# PCM2702 USB DAC Revision B



## Alf

I always wanted to build PCM2702 USB DAC also known as Guzzler’s DAC. I contacted Guzzler but he was completely out of boards. I realized that the only chance for me to build the DAC is to order the boards myself. Guzzler has kindly sent me his Eagle files and has been very supportive. The original design did not fit my needs 100%. So presented with the opportunity, I took the liberty of making some minor modifications to the board layout and to the schematic.

The new schematic 

The new board layout 

 The changes:
 * New board size 50.5mm x 57mm. The board now fits Hammond 1455C802.
 * Mounting holes in each corner.
 * Prominent USB connector (3.2 mm) for easier panel mounting.
 * An option to power the DAC directly from MINT/PIMETA.
 * All resistors are 1206.
 * No R7 (it was not used anyway).
 * Place for L2
 * The schematic and the board are now consistent.

 Your comments are very welcome!


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## grawk

I'm not qualified to comment, but right on with the design changes...now bring on the 1 box mint/usb dac combos!


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## MisterX

Nice job... mark me down for 5 of them when the time comes.


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## Edwood

When everything is finalized and ready for a group buy, just remember to contact Jude, and a thread can be posted in the Group Buy Forum.

 -Ed


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## dsavitsk

Neat, though if you are going to do it, why not go all out? Use a pcm2902, take the digital output and give it to an AD1865 or pcm1704 and then do the I/V right (I'll leave what that means to others, though my preference would be to use a transformer) rather than using the I/V builtin to the chip. Just a thought. This would, of course, cause the project to cost about 6x more, so maybe that's not what you're looking for ...


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## Nisbeth

Great initiative, Alf 
	

	
	
		
		

		
		
	


	





 /U.


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## bjackson

I would like to see a design that feeds it to a higher quality DAC also, however since this is to be portable I doubt that was the design intent.

 However if an alternate design could be fashioned I would be very interested in it to a upper mid/hi fi dac kit that doesn't cost an arm and a leg.


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## cetoole

The DAC is looking pretty good, but are you still using the Maxim MAX1722 IC? That, along with the WIMA MKS-02 caps that were origionally used, are very hard to source here, so if you could design it with other parts in mind, that would be great.


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## Botch

I'm interested in a few once the OK for a group buy happens.

 Nice to see the pad for external voltage (AV+) input before IC2. The last one I made didn't use the MAX1722 as I couldn't source one. Ended up with a reg'ed 5.5V going into it directly onto a resister pad.

 Nice work Alf.

 Botch.


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## DaKi][er

Certainly would be a good idea to replace the MAX1722 with something obtainable from digikey 

 Maybe change C18 to 1206 and move it as close as you can to the IC

 And an idea I was thinking of was a better output circuit than what is there, like an active HPF with 12dB/oct, something that you can use high quality small film caps in it and not have to worry about what load it is driving, though then you'd need the split supply but if you are running it in the same case as an amp that is no problem, just if you aren’t that it gets tricky


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## diablo9

nice job Alf, count me in when doing group buy!


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## CRS401

I missed on the first one, hope I don't miss out on this one.


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## skyskraper

nice work, keep it up


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## MASantos

I spoke with Alf during this week about the project an dhe told me that he wasn't going to use max1722. I think that it has been replaced by a BUF634U

 You can check that in he schematic.

 Manuel


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## Alf

Thank you for the warm feedback guys!

  Quote:


  Originally Posted by *cetool* 
_but are you still using the Maxim MAX1722 IC?_

 

 Quote:


  Originally Posted by *DaKi][er* 
_Certainly would be a good idea to replace the MAX1722 with something obtainable from digikey_

 

 Quote:


  Originally Posted by *MASantos* 
_I spoke with Alf during this week about the project an dhe told me that he wasn't going to use max1722_

 

I considered this. Guzzler suggested using TPS6107x and I even designed the first version of Rev B around it. 

 Unfortunately I could not find the component in the UK/Europe. So it would be no use to me and other European DIYers. MAX1722 seems to be easier to use and more suitable for the application. Because I did not like the design based on TPS6107x anyway, I reverted back to MAX1722 a couple days ago.

 MAX1722 availability is still an issue though. I plan to buy small quantities of MAX1722 and make them available to the community. If you know a good place to buy this part, please let me know. Where this part came from last time?

  Quote:


  Originally Posted by *cetool* 
_That, along with the WIMA MKS-02 caps that were origionally used, are very hard to source here_

 

The caps are available from Farnell UK. If you prefer not to buy from them, I will be pulling together a few kits. Part selection should not be a problem then.

  Quote:


  Originally Posted by *dsavitsk* 
_ Neat, though if you are going to do it, why not go all out? Use a pcm2902, take the digital output and give it to an AD1865 or pcm1704 and then do the I/V right_

 

 Quote:


  Originally Posted by *dsavitsk* 
_I would like to see a design that feeds it to a higher quality DAC also_

 

I am too interested in a high-end DAC design to complement my EMU0404 at home. However I am afraid that this is out of the project's scope. 

  Quote:


  Originally Posted by *DaKi][er* 
_And an idea I was thinking of was a better output circuit than what is there, like an active HPF with 12dB/oct,_

 

I think the DAC will be used primarily as a daughter card and placed in the same enclosure as the amp. There are better designs out there for standalone DACs.

  Quote:


  Originally Posted by *grawk* 
_now bring on the 1 box mint/usb dac combos!_

 

I designed the board with MINT in mind. There is enough space left to add a small amp and fit it all in Hammond 1455C802. 

 Guzzler mentioned he would like to do something like that too. He was not clear on the dates. If he does not come with anything, I will design Rev C after this project. I guess we are talking about November-December.


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## MASantos

So what is the buffer for?? Is it the power supply if you use a mint to power the dac? Is it optional if you are doing a standalone dac?


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## Francis_Vaughan

You might like to have a look over at DIYAudio in the digital group. In particular this thread:

http://www.diyaudio.com/forums/showt...threadid=64738

 The pointers by Guido Tent are especially valuable, and the articles on board layout and grounding a must read. Board layout has been covered quite a bit of late, so time spent browsing and reading would be very well spent. 

 There are a few issues with your layout as it currently stands. This is all about the layout for the 2702. The power and especially the ground trace layout is going to lead to all sorts of problems. It is important to realise that the different power and ground pins out of the chip lead very different lives. They serve different circuits in the chip, and each will have its own mess of noise, and sensitivity to noise. For instance the USB ground is on the same thin little trace as the clock generator ground, which then winds its way back to a tie to the groundplane though a single little via. Every bit of current thought the digital part of the device must traverse this path at some point, and you will have crosstalk between the various parts, plus some reasonable chance of coupling into the analog ground, as it wends its serpentine way nearby. The long trace taking AGND to its via is really worrying. You have the opportunity to pick up all sorts of noise here. You need to look to individual vias tying each ground right to the ground plane. You cant allow any loop area.

 Also the rather long traces to and from C13 give me worry. There seems to be quite a bit of scope for tightening up the layout to pull the bypass capacitors next to the pins they are serving, rather than sitting out at the end of an inductor, where their utility is seriously compromised.


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## Alf

Quote:


  Originally Posted by *MASantos* 
_So what is the buffer for?? Is it the power supply if you use a mint to power the dac? Is it optional if you are doing a standalone dac?_

 

It is for MINT/PIMETA. The DAC uses V- for ground while MINT/PIMETA have virtual ground. Therefore you cannot use the amp's V+ and V- to power the DAC. Also you cannot connect the DAC to V+ and the virtual ground because the TLE2426 can only handle up to 20mA. BUF634 is meant to solve this problem.

 If you would like to mate the DAC with your amp, then you should use BUF634 and leave out MAX1722 (and some other parts too).

 If you plan to use batteries <5.2V or USB for powering the DAC, then you should use MAX1722 and leave out BUF624.


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## skyskraper

Quote:


 I am too interested in a high-end DAC design to complement my EMU0404 at home. However I am afraid that this is out of the project's scope. 
 

mmm a nice simple spdif (and torx for those too cheap to buy a spdif source) dac would be very tasty.


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## Voodoochile

Guys, please save all the "interested in a board" comments for an actual group buy interest thread, please. Alf does know about the group buy drill, as noted by edwood. So if it comes to that, it will be a seperate thread.

 Let's keep this thread for dialog regarding the properties of the project.


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## Alf

Quote:


  Originally Posted by *Francis_Vaughan* 
_There are a few issues with your layout as it currently stands. This is all about the layout for the 2702._

 

Thank you Francis. You are making very valid comments indeed. I will make changes tonight and post a new layout.

 By the way, this part of the layout has not changed since Rev A and no one reported the noise issues you mentioned. I wonder whether there will be any audible improvement. I look forward to comparison tests.


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## Francis_Vaughan

You won't see this stuff show up as what is heard as a raised noise floor, rather it shows up as our old friend jitter in the digital parts, or actual distortion products. Noise still, where noise is defined as "that which is not part of the desired signal." 

 Do read this one:

http://www.tentlabs.com/Info/Article...decoupling.pdf


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## cetoole

If you are able to get a large quantity of MAX1722 IC's to make available to headfiers, along with the Wima MKS-02 caps, that would be great. For the origional USB DAC, I ended up having to resort to samples for these two parts, say what you will, there just isnt any availability in the States for these parts, and ordering from Farnell isnt really an option. While some here might not like it, if it was possible to add an optional stage using a DC-DC converter, so that instead of the DAC being powered from the Mint/Pimeta, the Mint/Pimeta is powered from regulated USB power, so that people arn't required to use batteries at all, saving vaulable space, and giving a runtime just as long as the laptop, that would be something that I would be very interested in seeing. Providing that the regulation was adequate, it would make the perfect portable laptop headphone amp/dac rig, as it would still fit in the Hammond 1455C802, along with a mint, with no need for an external power source.


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## MASantos

Quote:


  Originally Posted by *cetoole* 
_If you are able to get a large quantity of MAX1722 IC's to make available to headfiers, along with the Wima MKS-02 caps, that would be great. For the origional USB DAC, I ended up having to resort to samples for these two parts, say what you will, there just isnt any availability in the States for these parts, and ordering from Farnell isnt really an option. While some here might not like it, if it was possible to add an optional stage using a DC-DC converter, so that instead of the DAC being powered from the Mint/Pimeta, the Mint/Pimeta is powered from regulated USB power, so that people arn't required to use batteries at all, saving vaulable space, and giving a runtime just as long as the laptop, that would be something that I would be very interested in seeing. Providing that the regulation was adequate, it would make the perfect portable laptop headphone amp/dac rig, as it would still fit in the Hammond 1455C802, along with a mint, with no need for an external power source._

 


 The idea of poweriing the amp from the USB power is defenitely interesting, saving both space in the amp and batteries. But does USB have wnough power to feed both the dac and a mint or pimeta?? How would that affect SQ and Thd? 

 Then the best thing to do is to design 2 separate boards 
	

	
	
		
		

		
			








 , one that is a dac powered from a mint, for those who want the best sound quality and another which is powered from the USB cable, saving space in the enclosure and helping with portability!!. Both designs would save space in the PCB by removing components not needed!
 the second option would fit in the smallest hamond enclosure( the aluminium ones)


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## grawk

I'd also be really interested in a variant on this board that uses one of the DAC chips that can output balanced. It'd be a really nice thing to have stuffed inside a balanced m3 or dynamid...


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## Botch

Lots of ideas here but in a way I think we are getting away from the original scope of the project - to have a simple, small USB DAC. Something that Guzzler & the original team did a great job on.

 The addition of the interface for MINT is an advantage and only adds one IC but do we really need to complicate the design process by having 2 board designs?

 The only improvements that I would like to see are related to the grounding and decreasing the noise floor as per what Francis has posted. This DAC was not designed as a high end DAC, just a easy to build solutiuon and personally I like the simplicity of this design.

 Botch.


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## Alf

I see a conflict of requirements here. The original revision's design goal was to produce a simple DAC powered from a small battery pack (1 or 2 cells). A lot people asked for a USB powered solution and Guzzler added this option in Rev A. 

 It seems to me that no one actually wants to hassle with batteries. People use either an external power supply or USB power. When I started thinking about the new revision, I wanted to ditch the low voltage battery section completely. However, I was not sure whether it was a good plan and eventually reverted to the original design.

 OK I have to ask you a question now. How many people out there actually using batteries with Rev A? Is there anyone here who strongly advocates this option?

 If my guess about batteries is not far off, we have a whole lot of new possibilities. MAX1722 is only required because of the low voltage option. If we ditch this option, then we do not need to use this much hated part.

 Here is what I suggest:
 * Replace MAX1722 with another DC/DC step-up converter that can boost 5V to around 7-10V.
 * Add an additional regulating section that would clean up noise coming from USB and the switch even further.
 * Add an option to power an amp from the DAC

 Are there any power supply experts here? What can be done to improve the USB option and still fit the board? Can USB be cleaned to an acceptable level?


 If this is a go, then I would need your help with selecting the new step up converter and the regulator. Both of them must be:
 * (Very) low noise
 * Small size but easy to solder
 * Available from Farnell and Digikey. 

 What do you think guys?


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## Nisbeth

Allright, if it isn't too late, lets try to nip this "feature-request" discussion in the bud 
	

	
	
		
		

		
		
	


	




 What I'm hearing people ask for are essentially three different things.

 1) Small, portable, bus-powered USB-DAC to feed external amp. Enclosure target: Hammond 1455C801

 2) Portable, self-powered USB-DAC/MINT-style amp combo. Enclosure target: Hammond 1455C1201 (or smaller)

 3) High-end USB-dac using the I2S-output from a PCM290x to feed an HQ-dac IC. Balanced output preferred. Enclosure target: Probably a Hammond 1455J or larger. (1455K-type for balanced output due to the height of the XLR-connectors).



 My evaluation and recommendations are as follows:

 1) This is the original scope of this project and the one the thread should continue focusing on. My only comments on what's been achieved so far are that a) even if the board should be designed for the Hammond enclosure, in the interest of versatility on-board connectors should be limited to one edge of the PCB and b) the amp-power section should be retained if the board space allows it (also in the interest of versatility).

 2) A very nice concept which i believe many would be looking for, but I still think it deserves a separate thread. Not least because there are a lot of related projects which could be combined, including dougis' LiPo-project, tangent's MINT-revision and the other assorted AD8397-experiments from headwize and of course this project. Development of this design and 1) could easily run parallel to each other but with separate threads and two different persons to coordinate development because they might easily end up with conflicting requirements. 

 3) A great idea, but completely outsidde the scope of this thread. Start a new thread and use that for feature-requests etc. If necessary, ask Guzzler if he'll donate the files for the USB/SPDIF-board and anything else related he might have lying about to help start the project. There are a few others who have been exploring options like this before and they might be willing to chime in as well 
	

	
	
		
		

		
		
	


	




 My $0.02 for now 
	

	
	
		
		

		
		
	


	




 /U.


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## Alf

Here is the updated version of the board layout:

Board v2 

 Changes:
 * Moved C18 closer to the IC and changed it to 1206 (DaKi][er)
 * Added vias tying each ground to the ground plane (Francis)
 * Moved the bypass caps closer to IC pins they are serving (Francis)
 * Added an option to replace BUF634 with OPA511 (Nisbeth)

 The board is still based on MAX1722. I will replace it as soon as we agree on what we replace it with.


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## Francis_Vaughan

I think you still need to push things on the analog side a bit further. Think of the problem like this. You need to connect the power to ground at RF as closely as possible. 0 Volts is easy - just drop a via to the ground plane right on the pin. Power is harder - you need to put a capacitor in the way. But after that the layout is the same problem - get the capacitor right onto the pin, and then the other side straight to the groundplane. You should be able to turn most of the bypassing capacitors around so that they can be lined up along the edge of the chip, with essentially no distance to the pin they serve. The layout seems to have a curious idea that the ground pin for a functional unit should go to the groundplane through the same via as the bypass capacitor for that unit. Thus forcing extra (and bad) trace length. Don't do this. Push all the grounds straight down into the groundplane.

 Thus C10,11,13,14 all turn through 90 degees, all right up against the chip, and a via straight down on the other side. The analog ground pins get vias straight down. C12 get as close as possible after.

 I notice that there is no seperate bypass capacitor for pins 2 and 4. Egads! Pin 2 is power for the clock generator. Junk on Vdd (pin 4) wil couple straight into the clock - jitter here we come. Get another capacitor right onto pin 2. Same deal as above, via straight down on the other side.
 C18 will have to move, but that is no big deal, rotate it 90 degrees, and move the USB coupling resistors. You are going to end up with a transformer here anyway (trust me) so they are not important. There may be a case for supplying each of these power pins via a ferrite bead to keep them seperate.

 The crystal is a bit of a mess too. Long traces to the capacitors. Remember that the crystal oscillator determines a large fraction of the jitter in the system. Any signal pickup on those traces will directly cause jitter in the signal - since the signal will modulate the oscillator signal before the comparator from which the internal timing clock is generated. Thus any AC, and worst of all, audio frequency signals, that couple into those traces will cause signal correlated jitter. Lay the ocsillator out with as small a trace length as possible. The tends to mean laying it out like the circuit is typically drawn. Capacitors either side of the crystal with minimum trace lengths. Resistor parallel to the crystal. Right on top of the chip. Get those loop areas down.


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## Alf

I updated the schematic and the board. It took me quite long time to implement all suggestions Francis made in his last post (keep them coming!). I re-shuffled nearly all components on the board making the layout more efficient. I hope I got it right this time!

Schematic v2 
Board v3 

 Changes:
 * New board size 50.5mm x 54mm. Now the board is 3mm shorter.
 * Added a power switch (I guess it may be useful).
 * Added C19.
 * Moved the bypass capacitors closer to IC pins and rotated them. It is possible to move C10, C11, C14 a bit closer the board (~ 0.6mm) but not C13 and C12. The layout looked really ugly when I moved the capacitors. So I left them lined up.
 * Optimized layout around the crystal and MAX1722.
 * Many other minor changes.


 I have been in contact with Maxim regarding MAX1722. They can supply me with any quantities (50+) of MAX1722. The bad news is that the final price including postage, taxes, and fees will be around 3.0-3.5 USD each. I may be able to bring the price down. I will keep you posted on this.

 Now I am going to investigate potential replacements for MAX1722 and what can be used if the low voltage battery option is dropped. Any tips are welcome.


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## doobooloo

Ooh! Very interesting!

 Makes me want to get back into DIY. I'll be watching this thread closely...

 Thanks Alf!


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## Sinbios

Alf: if the USB power could be cleaned up to near the level of battery power, or even that of a nice power supply, then I'm all for it.

 One thing, I think the original DAC wasn't bit-perfect -- is it possible to make this version bit-perfect?


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## Botch

Alf, you are doing a super job. And I'm sure you thought this was going to be a simple mod. 
	

	
	
		
		

		
			





 As for the MAX1722, I will probably not use them. I want to use the DAC for a desktop PC so will make a regulated power supply for it. (OK, maybe I'll get one MAX1722 in case I make a usb mobile version one day.)

 Really minor point. Could you make the wire pads just a bit bigger? Seem to remember for the original they are a touch too small. 

 The oscillator is much cleaner. Could C15 & C16 be SMD parts? I'm not sure but it would give a little space so you could move IC3 to the left a bit, move C6 & C7 (rotate CW90°) down lower and make the 3.3V run shorter. Maybe C1 & C2 will have to move a little but there is lots of space up there. It a fun game. 
	

	
	
		
		

		
		
	


	




 Have a couple for Francis if he is still watching this thread.

  Quote:


  Originally Posted by *Francis_Vaughan* 
_I notice that there is no seperate bypass capacitor for pins 2 and 4. Egads! Pin 2 is power for the clock generator. Junk on Vdd (pin 4) wil couple straight into the clock - jitter here we come. Get another capacitor right onto pin 2._

 

Francis, will the new layout clean this up enough? 

  Quote:


  Originally Posted by *Francis_Vaughan* 
_C18 will have to move, but that is no big deal, rotate it 90 degrees, and move the USB coupling resistors. You are going to end up with a transformer here anyway (trust me) so they are not important._

 

Can you explain this one a little more regarding a transformer. 

 Is looking good Alf. Keep the updates coming.

 Botch...


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## Francis_Vaughan

It is looking much neater. 

 So a few more thoughts.

 As Botch says, I wonder is a few, if not all the bypass caps might not be SMD. This should help the layout, and potentially improve performance. You can glue them to the back of the board then too, which may be a win if space gets grim.

 The input transformer will, I think, be important - it gives you the freedom to get away from the vagaries USB power more easily if nothing else. 

 I think where I was trying to get to with the layout ideas is to look at the IC not as a monolithic thing, but as a system of connected units. The designers give you this ability since they bring out all the power pins. So if you refer to the block diagram in the data sheet it becomes clear what the goals are. Treat each of these units separately, give each its own well bypassed power so they can't interfere with one another, but also be cogniscent of the currents that must flow between the units, and thus the consequent return currents. Return currents are trivially dealt with with the solid ground-plane. It is hard to do better. So we worry about power. The digital power is in two places, clock and main digital logic. Each should be separately fed, and in this case this really means adding an appropriate ferrite bead isolator before each of the bypass capacitors. Thus split the pad C18 and C19 attach to, and feed each of the splits with an SMD ferrite bead.

 Something similar might be appropriate for the analog side, although the lower frequencies involved might suggest some R in series with a bead as well, and perhaps more C. 

 You are building a mini LRC power supply filter for each unit - one designed to keep the crud floating about the board out of each unit. Since the units each have different functions we can design the filter to match the unit.

 The exact choice of bypass capacitors should probably be revisited. The data sheet suggests significantly larger, but we must worry about series L. Guido provides some guidance on choice. There is much discussion on DIYAudio about this.


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## Francis_Vaughan

Groan, you are going to hate this one. It has been staring me in the face for ages, and it just didn't register.

 The ground-plane is the wrong plane.  That is: the component side should be the ground-plane. I kept thinking "why all these vias to ground" and then it hit me. I blame the antihistamines (spring here and the allergens are out in force.)

 This is a lot of work to change. But if done means that most of the bypass capacitors can become SMD and be glued on without vias. Overall it will become massively cleaner and the RF performance improved further.

 This does mean that to remain a reasonably clean layout quite a few components will swap to the other side, but that is, after all, part of the joy of proper double sided design. Some nice gains can be had. For instance you can drop R3 right under the crystal, improving the layout, reducing loop area further, and hauling back more space. Similarly you will see many more components that can swap sides and much that will tighten up. But much work.


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## Botch

Francis, I know that antihistamine blur.

 I was having a similar thoughts on the ground plane but 100% wasn't sure about it.

 Ideas at this stage:
 - move the ground plane to the top layer. 
 - Change bypass caps to SMD's where appropriate.
 - mount some components on the bottom layer when required (ie. for oscillator). 
 - add ferrite beads for the 3.3V digital supplies.
 - look at 5V supply for VCC, VCCP, VCCR &VCCL (RCL for each one ?)

 Can really clean up the over design but like you said, it's a lot of work. 

 Going to dig out the datasheet for the PCM2702 again tonight and have read up on the 5V supplies.

 Alf, what do you think about all of this? 

 Botch...


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## guzzler

Just to put my little word in, changing the ground plane side should be a (fairly) trivial exercise, as Eagle will autoroute the ground plane around other traces. Just create a polygon and name in GND. Changing the bypassing to SMD is a good suggestion, as I feel that is the weakest part of the original design. I'm not a big fan of putting components under the board, I only did it on the PCM2902 layout (which I'm happy to share if anyone wants it) to squeeze in a little extra without making the board bigger. The best arrangement I've come up with for the oscilator would be this, with the components perpendicular to the osc:

 CRC
 |X|

 Alf, in the CUSTOM.LBR library I sent you there should be a modified USB socket with pads around the hole. Connect these to ground and you get shielding of the plug and better mechanical stability

 RCL for each 5V supply is not necessary, especially considering the quality of the REG102s. Also, remember the RCL network IS resonant, but damped (considerably) by the purely resistive element.

 I don't have time to do much with this unfortunately, but best of luck and I will, of course, advise if requested


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## Alf

Quote:


  Originally Posted by *Botch* 
_And I'm sure you thought this was going to be a simple mod._

 

Yes, indeed. I guess it is not really Revision B anymore. It is now more of <b>The Ultimate PCM2702 USB DAC</b> Do you the sound of it? I do.

  Quote:


  Originally Posted by *Botch* 
_Could you make the wire pads just a bit bigger? Seem to remember for the original they are a touch too small._

 

Do you mean the pads or the holes?

  Quote:


  Originally Posted by *Francis_Vaughan* 
_This is a lot of work to change. But if done means that most of the bypass capacitors can become SMD and be glued on without vias. Overall it will become massively cleaner and the RF performance improved further. This does mean that to remain a reasonably clean layout quite a few components will swap to the other side, but that is, after all, part of the joy of proper double sided design. Some nice gains can be had. For instance you can drop R3 right under the crystal, improving the layout, reducing loop area further, and hauling back more space. Similarly you will see many more components that can swap sides and much that will tighten up. But much work._

 

I played with this a wee bit. My initial impression is favourable. The board looks much better. I will not be able to finish the new layout tonight though. Here are my additional ideas:
 * C10, C11, C13, C14 may have to be 0805 package. It is pain to solder but this will give us a much better layout. 
 * R4, R5, R6 may need to go to the bottom layer.
 * 5V may have to be routed to VCC and VCCR through the bottom layer.

 Can we safely use a tantalum electrolytic capacitor for C12? A smaller package would help a lot. 

 Another related thought, since we go hardcore SMD, should we change all other capacitors to SMD too? Obviously CL, CR, C3, C9 will stay as they are. If we add more components to the board, the space will quickly become an issue.


  Quote:


  Originally Posted by *Francis_Vaughan* 
_The digital power is in two places, clock and main digital logic. Each should be separately fed, and in this case this really means adding an appropriate ferrite bead isolator before each of the bypass capacitors. Thus split the pad C18 and C19 attach to, and feed each of the splits with an SMD ferrite bead.Something similar might be appropriate for the analog side, although the lower frequencies involved might suggest some R in series with a bead as well, and perhaps more C. 
 You are building a mini LRC power supply filter for each unit - one designed to keep the crud floating about the board out of each unit. Since the units each have different functions we can design the filter to match the unit._

 

 Quote:


  Originally Posted by *Botch* 
_- add ferrite beads for the 3.3V digital supplies.
 - look at 5V supply for VCC, VCCP, VCCR &VCCL (RCL for each one?)_

 

I have some subconscious prejudice against excessive use of ferrite beads and RCL on a small board. I may be just completely wrong about it though. I need to think about it.

  Quote:


  Originally Posted by *Guzzler* 
_RCL for each 5V supply is not necessary, especially considering the quality of the REG102s._

 

I am not questioning the quality of REG102s. However here is 
 RMAA comparison between battery and desktop PC USB made by Magsy for Revision A. It clearly shows that USB is not dealt with well enough. I think it is mostly because USB power is too noisy for REG102 to handle. Since we are moving towards powering the DAC and a paired amp from USB, this should be taken care of more efficiently.

  Quote:


  Originally Posted by *Guzzler* 
_Alf, in the CUSTOM.LBR library I sent you there should be a modified USB socket with pads around the hole. Connect these to ground and you get shielding of the plug and better mechanical stability_

 

Yep, I found it. Thanks.


----------



## guzzler

It's all relative on the USB power front; the noise level is still down at under -100dB, which is a figure any sound card would like to shout about. I do agree that the stereo crosstalk shows considerable variation (I don't know why), but is still down at -60dB. The distortion figures are actually better with USB, but the difference is much smaller there.

 Makes sense to go all SMD, not much harder. 0805 is fine, just get small solder and a nice precise pair of tweezers (a pharmacy is a good place to try, Rapid also sell very nice ones)

 I would very much recommend against R4,5,6 going on the other layer if you're going SMD. They are the primary input to the design, and therefore should be treated as delicate signals (which they are) and have no vias in them


----------



## Alf

Quote:


  Originally Posted by *guzzler* 
_It's all relative on the USB power front; the noise level is still down at under -100dB, which is a figure any sound card would like to shout about. I do agree that the stereo crosstalk shows considerable variation (I don't know why), but is still down at -60dB. The distortion figures are actually better with USB, but the difference is much smaller there._

 

I meant not enough for The Ultimate DAC 
	

	
	
		
		

		
		
	


	





  Quote:


  Originally Posted by *guzzler* 
_I would very much recommend against R4,5,6 going on the other layer if you're going SMD. They are the primary input to the design, and therefore should be treated as delicate signals (which they are) and have no vias in them_

 

It is a digital signal. It should not be sensitive to such things.

 Anyway I looked at the board again. It seems that I can avoid this.


----------



## Francis_Vaughan

A few more thoughts.

 Again the trick may be to look at the functional block diagram, and also think about what sort of signals, clock rates and power supply requirements exist within. We do know a few things about how the device operates.

 We have a 12 MHz ocsillator, this drives the spact USB logic. I am assuming that the 12 MHz does not get multiplied up - in the 2900 series chips it is, but they can use USB 1.1 and thus will need it. Since we are limited to USB 1.0 in the 2700 chips assuming 12MHz is probably safe.

 The digital filter and DACs proper run at 128fs, so 5.6MHz. We can expect to see some energy at that frequency on the analog PS pins. We want to decouple these pins to avoid it getting back to other inputs. (Never forget - the decoupling of a power pin is just as much about stopping stuff getting out as it is about stopping stuff getting in. It is all about reducing coupling between circuits.) 

 So in the analog world we have 5 pins to worry about. 2 for the DACs, one for general analog stuff, one for the PLL, and one for decoupling the internal reference. 

 As good as any upstream regulator is, it is not residual noise from the regulator we are primarily worried about. It is the ability of the 2702's seperate components to interfere with one another. This is because the noise these components generate will have a high level of signal correlated energy. Energy from a DAC PS pin getting back into the PLL power pin will cause signal correlated jitter on the clock, and will create audible distortion components. 

 Although not directly connected to power, the reference pin does have a trace, and need a capacitor. We can assume that it is feeding the current reference in the DAC, and as the DAC element switches at 5.6MHz it will draw some current from this lead with this sort of frequency. The capacitor chosen will need very low ESR and ESL. It may be best to leave this part big enough to play with options to find the best type.

 One thing we have no idea about is the PSRR of the 2702. TI are curiously mute on this subject, so we should assume the worst. We don't know the exact current draw into each component, which is a pity. But we can make some assumptions. The 5v supply is listed as having a max draw of 25mA. So since we have two DACs we might assume that each might draw a maximum of 10mA each. We could easily think of adding some 10s of Ohms of series resistance to decouple each DAC, and incorporate this R into a ferrite bead. Similarly for the PLL and general Vcc leg. The PLL could probably easily go up to 100 Ohms. 

 One could go on for quite a while. The option might be available to create an external clock - the 2702 will accept one. Then build a low jitter clock - for instance Elso Kwak's designs. They are not large. Once that was done one could think about a different DC-DC converter - one that can take an external sync, and then run the converter at a divided down DAC clock rate, avoiding the possibility of heterodyned image products appearing. And so it goes. But getting the PS and decoupling right will be a huge win.


----------



## MASantos

I think that all these changes look really promising but the board is already almost double of the original one. This design is supposed to be a portable one and if it gets any bigger than it's current size this will be a downside.

 Alf, how big are those mounting holes??? They look around 5 mils in diameter?? I think that that is overkill, and something like 3 mils is more than enough( from the fisical point of view) . thsi owuld shave some space from the board!!

 Manuel


----------



## doobooloo

Quote:


  Originally Posted by *MASantos* 
_This design is supposed to be a portable one..._

 

Is it? If the design is to be portable I think it really should be DAC+amp on one board - which I would LOVE to see.

 I think this is more like, transportable or just "small enough on a desk" concept... no?

 Anyway. Personally I am fine with the bigger size (it's much better this way if I can use better components and it will fit in standard cases without creative mounting) actually but I can see the portability concern as well.

 I honestly think someone should start an integrated usb dac + amp project soon.


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_I think that all these changes look really promising but the board is already almost double of the original one. This design is supposed to be a portable one and if it gets any bigger than it's current size this will be a downside._

 

The size of Rev A board is 1922 sq mm. The size of the new board is 2725 sq mm. The component areas are about the same size. The increase is caused by additional mounting holes and empty areas at the top and the bottom. The board is designed to fit the smallest Hammond and the empty areas are required to slide it in. It is still very portable and will be much easier to mount.

 Now we have more components on the board and will have even more than that soon (RCL filters). However we will change more components to SMD and the final board may be even shorter than it is now.


  Quote:


  Originally Posted by *MASantos* 
_Alf, how big are those mounting holes??? They look around 5 mils in diameter?? I think that that is overkill, and something like 3 mils is more than enough( from the fisical point of view) . thsi owuld shave some space from the board!!_

 

The pads are 2.15mm in diameter and the holes are 1mm.


----------



## Alf

Quote:


  Originally Posted by *doobooloo* 
_I think this is more like, transportable or just "small enough on a desk" concept... no?_

 

Agree. You need USB for it and therefore a laptop or a computer.

  Quote:


  Originally Posted by *doobooloo* 
_I honestly think someone should start an integrated usb dac + amp project soon. 
	

	
	
		
		

		
			



_

 

We need to get the DAC part right first. Then we will do an integrated revision with an amp. It should be easy comparing to what we are going through now. 
	

	
	
		
		

		
		
	


	




 The integrated revision is not really required. Right now there is still some space left even if you put the DAC in 1455C802. It should be enough add a simple amp on a separate board. You can build an integrated solution with an amp of your choice in a small enclosure.


----------



## Alf

Quote:


  Originally Posted by *Sinbios* 
_One thing, I think the original DAC wasn't bit-perfect -- is it possible to make this version bit-perfect?_

 

Sorry, missed your question. 

 The DAC is capable of "bit-perfection". The problem is that the standard Windows USB driver resamples the audio stream to 48kHz. This is a limitation of the driver, not the DAC. There is a commercial USB driver that solves this problem but you have to pay for it. I don't have a link for it right now. Ask in the computer source forum.


----------



## jhawk22

edit: will keep eyes out for a gb thread


----------



## MASantos

Quote:


  Originally Posted by *Alf* 
_The size of Rev A board is 1922 sq mm. The size of the new board is 2725 sq mm. The component areas are about the same size. The increase is caused by additional mounting holes and empty areas at the top and the bottom. The board is designed to fit the smallest Hammond and the empty areas are required to slide it in. It is still very portable and will be much easier to mount.

 Now we have more components on the board and will have even more than that soon (RCL filters). However we will change more components to SMD and the final board may be even shorter than it is now.




 The pads are 2.15mm in diameter and the holes are 1mm._

 


 I need new lenses in my glasses!!!!


----------



## Alf

Quote:


  Originally Posted by *Francis_Vaughan* 
_The option might be available to create an external clock - the 2702 will accept one. Then build a low jitter clock - for instance Elso Kwak's designs. They are not large. Once that was done one could think about a different DC-DC converter - one that can take an external sync, and then run the converter at a divided down DAC clock rate, avoiding the possibility of heterodyned image products appearing. And so it goes._

 

Honestly, I think it is overkill for this project. This will push the price up while giving not so much value. Also the board will become too big. The target enclosure is the smallest Hammond. And an amp should fit in it too!

 Why don’t we keep this idea for a high(er)-end DAC design? The size and the price will not be a problem then! A lot of people are asking for this too. 

  Quote:


  Originally Posted by *Francis_Vaughan* 
_I think where I was trying to get to with the layout ideas is to look at the IC not as a monolithic thing, but as a system of connected units. The designers give you this ability since they bring out all the power pins. So if you refer to the block diagram in the data sheet it becomes clear what the goals are. Treat each of these units separately, give each its own well bypassed power so they can't interfere with one another, but also be cogniscent of the currents that must flow between the units, and thus the consequent return currents. Return currents are trivially dealt with with the solid ground-plane. It is hard to do better. So we worry about power. The digital power is in two places, clock and main digital logic. Each should be separately fed, and in this case this really means adding an appropriate ferrite bead isolator before each of the bypass capacitors. Thus split the pad C18 and C19 attach to, and feed each of the splits with an SMD ferrite bead.

 Something similar might be appropriate for the analog side, although the lower frequencies involved might suggest some R in series with a bead as well, and perhaps more C. 

