# PCB for PCM2902 (digital out)



## dsavitsk

Does anyone here have a sense how difficult it would be to design a PCB to use a PCM2902 to go from USB to s/pdif? I have built one of the guzzler usb dac's (which I love, b/t/w) but I am really in need for a digital out. Anyone interested in this as a project? I'd prefer to power it from USB as this would make it an easy add on for existing DACs

 If a PCB could be designed and produced for not too much money, I'd be interested in being in charge of having them made and distributing them.

 -d


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## Nisbeth

Sounds interesting. Elektor published a design using the PCM2902 some time ago (issue 12/2002) and I've considered buying a PCB for it, but I'm sure the design can be improved. 
	

	
	
		
		

		
			






 /U.

 EDIT: I'm not sure how far along 00940 is with his project of combining the PCM2704 and the PCM1794 for a "reference" USB-DAC, but maybe that would be interesting as well?


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## 00940

I could design quickly a small pcb for the PCM2902. Should be rather easy. It would probably be nice to design it to fit easily into the smallest hammond. 

 Nisbeth : I sadly lost the *.brd files for the pcm2707/ad1896/pcm1794 dac, so I'm starting again from scratch. I'm trying to make it a bit easier to case. Anyway, I really think a small usb-spdif adapter could be useful.


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## Nisbeth

Quote:


  Originally Posted by *00940* 
_I could design quickly a small pcb for the PCM2902. Should be rather easy. It would probably be nice to design it to fit easily into the smallest hammond._

 

 That would be great. I would prefer something with both inputs and outputs 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *00940* 
_Nisbeth : I sadly lost the *.brd files for the pcm2707/ad1896/pcm1794 dac, so I'm starting again from scratch._

 

Sorry to hear that. If/when you make a new design, please keep us informed 
	

	
	
		
		

		
		
	


	





 /U.


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## dsavitsk

Quote:


  Originally Posted by *00940* 
_I could design quickly a small pcb for the PCM2902. Should be rather easy. It would probably be nice to design it to fit easily into the smallest hammond. 

 Nisbeth : I sadly lost the *.brd files for the pcm2707/ad1896/pcm1794 dac, so I'm starting again from scratch. I'm trying to make it a bit easier to case. Anyway, I really think a small usb-spdif adapter could be useful._

 

The smaller, the better. In addition to sizing for a hammond, perhape there are some "L" shaped screws we could find such that it could easily be panel mounted with just a hole cut out for the USB jack? I found panel mount USB type B adapters, but they are about $10 per, which seems too high.


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## 00940

Quote:


  Originally Posted by *Nisbeth* 
_That would be great. I would prefer something with both inputs and outputs 
	

	
	
		
		

		
		
	


	


_

 

inputs : usb/analog/spdif
 outputs : analog/spdif 

 I'm not sure the quality of the pcm2902 justifies a digital input and is A to D conversion really useful ? I would rather offer optical and coaxial outputs. 

 I had a first look at the datasheet. 

 As always, the problem is to feed it with a decent power supply. Seems like the device operates well from 4,35V to 5,25V (graphs are flat actually). It would be easy to just use a reg101-a configured for roughly 4.5V, with a lpf before it to cut the noise coming from the usb supply, just as on the USB dac rev. A. The 0.4V are allowing for some fluctuation of the usb supply from a computer to another.


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## dsavitsk

Quote:


  Originally Posted by *Nisbeth* 
_That would be great. I would prefer something with both inputs and outputs 
	

	
	
		
		

		
		
	


	


_

 

If it were to have both in and out, I'd prefer to be able to simply not populate the in portion. USB seems finicky enough that I am not sure I would trust the in enough to use it.

 -d


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## dsavitsk

Quote:


  Originally Posted by *00940* 
_I would rather offer optical and coaxial outputs._

 

The coax is particularly useful as it would be easy to build an internal switch into an existing dac. Also, Xitel has a cheap usb->optical (the DG2) that can be picked up on ebay for about $25 U.S. making this less of a needed item.


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## Nisbeth

Quote:


  Originally Posted by *dsavitsk* 
_If it were to have both in and out, I'd prefer to be able to simply not populate the in portion. USB seems finicky enough that I am not sure I would trust the in enough to use it.

 -d_

 

I just reread the datasheet and you're probably right - inputs aren't worth it. 


 /U.


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## 00940

Hum, what then ? A minijack for analog out and a rca for coax ? Or is optical really needed ? Advantage of coax is that it simplifies the layout


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## dsavitsk

Quote:


  Originally Posted by *00940* 
_Hum, what then ? A minijack for analog out and a rca for coax ? Or is optical really needed ? Advantage of coax is that it simplifies the layout 
	

	
	
		
		

		
		
	


	


_

 

That could work, though if it reduces the number of components, my need is just straight usb -> coax. I've got plenty of analog out converters, I just need to get them a signal


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## Garbz

I'm not sure how the USB dac work because I haven't been following it. But if it shares GND with the computer then I suggest offer optical as well. Call me paranoid but I'd rather put up with the slightly higher jitter of toslink adapters then contaminate the DAC on the otherside.


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## 00940

hum, a little problem, I'll update that later on.


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## Nisbeth

Looks good! 
	

	
	
		
		

		
		
	


	





 /U.


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## 00940

Ok. Here's a digital only version. It has a better (buffered) coaxial output, using a 74HC04. To be short, the TTL output goes into a first buffer, is tapped afterwards for the TOTX, goes into a pair of paralled buffer and then is finally sent to the RCA.

 Everything is powered from usb bus of course, the 74HC04 and the optical transmitter have their regulators. Following the evaluation board, I just put everything on a groundplane.







 estimated cost at roughly 40$, including enclosure but without pcb. If you put everything on it of course.


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## dsavitsk

Quote:


  Originally Posted by *Garbz* 
_I'm not sure how the USB dac work because I haven't been following it. But if it shares GND with the computer then I suggest offer optical as well. Call me paranoid but I'd rather put up with the slightly higher jitter of toslink adapters then contaminate the DAC on the otherside._

 

This gets mentioned as a theoretical problem with computer soundcards, but I've never actually seen it cause a problem. Perhaps others have?

 The point of this project for me is to make a little board that can be dropped into an existing DAC. That it might fit a hammond and might have other outputs is gravy. We'll see what 00940 comes up with 
	

	
	
		
		

		
			





 -d


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## dsavitsk

Quote:


  Originally Posted by *00940* 
_Ok. Here's a digital only version. It has a better (buffered) coaxial output, using a 74HC04. To be short, the TTL output goes into a first buffer, is tapped afterwards for the TOTX, goes into a pair of paralled buffer and then is finally sent to the RCA.

 Everything is powered from usb bus of course, the 74HC04 and the optical transmitter have their regulators. Following the evaluation board, I just put everything on a groundplane._

 

This looks great. If one wants to skip the optical, can it be left unpopulated, or does it need a jumper, or a resistor. or ...?


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## 00940

Quote:


  Originally Posted by *dsavitsk* 
_This looks great. If one wants to skip the optical, can it be left unpopulated, or does it need a jumper, or a resistor. or ...?_

 

You just let everything related to the optical section empty. You could also cut some traces. I'll post a pic.


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## dsavitsk

Just to be difficult (really I apologize. I don't mean to be indecisive), but the more i think about it, maybe there is a point to putting an analog out ... ?

