser stock but its not an issue as i dont intend to ever use the volume control anyway.  My work machine is also Windows 7 so it should work fine none the less, was just curious in case Windows 8 was a known issue and easily remedied.
  
 Cheers,
  
 Mark


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## BluePylons

Just finished my build two nights ago. The noise floor is dead quiet and it sounds great, a huge improvement over my laptop's terrible built-in sound card.

 Unfortuantely, this morning, it suddenly started attenuating mids/mid-highs, which is very obvious on the synth lines in the opening to Jaco Pastorius's "Continuum" (they sound distant and faint). Everything worked fine two days ago, so the parts are correctly soldered, and there are no solder bridges evident on the pins of the PCM2704. Could it be the flux? I used no-clean flux to solder the PCM2704.


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## Avro_Arrow

(scratching head) Pictures..?


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## tomb

avro_arrow said:


> (scratching head) Pictures..?


 

 Ditto.  I'm not aware of any situation that would result in the mids/mid-highs being attenuated.  The only section that could even remotely cause this is the analog out signal coming from the DAC chip to the output connections.  In that string, only the output capacitors are inbetween.  I guess you could check the solder connections on those caps.
  
 One other possibility is that you have loose output connections.  If you lose part of the wiring of one channel, it can perhaps have the effect of changing the effective frequency response.  Except that in those circumstances, the lack of in-phase channel combination usually means the bass has disappeared.
  
 Just an FYI, but there is absolutely nothing on the digital side that could cause this.


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## DingoSmuggler

bluepylons said:


> Just finished my build two nights ago. The noise floor is dead quiet and it sounds great, a huge improvement over my laptop's terrible built-in sound card.
> 
> Unfortuantely, this morning, it suddenly started attenuating mids/mid-highs, which is very obvious on the synth lines in the opening to Jaco Pastorius's "Continuum" (they sound distant and faint). Everything worked fine two days ago, so the parts are correctly soldered, and there are no solder bridges evident on the pins of the PCM2704. Could it be the flux? I used no-clean flux to solder the PCM2704.


 
 My best guess would be that you are summing L + R outputs together into mono somehow. Bass will always be in phase between L + R channels due to its long wavelength, but mids and highs will often be partly out of phase relative to the mic placement and/or any stereo effects used which results in attenuation when summed. So check your output connections, wiring, and any jacks and cables used.
  
 ps. nice choice in music


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## Armaegis

But he said it was the mid/highs which were being attenuated, which is opposite of what we'd expect if L+R were summed or if the ground line was broken.


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## BluePylons

Sorry for the late reply - I've been pretty busy the past week. Thanks for all the replies.

 Here's photos of the build as requested. (I apparently get "Your account does not have the required permissions to access this page" if I try to directly post photos...). I soldered 100 ohm resistors to the outputs as I have low impedence IEMs.
  
https://drive.google.com/file/d/0B7459wjgAgdlUTdkRlhEOUZxWGs/edit?usp=sharing
https://drive.google.com/file/d/0B7459wjgAgdlWjdHYzVoVkI4MnM/edit?usp=sharing
  

 Here's recordings of the intro to "Continuum" as played from my phone vs the skeletonDAC. Listening to it again, the attenuation is actually the highs, not the mids/mid-highs. Sorry about that.
  
 Phone:
https://drive.google.com/file/d/0B7459wjgAgdlV2FNa0ViSnFKUFE/edit?usp=sharing

 SkeletonDAC:
https://drive.google.com/file/d/0B7459wjgAgdlTE1qSFlhY1Jxb1E/edit?usp=sharing
  
 Looking at the files inside Audacity, it actually does look like the left and right are somehow getting summed as DingoSmuggler suggested, since the left and right look identical when played off the skeletonDAC. I probed the left and right outputs though (both before and after the output caps) and there's no short across them though.
  