 You are building a mini LRC power supply filter for each unit - one designed to keep the crud floating about the board out of each unit. Since the units each have different functions we can design the filter to match the unit._

 

Despite my complex relationships with beads and inductors, I think this is a good idea. Definitely it is worth a try. If things go terribly wrong and the beads cause problems, we can easily fall back by jumpering the beads and corresponding resistors.

 I updated the schematic and added new components as per your post. I plan to use Wurth 1206 package ferrite beads. Anything I missed there?

 Schematic v3 


 Francis, I leave the joy of calculating the values to you if you don’t mind.


----------



## Sinbios

Quote:


  Originally Posted by *Alf* 
_Sorry, missed your question. 

 The DAC is capable of "bit-perfection". The problem is that the standard Windows USB driver resamples the audio stream to 48kHz. This is a limitation of the driver, not the DAC. There is a commercial USB driver that solves this problem but you have to pay for it. I don't have a link for it right now. Ask in the computer source forum._

 

Aha, that removes all my reserves about this project. Sign me up for beta testing once it's in that stage or something


----------



## Botch

Quote:


  Originally Posted by *Alf* 
_Honestly, I think it is overkill for this project. This will push the price up while giving not so much value. Also the board will become too big. The target enclosure is the smallest Hammond. And an amp should fit in it too!

 Why don’t we keep this idea for a high(er)-end DAC design? The size and the price will not be a problem then! A lot of people are asking for this too._

 

Agree with you Alf. I've read that the SpAct is rather good anyway and let's try to keep it simple. 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *Alf* 
_Despite my complex relationships with beads and inductors, I think this is a good idea. Definitely it is worth a try. If things go terribly wrong and the beads cause problems, we can easily fall back by jumpering the beads and corresponding resistors._

 

Nice, schematic is looking good and I think this will bring a win for us. Just make sure the caps are as close to the ground pins as possilbe on the layout.

 Francis, nice post above. 

 Looking forward to the next update Alf. 

 Botch...


----------



## 00940

Some times ago, someone suggested to take the inputs of both regulators from the V+ rather than derivating the digital supply from the analog supply.

 As far as an external clock is concerned, here's what I was toldhere :

  Quote:


 No point to do it. You 'll not improve nothing. SPACT system has own VCO, which determine phase noise level of the output clock. XTAL clock only provide functionality of SPACT system, but it is not reference signal of SPACT. Phase random walks, which depend by jitter of XTAL clock, has enough high frequency spectrum to be eliminated by analog PLL, which followed after SPACT.


----------



## Francis_Vaughan

I totally agree. The quip about an external clock and bits was really to put in context what is trying to be achieved here. One can always argue that no matter how good the internal PLL is, it can never totally remove _all_ jitter, and any improvement on an upstream clock will have _some_ effect. But it is very likey to to be as close to a waste of time as one could get. I'm certainly not seriously suggesting it, and indeed would actually argue against it. (One could - and probably should - also argue that unless one actually tries the experiment no-one actually knows.)

 I'm not sure why the particular choice of Wurth ferrites, although they do rather nicely provide Eagle files for download.


----------



## Alf

Quote:


  Originally Posted by *Francis_Vaughan* 
_I'm not sure why the particular choice of Wurth ferrites, although they do rather nicely provide Eagle files for download._

 

That's why. 
	

	
	
		
		

		
		
	


	




 In fact, I have no preference.


----------



## Alf

I replaced MAX1722 with TPS6734 and LM317A. Both ICs are cheap and easy to get. This gives us 9V from USB to power an amp. It will not be as good as TREAD but should do for portable use.

 Schematic v4


----------



## cetoole

Alf, looks good, but any reason you chose to have 9v final? I think it would probably be a better choice to have about 12v after regulation, so maybe use a 15v DC-DC converter, and possibly an LDO regulator instead of the LM317. There are a couple 5v to +/-5v or so DC-DC converters available, which would probably take care of our issue completely right? Only problem would be the voltage being a little low on each rail.


----------



## diablo9

just curious, I heard Headroom Micro DAC use Cirrus CS4398, supposely a flagship part. Is there any reason not to use that?


----------



## Nisbeth

Quote:


  Originally Posted by *cetoole* 
_Alf, looks good, but any reason you chose to have 9v final?_

 

Max. input voltage for the REG102xx is 10V 
	

	
	
		
		

		
		
	


	




 diablo9: The CS4398 is "only" a DAC, it doesn't have a USB-interface.


 /U.


----------



## diablo9

what about giving BB PCM2902, which feed to CS chip? just like what they did on MicroDAC, 
 nevermind, that's becoming a clone. against the policy...


----------



## 00940

you would need a pcm2902, giving spdif, into a cs8416, giving I2S, into a cs4398. I wouldn't call it a clone though, even if parts are similar to the micro-dac, because the good choices for usb/spdif receivers are extremely limited and the power supplies, layout and so on matter a lot for dacs' sound, something you couldn't (and shouldn't) copy easily. You could of course substitute a WM8740 for example. 

 Another option is pcm2707 giving directly I2S to your cs4398 but then you don't have the possibility of a spdif input (coaxial or optical). It would be a bit stupid for a higher end dac.


----------



## Alf

Quote:


  Originally Posted by *diablo9* 
_just curious, I heard Headroom Micro DAC use Cirrus CS4398, supposely a flagship part. Is there any reason not to use that? 




_

 

CS4398-based DAC will be at least twice as big, will cost at least twice as much and what is more important it will not be PCM2702 DAC anymore


----------



## MisterX

lol.... when did that ever matter?


----------



## Francis_Vaughan

The important thing is that this is an evolutionary change to a known good design. With what one hopes are useful improvements to layout and PS, a body of experience can be built. 

 Doing such an evolution is more valuable than simply grabbing for the latest chip, and in a cargo cult design mentality doing a total scratch start.


----------



## Botch

Quote:


  Originally Posted by *Alf* 
_I replaced MAX1722 with TPS6734 and LM317A. Both ICs are cheap and easy to get. This gives us 9V from USB to power an amp. It will not be as good as TREAD but should do for portable use.

 Schematic v4 _

 

When reading this post I have assumed the LM317A is similar in noise and impedance behaviour to the larger 3 pin LM317T package. 

 A couple of questions/suggestions and something for everyone to read on power supplies:

 - Looking at the schematic for the LM317A there should be a cap over R15 (between adj and gnd) as this reduces noise. 
 - Should we have 2 diodes (1 across the input/output & 1 across the output/R14) for protection it the case of the output voltage exceed in input voltage on shutdown, which could cause damage (maybe)? 

 Have a look on the datasheet for examples of this.

 We also have to pay attention to the input and output caps for this regulator (ignoring 100nF caps). There is no large input cap and a 2 output caps currently - C25 (33uF) in parallel with C3 (1000uF). Not ideal at all, see the datasheet. 

 [edit] Oops, I missed seeing C20 (33uF) on the input but we still need to do something here as the output capacitance is far greater than then input capacitance.[/edit]

 We need something before the regulator (let say ~1000uF) and a medium sized (lets say ~220uF) cap on the output. The output cap should have a medium ESR (not low ESR). What will adding a big cap on the input do to IC1 (TPS6734)? Need to check this guy also but guess it will be okay.

 Why? I can try to explan badly but the easiest way it to have a read of these articles on TNT-Audio based on testing the LM117/317. The tests are based on the 3 pin version but should be applicable to the A version (similar technology I presume).

http://www.tnt-audio.com/clinica/solidstate.html

 particularly:
http://www.tnt-audio.com/clinica/reg..._noise2_e.html

 From this article:
 "....bypass[ing] the adjustment pin, in our case with a 22uF ZL. And what happens? Noise is reduced tenfold with about 20dB."

 and:
http://www.tnt-audio.com/clinica/reg...edance1_e.html

 From this article:
 "The output impedance of the LM317, even at DC, depends strongly on the load current, with impedance dropping with increasing load. This is not new, and it is precisely the reason why it is always recommended to ensure that such a regulator chip sources at least 10mA, preferrably 30mA, no matter what the actual load demands. At 100mA and more the impedance goes as low as 30mOhms or so, turning inductive above a low 400Hz. This is typical for a circuit relying on loop feedback, using an error amplifier with not a lot of gain and not a lot of bandwidth."

 [OK, we have a load of ~40ma for our DAC and this is could be area where the 317T & 317A could behave differently (maybe), but is still important to think about it.]

 and

 "Adding an output capacitor effectively bypasses the regulator at higher frequencies. As the LM317 is inductive in these regions, this makes for a resonant circuit and hence some damping in the shape of a not-too-low capacitor ESR is called for: it is good to follow LM317s with a relatively big cap, but it is bad to use a low-Z cap there!"

 [Need to do something about the status of the input and output caps.]

 All the TNT Audio articles are worth reading as they have interesting info on different types of regulators. 

 Just my afternoon post for the group, back to work now. Lets keep the evolution of this design going. 
	

	
	
		
		

		
		
	


	




 Botch...


----------



## diablo9

Quote:


  Originally Posted by *Alf* 
_CS4398-based DAC will be at least twice as big, will cost at least twice as much and what is more important it will not be PCM2702 DAC anymore 
	

	
	
		
		

		
		
	


	


_

 

hehe, that's OK, we can stick to PCM2702 this time, maybe next time someone will work out CS4398 design, in some distant future.


----------



## Alf

Good comment, Botch! I have updated the schematic. I also incorporated a few TREAD part selection hints from Tangent’s site. There are a few discrepancies between Tangent’s recommendations and those from tnt-audio. I wonder whether Tangent would care to comment this. 

 Schematic v5 

 Changes:
 * Updated LM317 section.
 * Implemented recommendations from the TI datasheet regarding REG102.
 * Decoupled 5V and 3V3 sections. Now they both are powered from 9V as suggested by 00940.
 * Sorted out the component names.


----------



## Alf

The last change has been quite a challenge. It took me about 20 hours to prepare this update. I hope the result is worth it.

 Schematic v6 

 Board v4 


 Changes:
 * Completely re-designed the board. 
 * Removed some ferrite beads – please comment if this makes any sense to you.
 * Made wire pads bigger (Botch).
 * Used a modified USB socket with pads around the holes for additional shielding and stability (Guzzler).

 The part list has changed significantly. I aim to post a BOM draft tomorrow.


----------



## doobooloo

Looks great! This is definately very exciting - I'm looking forward to the test results!


----------



## doobooloo

One question... what's the purple line on the board layout that is feeding from the 5V pad to underneath the PCM2702 chip?

 If this is just an external connecting wire that needs to be manually soldered, is it possible to:

 1. Eliminate this wire completely; if this is not possible...
 2. Have only one pad not three (connect the three pads on the board), and...
 3. Have the pad somewhere in the open, not underneath the DAC...

 OK so maybe it isn't a jumper wire... 
	

	
	
		
		

		
		
	


	




 Anyway, any input/enlightenment would be greatly appreciated!


----------



## cetoole

Quote:


  Originally Posted by *doobooloo* 
_One question... what's the purple line on the board layout that is feeding from the 5V pad to underneath the PCM2702 chip?

 If this is just an external connecting wire that needs to be manually soldered, is it possible to:

 1. Eliminate this wire completely; if this is not possible...
 2. Have only one pad not three (connect the three pads on the board), and...
 3. Have the pad somewhere in the open, not underneath the DAC...

 OK so maybe it isn't a jumper wire... 
	

	
	
		
		

		
		
	


	




 Anyway, any input/enlightenment would be greatly appreciated!_

 

That looks like a trace on the bottom of the board to me. Great job Alf, that looks really sweet.


----------



## Francis_Vaughan

Umm, you are going to hate me, but I think you have seriously missed the point. Despite all the work put in, I'm afraid it is misdirected, and has taken the design in exactly the wrong direction. 

 You seem to be trying very hard to, in some sense, protect the analog supply rail, so much so that you have really badly damaged what was a good ground-plane. Indeed the ground-plane is almost destroyed and won't function properly. The thinking seems to be very much DC or audio frequency based, and has lost sight of the RF nature of the system.

 The system will have harmonic switching components well into the hundreds of megahertz floating about. You _must_ design the layout with this in mind.

 Right, to the plot.

 The analog power rail is not nearly so important as you think. Remember in all electronics it is symmetric, the ground terminal introduces exactly as much distortion or interference as the supply. But it gets worse. The ground is the reference supply, everything in the system needs an intact ground. We must manage the ground return currents, including those that flow between the digital and analog sides. The most important thing you must do in your design is ensure the integrity of the ground. This design has almost totally destroyed it.

 The de-coupling of the power supply is a two terminal effort, that is why the functional units have brought out both power and ground, and very helpfully put them on adjacent pins. The best possible de-coupling of the power and ground is to short circuit the power and ground pins. Now, since that prevents the circuit from working we do the next best thing - we tie them together with a capacitor. That circuit between the pins must be as short as possible. If you look at the latest board you can find a number of examples where the power de-coupling has been forced to wend its way all over the place before connecting back to the relevant power pin. Trace out the path the current must take between any power pin and its ground pin via the de-coupling capacitor. Each of those paths is now an antenna, it will radiate or pick up energy from any nearby loop. You will find resonances and inter-component coupling that is rampant, leading to a very serious reduction in quality. The jitter will be very high, and the amount of energy coupling into the analog side from the digital side very high - so much so that the I/V converter will probably be well outside of its operational slew rate.

 Look at the ground return path for the analog supply. Despite the lovely carefully laid out power trace, the ground return is left to its own devices to find its way home through a maze of little routes, and even the route to the ground pin of the regulator IC (and thus a route by which noise can be introduced) is very circuitous. Any energy coupling into this - and any disturbance of the ground will get straight into the analog side and produce distortion.

 I'm sorry to say this, but the time invested has been wasted. There is nothing salvageable from this approach, and the board layout is vastly inferior to the previous version - which was pretty good, needing only some further pushing and tweaking to optimise.


----------



## 00940

Francis : I've got a short question.

 Does the PCM2702 really have to be put directly on the groundplane ? I designed the first version of this thing, the global layout of the beast is my fault 
	

	
	
		
		

		
		
	


	




 From what I remember, when trying first to put the groundplane on top, it was a real nightmare, mostly when trying to follow rules like "every digital line must be over a continuous groundplane".


----------



## Alf

Francis, I am a bit confused. You are talking about circuitous routes to the ground, while in fact the routes became much shorter with this layout.

 Let’s have a look.

 C19, C20, C21, C23 have the shortest possible direct routes to their ground pins.

 C22, C24 have a bit more complex routes but shorter than before (C22 route goes under C24).

 C18 - Not direct but quite short (under L5). I may be able to improve it though.


----------



## Francis_Vaughan

The idea is to get the critical traces and leads as close to the ground-plane as possible. The trick is to look at the system edge on. If you have the ground-plane on the other side all the ground pins must go to the ground-plane through a via - and so the loop area when viewed from the edge is much larger. When viewing the loop we include the lead-frame inside the package as well. These loops couple with one another. The bigger the area the greater the coupling.

 The reason for running any digital line over a ground-plane is that the return current at these frequencies will try as much as possible to stay in that part of the ground-plane next to the line. There will be little current flowing elsewhere in the ground-plane. By cutting the ground-plane or moving the trace further away this effect reduces and the disturbance around the line increases. The same logic is true of the actual power supply lines between the de-coupling capacitor and the IC.

 Luckily the adjacent power and ground pins help here - as opposed to those packages where the power enters and exits via opposite legs - which makes life much worse. But even with the gains due to these parallel power lines we must still cope with the remaining return currents for signals that move from unit to unit inside the IC, and at any instant these could be running from any power pin to any ground pin, so keeping the entire IC and lead-frame as close to the ground-plane is a good thing. Moving the ground plane from the opposite side to the near side reduces the distance from the plane to the traces dramatically, say 3 mm to much less than 1 mm.

 By doing so we are able to keep the individual component systems in the IC operating with as low a disturbance as possible of their individual power. In particular with the least RF energy introduced from other parts of the system.

 When the analog PLL for the DACs is so close to the other stages, and under certain circumstances there are close harmonic relationships between the different clocks (see later) there is significant danger of introducing signal correlated noise into the clock. This creates extremely unpleasant distortion products. 

 There is a special danger with inputs at 48kHz sample rate, as this will result in a 256fs = 12.288 MHz DAC clock, which is a bit close to 3/2 * 8 MHz - and there for a harmonic of the main system clock. So there is a possibility for some modulation products of particular worry to occur. Even more reason to keep the stages as clean as possible.


----------



## Francis_Vaughan

Alf, yes, there is some good improvement in some of the caps, and indeed C18 was the one I was referring to as sub-optimal. Actually around the IC the ground plane is OK, and the bypassing in that region is OK - although tweak-able still I bet. But the damage to the ground-plane everywhere else seems just plain odd. Getting a totally continuos ground-plan under the IC would be good however.

 Why stop using the other side? It just seems weird to have moved so many traces onto the top side - where they cut up the ground-plane - for no good reason. 

 With the cut up ground-plane you invite all sorts of cross coupling and resonances and invite much disturbance of the ground.

 For instance, there is a loop that starts at the IC ground-plane, heads down, left across the bottom of the design, up under the USB socket, up, past the 12 volt pin, around C15, right, under C14, under crystal and under the IC. This will pick up RF energy, and couple it into anything nearby, including the IC and the analog power trace. There are also long spindly bits of ground-plane with bits hanging off them that look for all the world like small capacitors and inductors teamed up.


----------



## 00940

/edit


----------



## Botch

Hi Alf, good to see the updated board and I can see a lot of work has gone into it. Well done (I mean it)! We have definately improved the schematic but we need to keep at it with the layout. There has been some very good comments from Francis here and they should not be taken as criticism but ways of improving the end product.

 Just looking at the layout I would like to add my suggestions/ideas. Think it is easier if I say where I would move things to but take these comments just as ideas only. 

 - What spacing do you have set for the ground plane? Looks very close to the tracks (note I don't have a lot of SMD experience so can not say what is should be). Maybe increasing the spacing a little will help remove the ground plane from places that it will not make a big difference too. Can anyone else with experience comment on this please.

 - Remove C4. As we have C5 I can not see a need for it. Or does anyone have a problem with this?
 - move the 12V pad to the top of the board out of the way. It just goes into IC3 so no need to have it where it is.
 - maybe move all of the IC2 stuff up a bit, L1 to the left a bit etc. There is some space there
 - shift D2 to the right and up a bit, maybe also C7 a little.

 This gives us a bit more space to play with for the 3.3V regulation and to look at its ground paths.

 Without having the layout in front of me to play with I'm just trying to visualise things. Have a play with these ideas and see how it goes.

 - move C15 to the other side of the IC5 and rotate it 180°. This cap should be as close as possible to the ground pin on the IC5 to minimise loop distance to prevent introducing noise on the ground.
 - rotate C13 it 180° (for reason above)
 - possibly move R4 down to where R5 is to free up space. You have to run 3.3V down there anyway.
 - Rotate C19 either 90°CCW or 180° and place the ground pad as close as possible to DGND.
 - Move C18 and place the ground pad as close as possible to DGNDC.

 Now we have to think a bit again. 
 - There is some space to move IC5 (and C13 & C15) to the left, possibly rotating it 90° (CW or CCW - see how it looks both ways). CCW may be better but have a play here, thinking about the ground paths also. 
 - C14 will move with IC5.
 - If you move the IC5, maybe place C16 & C17 to the top of the crystal giving more space to layout supply and ground paths to the left of IC1.

 Where is the 3.3V track running now? Do the ground paths for this supply have a direct path back from IC5? Can you see a way of removing the ground loop that Francis described in his last post?

 While we are looking at it, you have a 3V3 wire pad. I assume this is for having an external 3.3V supply (nice idea btw). If that is the reason why not add an extra GND pad close to the IC5 ground. Could also add an extra GND pad for the 5V supply next to IC4 and have 2 external power supplies, overkill maybe but would be an interesting test. 
	

	
	
		
		

		
			





 Analog output. Have not had a really good look at this but the principle locating the ground pad of the decoupling caps as close as possible to the gnd pin of the IC may need attention (C20, C21, C22 & C23). Space it tight here also but give it a shot. Maybe also rotate C24 around for the ground pad to close to the IC1 ground pin.

 Some of the grounds on the analog side also have a long loop back to the 5V supply. Would sending the output signals (VoutR & VoutL) to the bottom layer from IC1 with a via and routing to CL & CR improve this? Would it effect the output quality? Not sure here.

 Wow, this started out a little post but I think I got carried away (I'm not trying to design your board - honest 
	

	
	
		
		

		
		
	


	




 ). Better get back to work now. 

 Like I said these are just ideas to think about. Keep at it Alf, you will a happy man the day you get one of these boards in your hands. 
	

	
	
		
		

		
		
	


	




 Botch.


----------



## Clutz

Hey Alf,

 I cannot comment on the design - I don't know nearly enough. I just wanted to let you know I'm really excited about this!


----------



## Alf

I had no time to spend on the project today. I will try to move some traces to the bottom layer to improve the ground. I will work on C18 too.


 Botch: C4 cannot be removed. TPS6734 datasheet is very specific about this capacitor and its location. I will try your other suggestions.


----------



## Botch

Hi Alf,

 don't rush over this. 

 You know with C4 it is is parallel with C5 so your capacitance probably not to spec anyway. Have a look at it. 

 Sorry about the big post before but just got looking at it and had ideas. You know how it happens.

 I've printed out the latout and schematic and I'm trying to imagine how I would connect the grounds, especially in the power supply sections using a star ground method. Hmmm, try it out and see what you think. 

 Can we think about running some supply traces on the bottom layer to help out our ground plane? Especially the ones before we do the final 3.3V & 5V regulation?

 The USB 5V, 12V and 9V traces are all candidates.

 Just moving a few traces really starts to open the design up. We can now start to look at individual ground paths for the caps on each regulator now. 
	

	
	
		
		

		
		
	


	




 Time for bed.

 Botch...


----------



## Francis_Vaughan

Need to be careful here. A star ground is the wrong answer in any circuit with RF signals running about. 

 The whole idea of a star ground is to avoid interference of one ground return signal by another. That is if you have a signal ground return sharing the same conductor as a power ground return, the tiny resistance in the ground conductor will cause any change in current in the power return to create a voltage drop that will appear on the signal return. So we don't let the returns share conduction paths.

 With RF about this doesn't work anymore. The individual traces for the ground act as coupled antennae, and cheerfully make the interference worse, not better. A single solid ground-plane has the effect of confining the RF energy in the traces to the vicinity of the trace, effectively providing an automatic star ground that is always as perfect as possible. Whilst it might be argued that the solid ground plane might allow for some cross interference at low frequencies, if there are very large return currents about, in reality, in a low level, low power device like a DAC this isn't going to occur. 

 It is possible to argue for some separation in the ground-plane to avoid the most low level of disturbance from appearing in critical places - like the Vref and DAC grounds. But it is very difficult to manage, and a trade-off that could only really be understood with RF simulation tools. (There is a possibility of making two very small cuts in a precise location under the IC, but that should only be considered as a controlled experiment after circuits are built.


----------



## Botch

I should have been clearer. I'm not proposing to use a star ground at all. I was just using it as an example of imagining the paths the return currents would take. Several of the power supply grounds have very long return paths with the current design. Maybe moving some of the supply traces to the bottom layer will help this.

 It was late last night when I did the other post. What I wanted to say was clear in the head but.... 
	

	
	
		
		

		
		
	


	




 Botch...


----------



## Francis_Vaughan

OK, indeed this is exactly the right approach.


----------



## 00940

I was bored last night and couldn't sleep, so I came back to this old pcm2702. I tried to take some more care to decoupling, while preserving a decent groundplane on top. Certainly not a complete board but some food for thought. 






 (bigger )






 (bigger )


----------



## Alf

Moving the supply traces to the bottom should not be a problem. My concern is that even if it is done, we still have a few thin ground traces around PCM2702 running between the signal traces and potentially causing interference as Francis suggested. There is no way around it. We can either disregard this or move the ground plane back to the bottom as in the original design.


----------



## Alf

Quote:


  Originally Posted by *00940* 
_I was bored last night and couldn't sleep, so I came back to this old pcm2702. I tried to take some more care to decoupling, while preserving a decent groundplane on top. Certainly not a complete board but some food for thought._

 

Nice approach! 

 I agree that we should use less SMD components on the top layer. This can be achieved in two ways:
 * Move some SMD components to the bottom
 * Replace some SMDs with their through-the-hole equivalents.


----------



## Botch

Quote:


  Originally Posted by *Alf* 
_Moving the supply traces to the bottom should not be a problem. My concern is that even if it is done, we still have a few thin ground traces around PCM2702 running between the signal traces and potentially causing interference as Francis suggested. There is no way around it. We can either disregard this or move the ground plane back to the bottom as in the original design._

 

I have something to try for this off the top of my head. 

 Looking at the analog section supplies and thier coupling caps. If you move the vias for the 5V from under IC1 to the right of the chip you have a nice gound under the IC now (Francis hinted at this in a previous post). Wire the ground pins directly to under the chip to this ground. Then position C20 to C23 (rotate 180° from current orientation) so thier gnd pad is as close to the ground pins as possible. This makes the ground track lengths as short as we can get them.

 Drop the CR and CL signals to the bottom layer. Have the 5V coming in on vias for the analog supplies/coupling caps.

 The position of R7 may have to go to the bottom, maybe.

 Francis, could you please comment on this idea? Will having the analog ground running under the IC be a good solution here. Really busy at work today so not had a time to really think about this.

 Botch...


----------



## Francis_Vaughan

00940 seems to have beaten you to the punch a little, but yes, this is exactly the right approach. The idea of swinging the bypass capacitors even further around is good. The design above from 00940 is clearly well on the way there, and one can imagine ages of carefull jostling of placement to get it as close to perfect as one might wish, but the combination of ideas is very much on track. 

 It is just annoying how tight things are around the IC, even just a tiny bit more room would have been so helpful. (Why did they have to put the useless test pins right at the end?)


----------



## Clutz

Quote:


  Originally Posted by *Francis_Vaughan* 
_00940 seems to have beaten you to the punch a little, but yes, this is exactly the right approach. The idea of swinging the bypass capacitors even further around is good. The design above from 00940 is clearly well on the way there, and one can imagine ages of carefull jostling of placement to get it as close to perfect as one might wish, but the combination of ideas is very much on track. 

 It is just annoying how tight things are around the IC, even just a tiny bit more room would have been so helpful. (Why did they have to put the useless test pins right at the end?)_

 

Can't you use a larger PCB to address some of these problems? (I don't know anything about PCB layout- I'm just asking out of curiousity)


----------



## 00940

A little detail. On my board, I didn't use thermals (the little cross making it easier to solder to the groundplane) on the smd pads. It allows Eagle to route continuously in some places, where it wouldn't be able to do so with thermals on. And so some critical mils are gained. 

 Speaking of mils, what are you guys using for a grid ? I'm usually working with a grid of 12.5mil.


----------



## Alf

Quote:


  Originally Posted by *00940* 
_A little detail. On my board, I didn't use thermals (the little cross making it easier to solder to the groundplane) on the smd pads. It allows Eagle to route continuously in some places, where it wouldn't be able to do so with thermals on. And so some critical mils are gained. 

 Speaking of mils, what are you guys using for a grid ? I'm usually working with a grid of 12.5mil._

 

00940:

 The grid 12.5mil and thermals are turned off. I use the brd file Guzzler sent me which I presume he got from you. So I should have all your original settings.

 Speaking of Eagle, I have a few particular problems with this beast:
 * Why do I have to press F2 all the time? Can Eagle redraw automatically?
 * If I place a via under an SMD pad as in your picture above, I get a clearance error.
 * Can I make SMD ground pads to merge to ground plane without these annoying corner cut-outs?


----------



## cetoole

Eagle doesnt automatically redraw that I know of, quite annoying to me too. To place a via under a pad, and not get DRC errors, go into DRC, clearance tab, and change the same signal values to 0mil.


----------



## 00940

Quote:


  Originally Posted by *Alf* 
_Speaking of Eagle, I have a few particular problems with this beast:
 * Can I make SMD ground pads to merge to ground plane without these annoying corner cut-outs?_

 

Those cut outs are the thermals 
	

	
	
		
		

		
			





 Yes, go to "change", "thermals", "off" and then click on your groundplane.


----------



## Alf

00940, cetoole: Thanks for the Eagle lesson! 

 One more question. How can I put a picture on a board?


----------



## Alf

Here is an updated board layout following your suggestions. 

 Board v5 - Top

 Board v5 – Bottom

 Board v5 – All without bPlace


 Feel free to bash it!


----------



## Alf

Quote:


  Originally Posted by *Clutz* 
_Can't you use a larger PCB to address some of these problems? (I don't know anything about PCB layout- I'm just asking out of curiousity)_

 

No, this would not help. If you follow this thread from the beginning you will see that we fight for having the bypass capacitors as close to the IC as possible. The size of the IC and the unfortunate location of its pins makes this a challenge.


----------



## doobooloo

Looks great! 
	

	
	
		
		

		
		
	


	




 Is it possible to have shorter leg spacings for C6, C7, C10, and C14? Looks like in order to fit the right cap sizes the spacings need to be a bit shorter. I think those spacings are meant for machine-assembly types with pre-bent legs?

 Or I could be totally wrong, but it would be nice if all straight-legged electrolytics that most DIYers use could just slide in without much effort.


----------



## Francis_Vaughan

It looks most good.

 One could probably spend from now until the end of eternity fiddling with the exact layout, getting the last bit of tightness. But it is well on track.

 Might be worth sticking holes at a few separations for the output capacitors, so that those with boutique tastes can indulge them.


----------



## MASantos

Quote:


  Originally Posted by *Francis_Vaughan* 
_It looks most good.

 Might be worth sticking holes at a few separations for the output capacitors, so that those with boutique tastes can indulge them._

 

Absolutely right!!


----------



## MASantos

If we put this board next to a mint, are they the same size?


----------



## guzzler

I still recommend using the USB socket with the grounded tabs, makes the whole thing a lot more stable and could improve the shielding. You can just use change->package to do it. It's in CUSTOM.LBR that I sent you. Other than that, looks very nice :


----------



## Nisbeth

Quote:


  Originally Posted by *MASantos* 
_If we put this board next to a mint, are they the same size?_

 

I belive this board is a bit larger than a mint board so I will fit straight into the smallest hammond case (1455C801) 
	

	
	
		
		

		
		
	


	





 /U.


----------



## Alf

Quote:


  Originally Posted by *Francis_Vaughan* 
_It looks most good._

 

Wow! I thought I would never hear these words. 
	

	
	
		
		

		
		
	


	





  Quote:


  Originally Posted by *guzzler* 
_I still recommend using the USB socket with the grounded tabs, makes the whole thing a lot more stable and could improve the shielding. You can just use change->package to do it. It's in CUSTOM.LBR that I sent you._

 

I do use USB socket from CUSTOM.LBR




			
				doobooloo said:
			
		

> Is it possible to have shorter leg spacings for C6, C7, C10, and C14? Looks like in order to fit the right cap sizes the spacings need to be a bit shorter. I think those spacings are meant for machine-assembly types with pre-bent legs?
> 
> Quote:
> 
> ...


----------



## guzzler

Ok, cool. Connect the two pads to ground and the plane will fill around them


----------



## Botch

Hi Alf,

 Congrats on the latest layout, looking damn good.

 Just a couple of things, nothing big at all.

 I really do not like traces between caps and you have the 5V line running under the CL cap. Hard to see a way around it, shifting the CL via under IC1 up a bit and bring it in that side maybe? Dunno.

 Now the 5V line is on the bottom layer is the idea of having ferrites on all 5V supplies worth thinking about again? Anyone have an opinion here? Wonder if it will improve channel seperation. Have lots of space under there and if people do not want to use them then can just be jumped out.

 Can R2 & R3 be mounted flat instead of vertically? Hate vertical resistors. 
	

	
	
		
		

		
			





 About the only other point is that several of the tracks, especially on the bottom layer can be wider. 

 And like the idea of having different spacing for Cl & CR mentioned above.

 There are lots of little tweaks of course to think about but it is finally almost there. Will print it out and have a good look over it. 

 Nice work, the end of the tunnel is near. 
	

	
	
		
		

		
		
	


	




 Botch...


----------



## Francis_Vaughan

Quote:


  Originally Posted by *Botch* 
_I really do not like traces between caps and you have the 5V line running under the CL cap. Hard to see a way around it, shifting the CL via under IC1 up a bit and bring it in that side maybe? Dunno._

 

Can't do that. That puts the capacitor on the other side of the power input, so it is now working through a short inductor (the remainder of the trace to the pin) before it can de-couple the power. The trace must meet the capacitor before it reaches the pin.

 I don't really see any issue with the trace under CL. 


  Quote:


 Now the 5V line is on the bottom layer is the idea of having ferrites on all 5V supplies worth thinking about again? 
 

Absolutely. It think this is most important.

  Quote:


 About the only other point is that several of the tracks, especially on the bottom layer can be wider. 
 

Take care they are not made too wide. Avoid any temptation to create anything that resembles a power plane. Those tracks have a capacitive coupling to the ground plane, if that capacitance gets too big you have a distributed RF capacitor that can resonate.


----------



## Alf

I put together my notes regarding the parts used on the board. Please free to comment. In particular I would appreciate if you could make sure that all values/sizes/packages are correct and are available in your country. If not, please specify alternative parts. Also please suggest boutique parts the design would benefit from. I will try to accommodate all your suggestions.

  Quote:


 IC1 – PCM2702E. SSOP28 package.

 IC2 – TPS6734. SO8 package.

 IC3 – LM317/LM317A. SOT223 package.

 IC4 – REG102-5. SO8 package.

 IC5 – REG102-33. SO8 package.

 IC6 – Optional. BUF634U. SO8 package.


 USB – Type B receptacle. BERG 61729.

 X1 – Crystal 12MHz CL=30pF. HC49 package.


 L1, L5, L6, L7– Ferrite 600R. 1206 package. Murata BLM31AJ601SN1L 

 L2 – Radial. 18uH. >= 1A. High Q. 7.2mm diameter. 3.5mm pitch. Suggestions??????


 D1 – Schottky diode. 1N5817.

 D2, D3 – Standard recovery diode. 1N4004.


 C1 – Ceramic. 47uF. 6.3V. 1210 package.

 C2, C4 – Tantalum electrolytic. 33uF. 16V. Radial. 6.3mm diameter. 2.5mm pitch. Lowest ESR < 0.25R. SANYO OSCON SC/SA. 

 C3 – Ceramic. 1nF. 1206 package. AVX/EPCOS/MULTICOMP.

 C5 – Aluminium electrolytic 820uF. 16V. 10mm diameter. 5mm pitch. Height <=15mm if used with 1455C enclosure. Panasonic FC.

 C6 – Tantalum electrolytic 10uF. 16V. Radial. Up to 5mm diameter/pitch. AVX/MULTICOMP.

 C7 – Tantalum electrolytic >= 1uF. Medium ESR (>= 1R, the more the better?). 16V. Radial. Up to 5mm diameter/pitch. AVX/MULTICOMP.

 C8, C12 – Aluminium electrolytic 100nF (1uF????). Low ESR. 6.3V. Radial. 4.0mm diameter. 2mm pitch. SANYO OSCON SC/SA.

 C9, C13 – Optional. Ceramic 10nF. 0805 package. AVX/EPCOS/MULTICOMP.

 C10, C14 – Optional. Tantalum electrolytic >= 10uF (47uF). 6.3V. ESR >0.05R. Radial. 6mm diameter. 5mm pitch. AVX/MULTICOMP.

 C11, C15 – Optional. Ceramic 470nF. 0805 package. AVX/EPCOS/MULTICOMP. 

 C16, C17 – Ceramic 33pF. 0805 package.

 C18, C19, C20, C21, C22, C23 – Ceramic 100nF. 0805 package.

 C24 – Aluminium electrolytic 47uF. Lowest ESR, ESL. 6.3V. Radial. 6mm diameter. 2.5mm pitch. SANYO OSCON SC/SA

 CL, CR – Pro audio grade aluminium electrolytic 47uF. 6.3V. Radial. 6mm diameter. 2.5mm pitch. Black Gate Nx HIQ, ELNA Silmic II.


 R2 – Metal film resistor 750R 1/4W. Axial.

 R3 – Metal film resistor 120R 1/4W. Axial.

 R4 – Metal film resistor 1.5K. 1206 package.

 R5, R6 – Metal film resistor 22R. 1206 package.

 R7 – Metal film resistor 1M. 1206 package.

 R8, R9 – Metal film resistor 330K. 1206 package.