 I hate to compete with the guzzler dac, but perhaps there is a reason to include the option. This would make it a more universal device, but it also might raise cost and difficulty. Any thoughts?


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## 00940

If I skip the switch, it could be possible without too much problems. I'm gonna see that later in the evening.


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## Nisbeth

Quote:


  Originally Posted by *dsavitsk* 
_Just to be difficult (really I apologize. I don't mean to be indecisive), but the more i think about it, maybe there is a point to putting an analog out ... ?

 I hate to compete with the guzzler dac, but perhaps there is a reason to include the option. This would make it a more universal device, but it also might raise cost and difficulty. Any thoughts?_

 

FWIW, I think there should be an analog out unless the point was to create the absolute smallest USB -> SPDIF-converter possible (in which case the pcb should be a lot smaller than it is now) 
	

	
	
		
		

		
		
	


	





 /U.


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## Magsy

Quote:


  Originally Posted by *Nisbeth* 
_FWIW, I think there should be an analog out unless the point was to create the absolute smallest USB -> SPDIF-converter possible (in which case the pcb should be a lot smaller than it is now) 
	

	
	
		
		

		
		
	


	





 /U._

 

Seconded! Maybe just a header for analog and not a pcb mount jack, but provision to use the analog out would be a nice feature


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## Nisbeth

Quote:


  Originally Posted by *Magsy* 
_Seconded! Maybe just a header for analog and not a pcb mount jack <snip>_

 

 That would be even better! However it would be nice if it could still fit in the small Hammond, which means that there must be some space on the PCB on the part where the jack is located
	

	
	
		
		

		
		
	


	





 /U.


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## 00940

Ok, ok guys. Here it is, with analog out but without mute switch. Price should stay the same considering the price of a switch. It has one more regulator since we have to regulate the analog stage of the pcm2902.


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## dsavitsk

Quote:


  Originally Posted by *Nisbeth* 
_FWIW, I think there should be an analog out unless the point was to create the absolute smallest USB -> SPDIF-converter possible (in which case the pcb should be a lot smaller than it is now) 
	

	
	
		
		

		
		
	


	


_

 

This was my original idea -- to make a board that was tiny and simply converted from usb to spdif. I thought we could go with all surface mount stuff and keep it down to like a square inch, or something. It seems to me, though, that if the other options (toslink and analog) can simply be left unpopulated, then including them all saves making two different boards. This comes at the expense of a few extra square inches, but that's probably okay.

 Perhaps the biggest problem is that the analog is really just a convenience out. The 2902 is said to be inferior in quality to the 2702 (used in the guzzler usb dac.)

 Really, I am pretty torn and could go either way. I think if I were intending to make an analog out usb dac, I'd go with the guzzler option. I I just wanted digital out I'd want this one. What to do if one needs both is a toss up.

 Anyone have any thoughts?

 -d

 -d


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## dsavitsk

The pcm2902 has spdif input. Is this worth using?

 Never mind as that would involve a power supply ...


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## guzzler

Thought I should chime in, as I had a little look at doing this a couple of months ago, then ran out of time... I really like the idea, personally. But, I'm going to make some picky comments on the layout 
	

	
	
		
		

		
		
	


	




 1. Tombstone resistors are horrible, to my mind. Burnt fingers, bad joints, and a fragile final board are all the come from them. I'd go 1206/0805 surface mount if space is paramount and use vias right at the pins where necessary.

 2. More ceramic decoupling right near the PCM2902, and especially next to the logic chip (I presume it is...). tkerby suggested this, and I have to agree with him; he knows what he is doing 
	

	
	
		
		

		
		
	


	




 3. Remove any angles <90*, they're called acid traps in PCB manufacturing terms, and do exactly what they say on the tin. Basically, you can over etch into the corner of the joint as the acid doesn't flow out when washed. Put a shot straight section in, or rework the traces.

 Could be made smaller, as is obvious, but since we're going for a certain case size, that's not an issue. So, that's about it from me 
	

	
	
		
		

		
		
	


	




 best regards

 g

 PS, I'll do the group buy again if people would like it, and 00940 doesn't want to do it. I'm certainly in for a few...


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## Voodoochile

Don't you want pins 5 and 2 on that jack? It looks to me like you have the switch contacts in the layout.

 Nice looking board and project, I'm interested.


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## 00940

board above updated to reflect comments. Here's a clearer view of the bottom plane to show the 1206 ceramic caps added. Resistors are also in 1206 size.


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## guzzler

Another wee thing, I would turn the thermals off in the ground plane. I didn't do it on the original as it would have cost more to have the board house make a complete new tooling set. Basically, every little cross at a pin acts as an inductor. It's a last 2% type thing, but might as well. Just use the change command in Eagle and you're set. From the picture, it looks like to Isolate could be turned up a little as well, as the ground plane looks a bit close to things; could just be an artefact of the image. If the DRC says it's okay, it probably is as it's fairly conservative. Looking very nice 
	

	
	
		
		

		
		
	


	




 g


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## 00940

I'm affraid that the ceramic caps on the ground plane would be a real pain to solder without thermals. 

 Isolate up , certainly.


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## dsavitsk

Looking great. Any chance you could post a list of the parts you are using?


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## halman

I would suggest these changes. 

 1, put the decoupling caps on the same side as the dac (define and reduce the loop areas where the current flows whenever possible) and use 0805 or maybe even 0603 caps.

 2, put som inductance on those long power traces

 3, Use a bnc for the digital out. Sadly there are no 75ohm rca around..so these should be avoided

 4, Galvanicaly isolate the electrical output by using a good spdif transfomer, for example use SC982-04 1:2 with 499/750R resistors for your divider

 5, Use a better line driver ic is instead of the 74*04

 6, There is enough room to use a DIL8 oscillator..but something in the back of my head says there where some troubles with starting the ic while using those.. But even so there is enought space to make room for both.


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## 00940

Quote:


  Originally Posted by *halman* 
_1, put the decoupling caps on the same side as the dac (define and reduce the loop areas where the current flows whenever possible) and use 0805 or maybe even 0603 caps._

 

0603 are excluded, to let the project rather easy (I know the pcm2902 is a pain, no need to push further) and 0805 are still a bit too small for most as we want a good solder joint there. I'll see for the caps location. I could simply replace those two caps by a big 1uf ceramic cap (X7R), as done on the pcm2902 demo board. Strangely, while they advocate 10uF decoupling caps for the analog section in the datasheet, the demo board uses 1uf.

  Quote:


 2, put som inductance on those long power traces 
 

there's a crl filter still to come on the top trace

  Quote:


 3, Use a bnc for the digital out. Sadly there are no 75ohm rca around..so these should be avoided 
 

possible, most people have rca cables and rca inputs though, I'd like more feedback on this.

  Quote:


 4, Galvanicaly isolate the electrical output by using a good spdif transfomer, for example use SC982-04 1:2 with 499/750R resistors for your divider 
 

I would need more feedback from others people interested on this. It raises the price by almost 40% and the scientific conversion xformer aren't easy to come by in Europe.

  Quote:


 5, Use a better line driver ic is instead of the 74*04 
 

I'm not sure we would get huge benefits out of that, I'm gonna see.

  Quote:


 6, There is enough room to use a DIL8 oscillator..but something in the back of my head says there where some troubles with starting the ic while using those.. But even so there is enought space to make room for both. 
 

Considering the way the spact operates, there's no real point in putting a better clocking scheme.