 Phone:
https://drive.google.com/file/d/0B7459wjgAgdlMFNFYzJpbzh2SkE/edit?usp=sharing
  
 SkeletonDAC:
https://drive.google.com/file/d/0B7459wjgAgdlYVNJSmg1eXhCRk0/edit?usp=sharing


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## tomb

bluepylons said:


> Sorry for the late reply - I've been pretty busy the past week. Thanks for all the replies.
> 
> Here's photos of the build as requested. (I apparently get "Your account does not have the required permissions to access this page" if I try to directly post photos...). I soldered 100 ohm resistors to the outputs as I have low impedence IEMs.
> 
> ...


 

 No offense, but I'd cut off all that caulk-blob stuff, get yourself a decent 3.5mm jack, and some decent 22ga SPC-teflon hookup leads and start over with your output scheme.  Again no offense, but there's no way anyone can tell what's going on there - including you.


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## tomb

OK - I apologize if that was a bit rude, but sometimes you guys have us going when describing the symptoms ... but then we see the pics.  That probably doesn't make you feel any better, but we seriously want to find out how to fix your problem and help.


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## mcandmar

I've never seen or heard of anybody using OSCON caps in the signal path, i wouldn't be surprised if that's whats causing the high end roll off.  I would pick up a couple of the Wima or Vishay caps and see how you get on with those.
  
 Also this is the output jack that fits inside the Hammond enclosure http://ie.mouser.com/Search/ProductDetail.aspx?R=161-7400-EXvirtualkey11180000virtualkey161-7400-EX


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## tomb

mcandmar said:


> I've never seen or heard of anybody using OSCON caps in the signal path, i wouldn't be surprised if that's whats causing the high end roll off.  I would pick up a couple of the Wima or Vishay caps and see how you get on with those.
> 
> Also this is the output jack that fits inside the Hammond enclosure http://ie.mouser.com/Search/ProductDetail.aspx?R=161-7400-EXvirtualkey11180000virtualkey161-7400-EX


 

 Well ... just an FYI, but people have used OSCON's in the signal path going back to the BantamDAC.  It's not that common, but the people who've used them claim good results. So, I would not suspect them in this case.


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## tenacioustim

Hi,
 i've ordered the parts i need to build this. However, how will i adjust the volume to my headphones? I understand that there is a built in amp, but how will i adjust it?
 Will I be forced to control sound via in-software sound settings? Surely this will undermine the quality of the DAC, since changing volume via in-software will decrease the effective resolution of the sound?
  
 Thanks for any help and suggestions.
  
 Timothy.


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## Avro_Arrow

I think the assumption is that your amp will have the volume control...


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## tomb

Yes, but truthfully - at the quality level of the SkeletonDAC, I have not found the sound to suffer noticeably by just using the volume control in the media player.  I happen to use Foobar2000 for everything and perhaps that's better than most.  I don't know about other media players, but I can tell you that when using Foobar, it's not a problem using the Foobar volume with the SkeletonDAC.


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## tenacioustim

ok, but if i want to control directly on the amp, how would i do that?? is there a way to hook up a knob to the amp? Or would it be a hassle trying to control volume on amp??
  
 Thanks!


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## tomb

tenacioustim said:


> ok, but if i want to control directly on the amp, how would i do that?? is there a way to hook up a knob to the amp? Or would it be a hassle trying to control volume on amp??
> 
> Thanks!


 

 When Avro said "... your amp," he was not referring to the built-in amp of the DAC chip.  He meant that the SkeletonDAC is typically connected into a separate headphone amplifier.
  
 As I stated above, one of the options is that you can use it directly with headphones (preferrably with large caps on the output to prevent cutting out the bass).  So, you could rig up some sort of attenuator/volume pot on the outputs, but truthfully, it's a lot easier to use the media player volume and it's not going to make a noticeable difference with the SkeletonDAC
  
 Remember that you probably paid less than $25 for parts and PCB.  The SkeletonDAC gives great performance for its price, but don't expect an audiophile masterpiece.