----------



## diablo9

it looks like IC5 can't be found on digikey or mouser


----------



## MASantos

Quote:


  Originally Posted by *Alf* 
_I put together my notes regarding the parts used on the board. Please free to comment. In particular I would appreciate if you could make sure that all values/sizes/packages are correct and are available in your country. If not, please specify alternative parts. Also please suggest boutique parts the design would benefit from. I will try to accommodate all your suggestions._

 

All of these parts are impossible to get here in Portugal, so everything must be bought online. 

 regarding C5, you say:
 C5 – Aluminium electrolytic 820uF. 16V. 10mm diameter. 5mm pitch. Height <=15mm if used with 1455C enclosure. Panasonic FC

 is there a noticeable benefit if we use a bigger cap, say 1000uf or 2000 uf in a non portable version?
 also does the mint board fit in the case using this particular cap?

 The best thing would be a kit( the same deal guzzler offered) with all the parts necessary to complete a board excluding the IC's,( I have extra pcm's, both regs and the buf634, from the first usb dac, when I bought a few of each) and excluding also rca jack's etc..... 

 Just another question:

 comparing to the original USB dac by guzzler and 00940, what improvements in sound should be expected?


----------



## diablo9

why MINT? I thought this DAC should be in the same league with at least PIMETA, right? wouldn't it be wasteful to put it with MINT?


----------



## MASantos

Quote:


  Originally Posted by *diablo9* 
_why MINT? I thought this DAC should be in the same league with at least PIMETA, right? wouldn't it be wasteful to put it with MINT?_

 

It is certaintly not be wasteful because with a mint you can still put it in the smallest hammond case and have a really portable great sounding dac/amp solution. of course with a pimeta you get better amplification but you will need an enclosure at least 50% bigger.

 I will build a few of these, one portable with a mint and a home dac only version powered by a tread if possible, so the portable version must be the smallest possible!!


----------



## diablo9

Quote:


  Originally Posted by *MASantos* 
_because with a mint you can still put it in the smallest hammond case and have a really portable great sounding dac/amp solution. of course with a pimeta you get better amplification but you will need an enclosure at least 50% bigger.

 Personally I think a mint is the way to go,such as the SMD mint which is being developed in another thread. 

 I will build a few of these one portable with a mint and a home version powered by a tread if possible, so the portable must be the smallest possible!!_

 

looks like a great idea, you convinced me. for the SMD MINT, could you give a link?


----------



## MASantos

Quote:


  Originally Posted by *diablo9* 
_looks like a great idea, you convinced me. for the SMD MINT, could you give a link?_

 

Sure no problem: 

http://www6.head-fi.org/forums/showthread.php?t=136596

 It's really small and allows the use of single opamps

 PS: I never remember how to do those neat links!!!


----------



## diablo9

thanks for info. I wasn't aware that thread is already going onto PCB ordering stage. definitely joining you guys!


----------



## Alf

Quote:


  Originally Posted by *Botch* 
_Remove C4. As we have C5 I can not see a need for it. Or does anyone have a problem with this?_

 

 Quote:


  Originally Posted by *MASantos* 
_is there a noticeable benefit if we use a bigger cap, say 1000uf or 2000 uf in a non portable version?_

 

I have been thinking about this lately. I tend to believe that C5 might do more harm than good. TPS6734 is a low noise chip. Bundled with a very low ESR capacitor C4 it is capable of delivering <15mV ripple. C5’s value is too high to have any effect on this. On the other hand I am not really sure how TPS6734 will behave with an additional output capacitor. 

 At this point I am thinking about removing C5 and keeping C4. LM317 should not need it anyway. C4 should be able to serve both chips well.


----------



## Alf

Quote:


  Originally Posted by *diablo9* 
_it looks like IC5 can't be found on digikey or mouser 
	

	
	
		
		

		
		
	


	


_

 

Digikey part number: REG102UA-3.3-ND


----------



## MASantos

Alf can the dac be powered by a tread? This way the board gets cleaner power? should there be any audible diference?


----------



## .: ZMN :.

Just a question on the USB. 
 Is the design prepared for soldering just the wires of a USB cable to the PCB instead of using a USB B-type plug?


----------



## grasshpr

You should be able to solder the cable directly the board. I think the only concern is the stress applied to the leads if it is pulled, which entails finding a cable relief adapter for the case. Its probably more elegant to just have the USB B adapter on the PCB board.


----------



## MASantos

Quote:


  Originally Posted by *.: ZMN :.* 
_Just a question on the USB. 
 Is the design prepared for soldering just the wires of a USB cable to the PCB instead of using a USB B-type plug?_

 

well when I built the USB dac revision A by guzzler I did this. There is no difference at all, but you must be very careful connecting each wire to the correct place. You shouldalso take in consideration some kind of tension relief. I used a gromet in the hole and then glued the cable on the inside to the gromet with hot glue. This way, even if you hold the enclosure by the cable there isn't much tension in the solder joints. I plan to do this as well when I build this new board. You get a much cleaner look and remove a plug/jack from the signal path. 

 Manuel

 ps: I hope it wasn't confusing...


----------



## .: ZMN :.

I made a mistake sourcing the parts; the plug IS easily available. 
	

	
	
		
		

		
			





 Thanks for the advice (I will use to the plug). 
	

	
	
		
		

		
		
	


	





 /EDIT: Manuel, I was just looking at the Rev A thread. My guess is that portability should be better without the permanent wire, but I'll keep it in mind.


----------



## MASantos

Quote:


  Originally Posted by *.: ZMN :.* 
_I made a mistake sourcing the parts; the plug IS easily available. 
	

	
	
		
		

		
		
	


	




 Thanks for the advice (I will use to the plug). 
	

	
	
		
		

		
		
	


	





 /EDIT: Manuel, I was just looking at the Rev A thread. My guess is that portability should be better without the permanent wire, but I'll keep it in mind._

 


 I have cut the wire so that there is only about 5 inches from the enclosure, I couldn't find a USB cable which is 6 inches long!!!!


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_Alf can the dac be powered by a tread? This way the board gets cleaner power? should there be any audible diference?_

 


 Yes, it can be powered by a TREAD. Whether there will be any audible difference, it depends on the quality of your computer power supply. Also consider that the new board benefits from an additional LM317-based circuit which is essentially the same as TREAD. In theory all the changes we have made should make that difference minimal and hopefully inaudible.


----------



## MASantos

Quote:


  Originally Posted by *Alf* 
_Yes, it can be powered by a TREAD. Whether there will be any audible difference, it depends on the quality of your computer power supply. Also consider that the new board benefits from an additional LM317-based circuit which is essentially the same as TREAD. In theory all the changes we have made should make that difference minimal and hopefully inaudible._

 


 I see, already forgot about that! 
	

	
	
		
		

		
		
	


	




 Just one question, we can use the USB dac board with the new SMD mint which is being developed by cetoole? I think that both boards would fit the smallest hammond. Do you think I should go with tangents mint board? 

 I am really looking forward to this project!!


----------



## grasshpr

Quote:


  Originally Posted by *MASantos* 
_I see, already forgot about that! 
	

	
	
		
		

		
		
	


	




 Just one question, we can use the USB dac board with the new SMD mint which is being developed by cetoole? I think that both boards would fit the smallest hammond. Do you think I should go with tangents mint board? 

 I am really looking forward to this project!!_

 

I think that was the intended plan with the new layout for the Mint, i.e., both USB DAC board and the modified Mint will tightly fit into the Hammond 1455C802 case.


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_ Just one question, we can use the USB dac board with the new SMD mint which is being developed by cetoole? I think that both boards would fit the smallest hammond._

 

It should not be a problem. However if you plan to power both the DAC and the MINT from USB, then you need to take care of the MINT's virtual ground first.

  Quote:


  Originally Posted by *MASantos* 
_Do you think I should go with tangents mint board?_

 

I suggest you go for a bigger Hammond and use a PIMETA board instead.


----------



## MASantos

Alf said:
			
		

> It should not be a problem. However if you plan to power both the DAC and the MINT from USB, then you need to take care of the MINT's virtual ground first.
> 
> 
> 
> ...


----------



## .: ZMN :.

Quote:


  Originally Posted by *Alf* 
_I suggest you go for a bigger Hammond and use a PIMETA board instead. 
	

	
	
		
		

		
		
	


	








_

 

I hope it will fit in nicely then...


----------



## MASantos

First of all I apologise for all the posts about powering an amp through the dac, which isn't the threads purpose. I have read the entire thread now and still don't understand one thing:

 Can we use the usb to power an amp such as a mint (or pimeta)? 
	

	
	
		
		

		
		
	


	




 Does this current board layout allow this? 
	

	
	
		
		

		
		
	


	




 do we have to make any changes in any of the designs?

 Where in the board do we connect the wire which will take the power to the amp? 
	

	
	
		
		

		
		
	


	




 I am sorry for this but I haven't figured it out yet!!

 manuel


----------



## Botch

Quote:


  Originally Posted by *Alf* 
_ Schematic v6 _

 

Manuel,

 I'll bite on my view of the power supply. 

 The BUF634 has been added by Alf so that the DAC can be powered from a MINT/PIMETA (the other way round from what you want). Look at the first post from Alf at the start of the thread and you see it in his notes. Looking at the schematic above, it's used as a result of the +ve, -ve & gnd rails of the amp.

 So onto the question of using the USB to supply an amp. Lets look at the schematic.
 - USB is 5Vdc max 500mA.
 - The TPS6734 is a DC-DC converter that outputs 12V @ ~150mA max. How quiet is this supply as it uses a 170kHz current mode PWM controller? Look at the datasheet and there should be something. I'm lazy.
 - There is a 12V pad but you have to think about noise and the amount of current available.
 - after the LM317A its going to be cleaner at the 9V pad. Still no magic extra current here and we have to think about what the DAC needs.

 Now you need to think about:
 What sort of amp are you thinking of using? 
 Will it have a single voltage rail or dual +ve & -ve rails? How are you going to isolate the signal output gnd if you split the supply for dual rails?
 How much current are you going to need?

 Personally I like the way the DAC design is going under Alf's direction and can not really see any need to modify the supply circuit.

 Botch...


----------



## doobooloo

Another few cents on the headamp+dac idea...

 I've tried/seen a few diy-ish usb-powered dac+amp solutions, and in most cases the amp does not have sufficient current so it distorts heavily or the amp drawing too much power shuts down the dac and causes it to malfunction.

 The only acceptable combination I've come across is the Edirol UA-25 which apparently has a highly optimized and clean power supply unit that utilizes the full 500mA of USB power and has a very very efficient and optimized headphone amplification section. While I like the headphone amp section on the UA-25 (it's not high-end but it's frankly quite good) in order to get pimeta-quality traditional analog headphone amp then a separate power source should be considered.

 Someone here has suggested before to use two more more USB ports to pool in the power and raise current capabilities. I can't remember if there was ever a solution to that but if one builds a small USB power supply unit that can be paralleled, then maybe with using two USB ports on a laptop a decent headamp + dac solution can be created.

 Any ideas? Sorry, I'm not an EE so I really don't know all that much but hopefully what I've scrapped over the past few months can help.


----------



## 00940

I thought I could post that here since it's of direct interest :

 ASIO4ALL version 2.6 didn't work with the PCM2702 on my laptop. Version 1.8 works perfectly though.


----------



## DaKi][er

Quote:


  Originally Posted by *doobooloo* 
_the full 500mA of USB power_

 

The 500mA limit of the usb port isnt really something you have to stick that close to, there is no current limiting on it and the only limits you have that are of any effect are the psu at the computer end and the interconnects on the way to the device under power 

 MWP posted up on these forums a usb dac and headphone amp in one circuit that ran entirely off usb power and drew over 600mA from memory and he said it ran fine off his laptop. I've also read a app note/newsletter thing from Maxim who said they have had no problems drawing upto 2A off a range of PC's even, not that I'm suggesing to go that far just that you do have a little headroom in the 500mA spec

 I would be designing this to use the curren usb dac that has been done here and after that a tpa6810 headphone driver chip for the amp section and the only problem is finding a switchmode regulator to go from 5V to +/- 5 to 15V that does it cleanly enough, if I had the time I would look into the idea myself


----------



## MASantos

Quote:


  Originally Posted by *00940* 
_I thought I could post that here since it's of direct interest :

 ASIO4ALL version 2.6 didn't work with the PCM2702 on my laptop. Version 1.8 works perfectly though._

 

Is this the "bit perfect" windows driver that was spoken about in the beginning of the thread?


----------



## grasshpr

Quote:


  Originally Posted by *DaKi][er* 
_The 500mA limit of the usb port isnt really something you have to stick that close to, there is no current limiting on it and the only limits you have that are of any effect are the psu at the computer end and the interconnects on the way to the device under power._

 

Just curious, if this is true why don't manufacturers that build enclosures for HD's directly draw power from the USB port (and not just the laptop HD's) instead of requiring a separate switching PSU? If the limit is directly related with the PC's PSU, then wouldn't just a note on the necessary system requirements easily solve the HD enclosure manufacturer's problem? I think their may be other problems with this idea, but I'm not even vaguely familiar with USB specs and won't presume to know anything factual... (slowly covering my own arse


----------



## diablo9

Quote:


  Originally Posted by *grasshpr* 
_Just curious, if this is true why don't manufacturers that build enclosures for HD's directly draw power from the USB port (and not just the laptop HD's) instead of requiring a separate switching PSU? If the limit is directly related with the PC's PSU, then wouldn't just a note on the necessary system requirements easily solve the HD enclosure manufacturer's problem? I think their may be other problems with this idea, but I'm not even vaguely familiar with USB specs and won't presume to know anything factual... (slowly covering my own arse 
	

	
	
		
		

		
		
	


	


_

 

I am 90% sure there is a limit of current drawing from USB port directly from computer.


----------



## DaKi][er

Quote:


  Originally Posted by *diablo9* 
_I am 90% sure there is a limit of current drawing from USB port directly from computer. 
	

	
	
		
		

		
		
	


	


_

 

And I'm 90% sure there isn't 

 I'll do some testing here now to prove/disprove it, an old P2 motherboard can be my victim, results to be posted after I'm done


----------



## cire

if you draw too much, windows will error saying that the device is sucking too much juice and won't work.


----------



## diablo9

Quote:


  Originally Posted by *cire* 
_if you draw too much, windows will error saying that the device is sucking too much juice and won't work._

 

that's exactly what I am saying. 
 if you try a external hard drive enclosure on USB port without power connected, windows won't recognize it. 
 For some 2.5 inch hard drive enclosure, the power cord is often optional, meaning it usually works without power cord connected, but on some computer it won't recognize it, when this happens, you just connect the power and everything is OK.


----------



## DaKi][er

The setup - 
 1 * AB-AH6 motherboard
 a usb cable tapping into just the 5V and GND lines
 an 80mm PC fan as the initial load and to provide some cooling for the 1/2W 56ohm resistors that became the increasing load as i plugged more into a breadboard

 Some numbers - 

 At idle, the voltage was 5.07V coming out, and as i loaded it up more it slowly dropped 
 250mA - 4.62v
 315mA - 4.54v
 390mA - 4.48v
 390mA - 4.48v
 460mA - 4.42v
 523mA - 4.36v
 590mA - 4.30v
 650mA - 4.25v
 710mA - 4.20v
 775mA - 4.15v
 830mA - 4.10v
 890mA - 4.05v

 Conclusion? Seems there is some limiting but noting stopped me getting to 900mA and probably nothing stopping me further going over 1A, just that the voltage would continue to fall at the same rate


----------



## diablo9

we are not talking about the same thing. it's probably OK on hardward level, won't blow anything or fry anything, but on software level, Windows might freeze or do some weird things on the device of this USB port.


----------



## cire

obviously wasnt in windows when you did that experiment....


----------



## DaKi][er

Quote:


  Originally Posted by *cire* 
_obviously wasnt in windows when you did that experiment...._

 

It was in XP, and i wrote that post on that same computer while it was running


----------



## diablo9

Quote:


  Originally Posted by *DaKi][er* 
_It was in XP, and i wrote that post on that same computer while it was running_

 

XP could be running while you are doing the exp, but funny thing could be happening on that USB device, too. You can try to connect an external drive to that USB port and draw different current from the same drive while operating the drive.


----------



## cire

Quote:


  Originally Posted by *DaKi][er* 
_It was in XP, and i wrote that post on that same computer while it was running_

 

then you must not've been sending, recieving data from that slot. try that with something that actually interacts with the computer.


----------



## Francis_Vaughan

Quote:


  Originally Posted by *DaKi][er* 
_The setup - 
 Conclusion? Seems there is some limiting but noting stopped me getting to 900mA and probably nothing stopping me further going over 1A, just that the voltage would continue to fall at the same rate_

 


 What you have measured is pretty much a perfect output impeadance of 1.15 Ohms. Thus far you have not hit any internal current limiting, but this neither says that there is any, or where it is. But neither does it say that the USB power is totally happy with you either.


----------



## DaKi][er

Quote:


  Originally Posted by *cire* 
_then you must not've been sending, recieving data from that slot. try that with something that actually interacts with the computer._

 

No, i didn't have anything else connected to the port (or any other port) and it was just a straight cable that ZI chopped the end off and wired into the voltage lines
 Next weekend i'll do the same thing with a device connected if you want and see what happens there

 Francis_Vaughan, I could see the changes happening quite linearly, I just didn't bother to do any calculations on them


----------



## Francis_Vaughan

Exactly. The results are almost a perfect 1.15 Ohm output resistance. One might suspect that in fact there is a resistor in the way. The question about what you can reasonably draw is, however, not properly answered.


----------



## Sinbios

Quote:


  Originally Posted by *grasshpr* 
_Just curious, if this is true why don't manufacturers that build enclosures for HD's directly draw power from the USB port (and not just the laptop HD's) instead of requiring a separate switching PSU? If the limit is directly related with the PC's PSU, then wouldn't just a note on the necessary system requirements easily solve the HD enclosure manufacturer's problem? I think their may be other problems with this idea, but I'm not even vaguely familiar with USB specs and won't presume to know anything factual... (slowly covering my own arse 
	

	
	
		
		

		
		
	


	


_

 

Harddrives need a 12V rail too.


----------



## grasshpr

Quote:


  Originally Posted by *Sinbios* 
_Harddrives need a 12V rail too._

 

Absolutely right! Its probably not enough to include a DC/DC converter to boost up to 12V since wattage is probably going to be pretty high, i.e., 10Watts or more.


----------



## MASantos

Alf, any progress in the pcb revision?


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_Alf, any progress in the pcb revision?_

 

Sorry guys. I had no time to spend on the project last week. Now I am reviewing the parts list and tweaking the layout as per suggestions above. I will be posting an update in a couple of days. 

 I will not be tackling USB-powered amps at this stage. I think it is more important to get the DAC section right and make sure that squeezed everything out of this chip. We have made a lot of changes to the board. When/if we confirm that the direction is right, we will start thinking about a USB-powered dac+amp combo.


----------



## diablo9

Quote:


  Originally Posted by *Alf* 
_Sorry guys. I had no time to spend on the project last week. Now I am reviewing the parts list and tweaking the layout as per suggestions above. I will be posting an update in a couple of days. 

 I will not be tackling USB-powered amps at this stage. I think it is more important to get the DAC section right and make sure that squeezed everything out of this chip. We have made a lot of changes to the board. When/if we confirm that the direction is right, we will start thinking about a USB-powered dac+amp combo._

 

that's the correct direction, Alf. We already have so many excellent DIY amps on board, I think right now the main job is to "squeeze everthing out of this DAC chip". People can add their favorite AMP design later


----------



## Clutz

Quote:


  Originally Posted by *Alf* 
_Sorry guys. I had no time to spend on the project last week. Now I am reviewing the parts list and tweaking the layout as per suggestions above. I will be posting an update in a couple of days. 

 I will not be tackling USB-powered amps at this stage. I think it is more important to get the DAC section right and make sure that squeezed everything out of this chip. We have made a lot of changes to the board. When/if we confirm that the direction is right, we will start thinking about a USB-powered dac+amp combo._

 

I agree completely. I'm so completely excitd about this project! Keep up the good work Alf!


----------



## Alf

Changes:
 * Optimized layout around TPS6734.
 * Changed SMD resistors to 0805. They are easier to find.
 * Replaced L2 with 6mm x 6mm SMD inductor
 * Removed C1
 * Changed R2 and R3 (Botch)
 * Replaced C6, C7, C10, and C14 with D/6.3mm – P/2.5mm electrolytics. (doobooloo)
 * Grounded USB socket tabs for additional shielding (Guzzler).


 Board v6 - Top

 Board v6 – Bottom

 Board v6 – All without bPlace


----------



## doobooloo

Looks good, Alf! 
	

	
	
		
		

		
		
	


	




 Is it possible though to have thermals on for the final revision? I was soldering a project last night and was reminded how much of a pain is to work with groundplane pads without thermals. 
	

	
	
		
		

		
		
	


	




 Thanks!


----------



## Alf

Quote:


  Originally Posted by *doobooloo* 
_Is it possible though to have thermals on for the final revision? I was soldering a project last night and was reminded how much of a pain is to work with groundplane pads without thermals. 
	

	
	
		
		

		
		
	


	


_

 

I am afraid this is impossible with the current layout. The capacitors around PCM2702 are located in close proximity to the chip and the pins are tiny. Thermals block access to the ground pins. The capacitors would need to be moved MUCH further away from the chip.


----------



## Clutz

Alf,

 Any idea at this point how much it will cost to put one of these babies together? I am drooling with anticipation!


----------



## Alf

I have done some preliminary calculations based on Farnell UK prices. Components for a USB-powered DAC (the most expensive option) cost around £23 ($41). Components for a DAC powered by an external PSU (the cheapest option) cost around £16 ($29). 

 This includes all ICs, capacitors, resistors, USB connector, crystal, diodes, and inductors. I used SANYO OSCON, ELNA Silmic II, and AVX. 

 This excludes taxes (VAT), delivery, PCB, enclosure, and output connectors.


 PCB should cost 3-4 pounds depending on how many people join the group buy.


----------



## diablo9

Quote:


  Originally Posted by *Alf* 
_I have done some preliminary calculations based on Farnell UK prices. Components for a USB-powered DAC (the most expensive option) cost around £23 ($41). Components for a DAC powered by an external PSU (the cheapest option) cost around £16 ($29). 

 This includes all ICs, capacitors, resistors, USB connector, crystal, diodes, and inductors. I used SANYO OSCON, ELNA Silmic II, and AVX. 

 This excludes taxes (VAT), delivery, PCB, enclosure, and output connectors.


 PCB should cost 3-4 pounds depending on how many people join the group buy._

 

guess it's the time for a GB thread? 
	

	
	
		
		

		
		
	


	



 you can PM jude now...


----------



## guitz

Hi all, I landed here in a roundabout search for DIY DACs and after reading through some threads related to this project had a few questions,....Before asking specifics, I really need to ask , is this still a worthwhile project if I were to have no intentions of sending the output to a headphone amp? My main hope was, to DIY a DAC for low $$, that would be a step up in sound quality from my current SB Audigy 2, with the output going into a power amp,then to a pair of Yorkville Studio monitors, for critical listening/recording....I'd better wait and see if anyone can confirm or deny before asking more noob questions


----------



## MASantos

Quote:


  Originally Posted by *guitz* 
_Hi all, I landed here in a roundabout search for DIY DACs and after reading through some threads related to this project had a few questions,....Before asking specifics, I really need to ask , is this still a worthwhile project if I were to have no intentions of sending the output to a headphone amp? My main hope was, to DIY a DAC for low $$, that would be a step up in sound quality from my current SB Audigy 2, with the output going into a power amp,then to a pair of Yorkville Studio monitors, for critical listening/recording....I'd better wait and see if anyone can confirm or deny before asking more noob questions 
	

	
	
		
		

		
		
	


	


_

 

I don't know in regard to the audidy, but I have a revision A board and it is a huge step from my laptop "line out". This new revision brings more benefits, like better power regulation, etc so it should be a very nice dac for it's price and characteristics. But I don't know the quality of the audigy though...


----------



## Clutz

Quote:


  Originally Posted by *diablo9* 
_guess it's the time for a GB thread? 
	

	
	
		
		

		
		
	


	



 you can PM jude now..._

 

*Wrings hands* It is all very exciting. 
	

	
	
		
		

		
		
	


	




 Alf Dac -> PPA -> HD590... Emm.


----------



## Alf

Quote:


  Originally Posted by *diablo9* 
_guess it's the time for a GB thread? 
	

	
	
		
		

		
		
	


	



 you can PM jude now..._

 

Yes, it is about time. In fact, I sent a private message to Jude last week. My original plan was to order 15 PCBs initially for prototyping and then proceed with a group buy for everyone. I thought this case was quite straightforward and there would be no delays since this was a genuine design thread. I was wrong. So far, I have got no response from Jude. I also sent messages to other moderators a couple of days ago. I got two replies but nothing encouraging. I understand from their replies that currently there is no agreement among moderators on how to handle such cases. JMT indicated that our case will be discussed with Jude in a couple of weeks.


----------



## grasshpr

Geez, I never knew GB's where so difficult to manage. Oh well, I guess its for the better. Looking forward to this design Alf. Its my early (or late depending on the arrival of these boards) christmas present!


----------



## diablo9

Quote:


  Originally Posted by *Alf* 
_Yes, it is about time. In fact, I sent a private message to Jude last week. My original plan was to order 15 PCBs initially for prototyping and then proceed with a group buy for everyone. I thought this case was quite straightforward and there would be no delays since this was a genuine design thread. I was wrong. So far, I have got no response from Jude. I also sent messages to other moderators a couple of days ago. I got two replies but nothing encouraging. I understand from their replies that currently there is no agreement among moderators on how to handle such cases. JMT indicated that our case will be discussed with Jude in a couple of weeks._

 

Alf, YGPM.


----------



## Botch

Quote:


  Originally Posted by *00940* 
_I thought I could post that here since it's of direct interest :

 ASIO4ALL version 2.6 didn't work with the PCM2702 on my laptop. Version 1.8 works perfectly though._

 

Hi 00940,

 do you mind sharing the versions and settings you used for ASIO4ALL? I've just started looking at it with Foobar and I'm getting some errors with an RevA board. Honestly I have not spent much time chasing this as I'm knacked after a week away on work.

 Is there an improvement in sound quality over the standard windows drivers? It it worth investing the time in getting ASIO4ALL working? I've got no experience here yet.

 Cheers,
 Botch...


----------



## 00940

I'm not using foobar but winamp. This for a preliminary disclaimer. I'm using the asio plug in for winamp and asio 1.8. I just let all settings as standard. This means a buffer size of 1024, two KS buffers, I'm not resampling to 44.1khz (all the materials I've got on pc is 44.1), I didn't disable input, i didn't force 16Bit sample, I didn't active dma buffer I/O.

 There's an audible difference between asio4all and the other output plugins. Wheter it's an improvment is less clear, i should take the time to compare a bit. I've not my dac/amp combo here, i'll try by wednesday or so.


----------



## Botch

Cheers 00940,

 Have ASIO4ALL running with WinAmp. Now just have to find some time to sit down and see how it compares.

 Botch...


----------



## roibm

SPDIF is evil... why use it?
 Why not get a chip that converts the USB nto I2S and feed that to the chip? no SPDIF, no CS chip...
 An idea for doing just that, more expensive tho, is to take an m-audio transit and use it just for that... it uses TAS1020A...

 see here also:
http://www.diyhifi.org/forums/viewtopic.php?t=236


----------



## 00940

USB can be just as evil as spdif. 
	

	
	
		
		

		
			





 See here : http://www4.head-fi.org/forums/showthread.php?t=141238 (work in progress) and here : http://www4.head-fi.org/forums/showthread.php?t=90069

 I don't know if the transit operates as an asynchronous endpoint. If it doesn't and operates as adaptive, using that or a dir1703 on spdif shouldn't make a big difference.

 Anyway, for such a simple project, we have to operate with what we have. "Compromised" all in one chips operating as adaptive endpoints.


----------



## roibm

PCM2706 also has I2S... and it is supposed to be much easier to work with...


----------



## Botch

Hi Alf,

 have you made a move to order the prototypes yet? I'm just had my first good look at the layout in a while. Is looking good but I have something for you to think about.

 If you look at the 3.3V regulated supply, it wanders over to the right of the board towards the analog section. Could you move C14 to the left side of IC5. Would really shorten up this supply trace. 

 Can also move C10 to the other side of IC4 on the 5V regulated supply. Think some of the 5V supply traces here could be cleaned up a bit but nothing major.

 Finally, are the ferrites on the analog supply pins going to appear? Would be nice to have, even if people just jumper them out.

 Cheers,

 Botch...


----------



## 00940

Quote:


  Originally Posted by *roibm* 
_PCM2706 also has I2S... and it is supposed to be much easier to work with..._

 

The problem with the pcm2706 is that it gives you I2S just like a spdif receiver gives you I2S. With roughly the same problems and probably jitter. 

 Still, I don't really get your point. The PCM2702 doesn't use spdif. It has an integrated USB receiver directly feeding a DAC (based on the pcm1716), through a protocol similar to I2S. Or are you already thinking to another project ?


----------



## Alf

Well spotted, Botch! Previous updates freed up some space and I have not taken advantage of it. I moved the capacitors as per your suggestion and some other parts too. Now the board is 2mm shorter! The new board size is 52mm x 50.5mm.

 I added ferrites too, but I am not really convinced about them. L9 is in very close proximity to a signal trace. It may affect the signal. However, only practice can show whether this is true and whether this will improve the sound. I am pretty happy to go ahead with this layout. If prototyping proves it is no good, then we will remove it in the final version. By the way, the new ferrites add about £1 to the previously announced cost.


 Board v7 - Top

 Board v7 – Bottom

 Board v7 – All without bPlace

 Schematic v7


 Looking at the board at 1:1 scale, I start having concerns about “solderability” of this thing. The board is small and there are so many parts on it


----------



## Alf

I created a small support web site to keep all DAC related information in one place. The site is optimized for Firefox and Opera. Internet Explorer works too but presentation is different in some places. If you have a problem viewing the contents with your browser, just drop me a private message – I will try to fix it.

 http://www.myexposition.com/diy/usbdac/ 

 The site contains an up-to-date parts list. Please verify it if you plan to build the DAC.


----------



## Sinbios

Any chance of getting the part numbers for the appropriate caps on the parts list?


----------



## MASantos

Quote:


  Originally Posted by *Alf* 
_I created a small support web site to keep all DAC related information in one place. The site is optimized for Firefox and Opera. Internet Explorer works too but presentation is different in some places. If you have a problem viewing the contents with your browser, just drop me a private message – I will try to fix it.

 http://www.myexposition.com/diy/usbdac/ 

 The site contains an up-to-date parts list. Please verify it if you plan to build the DAC._

 


 Now that's a great website!!! But there are some things that can be improved. Let's create a: "PCM2702 USB DAC Revision B" website improvement thread! We need some further regulation around the overview, and if possible better noise rejection in the signal path!!!


----------



## Alf

The capacitors I plan to use for prototyping:
 C2, C4 – SANYO OS-CON 16SC33M
 C3 – AVX 08055C102KAT2A
 C5 – SANYO OS-CON 16SA150M
 C6 – SANYO OS-CON 16SC33M
 C7- ELNA RE3-100V220M (not sure about this one)
 C8, C12 – SANYO OS-CON 25SC1M
 C9, C13 – AVX 08055C103KAT2A
 C10, 14 – SANYO OS-CON 10SC10M
 C11, C15- AVX CM21X7R474K16AT
 C16, C17 – AVX 08051A330JAT2A
 C18, C19, C20, C21, C22, C23 – AVX 08055C104KAT2A
 C24 – SANYO OS-CON 10SC10M
 CL, CR - ELNA Silmic II

 Two questions about capacitors:
 * What would be the best choice for C7? It should be >0.1ESR.
 * What would be a good alternative for CL, CR? Would SANYO OSCON be a good replacement? OSCONs are easily available from Farnell, while Silmics have to be ordered separately.

 A question about SMD resistors:
 * Would there be any improvement if thin film resistors are used instead of thick ones. Yes, I know thin film resistors are superior, but is it worth paying extra in this particular case?


----------



## 00940

Quote:


  Originally Posted by *Alf* 
_* What would be a good alternative for CL, CR? Would SANYO OSCON be a good replacement? OSCONs are easily available from Farnell, while Silmics have to be ordered separately._

 

Black gate ? At those values, at 6.3V rating, they're not very expensive. That's what I used on my board. OSCON are known as decoupling caps, not really for coupling.

 On a budget, I quite like the pana FC.


----------



## Botch

Looking much better Alf,

 Can you please add a GND pad right in the middle of the board? Somewhere between C10, C12 & C13. I'm planning on using an external supply so would be nice to have a pad to solder the gnd wire to around here.

 Have a few more house cleaning ideas but I need to sleep/think on it more yet. 

 Web site is very nice also. 

 Botch...


----------



## Alf

Quote:


  Originally Posted by *Botch* 
_Can you please add a GND pad right in the middle of the board? Somewhere between C10, C12 & C13. I'm planning on using an external supply so would be nice to have a pad to solder the gnd wire to around here._

 

There is no need to add new pads because there will be plenty of them available already. Do not forget that the board is not meant to be fully populated. You can use ground pads of unpopulated parts. For example, if you plan to supply voltage to the 9V pad directly, you can use either R2’s or C7’s ground pads.


----------



## Alf

Quote:


  Originally Posted by *00940* 
_Black gate ? At those values, at 6.3V rating, they're not very expensive. That's what I used on my board. OSCON are known as decoupling caps, not really for coupling.

 On a budget, I quite like the pana FC._

 

Well… Black Gates are not available from Farnell yet 
	

	
	
		
		

		
			





 I thought Panasonic FC was the best for power supplies and could be used as OSCON replacement. Do you suggest that they can also be used as a cheap but still decent substitute for ELNA/BG?


----------



## 00940

Pana FC are decent coupling caps (they once were used by Pass Labs). Better than OSCON in this application IMHO. But still, it's worth shopping for BG, available at Farnell or not.


----------



## MASantos

I remember a site that sells blackgates cheaper than most places!! I think that it is in the DIY links list! Lets do a group buy for this board!!!!!! 
	

	
	
		
		

		
		
	


	










 I search the link and post it here. 

 Manuel


----------



## rickcr42

Quote:


 I remember a site that sells blackgates cheaper than most places!! I think that it is in the DIY links list! Lets do a group buy for this board!!!!!! 
 

You DO realise all  group buys need an OK from the Head-Fi administrator before they can proceed correct ?

 not a point of discussion,just a reminder

 continue..........................


----------



## MASantos

Quote:


  Originally Posted by *rickcr42* 
_You DO realise all  group buys need an OK from the Head-Fi administrator before they can proceed correct ?

 not a point of discussion,just a reminder

 continue..........................






_

 


 Yes, I know this, I wasn't being really serious here!!


----------



## guzzler

I use cheap bipolar caps for coupling, I think they sound 90-95% of the Black Gates in my personal DAC, and cost 7p each instead of £1.50.


----------



## Clutz

Quote:


  Originally Posted by *guzzler* 
_I use cheap bipolar caps for coupling, I think they sound 90-95% of the Black Gates in my personal DAC, and cost 7p each instead of £1.50._

 

Because this dac is likely to be so inexpensive to make - I will probably make two - one with more or less generic parts, and one with some higher quality parts to hear the difference. That said, I don't have anyway of making measurements of the differences.. so.. 
	

	
	
		
		

		
		
	


	




 It would be all in my head 
	

	
	
		
		

		
		
	


	




 Cheers,
 clutz


----------



## Alf

Quote:


  Originally Posted by *Clutz* 
_Because this dac is likely to be so inexpensive to make - I will probably make two - one with more or less generic parts, and one with some higher quality parts to hear the difference. That said, I don't have anyway of making measurements of the differences.. so.. 
	

	
	
		
		

		
		
	


	




 It would be all in my head 
	

	
	
		
		

		
		
	


	




 Cheers,
 clutz_

 

Good idea! I will do this too. I will assemble one DAC with OSCONs, Silmics and expensive resistors and the other one with Panasonic FC and cheap resistors. I wonder if there will be any audible difference.


----------



## Alf

The prototyping stage has been blessed and we are allowed to proceed with prototype PCB ordering.

 If you would like to participate in prototyping, please drop me a PM or email with a short description of which components you plan to use and which comparisons/reviews you can do. I will post the participant list, when it is finalized.