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## Nisbeth

Quote:


  Originally Posted by *00940* 
_possible, most people have rca cables and rca inputs though, I'd like more feedback on this._

 

I'm with 00940 here, BNC's are outside the scope of this project IMO 
	

	
	
		
		

		
		
	


	




 If you must have 75 Ohm RCA's, the Canare RJ-R jacks are listed as being 75 Ohms and made with Video/SPDIF transmission in mind. But they're a little big for a Hammond 1455C801


  Quote:


  Originally Posted by *00940* 
_I would need more feedback from others people interested on this. It raises the price by almost 40% and the scientific conversion xformer aren't easy to come by in Europe._

 

Elfa in Scandinavia sell SPDIF transformers from Pulse Engineering (Link to Datasheet The price is app. 5 EUR each in single quantities with a small quantity discount for more than 10 pcs. If these are suitable they would be a possibility, but I still think they are unnecessary for this project. Small size and easy asssembly are the key points of this project, it doesn't have to be the last word in audio quality. If 00940 ever gets his "reference USB-DAC" going again, then they are worth considering as far as I am concerned but for this application I simply don't see the need 
	

	
	
		
		

		
		
	


	




 (Incidentally, if anybody outside of Scandinavia needs one or more of these transformers for anything, let me know and I can order them 
	

	
	
		
		

		
		
	


	




 ) 

 EDIT: Forgot to mention, they only have the through-hole version 
	

	
	
		
		

		
		
	


	





 /U.


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## dsavitsk

Quote:


  Originally Posted by *Nisbeth* 
_I'm with 00940 here, BNC's are outside the scope of this project IMO_

 

I agree with this too.


 How about adding a couple of holes for mounting screws -- perhaps one by the usb jack, and one near the rca?


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## Glassman

I wonder if those Pulse Engineering xformers are suitable for higher than 7Mbps rates.. the price is not that bad.. or do anyone know about such xformers meant for higher rates?


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## Nisbeth

Quote:


  Originally Posted by *Glassman* 
_I wonder if those Pulse Engineering xformers are suitable for higher than 7Mbps rates.. the price is not that bad.. or do anyone know about such xformers meant for higher rates?_

 

Do you have something that uses 192 kHz sampling rate? 
	

	
	
		
		

		
		
	


	




 I would trust the manufacturer's specs in this case. 
	

	
	
		
		

		
		
	


	




 /U.


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## Glassman

oh yes I do.. I've done a bit of research and found:

 1) a newer Pulse Eng. xformers
 2) a few, rather old Schott xformers with exactly the same specs as those newer by Pulse
 3) Scientific Conversion xformers - these guys look like they really know what they are doing, have many models, you can see 'jitter' stated everywhere and officially support 32-192kHz rates with some models having bandwidth of more than 200MHz.. really cute!

 I've already contacted Spoerle which supply Pulse Eng., couldn't find any serious European distributor for Schott and yet have to contact Scientific Conversion, but I got a strong feeling those are the ones I'll pick..


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## 00940

What do you need those xformers for, exactly ?


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## Glassman

exactly for up to 192kHz S/PDIF transmission.. (CD/DVD-A/SACD)


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## dsavitsk

Not sure where this project is.

 I am still voting for simple rather than complex, particulary in light of the fact that guzzler has a bunch of his usb dac's in kitted form thus reducing the importance of analog out on this one as his should sound better. At any rate, I have picked up a couple (literally 2 extra) of pcm2902's from digikey that I can send out once boards are made.

 -d


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## guzzler

I suggest a deadline perhaps, for people who are interested and order from there. Obviously, the more people get, the cheaper it is per board but the total cost to the buyer goes up, so it would be helpful if people registered a definite interest as opposed to maybe. We could say the first weekend in March? That would give one month for final revisions and orders...

 Personally, simple is best for me on this project. The analog out isn't going to be too spectacular, and as there's not an amp built in, it's not even going to be useful for portable use. But, if we can fit it in without any problem, we might as well...

 g


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## 00940

I suppose we could put an AD8606 on the output of the analog out ?

 The use of reg101 could be too much of a cost, I'm looking for cheaper low drop regulators. Any idea ?

 I wondered if cut-out in the board wouldn't be a better alternative to pcb mounted output jacks ?


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## Magsy

I'll certainly be in for a board, assuming usual costs ($10-15?)

 I'm not really sure what I want, I would like spdif out for sure, if the analog requires a handful of components/space (which it looks like) then it might be nice to have the option there. I hadn't realised earlier the spec was worse on the 2902, looking at the datasheets shows it going to be average :/

 If the board is a perfect fit in the smallest hammond then the board mounted jacks, assuming availabilty to us all, are a great idea - it tends to look more professional


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## guzzler

The problem (again) is the 5V supply; not many headphones will be driven effectively at that level, although it could easily be omitted if you didn't want it. 5V could drive 32R phones I suppose, which would be all you needed for portable use. *edit:* 2 x BUF634 would fit there as well? Or an LM6172 would provide a bit of current at low voltages, but we'd have to be careful with the ground plane there and bypassing.

 Regards regulators, ST make two that are easily available in the UK. They are the LE33CZ, and LE50CZ. Annoyingly, the LE50 is available from DigiKey but not the LE33. They come in a TO-92 package. Dropout is .2V at 100mA; not fully read the datasheet though. They cost about 70p, cf REG102-AA £2.12. That said, I'd be happy with the REG102, as they're not too expensive.

 With the output jacks, I like the idea of space on the board, as wiring inside the smallest Hammond would be a bit of a pain. AFAIK, the pin out is fairly standard, and if it's not, they're not expensive to include with the boards, or people could wire directly from the boards....

 g


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## individual6891

Would analog out be that important with PCM2702 boards still available?


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## Nisbeth

My opinion on this is still that if the board is to remain the size of a Hammond 1455C, then the analog out should be included for flexibility (if you don't need it, leave the components out). If the idea is a simple USB-SPDIF converter without any extras, I would prefer to have the board made smaller (as small as possible actually).

 As for the jacks-issue, from my point of view the disadvantage of board-mounted jacks is that drilling has to be that much more accurate to yield a decent-looking result and board mounted jacks can also reduce the flexibility of the design because it will be more difficult to integrate it into a bigger amp if you have board-mounted jacks on both ends of the board. 


 /U.


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## 00940

Quote:


  Originally Posted by *guzzler* 
_The problem (again) is the 5V supply; not many headphones will be driven effectively at that level, although it could easily be omitted if you didn't want it. 5V could drive 32R phones I suppose, which would be all you needed for portable use. *edit:* 2 x BUF634 would fit there as well? Or an LM6172 would provide a bit of current at low voltages, but we'd have to be careful with the ground plane there and bypassing._

 

I considered the AD8606 because it delivers 80mA as output current, swings rail to rail and works out of 5V. http://www.analog.com/UploadedFiles/...8605_6_8_d.pdf

 I'm quoting Tangent on the AD8606:

  Quote:


 AD8606: Similar to an OPA132, but better in most respects. Not quite as good as an AD823, but quite respectable. Also, it claims 80 mA output current. Not bad at all! 
 


 Nisbeth : my feelings exactly on the jacks.