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## Armaegis

The simplest way would be to buy an extension cable with volume knob built-in. Maybe $5-10 from radio shack.


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## tenacioustim

Ok, i'm almost finished building! I have some questions, they are VERY BASIC, but I  cant find the answers to these anywhere (it's always just assumed that you know):
  
 1) Where do i solder in a connector for 3.5mm jack output? the construction guide doesn't mention where.
 2) What exactly is the cable DAC version? Is that simply you plug skeleton into computer via USB, and the computer uses the Skeleton to convert the binary into voltages, then outputs the sound through the computers built in amp and out  computers headphone jack/speakers as normal? Essentially, ONLY using the DAC as a DAC...
  
 Where can i buy the headphone out component to solder on my board??
  
 Ideally, I want to use the DAC as only a dac, then i want to output the dac into an amplifier of my choice... ( i dont want to use the rubbish on board amplifier of the computer)
  
  
 Thanks for any help!!!
 I want to post picture but it says my account doesn't have permission :/


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## mcandmar

I replied to your PM but i will post the link here for future reference,
  

  
  
 For the 3.5mm socket i used one of the following, if i had to guess i would say the first one.

http://www.mouser.ie/Search/ProductDetail.aspx?R=161-7400-EXvirtualkey11180000virtualkey161-7400-EX
http://www.mouser.ie/Search/ProductDetail.aspx?R=4832.2300virtualkey69300000virtualkey693-4832.2300
  
 The image below shows the output terminals labelled (Right, GND. GND, Left).
  

  
  
 You can either connect those pads to separate RCA sockets, or as i have done to a 3.5mm stereo headphone socket.
  
 As for the "CableDAC" version, i think you are confusing the GrubDAC with the SkeletonDAC.  On the GrubDAC a USB cable is connected to the board, and then another cable for the audio output with RCA plugs on it.   Due to the extra space inside the SkeletonDAC you can squeeze a USB & SPDIF input socket, and the 3.5" mm headphone into the main enclosure as i have done instead of having cables hanging out of the enclosure.
  
 Hope that helps..


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## tomb

Good answer!  Thanks!
  
 I think it's my fault about the CableDAC option.  I had planned to do a web page on making a SkeletonCableDAC, but never got around to it.  Unfortunately, the selection for "SkeletonCableDAC" is still on the menu at the SkeletonDAC website.  I'll try to fix that soon.  If nothing else, I'll simply link to the Bantam and GrubDACs, since the methodology is just the same.


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## tenacioustim

Thanks for the brilliant response. Also what is the other jack coming out of your case in top left corner? And how did you cut hole for USB?A drill seems easy for 3.5mm jack.


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## tenacioustim

Here is mine so far. Still need to solder big Caps and LED..


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## mcandmar

Its the SPDIF input, i.e. digital coax connection.  The isolation transformer (big black square) is part of that circuit which is entirely optional.  I have only ever used the USB connection, but figured it was nice to have so added those parts to the build, in for a penny, in for a pound and all that.
  
 The USB cutout was a tricky job, from memory i started by drilling two 3mm holes, then used a small file to join them together and make the rectangle shape.  The plastic is soft and easy to cut, just takes the right tongue angle and some patience.


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## tomb

mcandmar said:


> Its the SPDIF input, i.e. digital coax connection.  The isolation transformer (big black square) is part of that circuit which is entirely optional.  I have only ever used the USB connection, but figured it was nice to have so added those parts to the build, in for a penny, in for a pound and all that.
> 
> The USB cutout was a tricky job, from memory i started by drilling two 3mm holes, then used a small file to join them together and make the rectangle shape.  The plastic is soft and easy to cut, just takes the right tongue angle and some patience.


 

 Agreed.  Drill a couple of holes, then get out a small flat file.  The plastic is very soft.  You really need to watch out for filing/cutting too much away.


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