 I will be ordering 15 PCBs from www.eurocirtuits.com (same as Revision A) in a couple of days. The price will be £5 (around $9) per PCB payable via PayPal. I will confirm re-packaging costs later but it should be well under £1. Information on postage is  here but I cannot confirm the weight yet.

 Please note that if you volunteer, you are doing this at your own risk. The design is not proven yet and might not even work at all. Also the PCB cost is slightly higher than if you wait for the main group buy (around £1-£1.5 difference). On this bright side of things, you will be the first to assemble and review the DAC. Other people will have this opportunity 4-5 weeks later.

 If you do volunteer, I would like to ask you to provide a report answering the following questions:
 * How easy it is to solder? What can be improved?
 * How does the DAС sound? Do you like the sound?
 * If you assemble two DACs with different parts, how do they compare? 
 * How does the DAC compare to your other sources?

 If you can do RIAA tests, this would be much appreciated.


----------



## roibm

Quote:


  Originally Posted by *00940* 
_The problem with the pcm2706 is that it gives you I2S just like a spdif receiver gives you I2S
 ....
 It has an integrated USB receiver directly feeding a DAC (based on the pcm1716), through a protocol similar to I2S. Or are you already thinking to another project ?_

 

kinda late but I'll give it a shot anyway...
 It gives I2S directly from USB not from the piece of scrap called sp/dif.
 As about another project, I'm on the non OS boat, already built stuff, just wanna get rid of sp/dif once and for all.

 Anyway, the 1716 is not knows to be top, see here...
http://www.diyaudio.com/forums/showt...threadid=24003
 eventually search some more.


----------



## diablo9

Alf, YG email.


----------



## bigmike216

Alf, you've got a PM from me too.


----------



## 00940

Quote:


  Originally Posted by *roibm* 
_kinda late but I'll give it a shot anyway...
 It gives I2S directly from USB not from the piece of scrap called sp/dif.
 As about another project, I'm on the non OS boat, already built stuff, just wanna get rid of sp/dif once and for all._

 

If you're speaking of the PCM2706(-7), I think you missed my point. The way it uses the USB is just as crappy as spdif. USB can be just as bad as SPDIF.

 Picking USB to avoid spdif is just going from Charybde to Scylla, if you cannot configure your device in asynchronous mode. And you cannot do that with the PCM2*** serie.


----------



## Francis_Vaughan

There are a few points worth making here.

 The problems with S/PDIF are intrinsic to its design. Even with as close to a perfect a specified S/PDIF feed as one could imagine, one with no jitter, wonderfully perfect waveforms etc etc, the actual nature of the beast leaves you with intrinsic problems. The most fundamental is the difficulty in recovering the clock without it being contaminated by signal correlated jitter. 
 Now there is a lot of experience with this, and to a pretty reasonable extent it is solvable. But not without serious effort. 

 USB audio is an almost utterly different beast. But it too has intrinsic issues. The worst of which is the lack of any reference clock. So we must recover a clock from the received data here too. This leads to problems, but for different reasons to S/PDIF. 

 I2S is a better encoding of digital audio, in that is separates the clock from the data. So once we have a clean clock - and getting that clean clock may be quite a trial - we should be able to avoid it becoming contaminated with jitter - especially signal correlated jitter. But the I2S output from any receiver, be it an S/PDIF in a conventional system, or a USB device such as a PCM2706, will only be as clean as the internal capabilities of the receiver. If it were S/PDIF the likelihood of signal correlated jitter on the I2S clock will be very high, with a USB receiver, more likely just lots of auto-correlated noise in the jitter spectrum left over from the vagaries of the USB transmission.

 If you have not read the lovely story of the design of the PCM270x series, you need to. Understanding why the SPACT design does what it does is important to understanding the tradeoffs discussed.

http://www.planetanalog.com/showArti...cleID=12801995


----------



## ephrank

Very good discussion of the jitter problem, Francis_Vaughan


----------



## Alf

I placed an order with The PCB Shop last week. The order is currently in the production stage. The boards will be shipped to me on 25th of November 2005. 

 The bad news is the cost of the board will be a higher than I originally specified. Apparently I missed 2 things:
 * The boards can only be delivered by courier service for registered users
 * Second legend is required.

 I will confirm the final price when I get invoiced. It should be around £5.9 - £6


 I still have a few boards unallocated. If you would like to join prototyping, it is not too late. Just drop me an email or PM.


----------



## dsavitsk

Why are CL and CR so large? 1/2(pi)(Hz)(R), assuming that you want a corner around 4Hz (which limits all phase distortions to under 40Hz) and (worst case scenario) the input impedence of your headphone amp is 10K, 4uF is still plenty big. I would think a film cap would be a good choice here. With a 50K input, 1uF is even plenty.


----------



## ble0t

Alf....YGPM


----------



## 00940

IIRC, you also have to factor in the input cap of the following amp. So you don't want the output cap to be too small


----------



## dviswa

Alf,

 YGPM


----------



## MASantos

YGPM!!!


----------



## frdchang

what is the motivation for not using SMD caps?

 is it so people can swap out parts easily?


----------



## robzy

Gah, what now? Group buy is already happening?

 Did i miss it? Can i still get one?

 Where is the latest schematic/board layout?

 What are the details?

 So many questions - so little time, and i hope i havent missed out! 

 Rob.


----------



## 00940

Quote:


  Originally Posted by *frdchang* 
_what is the motivation for not using SMD caps?

 is it so people can swap out parts easily?_

 

In my (limited) experience, smd electrolytic caps are more expensive, don't offer as much choice, don't really save any board space, are harder to solder than smd resistors or ceramic caps. This is just for me.


----------



## grasshpr

Board is still in a prototyping phase. Small amount of boards were order to check the quality and functionality of the design. Alf still had a few boards left over and was asking for some help. Don't worry Rob, you didn't miss anything 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *robzy* 
_Gah, what now? Group buy is already happening?

 Did i miss it? Can i still get one?

 Where is the latest schematic/board layout?

 What are the details?

 So many questions - so little time, and i hope i havent missed out! 

 Rob._


----------



## guzzler

I agree with 00940 about SMD electrolytics; for DIY purposes they have no advantage, and have limited choice, especially for those of you wishing to put "exotic" output caps on (Nitals for me 
	

	
	
		
		

		
		
	


	




). They're a pain to solder (try one of P-As boards), and take up more board space for equivalent capacitance.

 Alf, personally I would ditch the second legend; just post a concise picture of the layout for people... I'd rather pay less and have to think (a little)


----------



## ble0t

I'd second that...having a good quality website as you do with the layout posted should be fine.


----------



## Alf

Quote:


  Originally Posted by *frdchang* 
_what is the motivation for not using SMD caps?

 is it so people can swap out parts easily?_

 


 As other people said, SMD electrolytics are more expensive. 

 But there are two other reasons:
 * SMD electrolytics are rather bulky. They cannot be soldered on the bottom layer. Putting them on the top layer would violate the continuity of the ground plane.
 * Some mounting holes of standard electrolytics are used as vias.


----------



## Alf

Quote:


  Originally Posted by *guzzler* 
_Alf, personally I would ditch the second legend; just post a concise picture of the layout for people... I'd rather pay less and have to think (a little)_

 

It is too late for the prototype boards. The second legend adds around 10 Euro. This would not make much difference for the main group buy. Anyway I will see if it can be safely ditched.

  Quote:


  Originally Posted by *robzy* 
_Gah, what now? Group buy is already happening?

 Did i miss it? Can i still get one?_

 

I have 1 prototype board left. The details are here http://www.myexposition.com/diy/usbdac/


----------



## guzzler

Suppose I should, you've got an email alf 
	

	
	
		
		

		
			





 Do you want to add the link to that soldering site from my page to your FAQ? A lot of people have found that helpful


----------



## Alf

Quote:


  Originally Posted by *guzzler* 
_Do you want to add the link to that soldering site from my page to your FAQ? A lot of people have found that helpful_

 

Yes, I will do that when I write a stuffing guide.


----------



## MASantos

Here is a semi finished BOM for the DAC. This BOM is for Farnell! 

 It is not finished yet, it's late and I'm sleepy . If you could double check it, expecially resistor and caps values/choices. 

 I'll finish it tomorrow afternoon and will make one with DIGIKEY parts numbers for the US DIYers. 

 Farnell has minimum quantities on resistors and this is still not reflected in the price estimates

 Comments and corrections are welcomed and needed!!! 

 Manuel


----------



## robzy

Quote:


  Originally Posted by *grasshpr* 
_Board is still in a prototyping phase. Small amount of boards were order to check the quality and functionality of the design. Alf still had a few boards left over and was asking for some help. Don't worry Rob, you didn't miss anything 
	

	
	
		
		

		
		
	


	


_

 

Phew - almost had a small heart attack there  Thank you 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *Alf* 
_I have 1 prototype board left. The details are here http://www.myexposition.com/diy/usbdac/_

 

Gotcha, getting in touch now 
	

	
	
		
		

		
		
	


	




 Rob.


----------



## dviswa

Manuel,

 I was not able to open your ZIP file, please repost.

 Dinesh


----------



## ble0t

Perhaps I'm missing something, but if you wanted to power the board from a 12V, 9V or 5V source, do we have a ground pad anywhere for that seperate PS? It would also be helpful if you were planning on powering something else from those pads.


----------



## MASantos

Here it is! I have the DIGIKEY BOM halfway done!! 

 Should be working now!


----------



## Alf

Here is Digikey BOM courtesy of .:ZMN:. I will put all BOMs together in one file after the prototype stage.

 EDIT: I have not validated the BOM. The BOM is posted to provide you with a starting point. Use it at your own risk.


----------



## grasshpr

Quick question Alf, is their a reason why your choosing KG series Panasonics for electrolytics rather than FM or FC series? I think FM or FC series caps are supposedly superior in terms of ESR and ripple.


----------



## Alf

Quote:


  Originally Posted by *grasshpr* 
_Quick question Alf, is their a reason why your choosing KG series Panasonics for electrolytics rather than FM or FC series? I think FM or FC series caps are supposedly superior in terms of ESR and ripple._

 

The BOM is provided by ZMN. I have not checked it. I will be using Panasonic FC and SANYO OSCON for my boards. I will post my BOM in a couple of days when it is finalized.


----------



## grasshpr

Sorry Alf,

 My mistake... Thanks for the clarification


----------



## .: ZMN :.

Quote:


  Originally Posted by *Alf* 
_Here is Digikey BOM courtesy of .:ZMN:. I will put all BOMs together in one file after the prototype stage.

 EDIT: I have not validated the BOM. The BOM is posted to provide you with a starting point. Use it at your own risk._

 

I can verify that it needs serious validation 
	

	
	
		
		

		
		
	


	










 The file is _NOT_ a finished BOM, mere suggestions to look at and an attempt to help Alf. 
 Especially the caps need more attention. 
	

	
	
		
		

		
		
	


	




 Alf, 
 The FCs/FMs have indeed some better alternatives (e.g. c5,c6,c7;P12375,P12924,P12922).


----------



## ble0t

I don't mean to be a pest, but perhaps my post got passed over? Are there any provisions for this?


----------



## Alf

Quote:


  Originally Posted by *ble0t* 
_I don't mean to be a pest, but perhaps my post got passed over? Are there any provisions for this?_

 



 The question has been answered a couple of pages ago.

  Quote:


  Originally Posted by *Alf* 
_There is no need to add new pads because there will be plenty of them available already. Do not forget that the board is not meant to be fully populated. You can use ground pads of unpopulated parts. For example, if you plan to supply voltage to the 9V pad directly, you can use either R2’s or C7’s ground pads._


----------



## ble0t

Doh! 
	

	
	
		
		

		
			





 Thanks Alf


----------



## dviswa

Alf,

 I am thinking of using an unregulated 12 V DC wall wart (option B). Do you know what current rating would be acceptable.

 According to spec sheets PCM2702E needs about 40ma. Making room for regulators and other loads, anything >100 ma should be fine, I think. 

 I am also considering, using TO-220 package for 317, instead of the SMD so that I can drive it from the STEPS that is driving the AMP. 

 What do you think?
 Dinesh


----------



## guzzler

100mA should be fine, althougth the drop across regulators is quite substantial if you get a high voltage one. 

 LM317T (TO220) would be fine as well, but you'd have to solder it as SMD, not as through hole as there are no holes on the board. The TO220 and SMD version are the same, just different physical arrangement


----------



## dviswa

Quote:


  Originally Posted by *guzzler* 
_100mA should be fine, althougth the drop across regulators is quite substantial if you get a high voltage one._

 

Thanks Gus, Yeah the drop is high, sure calls for some good heatsinking. Not needing another powersupply is tantalizing too.

  Quote:


  Originally Posted by *guzzler* 
_LM317T (TO220) would be fine as well, but you'd have to solder it as SMD, not as through hole as there are no holes on the board. The TO220 and SMD version are the same, just different physical arrangement_

 

Oh, well, Revision C maybe 
	

	
	
		
		

		
		
	


	




 Dinesh


----------



## Alf

Quote:


  Originally Posted by *dviswa* 
_Alf,

 I am thinking of using an unregulated 12 V DC wall wart (option B). Do you know what current rating would be acceptable.

 According to spec sheets PCM2702E needs about 40ma. Making room for regulators and other loads, anything >100 ma should be fine, I think. 

 I am also considering, using TO-220 package for 317, instead of the SMD so that I can drive it from the STEPS that is driving the AMP. 

 What do you think?
 Dinesh_

 

As Gus said, the only difference between these two packages is physical layout. There is no reason not to use SOT223. SOT223 has been chosen for its compactness.

 If you plan to use STEPS for powering the DAC and your amp, you may need to take care of the amp's virtual ground (if it is a virtual ground amp like MINT, PIMETA, PPA, etc). You should consider option D of the DAC. In this case you will not need LM317 at all.


----------



## bigmike216

Alf, when do you anticipate the prototype boards to ship?


----------



## Alf

I received the boards this morning. The quality is excellent. I will be sending them in a couple of hours (to those who already paid).


----------



## diablo9

Quote:


  Originally Posted by *Alf* 
_I received the boards this morning. The quality is excellent. I will be sending them in a couple of hours (to those who already paid)._

 

me, me, me!!!


----------



## MASantos

C'mon ALf

 give us some pics!!!!!!!


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_C'mon ALf

 give us some pics!!!!!!!_

 


 Here is a quick shot. I will make some decent pictures later.

 Gone soldering!


----------



## Alf

I have been playing with the prototype board tonight. I noticed one particular problem you should be aware of. There is not enough clearance between C24/CL/CR. Manufacturing tolerance is about +/-0.5mm. My C24 was about 6.8mm in diameter. It did not fit easily the 6.3mm space holder and interfered with CL/CR. If you are unlucky and all your C24/CL/CR capacitors are bigger than specified, this may present a problem. The capacitors would fit anyway but they would be sticking out like a bunch of flowers.

 To tackle this potential issue you may also order smaller capacitors 5mm in diameter as a fallback solution. The capacitors do not need to be 47uF. As low as 10uF should be enough for any of them. Just make sure CL and CR are the same value.

 I will move the capacitors around for the final version of the board to resolve this.


----------



## doobooloo

Looks great! Hope it sounds great too!

 Please keep us updated! This is exciting!


----------



## guitz

Quote:


  Originally Posted by *doobooloo* 
_Looks great! Hope it sounds great too!

 Please keep us updated! This is exciting! 
	

	
	
		
		

		
		
	


	


_

 


 yes! I will be in line for a finished board once all the prototypers have something they all like....I'm watching the thread with great interest to see all the proto builders thoughts/progress, etc....don't spare the details!


----------



## ntrl

It is interesting, whether new usbdac will sound better than esi-pro Waveterminal U24?


----------



## guzzler

I've built up mine now, approx time was 2.5hrs. All power caps are Pana FC, and outputs are my usual Nitai 

 Component side view:







 Solder side view:






 My build notes and some other little bits. I've not powered it up yet, and don't really like commenting on sound as it's too subjective

 1. Extra ground pads directly next to 12V and 9V inputs would be a good idea; definately enough room and would make life a little easier

 2. Spacing of output caps; already mentioned but worth mentioning again

 3. Maybe increase the size of the mounting holes for the USB socket. One socket I tried wouldn't fit snug. My fault as it's my library!

 4. Silkscreen on the bottom is EXCELLENT, contrary to what I said earlier. It will have little impact on final cost, and makes the build easier

 5. Fits EXACTLY into smallest Hammond with a TREAD 
	

	
	
		
		

		
		
	


	




 Overall impressions are very good, and the layout is VERY easy to work with and well spaced and thought out. As usual, Eurocircuits have made a very good job on the boards. The new RoHS compliant boards have far better flatness on the pads which is excellent for SMD. I compared this to a normal tin plate TREAD board, and the lead free board is a lot flatter. 

 Construction order (I made the >10V external supply version):

 1. PCM, REGs
 2. All bottom SMD
 3. Remaining top SMD (some of the pads have through hole, makes soldering a little tougher. Soldering the bottom first mostly fills these holes, and as the bottom is less cramped round the SMDs, this is easier)
 4. Resistors, diodes, X-tal (for low profile one)
 5. USB socket
 6. Electrolytic caps and X-tal (if tall, see the pic above)

 I'm in for another two when the final boards are made up

 Hope that's of use, and I look forward to seeing the final installment!


----------



## doobooloo

Wow! Looks great! 
	

	
	
		
		

		
		
	


	




 Regarding USB connector mounting holes... increase the size or decrease? You said that it won't fit snug, I am picturing the part fitting loose, not fitting too tight. I remember the holes to be a bit big on the previous USB DAC...

 Anyway, looks great, I can't wait to get my hands on one soon after the prototyping phase is over!


----------



## guzzler

A little too tight; the original version didn't have the mounting holes connected to the ground plane and was loose, but I added actual pads to the library, and think I've cut it a little too close to compensate


----------



## doobooloo

Quote:


  Originally Posted by *guzzler* 
_A little too tight; the original version didn't have the mounting holes connected to the ground plane and was loose, but I added actual pads to the library, and think I've cut it a little too close to compensate 
	

	
	
		
		

		
		
	


	


_

 

Aah, thanks for the clarification!


----------



## ble0t

Looks awesome...looking forward to getting my proto in the mail


----------



## ATAT

cant wait to get my hands on my board =p .. keep us posted guzzler!


----------



## dviswa

Quote:


  Originally Posted by *guzzler* 
_I've not powered it up yet, and don't really like commenting on sound as it's too subjective_

 

Gus,
 Maybe you can help dispell the suspence. Please power it up and let us know if it works.
	

	
	
		
		

		
		
	


	




 Dinesh


----------



## Clutz

I got two surprises in the mail this morning! One was a package from Alf containing two of the Prototype PCBs (unfortunately I leave for a vacation for two weeks tomorrow, so I won't be assembling it until I get back) - and the other was a package containing 16 different strains of Caenorhabditis elegans and 3 strains of E. coli! 

  Quote:


  Originally Posted by *dviswa* 
_Gus,
 Maybe you can help dispell the suspence. Please power it up and let us know if it works.
	

	
	
		
		

		
		
	


	




 Dinesh_

 

I agree, common Guzzler!


----------



## MASantos

Quote:


  Originally Posted by *Clutz* 
_ and the other was a package containing 16 different strains of Caenorhabditis elegans and 3 strains of E. coli!_

 

Do you use them for decoupling? I bet that they improve imaging!!!! 
	

	
	
		
		

		
		
	


	







 Serious now, what do you do with them? Investigation?


----------



## Sinbios

I believe Clutz works at the Biology department at UBC


----------



## diablo9

Quote:


  Originally Posted by *Clutz* 
_I got two surprises in the mail this morning! One was a package from Alf containing two of the Prototype PCBs (unfortunately I leave for a vacation for two weeks tomorrow, so I won't be assembling it until I get back) - and the other was a package containing 16 different strains of Caenorhabditis elegans and 3 strains of E. coli! 



 I agree, common Guzzler! 
	

	
	
		
		

		
		
	


	


_

 

I handles hundreds of vials of Drosophila Melanogaster everyday. 
	

	
	
		
		

		
		
	


	




 we are on the similar boat.


----------



## ATAT

'scuse my ignorance. whats UBC?


----------



## Nisbeth

Quote:


  Originally Posted by *ATAT* 
_whats UBC?_

 

University of British Columbia most likely 
	

	
	
		
		

		
		
	


	





 /U.


----------



## ATAT

Ahhhhhh Brilliant! being a silly California kid, I didn't know that =p Interesting that they let you ship E. Coli.. last time I tried to ship living material over the mail it got bounched.. ahwell maybe that the USPS hates me


----------



## Clutz

Yep, I'm a biologist at the University of British Columbia. 
	

	
	
		
		

		
		
	


	




 About two years away from being Dr. Clutz. 
	

	
	
		
		

		
		
	


	




 I'm always surprised I'm able to mail e. coli across the border so easily. 






 Anyway, I'm excited about this lil' DAC. Here are my plans for assembling them (I got two boards).

 I'm going to make one with basic parts, nothing fancy, USB powered. i.e. the "sane" configuration. The second one I plan on getting a little bit stupid with. Good caps (blackgates, oscons), external power supply.


----------



## ble0t

I managed to finish soldering everything up last night. I'm using configuration A i.e. powered from the USB. As far as components, I've got OSCONs in most of the cap spots as well as using tantalums for the switch mode power converter caps and a couple Pana FC. I'm using some decent quality Sanyo caps for the output coupling caps until my Black Gates get here (Kyoto Electro is slooooooooooow). It detects and installs properly under Win XP Pro for me, but I haven't had a chance to do any listening tests yet...I'll try to get it hooked up tonight and report back


----------



## ATAT

ohhhh nice.. keep us posted and are there any things for option A like jumpering pads?


----------



## MASantos

I still haven't received my boards! We had two national holidays here in portugal yesterday and last thursday. It seems that this has further slowed those lazy post office people!!!


----------



## ble0t

The only component I did not populate on the board was the BUF634 as I do not plan on powering it from any other amp. Other than that, I've used everything else


----------



## bigmike216

No boards for me yet either.. Hopefully on monday!


----------



## bigmike216

No boards for me yet either.. Hopefully on monday!


----------



## diablo9

OK guys, I got the board a few days ago and assembled an hour ago, 
 I chose option A, which is powered by USB itself. So I connect it to the USB cable. then... nothing happened??? The computer didn't even recognize the DAC, so I didn't even bother connecting it to amp. I was wondering if I did something seriously wrong. Could someone figure it out? 
	

	
	
		
		

		
		
	


	










 one thing: D1 was sooo close to L1 and being really hard to install once L1 is there. I took a look at the PCB layout pic and put the negative pole (the one with white bar) pointing to right side on my photo. I suppose that's the correct orientation. Other than that, I couldn't find any thing that could be wrong. I used the magnifier to check solder between small leads, no solder bridge.


----------



## Francis_Vaughan

Quote:


  Originally Posted by *diablo9* 
_one thing: D1 was sooo close to L1 and being really hard to install once L1 is there. I took a look at the PCB layout pic and put the negative pole (the one with white bar) pointing to right side on my photo. I suppose that's the correct orientation. Other than that, I couldn't find any thing that could be wrong. I used the magnifier to check solder between small leads, no solder bridge. _

 

D1 sounds OK, it faces from L2 towards C4. 

 (EDIT) BUT - you have put it on the wrong pads!!!! That pad you are complaining about being so close to L2 is actually L2's pad with a bit of solder mask missing. You have missed. The diode goes from the pad under the "1" in D1 to the pad that just touches the circle that delineates C4. At the moment D1 is simply sitting over the trace that leads from L2 to where D1 is supposed to connect.

 Yuk, this is going to be a painful fix I'm afraid.

 Sanity check. You did bridge S1 - or connect a power switch here?

 Other than that - voltages? Power supplies working?


----------



## ble0t

Quote:


  Originally Posted by *Francis_Vaughan* 
_Sanity check. You did bridge S1 - or connect a power switch here?_

 

Yea, the first time I plugged it in, I was checking voltages and realized I hadn't 'switched' it on either


----------



## guzzler

Mine's been plugged in, and works like a treat. I've got 13V going in, and all following voltages are spot on as well. Popped up straight away in Win XP. There's still the little tweak of the volume that has to be done, but a minor point there (and one that can't be avoided, AFAIK). Sound wise, I did a back-to-back comparison with the original, battery powered BETA version. 

 In short, the overall sound is very similar (as one would expect). The original was described as laid back, and while this quality is still retained, the presentation is a little more forward, more accuracy in the treble especially.

 This is a very worthwhile upgrade to the original, especially for the improved layout, and ease of assembly.


----------



## diablo9

uh-oh! stupid me! Francis was absolutely correct! I fixed D1, yes it was a pain but after I got rid of C5 which wasn't even meant to be there in option A at 1st place (Thank Alf to point it out), it became easier. Then I bridged S1. It's alive! Win XP recognized it without problem. Now I am gonna do some listening test and get back to you ASAP. 
 Thanks a lot! You guys are awesome!


----------



## diablo9

OK, I only tested it against my stock 0404. Here is the result:
 To my surprise, the nosie floor is VERY low even without any shielding, lower than 0404, which has a small amount of noise floor when my PPA was turned all the way up. With ALF USB DAC (AKA AUD 
	

	
	
		
		

		
		
	


	




 ), at highest level of volume, there is only a little hum, can't be called noise. 
 I tested it using Sheffield A2TB Test Disc (AKA "My Disc")






 I used track 33-40. 
 "In each of the successive tracks the record level has been reduced in increments of 10 dB. Playing these tracks while subsequently increasing the volume fro each track will give an indication of the ability of your system to accurately resoluve low level signals-the most task for digital systems. This is an excellent test to demonstrate the quality of D-to-A converters. THe farther your system can go without excessive noise or distortion the better." 

 AUD can go to track 39 without significant distortion. With track40, the starting piano was barely audible. 0404 was a little bit better than AUD in track 40, in which the piano and saxphone was a little bit clearer but for some reason it was giving alot louder electric hum. I am not sure about the reason, maybe EMI. So in terms of detail, I believe AUD is at least as good as 0404. 

 Comments and suggestion are very welcome.


----------



## diablo9

a little bit thoughts: 
 Flux pen is HIGHLY recommended. Fine tip of iron is recommende for SMD. 
 Only complaint is the D1 letter should be moved to right a little bit. I am afraid I wouldn't be the only silly one. 
	

	
	
		
		

		
		
	


	



 USB female connector could be another model? This specific one is out of stock in digikey as well as most other type B connectors.

 Other than that, nothing special, except the space between output caps. 

 excellent sound, I have to find a excellent housing for it.


----------



## Sinbios

RMAA measurements?


----------



## diablo9

Quote:


  Originally Posted by *Sinbios* 
_RMAA measurements?_

 

I am working on it...
 RMAA keep saying the input level is too low, 

 The input level is low. Try to increase recording or playback levels in your mixer.

 But for my 0404, in patchmixer I already drag the input level all the way up. 
 Anyone knows about this?


----------



## diablo9

Quote:


  Originally Posted by *Sinbios* 
_RMAA measurements?_

 

I am working on it...
 RMAA keep saying the input level is too low, 

 The input level is low. Try to increase recording or playback levels in your mixer.

 But for my 0404, in patchmixer I already drag the input level all the way up. 
 Anyone knows about this?


----------



## diablo9

I finally gave up on this RMAA thing after a couple of hours trying.. 
 I directly connect 0404 output to input, keep saying high distortion... connect it to AUD, input level too low...
 I gave up on this RMAA thing, anyone wants to play it go ahead...
 I am just happy with my AUD, guess that's enough...


----------



## Sinbios

Can't you increase the output level on the DAC?


----------



## diablo9

Quote:


  Originally Posted by *Sinbios* 
_Can't you increase the output level on the DAC?_

 

I put the output level of DAC to highest. Is that what you mean?


----------



## Sinbios

Odd, if the output is at its highest and input is also at the highest, and you can't reach a reasonable level, there must be a problem. Since the EMU0404's input is tried and true, the problem must be with the output.


----------



## ble0t

Just an initial review of the board...

 Detail and positioning are quite good. I'm running it into my CMOY (AD823) and I'm really enjoying it. Very low noise floor as well even while powering from USB. I'm going to try and run it head to head with my Monica 2 tomorrow.


----------



## Magsy

I had the same problem running RMAA on the original Guzzler USB DAC using my 0404, volume too low.

 I did make it work in the end though, I'm pretty sure you just adjust everything to high in Windows, and set the 0404's input level a little higher in patchmixuntill RMAA is happy.

 The original DAC did have a low output, it was not nearly as high as my 0404 or any standalone kit I have.


----------



## MASantos

I got my boards in the mail today just before I left for college!!!

 I will assemble everything tonight when I get home and hopefully have some impressions tomorrow morning!!

 I have panasonic fc's and elna silmic 2 for some positions. I will assemble first with the pana then swap to the silmics to see if there is any difference in sound!!


----------



## MASantos

I just finished to assemble the board!!

 All the soldering fumes gave me a headache 
	

	
	
		
		

		
		
	


	




 !!!! No testing today, I will post some initial impressions tomorrow!!!


----------



## dviswa

Quote:


  Originally Posted by *diablo9* 
_a little bit thoughts: 
 USB female connector could be another model? This specific one is out of stock in digikey as well as most other type B connectors._

 

I am in the same boat. My Digikey delivery came in today, so I can start soldering tonight, but I have no connector.

 I would hate cutting an USB cable and soldering the cable directly to the board. But then, I will if that is what it is.

 Never having dealt with an USB cable, can somebody tell me, if it is color coded, if so what color represents what.

 Thanks,
 Dinesh


----------



## dsavitsk

Quote:


  Originally Posted by *dviswa* 
_I am in the same boat. My Digikey delivery came in today, so I can start soldering tonight, but I have no connector._

 

Try part #154-2442 at mouser. cheaper than the ones at digikey too.


----------



## dviswa

Should have googled a bit. Answering my own question:
 Contact Number Signal Name Cable Color
 1 Vcc Red
 2 -Data White
 3 +Data Green
 4 Ground Black

 Dsavitsk,

 Thanks for pointing it out. For now I think I will directly solder it. One more delivery = 1 week delay. Can't wait to get this going


----------



## guzzler

Be careful cutting the cable, the USB standard is explicit on the quality of shielding in the cable, and there's the issue of reflections as well. I'd be interested to hear how you get on, but if you run into problems, that's the first port of call. I'd offer to send you a connector over, but it being Xmas and all, you wouldn't get it til 2006!


----------



## dviswa

Got a late start today, kid's concert at school 
	

	
	
		
		

		
		
	


	




 Gus,

 Thanks for the offer. I will be careful. Talking about ports of call in trouble, took out one of the 0805 capacitors, struggled with the packing and finally it popped out, fell on the table. Seeing it lying on the table, my heart sank. 

 This is my first SMD project. Yes, I had bought the USB-SPDIF PCB from you, but never got around to it. I am 40+ and my eye sight is not what it used to be, need reading glasses. As I struggled with the soldering, I decided, if this ever works at all, it will not be because of me, but inspite of me
	

	
	
		
		

		
		
	


	




 I am sure there will be many troubles 
	

	
	
		
		

		
		
	


	




 Dinesh


----------



## diablo9

Dinesh, please make sure you have a magnifier around when soldering. So that you can check the soldering right after you do it. PCM2702 is incredibly small to tell if there is a solder bridge between pins without a magnifier. Other than that, just take your time and enjoy SMD! 
	

	
	
		
		

		
		
	


	





 Yishi


----------



## dviswa

Yishi,

 I have Radio shack's Magnifier/solder stand/metal hand. I still had a lot of problems with the 2702. A Jeweller's loupe is probably better for me. Oh' well, next time... 

 Gus had indicated build time to be around 2 hrs. It took me a lot more. I think I have finished it. It is 2:00 AM, if don't get to bed I will get fired tomorrow


----------



## Voodoochile

Quote:


  Originally Posted by *dviswa* 
_It is 2:00 AM, if don't get to bed I will get fired tomorrow
	

	
	
		
		

		
		
	


	


_

 

That will certainly cramp your upgrade path a bit!


----------



## dviswa

Quote:


  Originally Posted by *Voodoochile* 
_That will certainly cramp your upgrade path a bit! 
	

	
	
		
		

		
		
	


	


_

 

Not to mention that it has already been cramped quite a bit by my wife


----------



## dviswa

Whoop de doo...........!!!!!
	

	
	
		
		

		
		
	


	




 I can't believe it worked the first time
	

	
	
		
		

		
		
	


	




 Thanks a lot everybody who helped. In particular, Alf for this wonderful revision and all the hard work. Gus for starting it all. 

 Thanks a lot. Real impressions will take time I guess.

 Foobar does not seem to like Kernel Streaming to it. I will try a few more things to see why.

 Dinesh


----------



## guitz

Great to see this working for you guys....so is the general consensus that the sound is pretty good? I hope the final design includes an LED option!....Also it will be interesting to see how everyone houses these, particularly the 'square hole' for the USB recepticle!....


----------



## MASantos

Quote:


  Originally Posted by *guitz* 
_Great to see this working for you guys....so is the general consensus that the sound is pretty good? I hope the final design includes an LED option!....Also it will be interesting to see how everyone houses these, particularly the 'square hole' for the USB recepticle!...._

 

Mine is just sitting uncased in a piece of antistatic foam! I am changing some of the electrolit caps for testing purposes so it is not practical to have it cased. When testing is over I must decide on an enclosure though...


----------



## dviswa

Quote:


  Originally Posted by *MASantos* 
_Mine is just sitting uncased in a piece of antistatic foam!_

 

Hehe, mine is hanging in the air below the table
	

	
	
		
		

		
		
	


	




 With the USB connector missing, and directly soldered USB cable, there is no way I can case this up.

  Quote:


  Originally Posted by *guitz* 
_so is the general consensus that the sound is pretty good?_

 

I have just a few hours on this and is too early to form any opinions. From what I have seen, I can say, that this clearly kicks my Chaintech AV-710's butt 
	

	
	
		
		

		
		
	


	




 For instance, Kraftwerk's Man Machine & Trans Europe Express used sound a little edgy and grainy. Gone now. The sound stage is much broader now.

 I am running this on Option B, powered by a wall wart. Coupling caps are Elna Silmic II. Some of the other cap values have been simplified.

  Quote:


  Originally Posted by *guitz* 
_I hope the final design includes an LED option!...._

 

I thought so too. Another nit is that it also needs a pad for the ground.


----------



## dviswa

Quote:


  Originally Posted by *guzzler* 
_Be careful cutting the cable, the USB standard is explicit on the quality of shielding in the cable, and there's the issue of reflections as well. I'd be interested to hear how you get on, but if you run into problems, that's the first port of call. I'd offer to send you a connector over, but it being Xmas and all, you wouldn't get it til 2006!_

 

Guzzler,

 You are right, I do have some problems. My USB 2.0 based external hard disk does not come on with the DAC connected. My USB based Laserjet works fine however. I guess older (1.1 & 1.0) slower devices are more immune to reflection issues.

 I cannot escape, another delivery afterall 
	

	
	
		
		

		
		
	


	








 Dinesh


----------



## diablo9

I cased mine up 5 mins ago. 
	

	
	
		
		

		
		
	


	



















 I am definite in for a couple of more PCBs after final revision. if possible, adding an LED will be very nice, I am thinking giving a treaded AUD+MINT combo as a birthday gift to a friend,


----------



## Teerawit

Nice work diablo9!

 How is the sound?


----------



## diablo9

Quote:


  Originally Posted by *Teerawit* 
_Nice work diablo9!

 How is the sound?_

 

I tested with my DIY PPA and was very good, with USB powered version, I think it's not worse than my 0404 analog output. I can't do RMAA test for some software problems but I will test it against Corda Aria's integrated DAC when it arrives.


----------



## Magsy

Quote:


  Originally Posted by *dviswa* 
_Guzzler,

 You are right, I do have some problems. My USB 2.0 based external hard disk does not come on with the DAC connected. My USB based Laserjet works fine however. I guess older (1.1 & 1.0) slower devices are more immune to reflection issues.

 I cannot escape, another delivery afterall 
	

	
	
		
		

		
		
	


	








 Dinesh_

 

Strange, my Rev1 Guz DAC has been used everyday for a few months on the end of an old, cut up Microsoft USB mouse cable and I haven't had any problems. The lead is short though, maybe 6 inches. I have six USB2 drives, usually 2 connected with no problems. 