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## 00940

TI has a very interesting line of LDO regulators, less than half the price of reg102, the TPS793*** line. There is a wide range of fixed output, they give 200mA, drop only 112mV at full charge, have very low noise and cost 1.14$ at digikey, which stocks thousands of them. They come in sot23-5


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## guzzler

Yep, nice little regulator that one. Here's my version of the DAC using it, only coaxial output and not on the board as people have said. No optical option on it, but it wouldn't be hard to add, just need some rearrangement. I've included an inductor on the USB line as well... Board is 43mm x 29mm. All passive SMD passives are 0805, and the inductor is 1210. Just noticed I missed a via to ground from the 7404, oops. I still need to add the decoupling caps as well, but it's more to get the general idea.







 Total cost for this one would be around £12 including tax. The boards would cost 2.40 euros per board for 50

 g


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## 00940

Nice little pcb. 
	

	
	
		
		

		
		
	


	





 I'm still completly reworking mine, the grounding of my previous doesn't satisfy me at all. The datasheet of the TPS793 also has very specific guidelines for the layout and I'm trying to see how to deal with those.


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## Glassman

maybe it would be better to use RS-422/485 line driver instead of 7404 gate..

 this one looks good - 3.3V, 1.2mA, 20Mbps:
http://www.analog.com/en/prod/0,,767...485E%2C00.html

 you should reconsider the usage of transformer, it is really benefical and since you are going to have a group buy of some sort, you can get good prices on them..

 for example:
http://www.digikey.com/scripts/DkSea...115284&Site=US


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## Nisbeth

Very nice layout Gus, that'ss more what I had in mind (and probably also what the original poster had in mind 
	

	
	
		
		

		
		
	


	




)


 /U.


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## dsavitsk

Quote:


  Originally Posted by *Nisbeth* 
_... and probably also what the original poster had in mind_

 

Indeed.


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## guzzler

Bump with gratuitous Eagle 3D rendering 
	

	
	
		
		

		
		
	


	









 I've tidied up the regulator section and taken account of the grounding recommendations.... Silkscreen has component values on. The board is still the same size. If anyone's interested, I can get a batch run out; NO SUPPORT ON IT THOUGH!!

 g


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## Latexxx

I'm sorry but your drawing doesn't look professional enough because it states "uH" instead of "µH".


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## dsavitsk

Quote:


  Originally Posted by *guzzler* 
_If anyone's interested, I can get a batch run out_

 

I'd be in for a few.

  Quote:


  Originally Posted by *guzzler* 
_NO SUPPORT ON IT THOUGH!!_

 

Could you post a list of the parts? Is there anything particularly difficult to get?

 -d


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## guzzler

Quote:


  Originally Posted by *Latexxx* 
_I'm sorry but your drawing doesn't look professional enough because it states "uH" instead of "µH"._

 

 Duly noted and corrected 
	

	
	
		
		

		
		
	


	





 I editted the ground plane as well, so you can drill through the two bottom corners without drilling into copper...

 Parts:

 1 x PCM2902 (SSOP28)
 1 x 74HC04 (SO14)
 1 x TPS793 4.75V (SOT23-5) <-- pain to solder!

 1 x 560µF 6.3V Panasonic FC
 2 x 22µF 10V OS-CON SC (or equivalent similar, FCs are fine)
 4 x 1µF Wima MKS-02 (or similar, tantalum should be ok, 2.54mm pitch)
 6 x 100nF 0805 ceramic capacitors
 1 x 10nF 0805 ceramic capacitor
 2 x 33pF 0805 ceramic capacitors

 1 x 1M 0805 resistor
 1 x 1K5 0805 resistor
 1 x 360R 0805 resistor (higher quality, if possible)
 1 x 91R 0805 resistor (higher quality, if possible)
 2 x 22R 0805 resistor

 1 x 12MHz HC49 crystal oscillator
 1 x 10µH 1210 inductor
 1 x USB B-type connector
 1 x RCA socket
 1 x case
 1 x USB cable 

 Total cost, about £10 - £12 I'd say. Nothing hard to get; apart from Wima MKS-02 in the States, easy in Europe (for once 
	

	
	
		
		

		
		
	


	




 )

 g


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## Nisbeth

Well, I can't see the rendering (server seems to be down atm), but I'm still interested in 3-4 boards 
	

	
	
		
		

		
		
	


	





 /U.


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## ~n00beR

Count me in for at least 1 maybe 2 boards.

 Will there be a kit available or just the bare boards?, or mabye a group buy for all the parts.

 Sorry im just too lazy to do it for myself 
	

	
	
		
		

		
			





 EDIT: crappy spelling


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## walangalam

Are there mounting holes in this version? The 2702 pcb only had holes on one side, it was not really secure.

 3 holes would be preferable.

 I'm interested in 1. If theres a kit, thats better for me.


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## Kenny12

if theres a kit i'll be intrested in one or 2 
	

	
	
		
		

		
		
	


	




 btw usb dac rocks ^.^


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## guzzler

I could put holes on the board, but it will make it quite a bit bigger (probably about 1cm each way). If there is more space after adding the holes, I could include some space for bigger filter caps and possibly even the transformer if it's not too expensive. Kits; we'll see. It's a lot of work to sort out kits (not to mention money!), although it makes life a lot easier for people to buy kits. For the last batch of the PCM2702 boards, I think there were about 1500 components to get sorted, some of them on reels 
	

	
	
		
		

		
		
	


	




 I'll add the holes tomorrow, and see how big the board becomes

*Deadlines: 

 Revision requests: 12pm Tuesday 1st March (will decide on kits by then too)
 Order requests: 12pm Thursday 10th Match*

 g


----------



## ~n00beR

Quote:


  Originally Posted by *guzzler* 
_I could put holes on the board, but it will make it quite a bit bigger (probably about 1cm each way). If there is more space after adding the holes, I could include some space for bigger filter caps and possibly even the transformer if it's not too expensive. g_

 

You could add the extra holes to the board but leave the existing layout as it is, if you dont need the holes you could just cut the board down, or you could add the option of a peforated brake point on the edge to remove the holes, but I have no idea how this would effect the cost of the board manufacture.

 I would rather the board would fit in the hammond 1455C also, but I'm happy to go with the majority.

 Would it be worth while having a poll to finalise a desicion on having holes or not, t'would be quicker 
	

	
	
		
		

		
		
	


	




 Hope no one minds me adding my 2p' worth 
	

	
	
		
		

		
		
	


	




 Cheers

 Craig


----------



## guzzler

I don't like to leave blank areas on PCBs that are meant to be small, as all it does is up the cost (you pay for area, not for content), and I don't want to do that. Anyway, holes added; less drastic than I thought it would be, only about 2mm added to the length of the board. I didn't use the full size holes in Eagle, with about 1cm of keep out zones, which makes life easier. So; here it is:






 I'm going to move the via for the TTL -> coaxial converter so it's not directly connected to a decoupling capacitor, should reduce noise on the output a little, and maybe segregate input/output ground planes...

 g


----------



## paologatto

Hello everybody!
 I made a lot of experiments with PCM2902 and PCM2906 (quite the same chip). Maybe of your interest my final PCB layouts and prototypes.. I made 2 versions: one with the only analog IN and OUT, very little and suits perfectly in hammond enclosures. The other, bigger, includes digital (coax and optical) IN and OUT and also a mic preamplifier and a stereo VU-METER.