 I have found power/lead length to be an issue with the drives. My faster 7200rpm bus powered drives do not work properly on my front USB ports or on a long 6 foot USB2 cable. I must use a short lead right into the onboard connectors.


----------



## dviswa

Yishi,

 Your DAC looks great. BTW, where did you buy the hammond case. Digikey was all out of them.

  Quote:


  Originally Posted by *Magsy* 
_Strange, my Rev1 Guz DAC has been used everyday for a few months on the end of an old, cut up Microsoft USB mouse cable and I haven't had any problems. The lead is short though, maybe 6 inches. I have six USB2 drives, usually 2 connected with no problems. 

 I have found power/lead length to be an issue with the drives. My faster 7200rpm bus powered drives do not work properly on my front USB ports or on a long 6 foot USB2 cable. I must use a short lead right into the onboard connectors._

 

Magsy,

 That's interesting, my cable is only a little bit longer maybe 1.5 ft. Further, the drive is powered from a wall wart. I have problems with my flash drive too. Once I pull the DAC out, the drives start working. Hehe, mine is also a cut up Microsoft USB Mouse cable


----------



## jerb

this project looks interesting, I dont suppose those kits were ever made up? 

 If they were I don't suppose there are any still available


----------



## diablo9

Quote:


 where did you buy the hammond case. Digikey was all out of them. 
 

I bought it from Mouser.


----------



## guzzler

Quote:


  Originally Posted by *jerb* 
_this project looks interesting, I dont suppose those kits were ever made up? 

 If they were I don't suppose there are any still available 
	

	
	
		
		

		
			



_

 

Still being prototyped, although as far as I know, everyone's made their boards up. Doubt there'll be kits available, as it's a BIG financial commitment for the organiser, and also arranging that many SMD components into bags is a right pain!


----------



## Clutz

I haven't built mine yet. They came in the mail just as I was about to leave to visit my parents over Christmas holidays. Doh!


----------



## Alf

Quote:


  Originally Posted by *jerb* 
_this project looks interesting, I dont suppose those kits were ever made up? 

 If they were I don't suppose there are any still available 
	

	
	
		
		

		
		
	


	


_

 

Repackaging SMD is a lot of hassle. Every SMD component needs an individual bag with a proper description. ICs need antistatic boxes/tubes. To be honest I am too lazy to do this myself. I could organize repackaging done by a third party but this would add £10 to the cost of the kit. I am not sure how this correlates with the new head-fi policy on commercial activities.

 The good thing is that all components are easy to get from either Farnell UK or Digikey US. I will publish an official BOM for both suppliers after the prototype stage is over. There will be a group buy for PCBs some time in January 2006 (if blessed by the mods).


----------



## guzzler

Quote:


  Originally Posted by *Alf* 
_Repackaging SMD is a lot of hassle. Every SMD component needs an individual bag with a proper description. ICs need antistatic boxes/tubes. To be honest I am too lazy to do this myself. I could organize repackaging done by a third party but this would add £10 to the cost of the kit. I am not sure how this correlates with the new head-fi policy on commercial activities.

 The good thing is that all components are easy to get from either Farnell UK or Digikey US. I will publish an official BOM for both suppliers after the prototype stage is over. There will be a group buy for PCBs some time in January 2006 (if blessed by the mods)._

 

Too right; for the last batch of Rev A boards, I separated over 1500 components, took nearly 3hrs... Don't think I made any mistakes though 
	

	
	
		
		

		
		
	


	




 as Alf has pointed out, a single supplier negates any need for kits anyway, as the saving on bulk buying (and even 100 components isn't really bulk buying in industrial terms) is mainly saving on shipping.

 For the USB-S/PDIF boards, dsavitsk put together an excellent script on his page for it that automatically filled up a Digikey basket with the required parts; very neat, and saved that annoying problem of being ONE resistor short!


----------



## Alf

Finally I have had some time to populate my board. It was my first SMD project and it felt awkward in the beginning. But after struggling with PCM2702 and first few 0805 capacitors, things went much better. I finished everything in about 4.5 hours of which soldering ICs took me 2 hours. Windows recognized the DAC straight away. Despite earlier warnings, ASIO4ALL v2.6 works flawlessly. 

 The sound. All I can say that the DAC exceeded my (low) expectations and I am happy with the results. I will not be reviewing the DAC myself because I am intimately involved in the DAC’s design and I feel that this would be unfair towards audio manufactures present on head-fi. Meanwhile I would like to ask all people participating in the prototype stage to prepare a review and either publish it in this thread or forward it to me. I will put all reviews on the support web site (with the author’s permission of course).


----------



## diablo9

Hi, Alf, I found every component is easiliy available from Digikey except the USB socket. Is it possible to keep more than one pair of hole on PCB to adapt different USB socket? or at least make it adapt to some USB socket that's easily available from Digikey. 
 And if possible, could you adjust the spacing between output caps? those caps on prototype board seem too "intimate". 
	

	
	
		
		

		
		
	


	



 One more thing is that, is it still possible to add LED power indicator on it? or it's too late to make this mod? 
 Whatever mod you are gonna do, I think it's best to keep the current width of the PCB as it fit EXACTLY in the smallest Hammond 1455.


----------



## MASantos

Quote:


  Originally Posted by *diablo9* 
_Hi, Alf, I found every component is easiliy available from Digikey except the USB socket. Is it possible to keep more than one pair of hole on PCB to adapt different USB socket? or at least make it adapt to some USB socket that's easily available from Digikey. 
 And if possible, could you adjust the spacing between output caps? those caps on prototype board seem too "intimate". 
	

	
	
		
		

		
		
	


	



 One more thing is that, is it still possible to add LED power indicator on it? or it's too late to make this mod? 
 Whatever mod you are gonna do, I think it's best to keep the current width of the PCB as it fit EXACTLY in the smallest Hammond 1455. 
	

	
	
		
		

		
		
	


	


_

 

could you just run a led with a resistor from one of the powr pads(3, 9v, 12v) to an empty ground pad? 

 and yes, please move those caps a bit apart!


 Alf, I think I will have a review ready bu the end of the week, I just started christmas hollidays so I have more time now!!


----------



## Alf

Quote:


  Originally Posted by *diablo9* 
_Hi, Alf, I found every component is easiliy available from Digikey except the USB socket. Is it possible to keep more than one pair of hole on PCB to adapt different USB socket? or at least make it adapt to some USB socket that's easily available from Digikey._

 

Which one would you like me to adapt to? I have been thinking about adding a mini type B socket.

  Quote:


  Originally Posted by *diablo9* 
_And if possible, could you adjust the spacing between output caps? those caps on prototype board seem too "intimate". 
	

	
	
		
		

		
		
	


	


_

 

Sure. 

  Quote:


  Originally Posted by *diablo9* 
_One more thing is that, is it still possible to add LED power indicator on it? or it's too late to make this mod?_

 

I will add this option. You can use C5/C8/C12 pads on the prototype board. They should be free now.


----------



## ble0t

Quote:


  Originally Posted by *diablo9* 
_Hi, Alf, I found every component is easiliy available from Digikey except the USB socket._

 

Actually, there is a socket available through Digikey. The part # is ED90003-ND. The two tabs that come off the sides are too large, but I just snipped them off and soldered the ground pad on the board to the side of the USB connector itself. When I get around to getting some decent pics of mine, I'll take a pic of it.


----------



## diablo9

Quote:


  Originally Posted by *ble0t* 
_Actually, there is a socket available through Digikey. The part # is ED90003-ND. The two tabs that come off the sides are too large, but I just snipped them off and soldered the ground pad on the board to the side of the USB connector itself. When I get around to getting some decent pics of mine, I'll take a pic of it._

 

yes, this is a good one, Alf, actually any TYPE B socket will do as long as Digikey has thousands of them in stock. Mini-USB socket will be nice, too.


----------



## MASantos

If you can find a usb b plug that is available from digikey and form farnell, that's great!


----------



## leftshoe

Soooooo

 The parts for this are availible from a company that ships internationally? Like to Australia for example?
 If there is a board group buy I'm in.


----------



## Francis_Vaughan

Here in Oz Digikey is the best bet. They are very good about international service - and don't charge ridiculous prices. Local companies are close to useless, and often breathtakingly expensive. There will likely be a bill of materials directly useful as a Digikey order generated at some point. Digikey allow the creation of public BOMs, so it if someone generates one it will be very simple one stop shopping. If I get enthused I might do it 
	

	
	
		
		

		
		
	


	




 Note that there is currently no mention of a group buy, and won't be in this forum. If it happens (which does seem likely) it will be done as per the appropriate rules in a separate thread.


----------



## ATAT

hahaha. I guess he was saying he had interest, not that he wanted to start one..

 BoM has a mistake.. it has a 220 ohm resistor where it should be 220k. I bougt using the BoM posted on the site, saw the discrepancy and kinda panicked. Fun. 

 Found a berg connector at a local shop (Halteds, if you're curious).

 Anyone know how good Rubycon CE W and Nichicon KL(M) are? I have a few...

 And ferrites ARE interchangable right? (I just picked one up from a random reel that had no values listed).


----------



## Francis_Vaughan

OK, as per the above, creating a Digikey public BOM seems like a nice idea. However, what would really help, is a name for the DAC. Name needs to be in two parts, a full name that makes it quite clear to the whole world what it is, and a short name (truncation of the long name would be a good idea) that allows easy reference (especially in these forums.) Everyone here knows Guzzler's USB DAC. (Partly, I suspect, because the name is, Ahem, unforgetable 
	

	
	
		
		

		
		
	


	




 ) Alf's contribution is significant, as is Guzzler's and 00940's.

 Who knows where the canon of these designs will go - so perhpas the name should reflect an ongoing revision history. This is the Rev B DAC. Rev C may well in the future, and so on. 

 So, some thoughts? I guess Alf gets first bite 
	

	
	
		
		

		
		
	


	




 , but what it is eventually called might be out of his hands


----------



## ATAT

Vote 1 for the name - G0AD - B = Guzzler, 00940 , Alf's DAC (Really wanted to make it G0AT - B, but there's no T)


----------



## rsabo

Maybe not an acronym, or something that contains an acronym...
 Some ideas that I just thought up...
 SuperG0AT (guzzler 00940 alf't)
 G0'NAUD (guzzler, 00940 'n alf's usb dac)
 The Magical 4-In-One Mystery MegaMini USB DAC by Guzzler, Alf, & 00940 (TM4IOMMMUDbGA0) 
	

	
	
		
		

		
			





 Can't wait for this to come into production - awesome job guys!


----------



## Francis_Vaughan

If you really want a "T" the word is "team".

 Could refer to the threesome, could refer to the rest of us cheering from the sidelines and stirring up trouble 
	

	
	
		
		

		
		
	


	




 The Rev-B G0AT DAC. Yuk!.


----------



## ATAT

YESSS =) 
 Rev-B G0AT DAC... you can't lose


----------



## Alf

I agree we need a name. Something catchy. 

 To be honest, I am not in favour of using an acronym. A lot of people contributed to the design. Perpetuating particular nicks is not fair to the rest of the guys. Also someone else might take over the project in the future. Will we want to change the name then?

 Why don’t we choose a well sounding word related to music in some way? Sonata DAC would be a good example of this approach. 

 Changing the version numbering may be a good idea too. Using v1.0, v2.0 instead Rev A, Rev B. What do you think?


----------



## Francis_Vaughan

I agree with Alf. I was wondering if we couldn't think of a name that somehow captured the spirit of the DIY community. Dunno what yet. There is probably a bit of sense in moving to a v2.0 denotation. If it were software it would be v2 by now. Enough has changed. The bugfixed version should be v2.1.

 There is much to be said for a more rigourous version numbering. (Speaking as someone who used to teach software engineering.)


----------



## MASantos

What about ATDAC v2.0? AT standing for All Together?


----------



## Alf

I have spent a few hours earlier today doing RMAA tests. The results are bizarre at least.

 My setup was: 
 * EMU 0404 with the standard I/O breakout cable.
 * Mono ¼ to RCA cables made of Van Damme unbalanced cable and Neutrik plugs.
 * Regular USB cable (came with my printer).
 * DAC board populated according to Option A with SANYO OSCONs (C2, C4) and Panasonic FMs (the rest including CL/CR).

 I plugged the DAC to EMU inputs and started the RMAA tests. RMAA complained that the levels were too low. The levels were about -60dba. I increased the master volume in Windows to 100%. This gave me -35dba. Still not enough. I used the knobs called “Amount of signal sent to Aux Bus” in PatchMix. Changing the number to 5.5 gave me the perfect -1dba RMAA was asking for.

 I ran a series of tests. The results were similar to those produced by Magsy for the Rev A. THD and IMD were about half of Magsy’s figures. The numbers for noise level and dynamic range were 84-85 for USB power and 90-91 for 9V battery. Not great but good enough for the first pass. I repeated the test a few times. The results were consistent.

 Then I decided to experiment a little bit and add C5 to see how it affects performance. I used Panasonic FC 330uF. I repeated the tests. Guess what? The noise/range numbers dropped to 65 for USB. It looked like I got some unwanted resonance with 33uF C4 due to close capacitor values. I removed C5 and repeated the tests. This is where my troubles started. Noise and range did not come back to the old values. I got 75 instead of old 85. The difference is too significant to be discarded. 

 A couple of minutes later I realized that I also soldered two wires for testing different powering options. One went to 12V pad and the other one went to AV+. Could this be the problem? I removed the wires and tested again. No change. I still cannot get the old values. Could that be EMI from a pile of cables behind my computer? I repositioned my computer and made sure that no power cable is within 10cm of the cables going to DAC. The USB cable and the audio cables were separated as much as possible. Still no luck. What is even more annoying, the more I test, the worse it gets. The figures consistently go down with every test. I ended up with 71 for USB power and only 80 for battery. 

 I noticed in PatchMix that there is persistent noise on EMU inputs when the DAC is powered up. More noise if the DAC is USB powered. I did not notice it the first time.

 I cannot explain the results. Your input is very welcome.


----------



## MASantos

this sound a bit dumb, but have you check your test equipment? Maybe there is somethign wron with it.


----------



## 1racerx

Nice work alf ... I was interested in getting my hands on guzzlers board (as you were) and was then directed here. I just read thru all 17 pages and am soooo excited!!

 I do alot of SMD prototyping at work and am eager to get my hands on one of these boards as the soundcard in my laptop is HORRIBLE!! 

 Q1 Do you have any prototypes left?

 Q2 Are you still thinking Jan 2006 as an ETA for the new boards?

 Q3 Would you post to Perth Australia?? If not would you mind passing me your final eagle files so I can get them made on this side of the world?

 Keep up the good work hey ... Its a fantasic effort!! you should be proud.

 btw, i can think of a good name


----------



## Alf

Quote:


  Originally Posted by *1racerx* 
_Q1 Do you have any prototypes left?_

 

No.

  Quote:


  Originally Posted by *1racerx* 
_Q2 Are you still thinking Jan 2006 as an ETA for the new boards?_

 

Yes, there will be a release in January. I am not sure yet whether it will be a full group buy or another limited prototype run.

  Quote:


  Originally Posted by *1racerx* 
_Q3 Would you post to Perth Australia??_

 

Sure.


----------



## 1racerx

Cheers Alf, Ill keep and eye on this thread

 Dan


----------



## tolly

Built mine up last night, and it's a good feeling to have it working first time. Sounds nicer than my laptop, and overall good. I'll write a review as soon as I have the time!

 One strange problem I did have - whilst listening to Gwen Stefani, I got a load of digital noise (no, not Gwen!), that seemed as if the usb had got out of sync. I restarted the track, and had no more problems. Anyone else had this effect? I'll try with the linux drivers this evening, but weird nonetheless.

 I think I'll build the other prototype and add a 9V battery (and possibly USB charging circuit), and see if I notice any difference.

 Tolly


----------



## guzzler

On the Rev A boards, a lot of noise was associated with low voltage (ie, batteries too low). Is is just Gwen that does this, or is it with other tracks?


----------



## Alf

I have done a few further tests today. I observed a couple of odd facts:
 * USB noise on my computer goes up and down spontaneously. This explains bizarre behaviour in my previous tests. It could be extremely noisy but then it becomes relatively quite without any changes to the test environment.
 * Different USB ports on my computer have different noise level. The difference is significant, up to 10db.

 There are two ways noise penetrates into the sound. The first one is powering from USB. While there is some improvement in terms of noise comparing to Rev A, the new design does not eliminate USB noise here completely. The new design reduces the difference between battery and USB to 5-6db (9-10db in Rev A). What can we do? I think that the value of C2 and C4 should be increased. An additional LPF after the switch may help too.

 The second way of noise is through traces between the USB connector and PCM2702. We have done nothing in this area and it shows. My tests confirm that it is the main source of noise now. The difference between noisy and quiet tests (odd fact #1) was up to 12-15db even with battery. The standard practice to fight this is to use a transformer. I doubt this would be practical in our case due to small size of the board. What would be an effective and compact way to tackle this issue? I am still not sure.


----------



## ble0t

Putting small inductors in those traces might help things...


----------



## Francis_Vaughan

We have to allow rise times that allow the USB signal to work. 

 But the USB noise is a problem. The USB signals are differential - and this probably helps quite a a bit, but there will be comon mode noise as well. This will come in common on the USB signals and across the power or ground. Since there is no signal in either of these reasonably agressive ferrites on those legs would seem to be a good idea. Indeed one wonders about significant low pass filtering. 

 Other than that, galvanic isolation is a good idea, but does indeed need a transformer. Still not a total panacea.


----------



## 00940

on my usb2.0 add-on pci card, there are ferrites on the ground and power usb lines just before the usb jacks. It probably cannot hurt to add two more at the dac side.


----------



## Francis_Vaughan

Another nasty thought - well potentially mitigating thought. Your test setup, I assume, uses the same computer for both input and output. So there is very likey a common ground led through the USB ground. This could easily cause significant problems. Problems that are never seen in normal operation of the DAC. Hard to know how to fix, but there may be some benefit in playing with dressing the cables, shorter USB cable, playing sith signal ground on the input to you sound card (such as tying it to the USB ground.)


----------



## Alf

I found the problem. A nut on a RCA connector got loose causing poor electrical connection to the ground. This caused excessive noise. The noise level changed every time I touched the board. I tightened up the nut and finally I started getting consistent results. Well, the difference between individual results now is within 1% for noise and DR. 

 Also I bought an expensive USB cable (Profigold 1.5m) to check whether it makes any difference. According to the description, the cable features some superior Interference Absorption Technology (yeah sure) eliminating EMI. It seems that the cable does make some difference. However it is within 1.5db which is very close to the 1% margin.

 With the new cable and the fixed connector I get figures around 85-86 for noise/DR if USB powered. If a battery is used, the figures go up a bit to 87-88. I cannot get 90-91 I got during my very first tests. I will continue my investigation tomorrow. Subjectively I cannot tell much difference between USB and battery. Maybe USB power sounds a bit better but I cannot tell for sure and I cannot explain why.

 We need alternative RMAA measurements to find out whether the figures above are specific to my test environment and my substandard soldering skills or it is indeed a feature of the new revision. Can someone help with this?


----------



## Sinbios

Hm, from the measurements, it sounds like Rev A is actually better when powered with batteries? 

 Then again, the Rev A tests were done with a 1212 - might that have contributed to better numbers?


----------



## Alf

Quote:


  Originally Posted by *Sinbios* 
_Hm, from the measurements, it sounds like Rev A is actually better when powered with batteries? 

 Then again, the Rev A tests were done with a 1212 - might that have contributed to better numbers?_

 

Magsy did tests with EMU0404. The best figures were when connected to a laptop. It did not matter whether it was USB or battery. Then goes PC/battery and the worst one is PC/USB.

 There is no information whether ITZBITZ used a laptop or a PC.


----------



## DaKi][er

Hmm, just thinking aloud here

 Transformer for the D+ and D-, something that is used in plain digital or networking type, and optocoupler for the power, as the pcm2702 only really needs a voltage here to say that the USB is plugged in, then run it off battery/external from there
 I would think that they will need to be coupled to the same ground still

 Just thinking


----------



## Alf

I have been playing with the DAC yesterday trying different powering options. And then I asked myself a question. PCM2702 requires only 4.5V to run properly. What would happen if I connect USB VBUS directly the 9V pad? How would REG102 react if only 5V is supplied? 

 I decided to check it out. I connected S1 to AV+. My DMM showed 4.9V at the 5V pad and perfect 3.3V at the 3V3 pad. It was close enough and the DAC was working! 

 Then I decided the check how (bad) it performs. RMAA produced results that indeed surprised me. Bypassing both the switch and LM317 improved the performance significantly. The figures went from mere 85db up to 92-93db. I repeated my tests a few times trying different configurations but the results were consistent.

USB
Battery
Comparison

 Well, it seems that Revision B is an over-engineered design. It is about time to take away what is superfluous. The switch section must be removed. It was not needed there in all revisions. I am not sure about the LM317 section yet – it may be useful for some people.

 I noticed quite a few factors that affect the DAC’s performance I cannot say it is audible, but RMAA shows some difference (1-2db each). These factors include but not limited to:
 * USB cable.
 * USB port.
 * HDD activity.
 * Output capacitors.


----------



## guzzler

Interesting Alf, how reproducable are the results on the cable and port? I'm tempted to think a 1dB difference is sensitive to the setup, and certainly not audible. A 7dB reduction by skipping the switching regulator is good, and definately remove it if it gives such a good improvement (although still probably not hearable 
	

	
	
		
		

		
			





)


----------



## MASantos

Alf I would like to apologise for not having a review or some coments yet. 
 I have tons of college work now but I will try to take some time to make some listening tests and comparisons between revision A and B.

 Manuel


----------



## 00940

Alf : if you consider going that road, you could perhaps change the REG102 for the TPS793** serie. Those regulators are cheaper, almost as good and there's one that outputs 4.75V if you feed him with 5V. It will allow you to cope better with varying usb voltages (some usb ports don't output the full 5V). The PCM2702 can live according to the datasheet with as low as 4.5V.


----------



## Mod_Evil

Hi,

 Me and a Friend have mounted this a DAC with the PCM2704.

 But in now we will balance my dac. How I make this? 

 Can I make my balanced DAC with the DRV134?

 Thanks.


----------



## ATAT

IIRC.. you need DACs for each signal (ie 4) since the PCM2704 is single-ended.


----------



## 00940

The pcm2704 is a stereo chip. 

 Yes, the DRV134 will give you a balance output. Considering the quality of those chips, no need to go to anything more complicated.


----------



## ATAT

Cue Rickr with his transformers.... =)

 mmm the DRV134 sounds like it'll end up easier than buying a transformer.. eh might end up doing it.. jensens arn't cheap


----------



## ATAT

Sighs.. it says "USB device not recognized"

 So far I've traced all the power pads, checks out according to schem (3.3 v & 5v to right parts).. 

 Looked for solder jumps, checked continuity on every pin.. No go.

 The 'Scope shows something weird.. D+ jumps to high and stays at high (with some rippling it seems) once plugged in.. D- stays at low. (I think thats what it is at least..) 

 All the power regulation sections check out as they're outputting the right voltage.. frequency of the crystal checks out.. 

 Any suggestions? (including how to desolder the 2704)


----------



## Alf

Quote:


  Originally Posted by *ATAT* 
_Sighs.. it says "USB device not recognized"_

 

I saw this once. I re-connected the USB cable and the problem was gone. I assume you have done this already.

  Quote:


  Originally Posted by *ATAT* 
_So far I've traced all the power pads, checks out according to schem (3.3 v & 5v to right parts).. 

 Looked for solder jumps, checked continuity on every pin.. No go._

 

Can you post a few pictures of your board? Meanwhile I suggest that you check again all PCM2702 pins and the USB socket.

  Quote:


  Originally Posted by *ATAT* 
_how to desolder the 2704_

 

Be prepared to damage either the chip or the board. If you decide to kill the chip, I suggest using good tweezers and desoldering each pin individually.


----------



## ITZBITZ

Quote:


  Originally Posted by *Alf* 
_Magsy did tests with EMU0404. The best figures were when connected to a laptop. It did not matter whether it was USB or battery. Then goes PC/battery and the worst one is PC/USB.

 There is no information whether ITZBITZ used a laptop or a PC._

 

My testing was done with a 1212m on a desktop PC with the USB card hooked to the same PC, albeit a different port. Battery power was the quietest of the three options. Even on a Dell 5100 (at that time), there was a small amount of noise on the bus-powered setup.

 Anybody tear down a Plantronics USB GameCom Pro 1 and see what's inside? It's a pretty basic chipset, but it's the same concept, is bus powered and I get no audible noise with the stock headset. I'm thinking of buying another one and tearing it apart to put a 3.5mm jack on it to hook up my Shure e4c's to see how they sound powered by it.


----------



## Alf

Quote:


  Originally Posted by *00940* 
_Alf : if you consider going that road, you could perhaps change the REG102 for the TPS793** serie. Those regulators are cheaper, almost as good and there's one that outputs 4.75V if you feed him with 5V. It will allow you to cope better with varying usb voltages (some usb ports don't output the full 5V). The PCM2702 can live according to the datasheet with as low as 4.5V._

 

Good point! The SOT23 versions of the chips seem to be pin-compatible. I will change the package to SOT23 catering for both chips.


----------



## Alf

Quote:


  Originally Posted by *guzzler* 
_Interesting Alf, how reproducable are the results on the cable and port? I'm tempted to think a 1dB difference is sensitive to the setup, and certainly not audible. A 7dB reduction by skipping the switching regulator is good, and definately remove it if it gives such a good improvement (although still probably not hearable 
	

	
	
		
		

		
			





)_

 

I can reproduce the results all the time. However the results are a bit odd. If I use switching regulator with USB, the expensive cable gives slightly better results (< 1db). If I skip the switch, the printer USB cable is better (~3db).


----------



## Clutz

I'm back after being on Christmas vacation for a few weeks. My boards are ready and I'm dying to get at them. Sorry for taking so long to put them together - life has just got in the way. Anyway, I'm going to put together a parts list tonight and make my order. Any general parts recommendations? I've noticed that Alf has made a number of modifications so far- have they been c ompiled anywhere yet?

 Cheers,
 Clutz


----------



## Alf

Quote:


  Originally Posted by *Clutz* 
_ Anyway, I'm going to put together a parts list tonight and make my order. Any general parts recommendations?_

 

* Output capacitors do matter. Get the best you can find. Elna Silmic II produces better results than Panasonic FM. If your amp benefits from input coupling capacitors, then do not populate CL/CR.

 * If you populate CL/CR, use a 5mm/D 2mm/P capacitor for C24. Soldering would be much easier.


 Everything else as described here http://www.myexposition.com/diy/usbdac/partslist.html

  Quote:


  Originally Posted by *Clutz* 
_I've noticed that Alf has made a number of modifications so far- have they been compiled anywhere yet?_

 

If you mean the changes since Rev A, then have a look here 

http://www.myexposition.com/diy/usbdac/overview.html


----------



## Clutz

Quote:


  Originally Posted by *Alf* 
_* Output capacitors do matter. Get the best you can find. Elna Silmic II produces better results than Panasonic FM. If your amp benefits from input coupling capacitors, then do not populate CL/CR._

 

Re: Capacitors, I was going to go with Blackgates- any particular line of black gates that are ideal in this case? Re: input coupling capacitors- I have no idea if it does or doesn't. I am going to use it with a Millet, a PPA, and (eventually) a Dynalo and a M3. 

  Quote:


 Everything else as described here http://www.myexposition.com/diy/usbdac/partslist.html 
 

I guess I meant more along the lines of some of the experimenting that you've done.

  Quote:


 I decided to check it out. I connected S1 to AV+. My DMM showed 4.9V at the 5V pad and perfect 3.3V at the 3V3 pad. It was close enough and the DAC was working! 

 Then I decided the check how (bad) it performs. RMAA produced results that indeed surprised me. Bypassing both the switch and LM317 improved the performance significantly. The figures went from mere 85db up to 92-93db. I repeated my tests a few times trying different configurations but the results were consistent. 
 

Have you done any more experimenting this way?


----------



## dsavitsk

Quote:


  Originally Posted by *Clutz* 
_Re: Capacitors, I was going to go with Blackgates- any particular line of black gates that are ideal in this case?_

 

I would use blackgate N series 4.7uF 50V caps. They sound quite good -- better than a lot of film caps -- and are easy to source. It appears they will fit the board, though they might be a tad small so you'll need to bend the leads. I know that the schematic says to use 47uF, but this is really silly. 4.7uF is more then large enough for source output caps. Here are my thoughts on some other (mostly cheap, mostly film) caps as well: http://www.ecp.cc/cap-notes.html

  Quote:


 Re: input coupling capacitors- I have no idea if it does or doesn't. I am going to use it with a Millet, a PPA, and (eventually) a Dynalo and a M3. 
 

The Millett has no input caps, and the others don't unless you put them there.


----------



## Clutz

Quote:


  Originally Posted by *dsavitsk* 
_I would use blackgate N series 4.7uF 50V caps. They sound quite good -- better than a lot of film caps -- and are easy to source. It appears they will fit the board, though they might be a tad small so you'll need to bend the leads. I know that the schematic says to use 47uF, but this is really silly. 4.7uF is more then large enough for source output caps. Here are my thoughts on some other (mostly cheap, mostly film) caps as well: http://www.ecp.cc/cap-notes.html_

 

What do you think of Aerovox AFPS 4.7uF film caps for this position? They're axial instead of radial - but with lead bending could be made to work.


----------



## dsavitsk

Quote:


  Originally Posted by *Clutz* 
_What do you think of Aerovox AFPS 4.7uF film caps for this position? They're axial instead of radial - but with lead bending could be made to work._

 

I like them. I use them on my own DAC (with a bit of lead bending.)


----------



## Alf

Quote:


  Originally Posted by *dsavitsk* 
_I would use blackgate N series 4.7uF 50V caps. They sound quite good -- better than a lot of film caps -- and are easy to source. It appears they will fit the board, though they might be a tad small so you'll need to bend the leads. I know that the schematic says to use 47uF, but this is really silly. 4.7uF is more then large enough for source output caps._

 

Agree. Even 4.7uF is overkill. 1uF should be enough. 

  Quote:


  Originally Posted by *dsavitsk* 
_Here are my thoughts on some other (mostly cheap, mostly film) caps as well: http://www.ecp.cc/cap-notes.html_

 

Great article!!! I wish I had ears like yours. I am doing a lot of testing now. I suspect I fail to notice a lot of obvious things. 

 Would you be able to review other electrolytics? Something well regarded and popular – Silmics, Muse, etc.


----------



## dsavitsk

Quote:


  Originally Posted by *Alf* 
_Great article!!! I wish I had ears like yours. I am doing a lot of testing now. I suspect I fail to notice a lot of obvious things._

 

Thanks. I'm not sure that any of the distinctions are obvious. A lot of times it is putting something in the circuit, and after a good long listen just having a sense that something is good, or amiss. Since it is so subjective and subtle, I did try to listen to each cap a couple of times and in different orders, though I really need to get someone else to do the swapping so I don't know what they are.

  Quote:


 Would you be able to review other electrolytics? Something well regarded and popular – Silmics, Muse, etc. 
 

It's a good idea, and something I should try. I know that my Millett which has Muse's sounds hard, but whether this is the caps or something else is a mystery to me. It doesn't see enough use to worry much about. I do have Duorex II's, Os-Cons, BlackGate's, FM's and Muses around, so maybe when I get a free evening or two I'll try them out.

 -d


----------



## Alf

Quote:


  Originally Posted by *Clutz* 
_Re: Capacitors, I was going to go with Blackgates- any particular line of black gates that are ideal in this case? Re: input coupling capacitors- I have no idea if it does or doesn't. I am going to use it with a Millet, a PPA, and (eventually) a Dynalo and a M3. _

 

Yes, you need CL/CR in this case. I suggest you try different output capacitors to find the sound you like. 

  Quote:


  Originally Posted by *Clutz* 
_I guess I meant more along the lines of some of the experimenting that you've done._

 

If you have some time to spend, it would be interesting to see how different parts affect the performance. The output capacitors is the most important factor here. But other parts contribute as well. It is always useful to use RMAA to confirm your findings. It helped me a lot.

  Quote:


  Originally Posted by *Clutz* 
_Have you done any more experimenting this way?_

 

I finished the noise tests. The results are consistent. I cannot improve it further. I cannot say whether Rev B is better than Rev A. The computer does makes some difference and I do not have a working Rev A DAC to compare it with. If someone can send me a Rev A for comparison, I would greatly appreciate this.

 Now I work on adding a headphone section to the DAC. Actually I am listening to a breadboard prototype while I am typing this. It sounds promising. We should be able to get a decent bus-powered USB headamp in the 1455C80x case.


----------



## dviswa

Alf and everybody,

 I am back from my vacation. Hope you all had a nice holidays and new year.

 I had forgotten that with the DAC connected, my machine would not start because of the USB issues I had. This frustated me enough to do some debugging. Because my setup is option B - Wall wart powered, thought D+, D- and GND, were all the connections needed for this. I removed VBUS connection and DAC was still working and my USB issues were gone. The flashdrive came on, camera came on. Connecting VBUS back brought back all the issues, the flashdrive gets no power (because the LED does not come on) and quits. That brings up the question; Does VBUS need a jumper?

 Regards,
 Dinesh


----------



## Clutz

I know this is overkill, but I'm going to order the parts from parts connexion anyway, and they have a $25 minimum order so I figured - why not? 

 I'm thinking of going entirely with Blackgates C2, C4, CL, C4, C24 = 33uF 50V, Blackgate N series. For C6, 100uF, 6.3V, C7, 220uF, 6.3V, Blackgate NX.. But I have absolutely no idea what to do for C10/C14..?

 (btw: I'm doing options A and B)..

 Is this overkill to the point where it's bad? Should I just go with some Panasonics for most of the caps except CL, CR, C24? If I should, let me know ASAP so I can add them on to my order that I just made with digikey.

 Thanks


----------



## ble0t

I'm not sure you'll see much difference using Blackgates everywhere aside from the coupling caps (CL, CR). I think what you're mainly after is low ESR, and pana FC's have very nice ESR measurements, so I think those would work just fine. I used OSCONs for everything except for C5, CR and CL as those have even lower ESR.


----------



## dsavitsk

For L and R, use the BG 4.7uF N series. For 24, how about an Os-Con. For the others, try BG standard or PK. The N series is not appropriate there. Hard to know if there will be any real benefit here, but it is only a couple of bucks.


----------



## ble0t

Also, in response to Alf's post, I did find something that may help out. I posted the links here in my thread concerning a PCM2704 design I'm working on.


----------



## Clutz

I'd get Oscons if I could get them from digikey, but they don't have any particularly good caps for output caps at digikey. I could order from Mouser, but delivery to Canada is extremely slow. So, this means I have to order from something like Parts Connexion or Welbourne Labs. Parts Connexion is in Toronto, ON, and I'm in Vancouver, BC, which means I won't have to pay any importing duties / brokerage fees, and my shipping fees will be a lot less than buying from Welbourne. Parts Connexion has a minimum of a $25 order, or you get a $5 handling fee, so I figured I might as well spend at least $25, since just getting the CL, CR, and C24 would bring me to $15 before shipping. It might jack the price up a bit- like to $30 - but if it's better, then I'll do it.. Otehrwise, I'll just go and tack on some Panasonic FMs or FCs (which are better here, FMs, righjt?) to my order to have some extras lying around in my kit.


----------



## Clutz

Quote:


  Originally Posted by *dsavitsk* 
_For L and R, use the BG 4.7uF N series. For 24, how about an Os-Con. For the others, try BG standard or PK. The N series is not appropriate there. Hard to know if there will be any real benefit here, but it is only a couple of bucks._

 

Okay, thanks. I figure I might as well put good quality parts in this, since it's not going to cost me a lot more to do that than put the cheaper alternatives - and I don't think I'll have the money to design and build a DaKiller level DAC for a while.. But I do plan on trying out yours dsavitsk.


----------



## Clutz

For C10/C14, it says medium ESR-- is it bad to use low ESR, or just that there isn't any benefit?


----------



## Alf

My suggestions:
 * Use OSCONs 47uF 16V for C2, C4 if you can get them. If not, choose the biggest value and the lowest ESR (for example, Panasonic FM 120uF 16V).
 * Do not populate C5 for option A. 
 * Do your own listening tests for CL/CR. Try different capacitors. You should be able to get away with 0.47uF. Therefore film capacitors could be an option – fitting them could be tricky but worth a try.
 * Use either of Panasonics for the rest. FMs are meant to be better.