 Here are some pictures:




 Small version PCB





 Small version PCB populated with components





 Inside an Hammond enclosure





 Digital IN/OUT with PCM 2906 (part of the big project)





 Complete Big project (3 different PCBs)





 Big version inside a bigger Hammond enclosure


----------



## Nisbeth

Quote:


  Originally Posted by *guzzler* 
_Anyway, holes added; less drastic than I thought it would be, only about 2mm added to the length of the board._

 

Very nice! Makes the board quite a bit easier to mount 
	

	
	
		
		

		
		
	


	





 /U.


----------



## Nisbeth

Hi Paolo and welcome to head-fi 
	

	
	
		
		

		
		
	


	




 I've seen your products before and I thought they looked very nice - now I can see that they look just as good on the inside 
	

	
	
		
		

		
		
	


	





 /U.


----------



## walangalam

Great that it worked out. Thanks


----------



## paologatto

Quote:


  Originally Posted by *Nisbeth* 
_Hi Paolo and welcome to head-fi 
	

	
	
		
		

		
		
	


	




 I've seen your products before and I thought they looked very nice - now I can see that they look just as good on the inside 
	

	
	
		
		

		
		
	


	





 /U._

 

Hi Nisbeth
 Thanks!

 I found a really interesting forum!! 

 Ciao


----------



## dsavitsk

Quote:


  Originally Posted by *guzzler* 
_
*Deadlines: 

 Revision requests: 12pm Tuesday 1st March (will decide on kits by then too)
 Order requests: 12pm Thursday 10th Match*_

 

Just a bump so that anyone who needs to be aware of these deadlines is.

 As a side note, my vote would be for 3/4 kits -- that is, the PCB with some of the hard to find parts (the wimas, the usb jack, etc.)


----------



## Kenny12

hrm.. maybie someone should make a website of what the boards / plans are, hard to find in all these posts


----------



## dsavitsk

To convince myself it could be done, here is a preliminary list of digikey parts for the project (based on Guzzler's earlier list of parts). Please PM me with changes, errors, omissions, etc.

 # Descr .................................................. .......... Digikey Part #..........Price / min quantity

 1 x PCM2902 (SSOP28) ................................................. 296-12986-5-ND ........ $9.00 / 1
 1 x 74HC04 (SO14) .................................................. . 296-12883-1-ND ........ $0.44 / 1
 1 x TPS793 4.75V (SOT23-5) <-- pain to solder! ....................... 296-12160-1-ND ........ $1.14 / 1

 1 x 560µF 6.3V Panasonic FC .......................................... P12705-ND ............. $0.48 / 1 (backordered)
 2 x 22µF 10V OS-CON SC (or equivalent similar, FCs are fine) ......... P11213-ND ............. $0.32 / 1 (inexact match - 25V (6.3V available))
 4 x 1µF Wima MKS-02 (or similar, tantalum should be ok, 2.54mm pitch). 399-1337-ND ........... $0.41 / 1 (tantalum - 25V)
 6 x 100nF 0805 ceramic capacitors .................................... PCC1843CT-ND .......... $0.06 / 10 (panasonic ecg)
 1 x 10nF 0805 ceramic capacitor ...................................... PCC1991CT-ND .......... $0.09 / 10 (panasonic ecg)
 2 x 33pF 0805 ceramic capacitors ..................................... PCC330CGCT-ND ......... $0.05 / 10 (panasonic ecg)

 1 x 1M 0805 resistor ................................................. RR12P1.0MDCT-ND ....... $0.15 / 10 (sasumu 0.5%, .1W)*
 1 x 1K5 0805 resistor ................................................ RR12P1.5KDCT-ND ....... $0.15 / 10 (sasumu 0.5%, .1W)
 1 x 360R 0805 resistor (higher quality, if possible) ................. RR12P360DCT-ND ........ $0.15 / 10 (sasumu 0.5%, .1W)
 1 x 91R 0805 resistor (higher quality, if possible) .................. RR12Q91DCT-ND ......... $0.15 / 10 (sasumu 0.5%, .1W)
 2 x 22R 0805 resistor ................................................ RR12Q22DCT-ND ......... $0.15 / 10 (sasumu 0.5%, .1W)

 1 x 12MHz HC49 crystal oscillator .................................... CTX058-ND ............. $0.94 / 1
 1 x 10µH 1210 inductor ............................................... DN10103JCT-ND ......... $1.02 / 1
 1 x USB B-type connector ............................................. WM17109-ND ............ $1.94 / 1
 1 x RCA socket
 1 x case
 1 x USB cable 


_Edit: added usb connector._


----------



## Nisbeth

Guzzler, I can't really see this from the renderings, but can the mounting lugs of the USB-connector be soldered to the board? If not, you should try to make pads for this on the bottom as it greatly helps mechanical stability. 
	

	
	
		
		

		
		
	


	





 /U.


----------



## paologatto

For the USB B-type connector I can suggest the Digikey part WM17109-ND, that suits perfectly the corresponding "Berg" component in Eagle 
	

	
	
		
		

		
			





 And.. yes, I recommend too the 2 metal mounting lugs of the connector being soldered in the bottom part of the PCB (and connected to digital ground), otherwise the connector isn't stable at all.

 Bye
 Paolo


----------



## guzzler

dsavitsk; lists looks ok apart from the 560uF *10V*. It's, unfortunately, too big to fit in the allocated space. I'll see if I can squeeze a little more space into there, I think there's room to move the logic and TTL conversion network back a few mill, hopefully get it up to 10mm diameter.

 Nisbeth; not on yet; but I have a plan 
	

	
	
		
		

		
		
	


	




 What usually happens is the holes on the USB libary part cut out a big keep out zone, which prevents a pad being added. So; I'm going to edit the libary a little to add the pads in, should be straight forward, and yes, very useful!

 g


----------



## paologatto

I haven't seen the schematic but.. is the 560 uF capacitor directly connected to +V from USB port? If yes, this could be a too high value for some USB cards or hubs, that see it as a short circuit when the device is connected. 

 Usually there is resettable fuse inside USB card and hubs and you will have to reboot the pc or disconnect and reconnect the USB hub to restore, so not a big problem. The solution could be a soft-start circuit or the use of a smaller value capacitor.

 The capacitor value can be modified later anyway and an high value could work with a good USB card..


----------



## guzzler

No, it's through an inductor; so that should provide enough DC resistance to prevent a short circuit. A soft start circuit could be implemented; but it would be a bit of a cram. I'll run through some numbers tonight and see what I come with

 g


----------



## halman

here is yet another pcm2902 spdif out layout.


----------



## dsavitsk

Quote:


  Originally Posted by *guzzler* 
_dsavitsk; lists looks ok apart from the 560uF *10V*. It's, unfortunately, too big to fit in the allocated space. I'll see if I can squeeze a little more space into there, I think there's room to move the logic and TTL conversion network back a few mill, hopefully get it up to 10mm diameter._

 

Digikey lists P12705-ND which is Panasonic FC 560uF 6.3V and appears to be 8mil wide. Unfortunatly, they are out of them. Are there better options?

 -d


----------



## Glassman

wow whwre did you get the library for the trafo? is that scientific conversion one? I've recently created my own library part for it.. very nice layout btw.


----------



## guzzler

Here's my latest, got the mounting holes sorted out, added more decoupling. I've put it just in board style so it's easier for people to see. If you'd like a 3D rendering, let me know and I'll put it up. Unfortunately, the 10mm capacitor isn't going to squeeze in there, just not possible without either overlapping the screw or enlarging the board. It's 3.5mm pitch, which means you essentially HAVE to use the 560uF I've specced at 6.3V. The alternative is 470uF or 390uF, both of which fit. To be honest though, by the time I can get these printed, they should be back in stock I should think. Anyway, enjoy...