----------



## Clutz

So you think that using Panasonic FMs is preferable over BlackGates? i can get them, but they'd be a bit of a pain cause I'd have to make another order with digikey, and I just made an order.. I can't get Oscon 47uF 16V, but I can get 20V, which should fit, right? Do you think it'd be worth spending ~$20 on two 0.47uF auricaps? Or maybe some Orange Drops or Solens which I can easily source locally?


----------



## Alf

Quote:


  Originally Posted by *Clutz* 
_So you think that using Panasonic FMs is preferable over BlackGates? i can get them, but they'd be a bit of a pain cause I'd have to make another order with digikey, and I just made an order.._

 

Panasonics are cheaper. I doubt one can hear any difference. If you placed an order already, there is no point to order FMs. Blackgates will do fine.


  Quote:


  Originally Posted by *Clutz* 
_I can't get Oscon 47uF 16V, but I can get 20V, which should fit, right?_

 

No, the 20V version would not fit. The board has space for a 6mm capacitor. Your choice of OSCONs is limited to SA 33uF 16V/20V, SC 33uF 16V, and SA 47uF 16V.

  Quote:


  Originally Posted by *Clutz* 
_Do you think it'd be worth spending ~$20 on two 0.47uF auricaps? Or maybe some Orange Drops or Solens which I can easily source locally?_

 

This depends on your ears and your budget. I would try local-sourced caps first.


----------



## Clutz

Quote:


  Originally Posted by *Alf* 
_Panasonics are cheaper. I doubt one can hear any difference. If you placed an order already, there is no point to order FMs. Blackgates will do fine._

 

Alright, then I'll get the blackgates.. or maybe order the parts to put together something like dsavitsk DAC from digikey, and try using some film caps sourced locally. I'll also try to find if I can find any other locally sourced OSCONs. I've never seen them at any of the local shops I've tried out, but I an look a bit further. 

 I'm still nervous about soldering the PCM2702E. I have a 40watt soldering iron, so maybe I'll pick up a higher quality 25 or 30 watt soldering iron this weekend.


----------



## dsavitsk

Quote:


  Originally Posted by *Clutz* 
_or maybe order the parts to put together something like dsavitsk DAC from digikey_

 

Not meaning to thread crap -- if you build one of mine, I recommend getting the offboard version of the transformer. I am getting a bit of noise, mostly into amps with highish (100K) input impedence and I think that the transformer proximity is to blame.

  Quote:


 I'm still nervous about soldering the PCM2702E. 
 

Don't be. It's not a big deal.


----------



## dviswa

Quote:


  Originally Posted by *Clutz* 
_I'm still nervous about soldering the PCM2702E. I have a 40watt soldering iron, so maybe I'll pick up a higher quality 25 or 30 watt soldering iron this weekend._

 

Radioshack 15W worked just fine for me. Not scaring you, but, You will put a few bridges across a few pins, nothing some Desoldering braid cannot fix.


----------



## diablo9

Quote:


  Originally Posted by *dviswa* 
_Radioshack 15W worked just fine for me. Not scaring you, but, You will put a few bridges across a few pins, nothing some Desoldering braid cannot fix._

 

one way to solder 1 side without any bridging is to: 
 flood each side with flux for both PCB and pins, 
 tin the iron with good amount of solder,
 pull the iron through the pins in fast and steady speed.
 solder on the iron will be "sucked" into the seam of pin and PCB, 
 this way you will never get bridge, 
 keep in mind that you need to "flood" the PCB with flux.

 enjoy

 Yishi


----------



## Clutz

So I tried your suggestion diablo9, and I'm not sure if it was successful. I lined up all the pins between the pcm2702 and the pcb, put lots of flux on both the pcb and the board, tinned up my soldering iron with lead, and pulled it across at a fast but steady pace. I got a few bridges, but they were easy to fix by either pulling the soldering iron across it again OR by using a bit of think solder wick. 

 However, I think the 2702 chip became slightly misaligned on the one side of the board. It looks fine on the left side (towards the USB connector), but a little bit off on the right... So I don't know. I don't have the time to finish soldering the other bits on right now, and my electrolytics aren'there yet - so I'll probably have to wait until next weekend to finish.. but if it doesn't work, I'm not sure what to do. Order a new chip and pry off this one? There is anelectronics technician in the department I work in - might he be able to help me get it soldered in place?

 Anyway, I'll go and find my magnifying glass and see if I can get a better look. If I get a chance to, on Monday I'll take a picture of it with a microscope and post it.

 *crossing fingers*

 Clutz


----------



## DaKi][er

Take a look under a real close light source pointed on the board like a desk lamp or something, you should easily be able to see if anything is bridged without any magnification as long as you have 1/2 decent eyesight 

 and diablo9 probably missed out one of the most important steps, setting your chip up square to begin with, by soldering one outer corner pin to the board and then the diagonal opposite one after that then adjusting to make sure it is perfectly square before soldering the rest of the pins


----------



## Clutz

So, if I have missoldered it (i.e. it's not quite square), how can I adjust it - or do I just have to scrap the chip? I'm not sure it's not square though.. I don't have ahlf decent eye sight.. ;(

 Thanks though, I'll try again if I can't get it to work.

 Clutz


----------



## dsavitsk

You should go to your local photography shop and buy a cheap loupe (8x is plenty) which will help you see the connections. 

 I think you are making this process too hard. You should put the chip on the board, tape it down with some scotch tape, and solder down a couple of pins on one side. When you are convinced that the chip is straight, solder everything and use some desoldering braid to suck up the excess. There is no reason to try to do a chip with tight spacing pin by pin, or to try to get it right without desoldering. These chips are built to take a ton of heat and it is very unlikely that you will overheat it.

 Anyhow, I doubt you can adjust it. By the time it is hot enough to move you won't be able to touch it with wnything but tweezers, and you are unlikely to be able to accurately adjust it with those. The only way I know to get a chip with a lot of pins off of a board is to hold the board upside down and hit it with a butane torch until it falls off ... then get a new chip ... and maybe a new board.


----------



## Francis_Vaughan

SOP to remove a SMD chip is to cut all the legs off and then take the individual legs off the board with solder braid. At least that only sacrifices the chip. The only alternative is a mega expensive specialty tip for a rework station. The tip alone costs more than the entire DAC project.

 (This from my EE brother who learnt this from the rework lab at a military electronics contractor he once worked for.)


----------



## diablo9

use a magnifier to check the pins, as long as you can see ANY contact between the pin and PCB pad, there shouldn't be any problem. alignment is important, too, but as long as the pins are all soldered onto the pad, a little bit mis-alignment is just cosmetic issue.


----------



## Clutz

Quote:


  Originally Posted by *dsavitsk* 
_You should go to your local photography shop and buy a cheap loupe (8x is plenty) which will help you see the connections._

 

Thanks - I'll do that. i had a friend look at it (he has better than 20/20 vision without glasses), and he said that it didn't look like the pins were connected to the incorrect pads. I don't think it looks like they're connected incorrectly either. 

  Quote:


 These chips are built to take a ton of heat and it is very unlikely that you will overheat it. 
 

This is what I was worried about - frying the chip. At least I have a second 2702 lying around and a second board to try it out with if all else fails. 

 I'm going to get the loupe and check it out. If all looks good, then I'll go ahead with assembling the rest of it and hope for the best. If it doesn't work, then I'll try the second board out with my other chip - and I'll order myself a few more of the 2702s from digikey.. or somewhere. 
	

	
	
		
		

		
			






  Quote:


 OP to remove a SMD chip is to cut all the legs off and then take the individual legs off the board with solder braid. At least that only sacrifices the chip. The only alternative is a mega expensive specialty tip for a rework station. The tip alone costs more than the entire DAC project. 
 

I hope it doesn't come to that, but thanks for the tip! 
	

	
	
		
		

		
		
	


	




  Quote:


 use a magnifier to check the pins, as long as you can see ANY contact between the pin and PCB pad, there shouldn't be any problem. alignment is important, too, but as long as the pins are all soldered onto the pad, a little bit mis-alignment is just cosmetic issue. 
 

My concern at this point isn't that I don't have contact between the pin and the PCB pad, or that I have bridges, it's that I may have a pin connected to two PCB pads - but my friend who looked at it said he didn't think so. I'll try to see if a local photography shop is open tomorrow. 

 Thanks,
 Brad


----------



## DaKi][er

If you can't see any bridges then it is safe to say that it should be fine how it is

 Seeing you used lots of flux, solder just doesn’t form bridges very well at all and if it does you will clearly see them as you have pointed out when you used too much solder and got rid of them just fine

 If you've given it a proper scrub and cleaned off the flux and you cannot see anything with your eyes then it is fine


----------



## dsavitsk

Quote:


  Originally Posted by *Clutz* 
_I'll try to see if a local photography shop is open tomorrow._

 

They'll try to sell you something expensive (and you can spend hundreds on a loupe if you want) but the $7 ones are good for your purposes. Here's a good example: http://www.bhphotovideo.com/bnh/cont...goryNavigation

 Good luck.


----------



## Clutz

Quote:


  Originally Posted by *Alf* 
_My suggestions:
 * Do your own listening tests for CL/CR. Try different capacitors. You should be able to get away with 0.47uF. Therefore film capacitors could be an option – fitting them could be tricky but worth a try._

 

How about a .56uF Solen film cap? The orange drop spragues that are 0.56 are about $5 each at a local supplier, and they are freaking huge... Bigger than my baby finger.


----------



## dsavitsk

Quote:


  Originally Posted by *Clutz* 
_ and they are freaking huge..._

 

Usually a good sign for a cap. One thing to be careful of with the orange drops, some of them have steel leads (I don't remember offhand which ones, so test with a magnet.)

 The Solen's are fine, but they are so cheap that you might move to slightly higher capacitance.


----------



## Clutz

The solen's at the shop I've seen them at are not inexpensive, and they had poor variety - the only capacitance level they had two in were 0.56. They had some other pretty big ones, but only one. They also had WIMA box caps, but I don't think they'd work - leads are too short. 

 I'll probably start with the Blackgates then when they arrive. The local shops around here all suck.


----------



## Clutz

I made a mistake when I ordered some parts from digikey- I ordered 1.5Ohm resistors instead of 1.5KOhm resistors for R4. I don't have any idea where I can source them locally or I'd just do that. I'd be happy to paypal you a $1 (or a 1 pound) for one or two of the SMD resistors and the cost of postage - I don't really want to spend $8 shipping + $6.50 handling fee (for small orders) to buy like $2 worth of parts, and since they don't have any other parts right now that I'm in need of, I'd appreciate the assistants.

 At the same time I found out that digikey made a mistake in the order and didn't send me the 1MOhm resistors and the 1N4004 diodes. 

 I'm so annoyed with myself.


----------



## Clutz

What the...!! I don't know how to get this thing to solder in place. I made the mistake of putting L1 in place first (eep!), and second - I don't know how to tell which way D1 should be pointing - either on the board, or looking at the part D1 itself. It has no visual references on it to indicate polarity!


----------



## Alf

Quote:


  Originally Posted by *Clutz* 
_What the...!! I don't know how to get this thing to solder in place. I made the mistake of putting L1 in place first (eep!), and second - I don't know how to tell which way D1 should be pointing - either on the board, or looking at the part D1 itself. It has no visual references on it to indicate polarity!_

 

The diode should have tiny stripes on one side. The marked side must point to the capacitor. The unmarked side must point to the inductor.


----------



## dviswa

Just use the multimeter to figure out which is anode, that is what I did, I could not tell visually either.


----------



## Clutz

That's a good idea. I think I also may end up assembling the >10V external PSU powered version too.

 The SMD stuff was *much* easier than I had expected it to be. I would like a finer tip for my soldering iron to do th 0805s, but other than that it was quite easy - esp. once I started soldering one of the pins to hoold the thing in place (thanks dsavitsk). The 1206 stuff was really breezy. The only problem I may have now is my girlfriend 'cleaned' and seems to have mixed up my 0805 capacitors, d'oh. Hopefully they're not too mixed up. (This is what I get for not putting the parts in little baggies before hand).

 Good news though, my capacitors came from parts connexion today. I bought two 10uF solens to use for CL / CR. Insane overkill, but what the hell.


----------



## Sinbios

So, when will the prototyping stage be over? I'm excited for the final version!


----------



## dsavitsk

Quote:


  Originally Posted by *Alf* 
_Great article!!! I wish I had ears like yours. I am doing a lot of testing now. I suspect I fail to notice a lot of obvious things. 

 Would you be able to review other electrolytics? Something well regarded and popular – Silmics, Muse, etc._

 

RE: http://www.ecp.cc/cap-notes.html

 I added a couple of electrolytics to the list (Panasonic Bi-Polar, Nichicon Muse ES Bi-Polar.) The results? The Panasonics are awful. The Nichicons are pretty nice and have the fattest bass I've ever heard.


----------



## dviswa

dsavitsk,

 That is an excellent comparison. I thought, Silmic was absent from that list. Can I send you a couple, so that you can add them to the list. PM me if you want.

 Regards,
 Dinesh


----------



## Clutz

Quote:


  Originally Posted by *dsavitsk* 
_RE: http://www.ecp.cc/cap-notes.html

 I added a couple of electrolytics to the list (Panasonic Bi-Polar, Nichicon Muse ES Bi-Polar.) The results? The Panasonics are awful. The Nichicons are pretty nice and have the fattest bass I've ever heard._

 

dsavitsk,

 re: Electric Goldmine- I can't seem to find the link to the $3.49 sets of capacitors. Can you provide it for me?

 Thanks,
 Brad


----------



## dsavitsk

Quote:


  Originally Posted by *Clutz* 
_re: Electric Goldmine- I can't seem to find the link to the $3.49 sets of capacitors. Can you provide it for me?_

 

Here's the item (look under capacitor assortments, then for the high voltage film cap assortment -- I'll make a note about this on my page). http://www.goldmine-elec-products.co...tem=2&mitem=13 They seem to have raised the price to $5.00 which is a little high considering you don't know what you are getting. I got one 20uF film cap that I was very excited about until I went to use it and discovered it only had one lead 
	

	
	
		
		

		
			





  Quote:


  Originally Posted by *dviswa* 
_That is an excellent comparison. I thought, Silmic was absent from that list. Can I send you a couple, so that you can add them to the list. PM me if you want._

 

That's very generous of you. Do they make a small value bi-polar? I haven't been able to find any.


----------



## dviswa

Quote:


  Originally Posted by *dsavitsk* 
_That's very generous of you. Do they make a small value bi-polar? I haven't been able to find any._

 

According to their site, they have as small as 0.47. What I have available is 100 and 220 mfd electrolytics. Don't think they come in bipolar. I bought it in a Group Buy here on Head-fi.


----------



## dsavitsk

Quote:


  Originally Posted by *dviswa* 
_Don't think they come in bipolar._

 

I think I don't want to get into the business of evaluating every electrolytic, so I am going to stick with the bi-polars for now. I have used them as ouput and cathode bypass caps in a millett, so I feel like I have a sense what they sound like, but not enough sense to say anything. If I change my mind I'll add some small ones to my next welborne order. Thanks again for the offer, though.


----------



## dviswa

Sorry guys it took me a while to get around to putting my thoughts. 

 Juggling CDs are not my favorite activities, so I never invested much in CD players. Chaintech AV 710 is the only source I have listened for any extended duration, thus am qualified to have an opinion on.

 This USB DAC throws an enormous sound stage adding a whole new dimension - depth, AV710 in comparison was almost 2D. The separation and air the music has now is absolutely fantastic. AV710 is also a little muddy in comparison in addition to sounding laid back. The DAC puts you in the front seat. With AV710 Female vocals was a little more enjoyable and tad warmer while with the DAC the male vocals sound great. You can actually hear the back of the throat of Enrique Iglesias in Hero for instance. 

 My Maxed out PPA with Glassman DB makes a great match to this gret DAC. My Millet-Hybrid do not seem to be a great match. 

 There is no going back for me now. Don't be surprised if you saw the 710, Millet Hybrid shows up in the FS forums.

 Thanks a lot to Alf, Guzzler, 00940, Francis Vaughan, dsavitsk and everybody else here, I now have a great DAC.

 Regards,
 Dinesh


----------



## Clutz

Well, it didn't go as planned. I guess I must have installed the DC-DC converter backwards or something cause it was overheatting and the DAC wasn't working. So I'm going to try and get it to work as an Option B DAC now instead of an Option A DAC. 

 Looking at the schematic however, it's unclear to me where I connect the +V and -V from my input (12 VDC)? I'm assuming the I connect the +12V to the 12V pad, but where does the -V lead from the PSU connect to - I think that any GND pad will work, right?


----------



## ble0t

Yep...any ground should work.


----------



## Clutz

Quote:


  Originally Posted by *ble0t* 
_Yep...any ground should work._

 


 Well, then something is wrong - I've got it connected it'snot working. I must've fried something else then. The LM317 is getting very warm - but it's probably overpowered, my 12VDC gives PSU gives off about 15volts. Crap crap crap.. The TPS chip I had when I was going self powered was getting super hot once it was connected. So I think I'll start all over with my last board.


----------



## Alf

Quote:


  Originally Posted by *Clutz* 
_Well, it didn't go as planned. I guess I must have installed the DC-DC converter backwards or something cause it was overheatting and the DAC wasn't working._

 

Can you post a picture?


----------



## Clutz

Quote:


  Originally Posted by *Alf* 
_Can you post a picture?_

 

Yes - as soon as I get my digicam working. I removed the DC-DC converter - thinking that it was the problem and then went with option B by connecting up +15V at the 12V pad, and connecting the 0V at the GND pad and tried it out that way. Still, no bones. Neither my PC or my Mac recognized the device. It didn't even say 'unrecognized device'.. It just ignored it altogether. 

 The only thing left I can think of trying is connecting the input voltage off of the USB to the +9V pad like you did earlier.. 

 I'm really beginning to wonder if the problem lies with that first PCM2702E chip. I tested out each pin using a continuity tester to make sure that nothing was touching the wrong pad but.. I dunno.


----------



## dsavitsk

2 things to check:

 -make sure that the resistors between the usb jack and the chip (R4, R5, and R6) are on correctly. 

 - Also, plug a usb cable into the DAC and check continuity from the other end of the cable to the board. These jacks are fussy, and this is a pretty easy thing to have go wrong.

 The chip is likely only bad if something went really wrong. They are sensitive to static and heat, but they are also intended for consumer gear that gets abused, so they can't be that sensitive.


----------



## Clutz

Quote:


  Originally Posted by *dsavitsk* 
_2 things to check:

 -make sure that the resistors between the usb jack and the chip (R4, R5, and R6) are on correctly. 

 - Also, plug a usb cable into the DAC and check continuity from the other end of the cable to the board. These jacks are fussy, and this is a pretty easy thing to have go wrong.

 The chip is likely only bad if something went really wrong. They are sensitive to static and heat, but they are also intended for consumer gear that gets abused, so they can't be that sensitive._

 

R4, R5 and R6 all checked out - but I wonder about some of the SMD capacitors, I think that they'd be more difficult to test out.. I'll try testing out the continuity- but I think that might be where the problem is. I've tried testing the continuity of the various pins, and it seems like there is a short between the pins.


----------



## dsavitsk

A badly soldered cap probably won't keep the computer from recognizing that something is plugged in. Do you have a voltage from the usb cable?

 If it makes you feel any better, I have 3 of the old guzzler dac's. One (which was the beta) seems to work, one used to (though you had to plug and unplug the usb cable twice to get it to be recognized) but has now inexplicably stopped, and the third has always played for a couple of minutes and then died.


----------



## Clutz

Quote:


  Originally Posted by *dsavitsk* 
_A badly soldered cap probably won't keep the computer from recognizing that something is plugged in. Do you have a voltage from the usb cable?

 If it makes you feel any better, I have 3 of the old guzzler dac's. One (which was the beta) seems to work, one used to (though you had to plug and unplug the usb cable twice to get it to be recognized) but has now inexplicably stopped, and the third has always played for a couple of minutes and then died._

 

Yes, I get voltage when it's plugged in. I'm wondering if I should try the experiment that Alf did a while back and connect the +ve up to the +V pad?


----------



## Clutz

Well I've tried it.. and still no bones.. but I have more information.

 When I connect VBUS to AV+ and then try to measure the voltage at 5V and 3.3V, I get 0 volts.. SoooOOOoOooOoo.. Could it be that I've managed to connect the REG102's wrong?? 

 Eep. Well, I guess I'll try to set up the last PCB I have and hope it works. I don't have another TPS chip (DC-DC converter), so I'm limited to going with the Option B - but I wonder if I'd be best to go with thbe setup bypassing LM317 altogether, since it worked so well for Alf? Otherwise I'mgoing to have to order some more REG's (which I don't mind doing). 

 Man- I should never have started DIY. It's cost me way more than double what a GS-1 and a Brick Dac would've cost me. 

 I think when people come to the DIY section we should adjust the welcome to

 "Welcome to Head-Fi and sorry about your wallet- really, really sorry about your wallet"

 Cheers,
 Clutz


----------



## drbig

Does anybody know the status of revision B? I haven't seen anything posted here for a while. Is there still a plan for a group-buy on boards? Thanks for any info. This looks like a great project!


----------



## Francis_Vaughan

Quote:


 Man- I should never have started DIY. It's cost me way more than double what a GS-1 and a Brick Dac would've cost me. 
 

But the knowledge? Priceless!!


----------



## .: ZMN :.

@drbig

 To worsen any impatience, consider reading  dviswas impressions again. 
	

	
	
		
		

		
		
	


	





 Just did that... *sigh* Patience never was my thing.


----------



## guzzler

I'll give Alf an email, see what's happened...


----------



## Alf

Guys, first of all I would like to apologize for abusing your patience. I have not had enough time to spend the design. It is VERY time consuming exercise and requires a great deal of concentration, which unfortunately I could not provide in the past months.

 Also I would like to thank you for all your emails offering help and enquiring about the status. To be brutally honest, I was surprised by the number of people still interested in this DAC despite of all recent projects on head-fi featuring similar chips.

 The good news is that starting next week I should be able to continue working on the project. I would like to finish it as soon as possible. 

 Now back to business. The prototyping stage served its purpose. The results are promising but I am not 100% happy with the current design. As I mentioned earlier, it seems to be over-engineered and should be simplified a bit. Being a perfectionist, I would like to try a few things before proceeding with a public group buy. Obviously this means another prototype stage.

 I need your feedback on the following prospective changes:

 1) I would like to remove TPS6734. It does not do any good. RMAA show much better figures without it. In USB-powered configuration, REGs will be connected to USB directly. I tried this and it works very well.

 2) LM317 might be useful but NOT required for the project. I am thinking about removing it as well. If someone needs it, Tangent’s TREAD would be an obvious remedy.

 3) Headphone driver. I am not sure whether we should do it but many people asked for this. We could use either MAX4410 (same as ble0t used in his DAC) or AD8397 (see Tangent’s PINT). Adding a headphone output makes the board bigger and therefore more expensive. The target enclosure still will be Hammond 1455C80x. Any alternative suggestions are welcome.

 4) Ground plane. While there may be some improvements to the sound, the RMAA figures are still far from the official datasheet. The only thing in our design that differs from the evaluation board is separate analog and digital grounds. All our revisions of the DAC feature a single ground plane. And all our revisions fail to reach the target figures. I suspect that the single ground plane is the reason for this. While it may be a good idea for bigger boards, our board is just too small. It is not capable to fight digital noise effectively due to its size. The noise penetrates the analog ground and affects the RMAA figures. Fixing the grounds should fix the figures.


 What do you think?


----------



## 00940

Quote:


  Originally Posted by *Alf* 
_4) Ground plane. While there may be some improvements to the sound, the RMAA figures are still far from the official datasheet. The only thing in our design that differs from the evaluation board is separate analog and digital grounds. All our revisions of the DAC feature a single ground plane. And all our revisions fail to reach the target figures. I suspect that the single ground plane is the reason for this. While it may be a good idea for bigger boards, our board is just too small. It is not capable to fight digital noise effectively due to its size. The noise penetrates the analog ground and affects the RMAA figures. Fixing the grounds should fix the figures.


 What do you think?_

 

How does the grounding differ from the evaluation board ? The evaluation board uses a common groundplane on the topside. See page 4 http://focus.ti.com/lit/ug/sbau025/sbau025.pdf The capacitors decoupling the analog and digital supplies are ending very near at the bottom groundplane (connected to the top one).


----------



## Alf

D’oh! You are right. My memory does not serve me well anymore. I must have picked up this idea somewhere else. Basically, the design I refer to had two separate ground planes connected via a 10R (?) resistor. The author claims that it improves the noise. Your opinion? 

 But then the main question remains unanswered. Why the TI evaluation board gives better figures?


----------



## rsabo

Purely non-technical answer: Marketing? Not falsifing measurements, but "pumping" them up a bit?


----------



## Nisbeth

Quote:


  Originally Posted by *rsabo* 
_Purely non-technical answer: Marketing? Not falsifing measurements, but "pumping" them up a bit?_

 

Hey, as someone who does technical marketing for a living I take offense at that 
	

	
	
		
		

		
		
	


	




 Knowing how to make the maximum out of the parts and using that knowledge to measure impressive specs (that sometimes borders on cheating..) is referred to as "specmanship" among the engineers where I work. Some consider this an artform 
	

	
	
		
		

		
		
	


	





 /U.

 EDIT: On topic responses to Alf's post:

 1) Go ahead and remove it is it doesn't help.

 2) As above.

 3) I would really like to see an on-board driver and I think the MAX4410 looks like the easiest to implement cf. the AD8397-discussions on headwize. The alternative solution is to keep this project on track and ask ble0t for his files and work from them in a separate project.


----------



## guzzler

*


----------



## n_maher

Quote:


  Originally Posted by *Alf* 
_Guys, first of all I would like to apologize for abusing your patience. I have not had enough time to spend the design. It is VERY time consuming exercise and requires a great deal of concentration, which unfortunately I could not provide in the past months._

 

Alf, don't sweat it man - First you've only got so many hours in a day to get stuff done and if you're anyting like me DIY usually comes at the end of the day which means some days it doens't happen at all. Second, after reading your list of options I can tell you there's probably not going to be any consensus with that many variables. My opinion would be to go with the design that offers the simplest approach which still giving builders options that they can add for themselves. You can please everyone all the time 
	

	
	
		
		

		
			





.

 Nate


----------



## 00940

Quote:


  Originally Posted by *Nisbeth* 
_Hey, as someone who does technical marketing for a living I take offense at that 
	

	
	
		
		

		
		
	


	




 Knowing how to make the maximum out of the parts and using that knowledge to measure impressive specs (that sometimes borders on cheating..) is referred to as "specmanship" among the engineers where I work. Some consider this an artform 
	

	
	
		
		

		
		
	


	


_

 

Indeed. Is it said anywhere that the measurements were taken on the evaluation board ?


----------



## steinchen

Quote:


  Originally Posted by *Alf* 
_I need your feedback on the following prospective changes: ..._

 

1) remove TPS6734

 2) if it doesn't hurt just leave it in and make the part optional

 3) I don't need the headphone driver. If you're going to implement it I'd advocate for MAX4410 and against AD8397 since AD8397 is a very finicky chip

 4) Fix the grounds


----------



## Francis_Vaughan

Be careful when you worry about the grounds. The idea of somehow improving things by separating the DAC proper analog grounds from the digital ground with a resistor is widely discredited, and if you read back to my initial commentary on the layout you can see the reasons why. "Fixing the grounds" by cutting the ground-plane and installing a resistor between them will seriously damage the performance of the DAC. 

 I will repeat the main point - a DAC is not an audio frequency device. Nor is it a simple digital device. The usual ideas of grounds in audio simply do not work. The only way of thinking about these systems is as a complex RF device which has significant switching energy that must be controlled. This cannot be done with a split ground-plane. At any moment current will be flowing through the wafer from any one of the +ve inputs and essentially flowing out via any one of the ground pins. If you cannot reason about the return ground path for every single possible switching current you will create a system which will induce significant energy into other parts of the wafer - energy that is very likely signal correlated and capable of seriously degrading audio performance. Splitting ground-planes will create such a system.


----------



## Alf

Quote:


  Originally Posted by *00940* 
_Indeed. Is it said anywhere that the measurements were taken on the evaluation board ?_

 

Good point! It must be one of those "specmanship" tricks. I don’t feel that bad anymore.


----------



## Alf

Assuming that a headphone driver is a go, which chip should we use? My only concern about MAX4410 is its availability in the UK (and presumably Europe). Otherwise it seems to be great. There are some other good chips around. LM4908, TPA152, MAX9722 – to name a few. Has anyone tried these chips? Which one is considered to be the best nowadays?


 There is one other thing that bothers me lately. If these headphone drivers are as good as their specs say they are, why people build CMOY and other entry-level headamps?


----------



## MASantos

The headphone driver would discard the need for and headphone amplifier right? If so, I don't really agree with this implementation since it will not allow the use of other amps such as mints or pimetas. If it is possible have this driver as an option and still be able to have a "line out" signal then it might be useful in some cases. 
 Adding the the headphone driver will change this project from a DAC to a all in one DACplus amplifier board, which was not the original goal. 
 But if both options are possible that's a plus!!

 Manuel


----------



## Nisbeth

Quote:


  Originally Posted by *Alf* 
_There is one other thing that bothers me lately. If these headphone drivers are as good as their specs say they are, why people build CMOY and other entry-level headamps?_

 

AFAIK noone's really tested these drivers in depth, so very few are able to offer qualified comments on SQ. Also, a CMoy or other small amp is much easier to layout and assemble than something which involves SMD's. After you get a few CMoy's running, most people "graduate" to building something more complex but a MAX4410 is not really a good way to practice soldering 
	

	
	
		
		

		
		
	


	





 /U.


----------



## dviswa

Quote:


  Originally Posted by *Alf* 
_What do you think?_

 

 Quote:


  Originally Posted by *Alf* 
_1) I would like to remove TPS6734. It does not do any good. RMAA show much better figures without it. In USB-powered configuration, REGs will be connected to USB directly. I tried this and it works very well._

 

I did not use this bus powered option, so no comments.

  Quote:


  Originally Posted by *Alf* 
_2) LM317 might be useful but NOT required for the project. I am thinking about removing it as well. If someone needs it, Tangent’s TREAD would be an obvious remedy._

 

Not sure I agree on this. I am using the DAC with a cheap wall wart. That would not be possible without LM317 and a TREAD is much more costlier, so I would suggest leave it in.

  Quote:


  Originally Posted by *Alf* 
_3) Headphone driver. I am not sure whether we should do it but many people asked for this. We could use either MAX4410 (same as ble0t used in his DAC) or AD8397 (see Tangent’s PINT). Adding a headphone output makes the board bigger and therefore more expensive. The target enclosure still will be Hammond 1455C80x. Any alternative suggestions are welcome._

 

I do not need this, so as long as this is an optional thing, I think it is OK.

  Quote:


  Originally Posted by *Alf* 
_4) Ground plane. While there may be some improvements to the sound, the RMAA figures are still far from the official datasheet. The only thing in our design that differs from the evaluation board is separate analog and digital grounds. All our revisions of the DAC feature a single ground plane. And all our revisions fail to reach the target figures. I suspect that the single ground plane is the reason for this. While it may be a good idea for bigger boards, our board is just too small. It is not capable to fight digital noise effectively due to its size. The noise penetrates the analog ground and affects the RMAA figures. Fixing the grounds should fix the figures._

 

The DAC when it was not yet cased up, had a very small amount of hiss, barely observable. After I put it in a Black Hammond case, it got really black 
	

	
	
		
		

		
		
	


	




 Seriously, this is one real black DAC even at full volume. Fiddling with the grounds I think moves it back into early Alpha, rather than at a Beta stage. I seriously doubt I can hear any further improvements, if any.

 Dinesh


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_The headphone driver would discard the need for and headphone amplifier right? If so, I don't really agree with this implementation since it will not allow the use of other amps such as mints or pimetas._

 

While you will not need to use an additional amp, there still will be an option to use it if you would like to. I plan to add 2 line outs: before the output capacitors and after.
  Quote:


  Originally Posted by *dviswa* 
_Not sure I agree on this. I am using the DAC with a cheap wall wart. That would not be possible without LM317 and a TREAD is much more costlier, so I would suggest leave it in._

 

You do not need LM317/TREAD to use the DAC with a cheap wall wart as long as it is <=10V. The REGs will do the job.


----------



## Alf

OK, I will not touch the ground. 



 I have been reading MAX4410 spec and found this:
  Quote:


 Proper layout and grounding are essential for optimum performance. Connect PGND and SGND together at a single point on the PC board. 
 

Two ground planes connected at a single point. Should it be disregarded? If not, how these grounds should be connected to the DAC ground?


----------



## cire

i sent you a PM regarding this a while ago, but can i get the eagle files for the DAC?


----------



## Francis_Vaughan

Quote:


 Two ground planes connected at a single point. Should it be disregarded? If not, how these grounds should be connected to the DAC ground? 
 

No, don't disregard this. We are no longer in DAC land. We are back in audio land. The charge pump runs at 320kHz, which is not RF (not really nowadays anyway.) The suggested seperation of groundplanes makes perfect sense here. It is done to control the imposition of power supply noise into the audio ground of the chip. But the audio ground is most likely a continuation of the DAC groundplane.

 In fact keeping the charge pump noise away from the DAC is a good idea too.


----------



## Alf

Major changes:
 * Removed the buffer, the switch, and the LM317.
 * Added optional LEDs. You can choose which one to use.
 * Added output ground capacitor for virtual ground amps.
 * Eliminated vias in output traces.
 * Improved layout around PCM2702. 
 * Added 2 ground pads.
 * New board size 48.6mm x 50.5mm.


 Things to do/discuss:
 * Change IC2/IC3 to SOT223-5. This will allow TPS793xx to be used instead of REGs. TPS793xx have higher PSRR and may be better suited for the application. (EDIT: Changed TPS30xx to TPS793xx)
 * Increase the size of the USB receptacle mounting holes. I had no problems whatsoever but other people reported the holes are too small.
 * Re-introduce the buffer and/or LM317. I am not sure about this. Is it going to be used? 


 I decided not to add MAX4410 at this time. I think a separate board should be designed. 


 Board v1.0 Rev 1 - Top

 Board v1.0 Rev 1 – Bottom

 Board v1.0 Rev 1 – All without bPlace

 Schematic v1.0 Rev 1


----------



## guzzler

1) I personally liked the buffered ground, it was one of the most frequently asked questions about the old DAC for portable use. 

 2) The LM317 wasn't so necessary and very easy to do off board if needed.

 3) How's the availability and cost of the TPS30xx _cf_ the REGs? At the end of the day, it's going to make a pretty marginal difference for this board.

 4) Could the ground pads be moved directly next to the power inputs, makes life simpler for wiring, and shouldn't obstruct any current routing


----------



## Alf

Quote:


  Originally Posted by *guzzler* 
_1) I personally liked the buffered ground, it was one of the most frequently asked questions about the old DAC for portable use._

 

I added an output ground capacitor CG. It resolves the conflict of different grounds. Also the DAC’s performance when USB powered is very good and it should be even better in the new release. An external PS is not really necessary. While the buffer was required in the previous revisions, I seriously doubt it is needed now.


  Quote:


  Originally Posted by *guzzler* 
_3) How's the availability and cost of the TPS30xx cf the REGs? At the end of the day, it's going to make a pretty marginal difference for this board._

 

Sorry, it was TPS973xx. I updated my original post.

 TPS973xx is cheaper but its availability is poor. Changing the package allows both TPS973xx and REG102 to be used.

  Quote:


  Originally Posted by *guzzler* 
_4) Could the ground pads be moved directly next to the power inputs, makes life simpler for wiring, and shouldn't obstruct any current routing_

 

The power input is supposed to be wired via S1. There is a ground pad next to it.

 3V3, 5V, and G3 pads are meant for testing only.


----------



## MASantos

Alf, here are my opinions:
 a)I think that removing the buffer is a good option, because if we can get good noise figures using USB then alternate power source shouldn't be necessary. regarding the LM317, I also agree that it is easy to implement outside the board.

 b)I don't think 2 LED positions are needed. Just put one position and people can use some wire and redirect it to wherever they want it.

 c) What is the purpose of the ground capacitor? Also, what are the differences between OG and G1?

 d) I just read the datasheet for those TPS793XX and saw something about different grounds being needed? Do you know anything about this?

 e) I think that the board could be made a little bit more compact.since he have all that empty space in the bottom, why not move the PCm2702 down and a bit to the left, the IC3 further to the left, and place the output holes more to the top? This could cut a few mils further. I think that 50,5 X 45 woudl be a great board size!
 Regarding the USB receptacle holes, I too had some trouble placing it.

 My 0,02 cents

 Manuel


----------



## .: ZMN :.

Nice to see activity on this project. 
	

	
	
		
		

		
			





 The change in board size made me wonder about enclosure options a bit.

 Can someone tell me what to expect for max height of components? 
 I wondered if the popular Serpac (H45) enclosures would now also be an option; there are plenty people using these for their portable amp, and might like a 'matching' DAC with it. With a decent bit of DIY (read cutting) on the board I think these colorful soap box enclosures could be used, if the height of board+components is max about 18mm.

 Anyone?


----------



## MASantos

Quote:


  Originally Posted by *.: ZMN :.* 
_Nice to see activity on this project. 
	

	
	
		
		

		
		
	


	




 The change in board size made me wonder about enclosure options a bit.

 Can someone tell me what to expect for max height of components? 
 I wondered if the popular Serpac (H45) enclosures would now also be an option; there are plenty people using these for their portable amp, and might like a 'matching' DAC with it. With a decent bit of DIY (read cutting) on the board I think these colorful soap box enclosures could be used, if the height of board+components is max about 18mm.

 Anyone?_

 

Well I'm actually going to put one inside a hammond 1455N1201 with a PIMETA, a batery pack and a charging circuit.


----------



## .: ZMN :.

Quote:


 Well I'm actually going to put one inside a hammond 1455N1201 with a PIMETA, a batery pack and a charging circuit. 
 

Nice! Dimensions 120x103x54mm, I quess that won't be your portable system 
	

	
	
		
		

		
		
	


	




 Anyway, if there is a need for compatibility, I *think* the current v1.0-r1 layout *could* also please the Serpac fans without much consideration - if height permits.

 Just a thought ...


----------



## Alf

I played with SOT23-5 packages tonight and I did not like the result. The layout around the chips is too cramped. The package is tiny and may be difficult to solder for some people. Well the regulators stay SO8. It means no TPS793xx for now.



  Quote:


  Originally Posted by *.: ZMN :.* 
_I wondered if the popular Serpac (H45) enclosures would now also be an option; there are plenty people using these for their portable amp, and might like a 'matching' DAC with it. With a decent bit of DIY (read cutting) on the board I think these colorful soap box enclosures could be used, if the height of board+components is max about 18mm._

 

The height of the board and components is about 18mm +/- 0.5mm. One of the problems that need to be solved is accessibility of the receptacle. I have never seen H45. Do you think the layout needs any modifications to please H45 fans?

 By the way, Hammond 1533 seems to be a worthy contender too. It is a bit wider. No creative cutting should be required.



  Quote:


  Originally Posted by *MASantos* 
_b)I don't think 2 LED positions are needed. Just put one position and people can use some wire and redirect it to wherever they want it._

 

I could not decide which one would be better. 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *MASantos* 
_c) What is the purpose of the ground capacitor? Also, what are the differences between OG and G1?_

 

If you use the same PS for the DAC and a virtual ground amp, you have a conflict of grounds. You can find more details here. Using an output ground capacitor solves the problem.

 G1 (also G2 and G3) – direct access to the DAC’s ground. Use it if you have no ground conflict. 
 OG – the DAC’s ground via the output ground capacitor. Use it if you have a shared PS.

  Quote:


  Originally Posted by *MASantos* 
_e) I think that the board could be made a little bit more compact.since he have all that empty space in the bottom, why not move the PCm2702 down and a bit to the left, the IC3 further to the left, and place the output holes more to the top? This could cut a few mils further. I think that 50,5 X 45 woudl be a great board size!_

 

C14 is a showstopper. I would not want it to be too close to the receptacle. Anyway 1mm-1.5mm could be gained by moving PCM2702 slightly to the left.

 Additional 2mm-3mm millimetres can be gained by moving the receptacle to the left. However this would make the receptacle more prominent. It would stick out of the enclosure. I am not sure how this will look. Any thoughts?


----------



## MASantos

I would keep LED2, its nearer the receptacle and people can mount it directly to the panel without any extra wire.

 Thanks for the explanation about the grounds.

 Regarding the board size, if during the layout changes it can be made smaller that's great, if not, it's great anyway! 
	

	
	
		
		

		
		
	


	





 would there be any advantage if we move the PCM2702 down to place further away for the power regs? Would less noise go into the signal?(this just crossed my head, I always heard to keep the PS away from the amp, does this apply in this case?)


----------



## .: ZMN :.

Quote:


 By the way, Hammond 1533 seems to be a worthy contender too. It is a bit wider. No creative cutting should be required. 
 

Looks like a nice sollution too, good you mentioned.

  Quote:


 Do you think the layout needs any modifications to please H45 fans? 
 

I don't think the layout needs changes, current setup will keep some H45 DIYers bussy. 
	

	
	
		
		

		
		
	


	



 Have a look yourself. If it will fit the H45, it will do so tightly. The usb-connector might be a problem.


----------



## MASantos

What program do you use to make those case drawings?


----------



## Francis_Vaughan

Looks a lot like Omnigraffle to me.

www.omnigroup.com

 of course if you are stuck in the dark ages and don't have a Mac....


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_would there be any advantage if we move the PCM2702 down to place further away for the power regs? Would less noise go into the signal?_

 

I don't think so.

  Quote:


  Originally Posted by *MASantos* 
_this just crossed my head, I always heard to keep the PS away from the amp, does this apply in this case?_

 

They mean the transformer, which is a source of noise.


----------



## Alf

The updated layout is just around the corner. However I feel that the layout can be improved if smaller vias are used. What is the smallest via size one can use with the PCB Shop? What are downsides of using smaller vias?


----------



## Clutz

I've got all of the resistors and capacitors I need to finish the second DAC board I have - fingers crossed. I'm going to power it by connecting S1 to AV+ as Alf described doing in http://www6.head-fi.org/forums/showp...&postcount=339. *Crosses fingers* I never managed to get the last one to work, unfortunately. 

 Any suggestions on how to get rid of the flux from the board? I can bring home some 95% ethanol home to use it and a toothbrush if that'll work...?

 Thanks,
 Clutz


----------



## Sinbios

99.99% isopropyl is probably your best bet. Those are like a buck a litre at the grocery store around here.


----------



## MASantos

Quote:


  Originally Posted by *Clutz* 
_I've got all of the resistors and capacitors I need to finish the second DAC board I have - fingers crossed. I'm going to power it by connecting S1 to AV+ as Alf described doing in http://www6.head-fi.org/forums/showp...&postcount=339. *Crosses fingers* I never managed to get the last one to work, unfortunately. 

 Any suggestions on how to get rid of the flux from the board? I can bring home some 95% ethanol home to use it and a toothbrush if that'll work...?

 Thanks,
 Clutz_

 

I've always used 96% medical alcool and an old toothbrush to clean the boards. Works fine for me!


----------



## Alf

Changes:
 * New board size 45.7mm x 50.5mm
 * Added BUF634.
 * Adjusted receptacle mounting holes.
 * Reduced the size of the vias around IC1.
 * Fiddled with C14 and C15.
 * Removed the ground capacitor. It does not need to be on the board.
 * Removed one of the LEDs.

 Board v1.0 Rev 2 - Top

 Board v1.0 Rev 2 – Bottom

 Board v1.0 Rev 2 – All without bPlace

 Schematic v1.0 Rev 2


----------



## 00940

Why remove the RC filter on the VBUS before the regulators ? The quality of USB ports varies a lot and I'm not sure it's a good idea to feed the regulators directly from the VBUS (or only through a ferrite). 

 Using a REG101-5 is also a bad idea in my view. I've measured usb ports giving slightly less than 5V. In those cases, the reg101 won't work properly. The TPS793** is better suited here since it includes a 4.75V regulator allowing for some margin.


----------



## Clutz

It's alive! It works! Both my PC and my iBook recognize it! I (unfortunately) don't have an amp at home to test it out with, and I somehow doubt my girlfriend is going to let me go in to work to give it a test - but I'll be able to on Monday. 

 I'm so freaking excited. =D


----------



## MASantos

Alf, that looks great! 

 In order to use an amp's virtual ground as power source to the DAc, where in the amp should we connect the wires?
 Do you think that this option will be audibly noticeable?


----------



## Alf

Changes:
 * New board size 45.4mm x 50.5mm.
 * Added C1 and C2 to form a CLC filter.
 * Changed REG102-5 to REG101-A. REG102-A, REG101-5 and REG102-5 can be used as well.
 * Changed REG102-33 to REG101-33.

 Board v1.0 Rev 3 - Top

 Board v1.0 Rev 3 – Bottom

 Board v1.0 Rev 3 – All without bPlace

 Schematic v1.0 Rev 3


 The new design allows for the following powering options:
 1. Regulated USB. REG101-A (or REG102-A) regulates the voltage to 4.7-4.8V.
 2. Direct USB. AV+ and 5V pads are jumpered. Alternatively a resistor can be used. No need to populate IC3.
 3. Virtual ground amp. Use AV+, AV-, and AG pads. IC4 must be populated.
 4. External PS. Use either AV+/G2 or S1/G1. 
 5. "Overclocking". Same as options 3 or 4 but use REG101-A (or REG102-A) to regulate the voltage to 5.4-5.5V. This should result better performance.


----------



## 00940

Seems quite ok to me. 
	

	
	
		
		

		
			





 The last little change I would do is to rotate C12 by 180° to push it away of the analog section.


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_In order to use an amp's virtual ground as power source to the DAc, where in the amp should we connect the wires?_

 

Option 3 above.

  Quote:


  Originally Posted by *MASantos* 
_Do you think that this option will be audibly noticeable?_

 

I doubt it. I cannot tell any difference between different powering options with Rev B. For me (and 99.99999999% of people out there) this option is just the matter of convenience. However I admit that some audiophiles might hear something.


----------



## Alf

Quote:


  Originally Posted by *00940* 
_Seems quite ok to me. 
	

	
	
		
		

		
		
	


	




 The last little change I would do is to rotate C12 by 180° to push it away of the analog section._

 

Do you mean C12, C2, or both?


----------



## 00940

C12, the ceramic cap of the crystal.


----------



## Alf

Changes:
 * Removed C24 and C34.
 * Changed position of C14. It did not look right in a Gerber viewer.

 Board v1.0 Rev 4 - Top

 Board v1.0 Rev 4 – Bottom

 Board v1.0 Rev 4 – All without bPlace

 Schematic v1.0 Rev 4

 I played with C12 but decided against rotating it. While unlikely there will be any difference in sound, it may be more difficult to solder.

 If there are no further comments/suggestions, I will order the boards on Thursday.


----------



## drbig

Great news Alf. I'm really looking forward to this. Are you going to do an official group buy?


----------



## MASantos

The is a second prototiping stage, and then if everything goes well a group buy will be started. From what I know, there is no ETA on the group buy yet.

 Alf will be able to confirm this.


----------



## MASantos

Al, I remember you speaking about giving the option in the board not to use the output caps (CL and CR). Is this just a matter of placing a jumper in place of the caps? Also couldn't we use some sort of film cap instead of electrolytic?


----------



## Clutz

The problem with film caps is that their values are somewhat low. Large value film caps are harder to find, pretty expensive, and will require some trickery to get them into the holes. That said, if the holes for CL and CR could be widened a bit, that would help. 

 I managed to get a 0.56uF Solen + a 10uF solen in the CL and CR of the previous prototype board (which I'm listening too right now and it sounds very good, imho- the DAC, not the caps necessarily)


----------



## Sinbios

Output caps don't need to be very big, though. 2.2uF should be plenty, and those are available in pretty small sizes if you're not all boutique.


----------



## Clutz

So I'm a bit confused - output caps on the end of a headphone amp are bad because they end up creating a high pass circuit - which cuts out some of the bass frequencies. So is the reason that a we can get away with a relatively small value for the output caps in this case because the input impedence of the amp is much much higher than that of headphones, so the high pass filter doesn't cut out the bass frequencies?

 Cheers,
 Clutz


----------



## dsavitsk

The input impedence of headphones is generally between 32 and 600 ohms. The input impedence of an amp is usually 50000 to 100000 ohms, though they sometimes dip down to 10000.

 To determine the size of output cap you need, use 

 C = 1/(2 * pi * Hz * R)

 where C is the capacitance and Hz is the 3dB corner frequency and R is the impedence the amp sees. Don't forget that there is a resistor from out to ground, so the cap sees this resistor in parallel with the input impedence. Also, for the corner frequency, there are phase distortions for frequencies about 10X higher than the 3db point, so people generally use 2Hz as a good point, though a bit higher is also fine. Also, some feel that it is better to use a higher qualty cap with a higher 3dB than a lower quality with a lower. So, if a 4uF MKP and a 1uF FKP are the same price, you might do better with the FKP.

 On the output of the Millet amp, you'll notice that Pete uses a 1K resistor while most preamps use a 50K. This is because the 1K makes no difference to a 32 ohm load, but when paralleled with a 50K input impedence it would greatly influence the choice of cap.

 So, your 10uF cap is a little large, but does not hurt anything. 4.7uF is a good safe value, though it is also generally larger than you need. 

 Last, paralleling caps can cause problems since the caps fire at different speeds so you get weird phase issues. It is sometimes worth it to use a very high quality cap for the small one, but if the small one is not a lot better, it probably does more harm than good. Your DAC will probably sound a bit better if you take out the .56uF cap and just use the 10uF (unless the .56 is one of the new solen teflon caps.)


----------



## rickcr42

Quote:


 The input impedence of headphones is generally between 32 and 600 ohms. The input impedence of an amp is usually 50000 to 100000 ohms, though they sometimes dip down to 10000. 
 

you can probably make your life easier if you drop 600 ohms entirely from your requirements list and limit it instead to 20-300 ohms.
 I not not yet met the 600ohm can that could be properly driven by anything less than a full blown power amp.It will play but not even close to the way it should sound


----------



## Alf

My thoughts on output capacitors:
 * The best electrolytic capacitors are better than mediocre/standard film capacitors. 
 * Good film capacitors are big and the best film capacitors are huge. 
 * The difference between best electrolytics and practical film capacitors is not that big.
 * Adding film capacitors would mean increasing the board size.

 If you would like use the best there is, nothing stops you from using your favourite film capacitors. Yes, you need a bit of creativity and a bigger enclosure but it is doable. 

 Also the DAC is not meant to be used completely standalone. There is always going to be an amp to connect to. Many amps have some kind of input DC protection circuit. If this is the case, you do not need CL/CR at all. You can either jumper them or connect output wires to the capacitors’ plus pads.

 After a lot thinking on the subject I decided to leave electrolytics on the board. 47uF is overkill for the application but it is very common and does not hurt anyway. So what we have is a cheap and compact solution with very decent sound. This is a fallback strategy if nothing else is available.


----------



## MASantos

So what do you think will be the best solution, using the CL/Cr caps or using the MKT imput caps in a PIMETA amp? 

 Alf did you read in that TI text regarding the pad format(using a "rounder" approach to the cap) near the coupling caps? What do you think about applying that in the board? I was also intriged regarding mounting the caps vertically...

 Manuel


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_So what do you think will be the best solution, using the CL/Cr caps or using the MKT imput caps in a PIMETA amp? _

 

It depends on what you can get for your CL/CR and your personal preferences. Just choose the ones you like better.

  Quote:


  Originally Posted by *MASantos* 
_Alf did you read in that TI text regarding the pad format(using a "rounder" approach to the cap) near the coupling caps? What do you think about applying that in the board? I was also intriged regarding mounting the caps vertically..._

 

If you mean decoupling caps from the piece about proper decoupling, the way I understood it is a bit different. They suggest putting vias as close to the corresponding SMD pads as possible and ideally integrate them into the pads. 

 If you look at the layout pictures I posted previously, you can see that this very approach is used for all decoupling caps.


----------



## Alf

Last minute change:
 * Moved traces connecting X1 and IC1 to the top.

 Board v1.0 Rev 5 – All without bPlace


----------



## MASantos

Quote:


  Originally Posted by *Alf* 
_It depends on what you can get for your CL/CR and your personal preferences. Just choose the ones you like better.



 If you mean decoupling caps from the piece about proper decoupling, the way I understood it is a bit different. They suggest putting vias as close to the corresponding SMD pads as possible and ideally integrate them into the pads. 

 If you look at the layout pictures I posted previously, you can see that this very approach is used for all decoupling caps._

 

I read it again and understadn it now! *Sits back and thinks to himself:looking at the pictures is not enough...


----------



## drbig

Alf, any chance of getting in on the next prototyping stage for this? I could provide feedback on the build process (from a novice viewpoint) and my impression of SQ ( for what it is worth).


----------



## Alf

I ordered 15 PCBs from www.eurocircuits.com today. I expect the boards to be delivered to me around 3rd of April. 

 As before, I would greatly appreciate it if you could help me with prototyping and provide feedback on building process and sound quality. Please remember that this is a prototype. It might not work at all. So if you decide to participate, you do it at your own risk. However, this is a great opportunity to lay your hands on the new design in about 3 weeks. The next batch of boards (group buy or another prototype) will not be around until mid May the earliest.

 The price will be £6.20 per board. You can have max 2 boards at this stage. P&P will be £2.5 to all destinations. This now includes PayPal charges (I had to upgrade my account to accept CC payments).

 If you are interested, please PM or email me specifying the number of boards you would like to order and your PayPal email.


 EDIT: The PCBs are no longer available


----------



## MASantos

Quote:


  Originally Posted by *Alf* 
_I ordered 15 PCBs from www.eurocircuits.com today. I expect the boards to be delivered to me around 3rd of March. _

 

Do you mean 3 of April?

 I don't know if I will be able to participate in this second prototiping stage, could you reserve a board for me and I will let you know afterwards

 Manuel


----------



## Alf

I updated the support web site:
 * Overview
 * Parts List

 The new version of the DAC seems to be cheaper to build. If ordered from Farnell, the parts cost approx £16-£17 of which ICs cost £8.5. Of course, you need to add relevant taxes, the cost of PCB and enclosure.


----------



## guzzler

Put me down for another Alf, i'm on holiday just in time 
	

	
	
		
		

		
		
	


	




 I'll get some pictures of the build while I'm at it too for the construction guide


----------



## MASantos

ALf I was reading through note 4 in the parts list and you speak there about powering the dac directly through USB. Wouldn't this be really bad in terms of noise? 

 Do you think that there will be a audible difference between using an external PS and overclocking the chip to 5,4v and regulating the voltage to 4,5v using USB power?

 I understand that this question is difficult to answer before assembly and listening tests, but from a teorical point of view what do you think?

 Manuel


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_ALf I was reading through note 4 in the parts list and you speak there about powering the dac directly through USB. Wouldn't this be really bad in terms of noise?_

 

Well, it is not direct. It is rather unregulated. There is CLCLC filter that takes care of some noise. In theory, you can select values of C1, C2 to tackle the noise from your computer in the most effective way and make it a non-issue. We will see how it performs in real life.


  Quote:


  Originally Posted by *MASantos* 
_Do you think that there will be a audible difference between using an external PS and overclocking the chip to 5,4v and regulating the voltage to 4,5v using USB power?

 I understand that this question is difficult to answer before assembly and listening tests, but from a teorical point of view what do you think?_

 

I expect RMAA to show < 2-3 db difference for the main parameters. Even the worst figures should be over 90. I cannot hear this difference. Someone might.

 Important point. The DAC is going to be connected to an amp. The worst component of this combination dominates. You need to have a VERY good amp to make this DAC the weakest link. It may be that I cannot hear the difference because my PIMETA is just not up to the task.


----------



## dviswa

Guys,

 I had taken this DAC to the Maryland Meet.
impressions are here


----------



## drbig

Guys, I was able to find all the parts for the second prototype on Mouser, except IC1, IC2 and IC3. Those are available from Digi-Key. The Mouser part numbers are in the attached .txt file. For CL and CR, I found Xicon 47uF low ESR electrolytics. They may not be the best for the application, but maybe the best available from Mouser. Any other suggestions would be appreciated.


----------



## .: ZMN :.

Panasonic FC are said to have low ESR. If you are planning to order from Digikey have a look at them.

 The attached list might help with the part numbers - work in progress, check first. 
	

	
	
		
		

		
			






 /EDIT: Okay, Alf pointed me at a couple of errors in the attached BOM. 
	

	
	
		
		

		
		
	


	




 Updated... 

 /EDIT2: Updated 2006-06-18, but please check if these values are good for v1.1 as well.


----------



## dsavitsk

Quote:


  Originally Posted by *.: ZMN :.* 
_Panasonic FC are said to have low ESR._

 

FM series is better.


----------



## Clutz

I reduced my output caps from the 10uF solen + 0.56 uF solen in parallel with each other to just the 10uF solen. It was kind of tricky cause I brought my soldering iron to work and didn't bring any solder.... but i didn't want to be without tunes. 

 Anyway, like you said dsavitsk - it made a difference to the sound quality - for the positive. Bass is better- things just sound more coherent.


----------



## drbig

Alf, could you post here when you send out the prototype PayPal emails? I want to be sure your email makes it through my spam filter.


----------



## Alf

Quote:


  Originally Posted by *drbig* 
_Alf, could you post here when you send out the prototype PayPal emails? I want to be sure your email makes it through my spam filter._

 

OK


----------



## Alf

I just confirmed that the PCBs are going through post-production checks. They should be with me next week. I sent PayPal invoices to all interested folks. 

 There are 2 boards unallocated. If you would like one, please email or PM me.

 EDIT: PCBs are no longer available


----------



## Alf

The PCBs arrived yesterday. Here is a picture of the new boards. 

 The through-the-hole pads are slightly bigger than I expected. This causes some minor cosmetic issues with the top white screen legend. Note the text around the wire pads. I need to figure out why this happened. Solderability is not affected. 


 I posted the boards this morning to those who have paid already. Typical delivery time to US and Europe is about 5-6 working days.


----------



## guzzler

Farnell BOM here, uses Panasonic FC for coupling caps, unfortunately the non-polars aren't stocked anymore apart from 4.7uF. The order code for those is 3174852

 Total cost is just over £22


----------



## Alf

I just finished soldering v1.0 DAC. Relatively straightforward. No showstoppers. My computer recognized the DAC immediately. I had no time to listen.


----------



## Alf

I have done some RMAA tests tonight. Noise and dynamic range improved a bit comparing to Revision B. It is a good start. I think that with careful capacitor selection I can achieve even better results. Right now I use leftovers from the last build.

V1.0 vs Rev B


----------



## Clutz

Alf, I currently have the previous revision running directly off of USB power (i.e. VBUS is directly connected to AV+). In the latest revision of the DAC, on your webpage you said that the 5 volt REG101 doesn't do a good job when directly powered by the USB, because USB isn't providing enough power (<4.9V). Would I be able to disconnect VBUS from AV+ and just connect <=10DCV Wallwart to AV+ and ground? Do you think this would improve performance?


----------



## blueworm

Quote:


  Originally Posted by *Alf* 
_I have done some RMAA tests tonight. Noise and dynamic range improved a bit comparing to Revision B. It is a good start. I think that with careful capacitor selection I can achieve even better results. Right now I use leftovers from the last build.

V1.0 vs Rev B_

 

What kind of 5v regulation did you use on the usb dac-1.0 ? none, or 4.8v as suggested in notes?


----------



## Alf

Quote:


  Originally Posted by *Clutz* 
_Alf, I currently have the previous revision running directly off of USB power (i.e. VBUS is directly connected to AV+). In the latest revision of the DAC, on your webpage you said that the 5 volt REG101 doesn't do a good job when directly powered by the USB, because USB isn't providing enough power (<4.9V). Would I be able to disconnect VBUS from AV+ and just connect <=10DCV Wallwart to AV+ and ground? Do you think this would improve performance?_

 

Look at the link above. It has graphs for Rev B too. The difference between USB power and external PS is negligent in my setup. However, if you have a good Wallwart and a poor computer PS, Wallwart may improve things a little.


----------



## Alf

Quote:


  Originally Posted by *blueworm* 
_What kind of 5v regulation did you use on the usb dac-1.0 ? none, or 4.8v as suggested in notes?_

 

I did not have resistors to set 4.8V. So I just used REG101-5. The configuration is similar to what I used for Rev B tests. 

 I plan to build another DAC soon to see whether 5V regulation may be safely omitted. It may take some time because I ran out of leftover parts and need to place a new order with Farnell to continue.


----------



## guzzler

*WORKS*

 Picture 1: All top SMD components in place (bar one capacitor I didn't see 
	

	
	
		
		

		
			





)






 Picture 2: All underside SMD components in place






 Picture 3: Complete One






 Picture 4: Complete Two






_*Comments*_

 1. It works fine at Vcc = 4.73 (using 12K and 33K resistors). No comment on sound yet, haven't listened

 2. Some ambiguity regards R32/C32. On the top of the silkscreen it says "R32, C32". If you are using an adjustable regulator, you put the resistor on top, and the capacitor for a fixed regulator. My quibble here is the C32 isn't in this position on the schematic, I would make it explicitly "R32/C34" for example (and put C34 in the correct position on the schematic). Not a big problem, but I'm sure someone would mess it up otherwise 
	

	
	
		
		

		
		
	


	




 3. Layout allows easy soldering, and good access. My suggestion if you're not too confident in your ability to solder the PCM2702 to check if it's recognised BEFORE putting CL/CR in place, as they make it a little harder to get in to fix it.

 4. *Tweezers* and *flux* are very useful, if not essential!


----------



## drbig

Quote:


  Originally Posted by *guzzler* 
_... I'm sure someone would mess it up otherwise 
	

	
	
		
		

		
		
	


	




!_

 


 Well, that would be me. Guzzler, could you clarify your comment here. You refer to C34, but there is no C34, so I'm assuming you mean C32. Are you saying the schematic should show C32 going from pin 3 to ground instead of pin 3 to pin 1 of the variable regulator? That is what I think I'm seeing on the board diagram. Also, are you leaving one of R31, R32 or C32 out? Thanks for any clarification here. I'm really looking forward to getting the board. I have all the other parts ready to go.


----------



## Alf

Quote:


  Originally Posted by *drbig* 
_Well, that would be me. Guzzler, could you clarify your comment here. You refer to C34, but there is no C34, so I'm assuming you mean C32. Are you saying the schematic should show C32 going from pin 3 to ground instead of pin 3 to pin 1 of the variable regulator? That is what I think I'm seeing on the board diagram. Also, are you leaving one of R31, R32 or C32 out? Thanks for any clarification here. I'm really looking forward to getting the board. I have all the other parts ready to go._

 

There are two C32 positions. On the top layer it says R32/C32. On the bottom layer it is called C32. You can see them on the pictures I posted previously.

 If you use an adjustable regulator you put R32 on the top layer and C32 on the bottom layer. If you use a fixed regulator, put C32 on the top layer in the R32/C32 position (you do not need the resistors on this case). I meant to describe this trick in the assembly guide but still have not done it.

 Guzzler suggests using C34 and C32 names instead two C32s to fight the ambiguity. It was like this in one of the earlier board versions. But then I decided to change it after failing to describe it clearly in the parts list. I hope that with proper assembly comments this should not be an issue.


----------



## blueworm

As far I can make out the real C32 goes on the bottom.
 C32 is erroneously silkscreened on the top.

 I have a question does the crystal X1 have a position, and is the farnell part # 971-2763 OK for this project?


----------



## Alf

Quote:


  Originally Posted by *blueworm* 
_As far I can make out the real C32 goes on the bottom.
 C32 is erroneously silkscreened on the top._

 

No, this is not a mistake. Read my post above.

  Quote:


  Originally Posted by *blueworm* 
_I have a question does the crystal X1 have a position, and is the farnell part # 971-2763 OK for this project?_

 

Yes. This is what I use.


----------



## blueworm

Sorry simultaneous post see time 
	

	
	
		
		

		
		
	


	



 Thanks for the fast awnser anyhow. 
	

	
	
		
		

		
		
	


	



 Yeah but guzzlers crystal is prettier.


----------



## blueworm

Here its done.
 I dont have "golden ears", but to me it sound awsome.








 Thanks too Alf for sending the pcb so fast and for leading this great project.

 Problems I had:
 - forgot to order RLED 
 stacked 2 1K5 resistors 
	

	
	
		
		

		
		
	


	




 - I have no idea What chip farnell sent me but its not the one I ordered part #843-5235. (its in the bottom right hand corner in the photo.)
 it says REF 0425 4AZJ3 
	

	
	
		
		

		
		
	


	



 So that got ripped out and bridged pin 1 and pin 8.

 - Elna silmic caps not arrived yet. (for CR and CL)
 Used some more Panasonic FC's


----------



## Alf

Great!

  Quote:


  Originally Posted by *blueworm* 
_So that got ripped out and bridged pin 1 and pin 8._

 

I suggest you jumper 5V and AV+ pads instead. Or even better, connect these pads with a 20uH-30uH axial inductor. This way you introduce an additional CLC filter that should help fighting USB noise.


----------



## blueworm

Quote:


  Originally Posted by *Alf* 
_Great!



 I suggest you jumper 5V and AV+ pads instead. Or even better, connect these pads with a 20uH-30uH axial inductor. This way you introduce an additional CLC filter that should help fighting USB noise._

 

I moved the bridge as you suggested.


----------



## drbig

Alf, I got my boards today. They look very nice. Thanks for organizing this project, and sending the boards out so fast. I got started soldering, and IC1 and some of the small caps are in place. This is my first time with smd, so I was a little nervous, but it seemed to go OK, thanks to all the good information gleaned here. Anyway, as I study the board and the schematics, I realize that I'm a little unsure about how to implement the powering options. For now, I just want to power with a battery, and maybe try the USB power. So to power with a battery, I believe I need to attach the battery to AV+ and G2, and set proper regulation on IC3, is that correct? Also, to power by USB, I would just leave out the battery connection and set IC3 for 4.8 volts correct?

 Thanks for the help. This is only my second project. My first was a CMOY.


----------



## Alf

Quote:


  Originally Posted by *drbig* 
_ So to power with a battery, I believe I need to attach the battery to AV+ and G2, and set proper regulation on IC3, is that correct?_

 

Correct. You can also use G1 and one of the S1 pads.

  Quote:


  Originally Posted by *drbig* 
_Also, to power by USB, I would just leave out the battery connection and set IC3 for 4.8 volts correct?_

 

You need either to jumper S1, or to put a switch there. 

 Do not forget to measure USB voltage first. You computer may produce less than 5V. You need to set IC3 accordingly taking into account the dropout voltage of your chip (check the datasheet).


 Also you have an option to use an on-off-on switch. This will help you to switch between USB and battery easily. In this case you need to use G1 and both S1 pads.


----------



## Alf

I updated the Assembly page. If you would like other topics to be covered, do not hesitate to ask.

 EDIT: Fixed the link


----------



## drbig

Alf,

 Thanks for the Assembly page. It is very helpful. One question: If CL and CR are left out, it is necessary to jumper across those positions, correct?

 By the way, I plugged the DAC into my computer,and it was recognized! I just have a few final parts to finish up before I can listen to it.


----------



## blueworm

I just switched CL and CR from panasonic FC to the recomended elna silmic.
 WOW!!! 
	

	
	
		
		

		
		
	


	



 Its another animal now. 

 Thanks again Alf.


----------



## robzy

Sorry to come into the party so late (again) but are there any PCBs left?

 Rob.


----------



## Alf

Quote:


  Originally Posted by *robzy* 
_Sorry to come into the party so late (again) but are there any PCBs left?

 Rob._

 

No. The next round should be around May-June 2006.


----------



## robzy

Quote:


  Originally Posted by *Alf* 
_No. The next round should be around May-June 2006._

 

Okay, thanks 
	

	
	
		
		

		
			





 Rob.


----------



## drbig

I finished the alien today and attempted to listen to it through my CMOY. I can only hear a very faint sound. The DAC is recognized by Windows and becomes the default playback device. I checked voltages on the board. I'm getting 3.30v at the 3.3v pad and 4.86v at the 5v pad. On the outputs, I'm getting 2.4V DC on each channel! I'm not using output caps. the CL and CR positions are jumpered, and R15 and R16 were left out.

 Any ideas what I should look at next?

 Thanks for any help.


----------



## DaKi][er

Quote:


  Originally Posted by *drbig* 
_Any ideas what I should look at next?_

 

The volume in windows, as on first plugin it sets itself up quite low so you need to turn it all the way up


----------



## Alf

Quote:


  Originally Posted by *drbig* 
_I finished the alien today and attempted to listen to it through my CMOY. I can only hear a very faint sound. The DAC is recognized by Windows and becomes the default playback device. I checked voltages on the board._

 

As DaKi][er suggested check the volume control first. There are two volume controls – master volume control and device volume control. 

 If volume controls are 100% but sound is "thin", check you wiring. Especially, the ground connection.

 If nothing helps, check the gain on your CMOY. It has to be at least 2. Pump it up a bit.


  Quote:


  Originally Posted by *drbig* 
_ On the outputs, I'm getting 2.4V DC on each channel! I'm not using output caps._

 

2.4V DC is OK on the DAC output if you don’t use the output caps. It will be eliminated by the input capacitors in your CMOY. You do have input capacitors in your CMOY, don’t you?


----------



## drbig

OK, it is working now. Just needed to set the master volume. When I saw the high output voltage, I thought something must be seriously wrong, but I guess that is normal for this device. The input caps on my CMOY should take care of it. The sound is really nice! I'll give more details later. Thanks for the help.


----------



## Jam_Master_J

Quote:


  Originally Posted by *robzy* 
_Okay, thanks 
	

	
	
		
		

		
		
	


	




 Rob._

 

I too am interested in getting a board.


----------



## tola555

put me on PCB list. I'll take 2 if less than 10$ each.


----------



## drbig

I've had the prototype board working for a few days now, and I'm really impressed. First off, the assembly was no problem. The board placements and everything were very logical. Also, working with the SMD components was easier than I thought it would be, even though it was my first time. The board has a lot of flexibility, and it seems like it has all the pads you would need to use it in a variety of configurations, and since it is so tiny, it could go almost anywhere.

 I did an A-B test between my Nomad MP3 player and the Alien. I really wanted to compare it directly with my computer soundcard, but I couldn't figure out how to do that easily. But, I already know I like the sound of my MP3 player better than the computer, so the comparison would still be useful. Both units were playing through a CMOY into Grado SR60's. I used a couple of different songs with different kinds of music, rock, jazz and classical. These were high quality MP3's. It was quite apparent that the Alien has better detail in the high end especially. I'm not sure how to describe it exactly, but I could definitely hear the difference, and the Alien was better. Less muddy, better definition perhaps gets close. 

 Just listening to the Alien on it's own, both with CD's and MP3's on the computer, I am very pleased. I can hear new features in certain songs that I never noticed before.

 I have used both direct USB power and also power from a 9 volt battery. On one of my computers, I could not hear any difference. However, on another one, with direct USB, there was some crackle in the high end which went away with the battery.

 I tried using the Alien with no output caps for a while, and that is how the A-B testing was done. Now I have added 47 mF Blackgate's on the output. The sound did not change much. I needed this configuration to try the Alien as an input to my living room stereo. It worked very well.

 This is a great little board. I'm sure lots of people are going to want them when the final version is ready. I want to pair one with a Pimeta in a single case so I can have a nice little box for listening to my computer. I also want to build a second one to use as a dedicated input from my computer to the stereo.

 Thanks to Alf and all the other folks who came up with this great design.


----------



## blueworm

Update:

 I have encountered a similar problem to this.
  Quote:


  Originally Posted by *tolly* 
_Built mine up last night, and it's a good feeling to have it working first time. Sounds nicer than my laptop, and overall good. I'll write a review as soon as I have the time!

 One strange problem I did have - whilst listening to Gwen Stefani, I got a load of digital noise (no, not Gwen!), that seemed as if the usb had got out of sync. I restarted the track, and had no more problems. Anyone else had this effect? I'll try with the linux drivers this evening, but weird nonetheless.

 I think I'll build the other prototype and add a 9V battery (and possibly USB charging circuit), and see if I notice any difference.

 Tolly_

 

I've tried to trouble shoot this.
 After several days I ve isolated it to the linux kernel usb stuff.
 It works fine in winXP.
 Broke in debian "sarge" 2.4 kernel OSS sound driver.
 Broke in ubuntu "breezy badger" 2.6 kernel alsa driver.