 Halman, nice alternative, especially PCM2902 on the solder side, but increases height and vulnerability IMO (I've got a couple of 0805 on solder side, optional though). Still not convinced by the transformer output. The way I see it, if people want to use a transformer, they can just run a couple of wires or to an optical chip or whatever... Think you forgot the the 1uF capacitors as well (4 in the top right), unless you're going surface mount ceramics instead of polyester..

 g


----------



## paologatto

Very nice layout guzzler. Bravo!

 The idea of an inductor before the big capacitor is good, I suppose it works well also for filtering the digital noise from the USB line.


----------



## dsavitsk

Quote:


  Originally Posted by *guzzler* 
_Unfortunately, the 10mm capacitor isn't going to squeeze in there, just not possible without either overlapping the screw or enlarging the board. It's 3.5mm pitch, which means you essentially HAVE to use the 560uF I've specced at 6.3V. The alternative is 470uF or 390uF, both of which fit. To be honest though, by the time I can get these printed, they should be back in stock I should think._

 

Expected ship date from DigiKey is March 31, so perhaps right on time.


----------



## Nisbeth

Gus, one more thing I think you should consider adding to the board, if you can fit it in, is an indicator LED for the USB power. There's no need to put the LED on board, because the LED will most likely be panelmounted anyway, but a single pad in the V+ line would actually be enough (a second pad in the ground plane would be good but not essential) 
	

	
	
		
		

		
		
	


	





 /U.


----------



## dsavitsk

Quote:


  Originally Posted by *guzzler* 
_means you essentially HAVE to use the 560uF I've specced at 6.3V. The alternative is 470uF or 390uF, both of which fit._

 

How about using a 820UF 6.3V? It appears that it will fit.

 -d


----------



## guzzler

Yep, 820uF would fit too, but as paulo said it might be a little hard on the USB supply.

 g

 PS, not had time to look at putting a pad on for an LED, should be okay though


----------



## 00940

A simple question. 
	

	
	
		
		

		
		
	


	




 - Why do you bother with an external regulator when it doesn't seem to affect purely digital performances ? TI only publishes a difference only for the ADC. (thd going from 0.1% to 0.01%). I understand from the function block that it could be useful for the DAC too but... you don't have pads to get the analog out, so I don't see the need to put it onboard.


----------



## guzzler

00940; you may have a point there. If you look at Figure 39 in the datasheet, they don't have a separate regulator. And from the block diagram it appears that the Vbus is regulated to 3.3V internally. I've not really had time to look in detail at the PCM2902 datasheet, just did a layout for it. Figure 39 certainly implies we could get rid of it. It would leave more space around the bottom left to reorientate the inductor and move the capacitor a little which would probably allow space to put an RCA connector directly onto the board. I'll look into it within the next week or so, got some project work to do but when that's out the way it should be okay!

 g (idiot)


----------



## 00940

I've sent my pcb to the hell of the forgotten designs btw. I am currently working on a modular dac. A section for coax, optical and usb input, a section for the dac itself and a section for the I/V. I hope to fit each section in 1/3 of an eurocard (50/103mm). I've only finished the usb input though


----------



## walangalam

00940,

 any chance of the usb->i2s ? This is what I really need...


----------



## 00940

Don't want to hijack this thread, i'll continue in another. To answer : no direct USB to I2S, but USB-SPDIF-isolation transformer-SPDIF receiver-I2S. I want a way to completly isolate the pc from the dac itself and it's not practical with I2S.


----------



## dsavitsk

Quote:


  Originally Posted by *00940* 
_I've sent my pcb to the hell of the forgotten designs btw._

 

Even so, I'd like to thank you for the effort you put into this project. If you hadn't stepped up and done the work you did I doubt it would have taken off like it has.

 -d


----------



## halman

>>Glasman

 I got it from JWB over at diy its in the cheap cs4122 thread should you want/need it.


 >> everyone else

 This baby is 35x43mm and after one final check when I have got some sleep I will send it of to production.


----------



## 00940

Halman : same point. I suppose those TO92 things are regulators ? Why a regulation of VCCCI without analog section's use ?


----------



## halman

It wouln't make my board any smaller if I removed it so it might aswell stay. You are right however.


----------



## KARMAZ

Hi
 too many crossed project here... what a shame!
 Very interesseted but very difficult for me (I'm not fluent in English) to follow this thread.
 Is it possible to make ONE modular project (unpopulated) or a full project and many simple ?
 An make a summary/status on the first page.
 Thnks for these great contributions, nice project at all.


----------



## robzy

Quote:


  Originally Posted by *halman* 
_It wouln't make my board any smaller if I removed it so it might aswell stay. You are right however._

 

I am fairly new to this - but why would you bother adding regulation for parts of the chip that arent in use? Whether it adds to board size or not all it does is add more parts to go wrong that dont actually do anything in the first place.

 Rob.


----------



## TV Man

How do we sign up for boards?

 Nice job on the design. I'd like a few of these to play with


----------



## dsavitsk

Just to keep this rolling 
	

	
	
		
		

		
		
	


	




 We've passed the revision deadline. Any thought on kits? My sense would be that since parts are easily sourcable from digikey and cost just enough to not incur the handling charge, that at least for those of us in the States we not bother with kits. It doesn't really save anyone any money (save for resistors coming in set of 10 in some cases) and just requires a great deal of sorting on sombody's part.

 -d


----------



## guzzler

I'm still happy to order boards; assuming Halman hasn't gone ahead with his; if he has; well his are fine 
	

	
	
		
		

		
		
	


	




 More orders, the cheaper it is 
	

	
	
		
		

		
		
	


	




 Please could you PM me; or email me regards if you want one (pending Halman of course)

 g

 PS; what's the consensus on the regulator? The boards not really going to be any smaller without it, and I'm not entirely sure how it will affect the overall operation (could even squeeze some analog pads in possibly)


----------



## halman

I did go ahead with mine, but I only ordered a few sets of boards, with different line drivers. (one pair of each actually) I will have them in a few weeks time or so. It will be fun to se wich will work best..if there will be a noticable difference at all ,)

 The board was made to cater to my own personal needs (BNC connector /galvanic isolation) So i.e it is less universal and thus less suitable for a group buy effort.


----------



## clarke68

Is anybody working on a reference-quality usb/spdif pcb? Something along the lines of the modded M-Audio Transit over at Empirical Audio, that will rival mega-buck dedicated transports.

 I still may pick up a few of these (especially after reading dsavitsk's glowing review of Guzzler's last project), but I'd be interested in a more 'no holds barred' version.


----------



## Magsy

Quote:


  Originally Posted by *clarke68* 
_Is anybody working on a reference-quality usb/spdif pcb? Something along the lines of the modded M-Audio Transit over at Empirical Audio, that will rival mega-buck dedicated transports.

 I still may pick up a few of these (especially after reading dsavitsk's glowing review of Guzzler's last project), but I'd be interested in a more 'no holds barred' version._

 

Same here, I would like to build a high end usb dac! 
	

	
	
		
		

		
		
	


	




 edit: woops, you say usb>spdif, I'm after usb>analog!


----------



## halman

I got my boards today


----------



## audioengr

Quote:


  Originally Posted by *Magsy* 
_Same here, I would like to build a high end usb dac! 
	

	
	
		
		

		
		
	


	




 edit: woops, you say usb>spdif, I'm after usb>analog!_

 

I am prototyping a 2706 circuit with I2S out for use with the P-3A DAC (I2S input). I would rather do a 3200-based board with both I2S and S/PDIF outs as a product though.

 BTW - there is a way to isolate I2S from the PC: Differential signalling.

 Steve N.


----------



## BradJudy

Quote:


  Originally Posted by *audioengr* 
_I am prototyping a 2706 circuit with I2S out for use with the P-3A DAC (I2S input). I would rather do a 3200-based board with both I2S and S/PDIF outs as a product though._

 

It will be interesting to see what comes of this. I own an AA DDE 3 which also has i2s input.


----------



## steinchen

Quote:


  Originally Posted by *Magsy* 
_Same here, I would like to build a high end usb dac! 
	

	
	
		
		

		
		
	


	



 edit: woops, you say usb>spdif, I'm after usb>analog!_

 

me, too


----------



## Stuge

I've made one of these. It's just the simple reference design in the PCM2902 data sheet along with a TOTX179 and TORX179 and their respective suggested operating circuits.

 The motivation was to record music from laptop on my Sony MDS-JE520 MD deck bypassing the DAC and noise in the laptop. DIY because, well, I didn't want to spend 350SEK on consumer electronics in a store when I could DIY for around 250SEK. ($50 vs. $35)

 Optical transmission because I like optical signalling in general. Plus my desk has lots of signals back and forth and the laptop is a noisy system, so the noise-resistant factors of optical outweigh price of electrical, plus there's the subjective argument that optical feels better. I've read some posts and articles stipulating that optical transmission actually introduces more bit errors in the data stream than electrical signalling but I haven't decided how much I believe that just yet. I guess it comes down to the quality of the components in the system; the attenuation in transmitter, cable and receiver.

 At first I planned on only having an optical output but a friend of mine with a synth said he could probably use a digital input soundcard so I put a receiver on it as well.

 I had some 15 boards made and have populated one so far. It sort of works. The MD deck unlocks stochastically, causing short glitches in sound, rarely more often than once a minute but sometimes it runs for hours without a glitch. Suggestions on a remedy for this are appreciated. I haven't made any thorough tests since I have other priorities at the moment. I read a post on a japanese board where a TI tech seemed to reply about how one of the DIR S/PDIF receivers had to be externally reset if the sample rate changed, but I don't believe that's what I'm seeing, and I doubt there's a TI TosLink receiver in the Sony deck, and the source applications (xmms/mplayer) don't just switch sampling rates.

 Bus powered, all SMD, hand soldered. One bug in the PCB, forgot to ground the TOTX179; that's the red wire.. Just wish the deck wouldn't unlock. Need to investigate further. There's a lot going on in the ALSA USB driver right now as it seems too, my keyboard stops working if I unplug and replug the device because of bugs in the Linux kernel..

 Photos: http://cdy.org/~stuge/usnd/






 //P


----------



## drewster

Hi folks,

 First time poster here. I found this thread while googling for information on the PCM2902 chip.

 This might be out of place in a DIY thread... but a vendor sells just this kind of product - ADS Technologies. They use the 2902e, and the device has USB, RCA in/out and S/PDIF in/out. They call it the Instant Music RDX-150.
 Product: http://www.adstech.com/products/RDX-...sp?pid=RDX-150
 Froogle: http://froogle.google.com/froogle?q=...b=wf&scoring=p

 No relationship, no affiliation, yadda yadda. I never heard of the ADS device until the other day, and saw it tonight when a friend brought one to my house. My curiousity led me googling, and here I am.

 Cheers!


----------



## dsavitsk

There seem to be tons of usb cards with toslink out, but ours has wired output specifically to facilitate putting it inside an existing dac with a minimum of fuss. It is interesting to note that this one uses the 2902, however, How does the analog sound? we opted to not bother since there are better chips for it.

 In case you didn't see it, the group buy thread for this is at http://www6.head-fi.org/forums/showthread.php?t=109671 and the project page is at http://www.ecp.cc/usb-spdif.html

 -d


----------



## needlz

Anyone using a Mac with this board? I just finished building mine and after plugging it in the LED lights but nothing else happens. Do I need a driver or USB utility installed or is there probably something wrong with my board?

 thanks.


----------



## dsavitsk

I would guess something wrong with the board. To be sure, find a win32 computer to try it in, however. The pcm2902 should be fully supported under osx.

 -d


----------



## Nisbeth

You need to choose the board as your output device in the "sound" pane of your system preferences 
	

	
	
		
		

		
		
	


	





 /U.

 EDIT: You can also check if the board is listed as "BB PCM2902" (or something like that) in the information for the USB-bus in your system profiler. If it is, that part of the board is working 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *needlz* 
_Anyone using a Mac with this board? I just finished building mine and after plugging it in the LED lights but nothing else happens. Do I need a driver or USB utility installed or is there probably something wrong with my board?

 thanks._


----------



## paologatto

Yep, I confirm!
 The PCM2902 and PCM2906 work perfectly with Mac!











 After connecting it, the new USB device will appear in the list of audio devices. No drivers needed.

 And works ok also in linux. 
 Well.. the latest Mac OS is a sort of linux, AFAIK..

 Bye!

 EDIT: read an additional note about a Mac problem here:
http://www6.head-fi.org/forums/showp...&postcount=193


----------



## dsavitsk

Quote:


  Originally Posted by *paologatto* 
_Well.. the latest Mac OS is a sort of linux, AFAIK._

 

Nope, the Darwin core (what OSX is built on) is based on FreeBSD which is quite distinct from Linux. FreeBSD, however, does support USB audio (using a driver originally from OpenBSD.)

 -d


----------



## drewster

Quote:


  Originally Posted by *dsavitsk* 
_There seem to be tons of usb cards with toslink out, but ours has wired output specifically to facilitate putting it inside an existing dac with a minimum of fuss_

 

Ah, I missed that essential detail. My apologies.
  Quote:


 . It is interesting to note that this one uses the 2902, however, How does the analog sound? 
 

I haven't wired it up to the receiver just yet. I'll update this thread when I do, however.


----------



## agentpt5

Getting ready to solder this little guy, I am asking if anyone has a link to the schematic?


----------



## halman

I finaly got around to build and house my digital output It feeds my little TDA1545 based thingy very nicely


----------



## nleahcim

Quote:


  Originally Posted by *halman* 
_I finaly got around to build and house my digital output It feeds my little TDA1545 based thingy very nicely 
	

	
	
		
		

		
			





 http://www.ljudochteknik.se/Digital3.jpg[IMG] 

 [IMG]http://www.ljudochteknik.se/Digital4.jpg[IMG] 

 [IMG]http://www.ljudochteknik.se/Digital2.jpg[IMG][/i]
 [/td] [/tr] [/table]


oh that's such a cute little case! What brand/model is it, and how much did it set you back?_


----------



## halman

Its a hammond 1455C801 I paid around 15usd in Sweden.


----------



## Mod_Evil

Quote:


  Originally Posted by *guzzler* 
_Bump with gratuitous Eagle 3D rendering 
	

	
	
		
		

		
		
	


	









 I've tidied up the regulator section and taken account of the grounding recommendations.... Silkscreen has component values on. The board is still the same size. If anyone's interested, I can get a batch run out; NO SUPPORT ON IT THOUGH!!

 g_

 

Hi! Where you download this program? I not found this in Google 
	

	
	
		
		

		
		
	


	




 ... May you send to me the Eagle 3d? my email is this: felnavarro@gmail.com

 Thanks!


----------



## Nisbeth

Quote:


  Originally Posted by *Mod_Evil* 
_Hi! Where you download this program? I not found this in Google 
	

	
	
		
		

		
		
	


	




 ... May you send to me the Eagle 3d? my email is this: felnavarro@gmail.com

 Thanks!_

 

Download it from http://www.matwei.de/






 /U.


----------



## chrisfromalbany

Quote:


  Originally Posted by *halman* 
_Its a hammond 1455C801 I paid around 15usd in Sweden._

 

How did you decide on that DAC chip. Could you have used a better chip like AD1853 one used in the Benchmark DAC1.


----------



## Nisbeth

That's not a DAC-chip, that's the enclosure p/n 
	

	
	
		
		

		
		
	


	





 /U.


----------



## audioengr

Quote:


  Originally Posted by *BradJudy* 
_It will be interesting to see what comes of this. I own an AA DDE 3 which also has i2s input._

 


 I prototyped an I2S version of the Off-Ramp about a week ago. It uses Superclock3 and I am driving the P-3A I2S input. It is the best computer sound that I have ever heard. About 10-15% better than the Off-Ramp Turbo with S/PDIF output.

 Unfortunately, it is not something that I can currently mod and ship. Too complicated and fragile using the Transit board. I like the Transit better than the 2907 because I can do 24/96 and the drivers bypass Kmixer. I will be starting on a PC board for this converter after the Rocky Mountain Audio Fest in Oct.

 Steve N.
 Empirical Audio


----------



## BradJudy

Interesting Steve. BTW: I'll try to keep my eye out for you at the RMAF and say hi.


----------



## halman

A more elaborate version made to fit a hammond case exactly.











 and yeah.. I will clean the flux of the board =)

 Merry Christmas!


----------



## DaKi][er

The other day, I scoped the output clock of the pcm2902 (after it had been decoded to I2S in my dac) and it is outputting 44.1 kHz audio

 This is with a stock standard install of XP with Foobar set to output via DirectSound v2.0

 So by that we could make the assumption that it is indeed bit perfect output and no resampleing is being done by the kmixer ? No need to stuff around with ASIO and kernal streaming then


----------



## audioengr

Quote:


  Originally Posted by *DaKi][er* 
_The other day, I scoped the output clock of the pcm2902 (after it had been decoded to I2S in my dac) and it is outputting 44.1 kHz audio

 This is with a stock standard install of XP with Foobar set to output via DirectSound v2.0

 So by that we could make the assumption that it is indeed bit perfect output and no resampleing is being done by the kmixer ? No need to stuff around with ASIO and kernal streaming then_

 

I dont think so. I had 44.1 from Foobar as well, but it was going through Kmixer. I installed ASIO for M-Audio and only then did the Windows slider stopped working. Sound was a bit better too.


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## audioengr

Quote:


  Originally Posted by *BradJudy* 
_Interesting Steve. BTW: I'll try to keep my eye out for you at the RMAF and say hi._

 

Brad - the Off-Ramp I2S is complete and in production now. First ones sound amazing driving a P-3A DAC. I will be demoing it at THE Show. San Tropez room 1203.


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## DaKi][er

Quote:


  Originally Posted by *audioengr* 
_I dont think so. I had 44.1 from Foobar as well, but it was going through Kmixer. I installed ASIO for M-Audio and only then did the Windows slider stopped working. Sound was a bit better too._

 

Ahh yes, the volume slider never worked for me, I just put it down to the fact that it was digital out that it did that (as the analog one using the pcm2702 did have windows volume control)


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## paologatto

Quote:


  Originally Posted by *DaKi][er* 
_The other day, I scoped the output clock of the pcm2902 (after it had been decoded to I2S in my dac) and it is outputting 44.1 kHz audio

 This is with a stock standard install of XP with Foobar set to output via DirectSound v2.0

 So by that we could make the assumption that it is indeed bit perfect output and no resampleing is being done by the kmixer ? No need to stuff around with ASIO and kernal streaming then_

 

I think that DirectSound may do some resampling if you have not the right settings. If I remember well somewhere in windows you have to set the sample rate of DirectSound. Other sample rates played through it are resampled. 

 WDM or MME drivers are more safe to avoid resampling.
 By the way, the output clock of PCM2902 changes according to sample rate, if 32, 44.1 or 48 kHz, as I found from a test that I made time ago:

http://www.diyaudio.com/forums/showt...696#post746696


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## StevieDvd

If you have one of these you built and don't use and would like to offload it somewhere PM me with details.

 I'd like to add it to a DAC which has coax digital in only so this should fit quite nicely.

 Steve

*Thanks for PM's guys, all sorted now.*

 Steve


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## Nisbeth

YGPM! 
	

	
	
		
		

		
			






 /U.


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## Parout

I am looking for a USB powered PCB with the 2902 chip or somthing similar. I want to deliver sound to two computer speakers with at least 2W per channel. I will buy over 100 now if they exist. Please let contact me via email if you need to.

parout66@yahoo.com


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## BradJudy

Hagerman Tech sells a 2704 on PCB, but it's just designed for headphones/digital out, so I don't know that it will put out 2W, but here's the link:

http://www.hagtech.com/hagusb.html

 Edit - just noticed you want a 2902, not 27xx.


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## peterpan188

guzzler, what happened to your design and boards? Count me in if you guys are having a board purchase.

 Cheers,
 Peter


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## Nisbeth

Quote:


  Originally Posted by *Parout* 
_I am looking for a USB powered PCB with the 2902 chip or somthing similar. I want to deliver sound to two computer speakers with at least 2W per channel. I will buy over 100 now if they exist. Please let contact me via email if you need to.

parout66@yahoo.com_

 

Getting 2Wpc from something that runs on USB-power is going to be difficult... 
	

	
	
		
		

		
		
	


	





 /U.


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## guzzler

I was actually considering doing some more, but with space for a small output transformer, and pads for the analog out if anyone's interested still. The last order was for 150 PCBs


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## theexec

anyone else interested in this?

 I'd be interested in 3-4 boards, i think there are lots of ppl in the source forum who want a usb-spdif solution.


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## hanon

I'm looking to add a usb input to a dac currently with only coax so would definitely be interested in an assembled usb-spdif board; would also be delighted to participate in a gb for a pcb.


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## flyhyena

I'm also looking for a usb-spdif(coax) convertor. If any one has an assembled usb-spdif board or has extra pcbs(better with all the other parts as well) want to sell, please PM me.


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## dsavitsk

Quote:


  Originally Posted by *flyhyena* 
_I'm also looking for a usb-spdif(coax) convertor. If any one has an assembled usb-spdif board or has extra pcbs(better with all the other parts as well) want to sell, please PM me._

 

You might look at http://www.hagtech.com/hagusb.html


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## MisterX

Or maybe this one-----> http://us.hifidiy.net/Article.asp?ArticleId=180

 There is one on ebay if you are so inclined: 

http://cgi.ebay.com/USB-to-SPDIF-Con...QQcmdZViewItem


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## flyhyena

thanks guys for the input info, the one from hifidiy.net seems more attractive to me given the price. Maybe I just order one from ebay then. 

 nice weekend.


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