 I contacted Clemens Ladisch the usb kernel developer. He said the problem should be fixed in the next kernel/alsa version. 
	

	
	
		
		

		
		
	


	




 All cased up
	

	
	
		
		

		
		
	


	




 Update:
 Just installed kernel 2.6.17-rc1 works perfectly


----------



## guzzler

In the original, this was often to do with the voltage dropping too low. Shouldn’t be a problem with a well regulated USB line, but it’s something to consider. Fair point on Linux as well


----------



## dviswa

Hi guys,

 I have to tell about this one. My DAC uses an external wall wart. You know I have been very happy with this dac, which is a great improvement over my standby Chaintech AV 710. It has an amazing amount of air and depth. Although at high volumes would leave you with a little fatigue after an extended listening. So I would usually keep it at lower / comfortable volumes.

 There was a 2200 mfd cap lying around for a long time, so why not put it into the dac. Did that and boy, what a change. The graininess is gone. I can push it all the way up and feel no fatigue. The difference is massive. I used to wonder about a USB bus powered device. After this experiment, that option is nixed for ever 
	

	
	
		
		

		
		
	


	




 Don't think, I would want to throw large caps on the rails of an USB bus.

 Seriously, the change is amazing. All you guys with bus powered should just for kicks try a wall wart powered and throw in a large cap.


----------



## cire

sorry if this is a dumb question, but when powering off the USB, could you power a (for example) PINT with the DAC off IC3?


----------



## Alf

Quote:


  Originally Posted by *dviswa* 
_There was a 2200 mfd cap lying around for a long time, so why not put it into the dac. Did that and boy, what a change. The graininess is gone. I can push it all the way up and feel no fatigue. The difference is massive._

 

Where did you put it?


----------



## Alf

Quote:


  Originally Posted by *cire* 
_sorry if this is a dumb question, but when powering off the USB, could you power a (for example) PINT with the DAC off IC3?_

 

Yes you can but you must take care of your PINT’s virtual ground first. You have two main options:

 1. Put a capacitor between the DAC’s OG and PINT’s IG (similar to left and right channels). 47uF should suffice.

 2. Use an inverter to build a negative rail. This is more complex. However this way is preferable because it gives you more voltage to power your PINT and you do not need a coupling capacitor for the ground.


----------



## K2Grey

Would the performance of the PINT suffer if powered this way?


----------



## cire

in the part list it says 100nF for C14(et al). is this a typo for 100pF ?


----------



## dviswa

Alf,

  Quote:


  Originally Posted by *Alf* 
_Where did you put it?_

 

You know I have the version 1 prototype, which still has the LM317 external supply option. I put the cap before the regulator at the 12 VDC point.

 I know the USB bus is already regulated and probably has a lower magnitude of ripple. YMMV, but the level of improvement I see is just astonishing, in my case.


----------



## Alf

Quote:


  Originally Posted by *cire* 
_in the part list it says 100nF for C14(et al). is this a typo for 100pF ?_

 

No, it is not a typo. 100nF (or 0.1uF) is a standard value for this application.


----------



## cire

doh i shoulda known that. no wonder digikey nor mouser had any 100nF caps.


----------



## Alf

Quote:


  Originally Posted by *K2Grey* 
_Would the performance of the PINT suffer if powered this way?_

 

Yes, it would. Can you hear it? It all comes down to the quality of your computer’s power supply. If it is good, you might not notice any difference. If not, it may be really nasty. Laptops tend to be better in this respect.


----------



## cire

Quote:


  Originally Posted by *Alf* 
_Yes, it would. Can you hear it? It all comes down to the quality of your computer’s power supply. If it is good, you might not notice any difference. If not, it may be really nasty. Laptops tend to be better in this respect._

 

so the regulator doesn't clean up the power very much?


----------



## Alf

Quote:


  Originally Posted by *cire* 
_doh i shoulda known that. no wonder digikey nor mouser had any 100nF caps._

 


 This is what I use 08055C104KAT2A. Both Digikey and Mouser have them in stock.


----------



## cire

whats an acceptable alternative to crystals at mouser? i found 12mhz ones and 32pf ones, but none that were both. also whats the difference between the HC49s? there's different letters and stuff after it


----------



## guzzler

12MHz is simply the frequency, and the capacitance refers to the load capacitance (make sure you get this right!). Some HC49 crystals will be surface mount, so don't get those. The only real differences are:

 package type
 package height
 load capacitance
 tolerance


----------



## cire

http://www.mouser.com/index.cfm?hand..._pcodeid=73000

 does that work? 13.67mhz and 30pF


----------



## guzzler

No, must be 12MHz, and the loading capacitor is crystal dependent. 

 Mouser code: 815-AB-12-B2
 Loading caps: 18pF


----------



## cire

what do you mean by loading cap? can you explain this cap/crystal combination to me?


----------



## DaKi][er

Quote:


  Originally Posted by *cire* 
_what do you mean by loading cap? can you explain this cap/crystal combination to me?_

 

on the schematic, you'll see 2 capacitors of very small value hanging off the crystal, they're the loading capacitors and you choose their value to what the crystal manufacture lists


----------



## cire

just making sure here: those two caps would be C11 and C12. the values they have on the part list don't match the cap value of X1.


----------



## Alf

Quote:


  Originally Posted by *cire* 
_just making sure here: those two caps would be C11 and C12. the values they have on the part list don't match the cap value of X1._

 

You cannot find 30pf capacitors. Just get the closest value to whatever you crystal requires.


----------



## cetoole

Quote:


  Originally Posted by *Alf* 
_You cannot find 30pf capacitors. Just get the closest value to whatever you crystal requires._

 

Sure you can, check Mouser.


----------



## steinchen

finally got my DAC running, I was short of a reg102-a and it took me some weeks to get one from digikey. The build was easy and the DAC worked on the first attempt. I just found the R31/R32/C32 options a little confusing. 

 atm I'm trying different output caps, e.g. a 0.68uF polyprop film. Even at only 10k input impedance of the amp the corner freq is still far below 10Hz and the Hammond 1455c has more than enough space for these caps. pics soon to come.


----------



## RichA

I really fancy having a go at this. Is it possible to download the eagle files so I can print off my own PCB? I've got some time on my hands over the next few days 
	

	
	
		
		

		
			





.

 Cheers,

 --Rich


----------



## MASantos

Quote:


  Originally Posted by *RichA* 
_I really fancy having a go at this. Is it possible to download the eagle files so I can print off my own PCB? I've got some time on my hands over the next few days 
	

	
	
		
		

		
		
	


	




.

 Cheers,

 --Rich_

 


 The DAC is still in it's prototiping stage. I don't know if you wuld get satisfactory results etching your own boards. Some of the traces are really thin!!


----------



## Clutz

I've seen someone do a self etched board using a 2706 which is a 32QTFP chip - and it had thin traces too.


----------



## RichA

Quote:


  Originally Posted by *MASantos* 
_The DAC is still in it's prototiping stage. I don't know if you wuld get satisfactory results etching your own boards. Some of the traces are really thin!!_

 

Can't hurt to have a go - it beats waiting for the official boards! 
	

	
	
		
		

		
		
	


	




 --Rich


----------



## cire

just finished building mine and its not recognized by windows 
	

	
	
		
		

		
		
	


	




 the regs are all working properly, so i really have no clue as to where to start. i fear its the PCM that's shot...aw damnit....


----------



## Nisbeth

Quote:


  Originally Posted by *cire* 
_just finished building mine and its not recognized by windows 
	

	
	
		
		

		
		
	


	




 the regs are all working properly, so i really have no clue as to where to start. i fear its the PCM that's shot...aw damnit...._

 

SSOP's can have very small solderbridges that are nearly impossible to see, or if you're using the flood-and-suck method, you may have wicked too much solder away from the pins, so before you do anything, check the connections for the PCM under a magnifier and a bright light source. Reflow anything that looks questionable and try again 
	

	
	
		
		

		
		
	


	





 /U.


----------



## Clutz

I would also bring out your DMM and make sure you've got voltage where you need to have voltage.


----------



## drbig

I need some help troubleshooting a problem that developed with my Alien DAC. I changed the power supply from USB powered to amp powered, and now I'm not getting any more sound. I put in IC4 and powered AV+, AV- and AG with +11, -11 and G from a pimeta. This may have been too much voltage for the regulator because I was getting 6.6 v from the 5v pad. The board was still recognized on USB, but I couldn't get any sound out of the outputs. So, I reverted back to USB power by jumpering S1 and removing the power from AV+ and AV- ( I left IC4 on). Still no sound. I'm getting a constant 1.7 mA from the outputs, but no sound. Is it possible I fried the PCM 2702 chip? Any way to test this? It is still recognized by USB, but maybe just the analog part is done for. Anyone have an idea what went wrong, or how to troubleshoot from here? I'm thinking of cutting off the chip and putting another one on, but that would be drastic. By the way, are there going to be anymore boards for this project?

 Thanks for any help!


----------



## Alf

Quote:


  Originally Posted by *drbig* 
_I need some help troubleshooting a problem that developed with my Alien DAC. I changed the power supply from USB powered to amp powered, and now I'm not getting any more sound. I put in IC4 and powered AV+, AV- and AG with +11, -11 and G from a pimeta. This may have been too much voltage for the regulator because I was getting 6.6 v from the 5v pad. The board was still recognized on USB, but I couldn't get any sound out of the outputs. So, I reverted back to USB power by jumpering S1 and removing the power from AV+ and AV- ( I left IC4 on). Still no sound. I'm getting a constant 1.7 mA from the outputs, but no sound. Is it possible I fried the PCM 2702 chip? Any way to test this? It is still recognized by USB, but maybe just the analog part is done for. Anyone have an idea what went wrong, or how to troubleshoot from here? I'm thinking of cutting off the chip and putting another one on, but that would be drastic. By the way, are there going to be anymore boards for this project?

 Thanks for any help!_

 

You may have fried your regulators too, if you used REG101/REG102. The regulators are rated for 10V max (you applied 11V). Re-check the voltage on 3V3 and 5V pads. If the voltage is not what it is supposed to be, replace the faulty regulators first. If/when the voltage is OK but the there is no sound, replace PCM2702.

 You have 2 options powering the DAC from your PIMETA. 
 1. Lower the voltage on your PIMETA (< 20V rail-to-rail).
 2. Use REG103. It is rated for 15V. I am not sure about the ERROR pin though. It is difficult to say how it would behave. You may need to lift it preventing any contact with its pad. I hope other people can comment on this too.


----------



## steinchen

finally the promised pic (click on pic for full scale image): 




 I had to cut and insert a piece of perfboard, otherwise the board/caps would get crammed together when inserting the USB plug. I picked 2.2uF polyprop caps from Intertechnik (the value series to the Auryn cap) for the output coupling caps, they are the largest that fit the Hammond 1455C case. I ommit the shunting smd resistors on the pcb and air wired them to the RCA jacks instead.

 Sound is pretty nice, I think I'm going to build another one and power it from a dedicated psu, this one is USB powered.


----------



## MASantos

Do you guys think that the DAC is ready for the group buy or will another proto stage take place?


----------



## ezkcdude

What is the reason for having such gigantic caps, other than their impressive looks?


----------



## steinchen

because they are polypropylene caps instead of electrolytic caps, they are much better but unfortunately much larger, too


----------



## MisterX

Here is my second one:




 (Click for the larger version)

 I used a peice of aluminum plate for the gap filler, USB powered and all black gates caps. 
 Sound is pretty nice considering the price.


----------



## Clutz

Quote:


  Originally Posted by *ezkcdude* 
_What is the reason for having such gigantic caps, other than their impressive looks?_

 

In order to answer this, lets break the question down into it's various parts.

 This DAC chip produces a lot of DC offset, in the range of 1-2 volts if I recall correctly, and ideally, we want to keep the DC offset coming out of the headphone amplifier less than 10mV (my personal goal is in the 1-5mV range). If we plugged the output of this DAC directly into a headphone amplifier, the headphone amplifier would amplify the DC just as readily as it will amplify what we want it to, the AC signal. 

 Capacitors block DC current, but let AC current pass through (albeit, with some distortion). Hence, if we want to block the DC offset voltage, we can place a capacitor somewhere between the headphones and the source of the DC offset.

 We could place the output capacitors (typically called coupling capacitors) on the output of the headphone amplifier, or we could place them on the output of the DAC itself.

 What the capacitor does, is blocks current in a frequency dependent fashion. When you couple a capacitor in series with a resistance, you end up creating a frequency dependent filter, the corner frequency of which is given by the following equation:

 F = 1/(2 * pi * C * R)

 Now, we want this F to be as low as possible in this case (we're creating a high pass filter, we want to block DC, which is essentially a frequency of 0, but allow the audio signals to pass through). In this equation, C is the value of the capacitor in farads and R is the input impedence of the following device. 

 If we place the coupling (output) capacitor in the headphone amplifier, then R will be the nominal impedance of the headphones. In the case of the Sennheiser HD580s, that's 300 ohms. If we wanted to have a low corner frequency low enough so that it is inaudible (and the general rule of thumb is to have the corner frequency an order of magnitude lower than you want to hear distortion created), e.g. ~ 2Hz, we'd need approximately a 220 to 330uF capacitor. Which is fine, if you're willing to use electrolytic capacitors, but the general consensus is that they sound like crap, except maybe for blackgates - but even then, a 220uF blackgate capacitor will not sound as good as an film capacitor that costs the same amount of money (probably looking $30 or so, per capacitor to get an output capacitor of 220uF with a sufficiently high voltage rating - and you need two..). So $60.

 If you wanted to use a pair of AKG K701s or Grados, you'd need around 1000 to 2000uF of output capacitance. Ouch!

 Or, we can place the output capacitor between the DAC and the headphone amplifier.

 The input impedance of a headphone amplifier is going to be much much higher - and - it isn't going to vary as you change headphones. The input impedance of a headphone amplifier is going to be between say 5K and 50K, on average. Lets work with the 5K value, because it's relatively conservative.

 With a 5K input impednece, we only need to have a 10uF coupling capacitor to have a nice low pass filter - approximately 3.1 Hz. Or, if you can pick your headphone amplifier to have a higher input impedance (all else being equal, this is probably a good thing), and it has a 50k input impedance, then a 2uF coupoling capacitor gives you a 1.5Hz corner frequency.

 So why is it so big? 

 Because it's a film capacitor, and film capacitors need to be physically larger for a given capacitance than an electrolytic capacitor. Electrolytic capacitors don't sound very good (Generally speaking). A 2uF film capacitor is a pretty large item. Hell, I'm using a 10uF output capacitor and it makes that thing look tiny.

 I know this explanation was probably a bit overblown, but I think this will answer all of your questions.


----------



## ezkcdude

Clutz, you had me at "let's break this down..." 
	

	
	
		
		

		
		
	


	




 I wasn't sure whether these were coupling or de-coupling caps, so you answered that for me.


----------



## Alf

Great builds guys!

 I have fixed the stop mask issue with the last revision (in case if anyone noticed it). I also tweaked the silk a bit. It should be more readable now. If there are no critical comments on the board layout, I am happy to go ahead with the group buy.


----------



## MASantos

Hurray!!!! Lets do it! If you need any help please let me know.


----------



## doobooloo




----------



## peterpan188

Been waiting for you to say it!
 LET"S GOOOOOOOOO
	

	
	
		
		

		
		
	


	




 Peter


----------



## MisterX

Quote:


  Originally Posted by *Alf* 
_ If there are no critical comments on the board layout, I am happy to go ahead with the group buy._

 

Now that you mention it a little more space around C13 and a polarity indicator for the LED would be nice.


----------



## threepointone

arrrrrrrghhhh another group buy???? diamond buffers, then SMD PPA, then PIMETA SMD soon, and now a DAC???? 

 How much would the board cost if there's another group buy, and how much do the parts cost for this DAC?


----------



## peterpan188

Clutz, here's a question I have about output caps.

 Many designs that this forum discuss has input capacitor or DC servo built-in to take care of DC offset from the input. In that perspective, what would be the advantage of having output caps for the DAC?

 Thanks,
 Peter


----------



## cetoole

Quote:


  Originally Posted by *peterpan188* 
_Clutz, here's a question I have about output caps.

 Many designs that this forum discuss has input capacitor or DC servo built-in to take care of DC offset from the input. In that perspective, what would be the advantage of having output caps for the DAC?

 Thanks,
 Peter_

 

Many people, such as myself, do not use input caps on their amplifiers, because they are not necessary with most of our sources. I know I prefer to only couple when necessary, and if the caps are in the amp, this cant be done.


----------



## MASantos

Quote:


  Originally Posted by *threepointone* 
_arrrrrrrghhhh another group buy???? diamond buffers, then SMD PPA, then PIMETA SMD soon, and now a DAC???? 

 How much would the board cost if there's another group buy, and how much do the parts cost for this DAC?_

 


 I believe parts should cost around 40$ without enclosure.

 The prototipe boards cost around 6$ if I remember correctly so the GB one should be around 4-5$ each. I'm just speculating. THe final price will depend on the number of boards ordered.

 Regards


----------



## drbig

Alf,

 What are your thoughts about support for REG103? Pads between pins 6 and 7 on IC2 and IC3 would be nice.


----------



## Clutz

Quote:


  Originally Posted by *drbig* 
_Alf,

 What are your thoughts about support for REG103? Pads between pins 6 and 7 on IC2 and IC3 would be nice._

 

Reg103? 500mA of current is a lot for this project when the PCM2707 only takes ~ 100.


----------



## drbig

Quote:


  Originally Posted by *Clutz* 
_Reg103? 500mA of current is a lot for this project when the PCM2707 only takes ~ 100._

 

I was thinking of reg103 for the increased input voltage rather than output current. This would allow it to be powered from an amp up to 15 V rather than the limit of 10 V with reg101.


----------



## MASantos

Quote:


  Originally Posted by *drbig* 
_I was thinking of reg103 for the increased input voltage rather than output current. This would allow it to be powered from an amp up to 15 V rather than the limit of 10 V with reg101._

 

IMHO, I think that a regulator that allows up to 20 volts makes much more sence because it would allow using 2x9v batteries. many DIY portable amps use this setup. I think that 15v is almost the same as 10v

 manuel

 (ps: lets concentrate on the group buy 
	

	
	
		
		

		
			











 )


----------



## splaz

Sorry if this may have been mentioned but I haven't had an opportunity to read through all 500 odd replies.

 You're from the UK Alf so are all the parts available through RS Components or Farnell ?


----------



## Alf

Quote:


  Originally Posted by *peterpan188* 
_Many designs that this forum discuss has input capacitor or DC servo built-in to take care of DC offset from the input. In that perspective, what would be the advantage of having output caps for the DAC?_

 

Read Note 3 here


----------



## Alf

Quote:


  Originally Posted by *drbig* 
_What are your thoughts about support for REG103? Pads between pins 6 and 7 on IC2 and IC3 would be nice._

 

I decided not change the design for 3 reasons:
 * This would make the design more difficult to understand for inexperienced builders. I would like to keep it as simple as possible. One can view this project as a CMOY-type tutorial for SMD and/or DACs.
 * Being that close to an official release, I would not want doing anything that even remotely suggests another prototype stage without truly compelling reason to do so.
 * REG103 can be used without changing the design as long as the ERROR pin is lifted.


----------



## Alf

Quote:


  Originally Posted by *MASantos* 
_IMHO, I think that a regulator that allows up to 20 volts makes much more sence because it would allow using 2x9v batteries. many DIY portable amps use this setup. I think that 15v is almost the same as 10v_

 

The regulator is placed between V+ and ground. Thus you need to double the regulator’s max voltage to calculate the amp’s max voltage. With REG103 (15V max) you can have an amp powered from +/-15V power supply, which makes it 30V rail-to-rail.


----------



## Alf

Quote:


  Originally Posted by *splaz* 
_You're from the UK Alf so are all the parts available through RS Components or Farnell ?_

 

All parts are available from Farnell. I have not checked RS Components due to their poor search engine. 

 The only parts may choose to order somewhere else are CL/CR if you go with electrolytics there. Farnell do not stock any suitable audiophile parts (Blackgates, Silmic II, etc).


----------



## Alf

Updated PCB layout:

 Board v1.1 Rev 1 - Top

 Board v1.1 Rev 1 – Bottom

 Board v1.1 Rev 1 – All without bPlace


----------



## MASantos

I will probably build a board with Pana FC's one with blackgate NX series and one with nice film caps such as those shown in steinchen's amp. THis one will probably be powered by a tread. I want to see if there are any big differences between a normal configuration and a maxed one.

 Alf that layout looks great, I can't wait to start building.

 Manuel


----------



## MASantos

I just simulated an order from DIgikey for parts to build 25 USB DAC's and the total was 28€ per DAC.

 This included the hammond enclosure with metal end panels. The only thing missing is the output jack since people may choose RCA's, mini, etc. Total was 590€ I added 110€ for shipping (estimated) because of the weight of the aluminium enclosures. I believe that if you order parts for two amps it will still be under 35-40, which is a very good price!!!

 Manuel


----------



## Sinbios

What's the point of a group buy for components? Unless the savings are monumental, the re-shipping would probably kill the deal. Why not just do a group buy on the boards, and have everyone buy their own components?


----------



## MASantos

Quote:


  Originally Posted by *Sinbios* 
_What's the point of a group buy for components? Unless the savings are monumental, the re-shipping would probably kill the deal. Why not just do a group buy on the boards, and have everyone buy their own components?_

 

I am not proposing agroup buy onthe boards. I just posted that information so people can have a general idea of costs. I will made it just for one or 2 boards so we can have a better idea of component costs.


----------



## Alf

[size=xx-large]Group Buy!!![/size]

 I started  Alien DAC v1.1 PCB Group Buy. Feel free to order as many boards as you need.


----------



## doctorkelsey

i am SURE this has been discussed but I dont know how to search within a single thread and 30 pages is too much to look through 
	

	
	
		
		

		
		
	


	




 , so here is my question: 

 How much current does the alien draw from batteries? 

 thanks a bunch!


----------



## MASantos

Quote:


  Originally Posted by *doctorkelsey* 
_i am SURE this has been discussed but I dont know how to search within a single thread and 30 pages is too much to look through 
	

	
	
		
		

		
			





 , so here is my question: 

 How much current does the alien draw from batteries? 

 thanks a bunch!_

 

Well I'm not going to answer your answer but I'll help:

 go to TI's website and search for the PCM2702 and the both reg's. Download the datasheet and read it. You should find the current draw of each of the IC's. Be sure to also check the DAC's website to check which other IC's and components draw current with you desired configuration. THe overall current draw should be equal to the sum of all the current draws of different IC's. 

 One of the most rewarding aspects of DIY is learning this kind of stuff. At least for me and that's what I learned with other DIY headfiers.

 Manuel


----------



## splaz

There I was naively thinking that my wallet had gotten a well deserved break.


----------



## doctorkelsey

Quote:


  Originally Posted by *MASantos* 
_Well I'm not going to answer your answer but I'll help:

 go to TI's website and search for the PCM2702 and the both reg's. Download the datasheet and read it. You should find the current draw of each of the IC's. Be sure to also check the DAC's website to check which other IC's and components draw current with you desired configuration. THe overall current draw should be equal to the sum of all the current draws of different IC's. 

 One of the most rewarding aspects of DIY is learning this kind of stuff. At least for me and that's what I learned with other DIY headfiers.

 Manuel 
	

	
	
		
		

		
		
	


	


_

 

Thanks Manuel,

 Got it. It looks to be around 30 mA or so! Can't wait to build one... or five.


----------



## robzy

Hi guys,

 Im sorry for coming into the thread so late with a very noob question, im not after a very indepth answer, just a quick overview (one or two lines will do me ):

 How does this differ from the original guzzler DAC? What improvements have been made?

 Rob.


----------



## MisterX

Quote:


  Originally Posted by *robzy* 
_How does this differ from the original guzzler DAC? What improvements have been made?_

 


http://www.myexposition.com/diy/usbdac/overview.html


----------



## theexec

Lets have an Australian group buy for the parts 
	

	
	
		
		

		
		
	


	




 I'm a newbie, so not sure where to source parts in Australia, jaycar doesn't seem to have the rarer parts... and I saw that digikey shipping is very expensive for less than 1lb of components. If we group buy say 1lb of component and just send it around by aust post it'll save us heaps


----------



## robzy

MisterX: Thanks for the links (shoulda thought of looking there first, RTFM rob). Would i be correct in stating that RevB consists of an upgrade to its PSU, as well as a better layout of parts?

  Quote:


  Originally Posted by *theexec* 
_Lets have an Australian group buy for the parts 
	

	
	
		
		

		
		
	


	


_

 

Sounds like a very good idea to me! We should get in contact with some other Australians too.

 Rob.


----------



## splaz

Well I may be building 1 or 2. Probably a USB one then some sort of battery powered one.

 Unlike a certain someone I don't feel the need to purchase 10 boards... 
	

	
	
		
		

		
		
	


	




 RS components might and Farnell definitely stock parts according to Alf. Of course there may be slight differences in stock with their Australian counterparts.

 Unless digikey or mouser or whoever else is significantly cheaper a group buy might not be needed. Although it could be cheaper even after shipping. BUF634 as an example are atleast double the price over here as compared to America and Asia.


----------



## MASantos

Quote:


  Originally Posted by *robzy* 
_MisterX: Thanks for the links (shoulda thought of looking there first, RTFM rob). Would i be correct in stating that RevB consists of an upgrade to its PSU, as well as a better layout of parts?


 Sounds like a very good idea to me! We should get in contact with some other Australians too.

 Rob._

 

The layout around the pcm2702 was improved, the dac can be powered from an amp. Ps filtering was inproved, board size was optimised to fit the smallest 1455 hammond enclosure. I think that was it!


----------



## Alf

Quote:


  Originally Posted by *splaz* 
_BUF634 as an example are atleast double the price over here as compared to America and Asia._

 

The board also accepts OPA551, which tends to be cheaper and easier to find.


----------



## splaz

I have some SO8 BUF634 already. Just noting that they're a tad expensive here.
 I didn't mean to actually say I'd buy from America/Asia just for them. Just using them as an example of how expensive some parts can be over here.


----------



## NeilR

Hmmm... I'm looking at the footprint of the Hammond 1455C cases and looking at the board, which is 2" wide, and the USB jack, which has to be flush with the back panel, putting the board against the back panel, and that huge 1" (maybe) left on the panel and thinking about where I'm going to put a pair of RCA jacks. Never having worked with this case before, maybe I'm missing something. I'm curious what others are doing for output jacks and their rear panel layouts.

 Edit: the way I see it, there is only about 5/8" clear space between the side wall and C23 for any additional jacks...


----------



## robzy

As was being discussed in a thread i created about output caps for the Alien DAC: Is there any reason i cant hook up ground on my output RCA jacks to Vcom on the PCM2702 and forget about output caps?

 Assuming there is only 1-2mV of dc offset from vcom im sure my Dynalo (Gain ~6) will be able to handle it.

 Thanks,
 Rob.


----------



## Alf

Quote:


  Originally Posted by *robzy* 
_As was being discussed in a thread i created about output caps for the Alien DAC: Is there any reason i cant hook up ground on my output RCA jacks to Vcom on the PCM2702 and forget about output caps?

 Assuming there is only 1-2mV of dc offset from vcom im sure my Dynalo (Gain ~6) will be able to handle it.

 Thanks,
 Rob._

 

I have 18.6mV and 13.1mV dc offset relative to vcom.


----------



## robzy

Quote:


  Originally Posted by *Alf* 
_I have 18.6mV and 13.1mV dc offset relative to vcom._

 

Well..... there goes that idea. Methinks ill just splurge on some nice caps then.

 [edit]: Shoulda said thanks for doing the measurements. Thanks muchly, 'tis apreciated 
	

	
	
		
		

		
		
	


	




 [edit2]: I do realise that while this is an awesome DAC it might not warrant fancy-ish caps, but i cant resist.

 Rob.


----------



## DaKi][er

Quote:


  Originally Posted by *robzy* 
_Well..... there goes that idea. Methinks ill just splurge on some nice caps then.

 [edit]: Shoulda said thanks for doing the measurements. Thanks muchly, 'tis apreciated 
	

	
	
		
		

		
			





 [edit2]: I do realise that while this is an awesome DAC it might not warrant fancy-ish caps, but i cant resist.

 Rob._

 

that is <20mV and you think that is too high? your dynalo will take that just fine


----------



## robzy

The gain of the Dynalo is around 6/7. That would mean just under 130mV of offset for the servo to deal with. From my experience of mucking around with the dynalo it can take it a while too bring this down to a usable level.

 Am i mistaken though? (At the time i tested it by dynalo had major problems which could have contributed to problems with the servo, so its a possibility)

 Rob.


----------



## DaKi][er

Quote:


  Originally Posted by *robzy* 
_The gain of the Dynalo is around 6/7. That would mean just under 130mV of offset for the servo to deal with. From my experience of mucking around with the dynalo it can take it a while too bring this down to a usable level.

 Am i mistaken though? (At the time i tested it by dynalo had major problems which could have contributed to problems with the servo, so its a possibility)

 Rob._

 

do you listen at full volume all the time? the pot on the input is going to attenuate that otherwise

 as well as 130mV while not a good value, wont be damaging to headphones


----------



## tomb

From the looks of things, the Group Buy deliveries may be received soon. Sorry for being such a lazy you-know-what: but if anyone comes up with a spreadsheet that has specific Mouser/DigiKey catalog numbers for Alf's part list - please post it.


----------



## MisterX

A BOM is posted here-----> 

http://www6.head-fi.org/forums/showp...&postcount=483


 You may want to double check the # given for R15 & R16 though


----------



## Alf

Just a thought. Maybe we should start a separate construction thread. This one is already 31 pages long. With over 50 people joining the group buy, this thread would become unreadable in a matter of days.


----------



## panterka

My DAC << link

 Capacitors in analog part Panasonic FC 1000uF for +-15V and for 3,3V I put in Rubycon ZL 2200uF. Uncoupling this Panasonic FC 100uF - in future I would want to check Rubycon BG STD 100uF/16V. For lini 3,3V and 5V work Sanyo OSCON 220uF. Coupling mass Aanalog and Digital - Rubycon ZL 180uF. Diode in bridge of analog part - BYV27-200. Solid capacitors in most WIMA. 
 Capacitors out WIMA MKP10 4,7uF.
 Exchanged stabilisers became also on low pompous: 5V - LM2940T and 3,3V LM2937ET.

 From amplifiers I tested OPA2604, AD797, AD8066. OPA627BP, became favourite at present AD797.


----------



## robzy

Quote:


  Originally Posted by *DaKi][er* 
_do you listen at full volume all the time? the pot on the input is going to attenuate that otherwise

 as well as 130mV while not a good value, wont be damaging to headphones_

 

*slaps forhead* I forgot about the pot.

 I guess what the best thing to do would be to wait, build it, hook it up with a dummy load, and try it out and see if im comfortable with how its operating.

 Thanks for the help,
 Rob.


----------



## .: ZMN :.

@ MisterX

 That Digikey BoM was for Alien DAC v1.0R5. Please check if it suitable for v1.1, there were some changes in the recommendations on Alf's website since I ordered parts, IIRC, but it could still be helpfull anyway.


----------



## .: ZMN :.

Just finished a v1.0R5 Alien DAC.

 Few comments:
 - Alf, thank you! 
 - And all others that contributed, thank you! 
 - I had never done anything smaller than through-hole resistors. The links to tutorials were very helpfull (I settled for DaKiller's method combined with what I saw in tangent's videos)
 - The description on R32/R31/C32 was a little confusing. In an 'adjustable' setup the C32 goes below, the R32 on top and the R31 must also go below, right??
 - I can only add to the advise to use magnifying glasses and a lot of light.
 - It's hard to leave it alone while burning in, it sounds very good allready!

 I shall post some pictures of my Pimeta-Alien DAC combination soon. Hopefully it will pursuade others and get a second GB for the boards on it's way! 
	

	
	
		
		

		
		
	


	




 (yeah, I missed the first one 
	

	
	
		
		

		
		
	


	




).

 A last thing on parts costs:
 My options were limited to a single order from Digikey, which resulted in a considerable addition to the costs (P&P by Express, high clearance costs; total to approx. $60 for my location). A GB for the ICs would be benificial.


----------



## threepointone

just wondering, how exactly do you choose a low-jitter oscillator?


----------



## t52

hi all!

 first of all thanks to everyone who contributed to this nice little circuit and pcb. my question is about the ferrite beads in the supply lines of the pcm2702 - how does one choose these thingies? based on inductivity, when yes - what's a good starting point (i remember reading that 10uH was a good value to start with). when checking farnell i only could find smd beads where the impedance at working frequency was given in Ohms, are these suitable as well, if so - which impedances?

 thanks in advance and best regards, juergen


----------



## Alf

Quote:


  Originally Posted by *threepointone* 
_just wondering, how exactly do you choose a low-jitter oscillator?_

 

Go for the one with the best accuracy. It also happens to be the most expensive one.


----------



## Alf

Quote:


  Originally Posted by *t52* 
_hi all!

 first of all thanks to everyone who contributed to this nice little circuit and pcb. my question is about the ferrite beads in the supply lines of the pcm2702 - how does one choose these thingies? based on inductivity, when yes - what's a good starting point (i remember reading that 10uH was a good value to start with). when checking farnell i only could find smd beads where the impedance at working frequency was given in Ohms, are these suitable as well, if so - which impedances?

 thanks in advance and best regards, juergen_

 

Farnell stocks Murata BLM31AJ601SN1L specified in the part list. It is perfect for the application.


----------



## threepointone

Quote:


  Originally Posted by *Alf* 
_Go for the one with the best accuracy. It also happens to be the most expensive one._

 

so do i go for the one with the lowest ppm rating or most zeroes, or what?


----------



## robzy

Quote:


  Originally Posted by *threepointone* 
_






 so do i go for the one with the lowest ppm rating or most zeroes, or what?_

 

A quick google turned up this:

http://www.sparkfun.com/cgi-bin/phpb...4eaa9aafb2b300

 The lowest ppm = the highest accuracy.

 Please someone confirm 
	

	
	
		
		

		
		
	


	




 Rob.


----------



## DaKi][er

Best accuracy != lowest jitter

 If you want something good, you could try this - http://www.diyaudio.com/forums/showt...928#post199928


----------



## .: ZMN :.

Some pictures...

 1. It started with an idea:





 2. And it turned out to work well! 
	

	
	
		
		

		
		
	


	







 Not exactly portable compared to the iPod, but it is transportable with a laptop. 
 When placed upside down tangents crossfeed (with orange drops) can be installed, though Foobar2k can do similar things with plugins. I prefer having a 9V battery for the AMP (7-8 AAA batteries will also fit) for portable 
	

	
	
		
		

		
		
	


	




 use. 

 3. I used some carafines that I happen to have. The SMD soldering was a first time try.


----------



## t52

i couldn't resist and ask ti technical staff about the vcom pin, i received the following answer:
 ---------------------------------------------- 8< ----------------------------------------------
 Vcom-pin is prepared for just noise de-coupling function of internal 0.5Vcc DC bias
 which is generated by simply resistor network as shown in below.

 Vcc---
 |
 R= 40K
 |-------- Vcom-pin
 R= 40K
 |
 GND

 Therefore, if connected low impedance DC load, 0.5Vcc bias would be shifted.
 It accepts connection high impedance DC load such as non-inverting(+) input
 of OmAmp.
 ---------------------------------------------- 8< ----------------------------------------------


----------



## threepointone

Quote:


  Originally Posted by *t52* 
_i couldn't resist and ask ti technical staff about the vcom pin, i received the following answer:
 ---------------------------------------------- 8< ----------------------------------------------
 Vcom-pin is prepared for just noise de-coupling function of internal 0.5Vcc DC bias
 which is generated by simply resistor network as shown in below.

 Vcc---
 |
 R= 40K
 |-------- Vcom-pin
 R= 40K
 |
 GND

 Therefore, if connected low impedance DC load, 0.5Vcc bias would be shifted.
 It accepts connection high impedance DC load such as non-inverting(+) input
 of OmAmp.
 ---------------------------------------------- 8< ----------------------------------------------_

 

so would that mean that it should be fine to use the Vcom pin as ground when connecting with an amp w/o any decoupling caps? 

 or better yet, couldn't we just make a virtual ground with the standard tle2426 circuit and avoid the decoupling caps even without an amp?


----------



## robzy

Quote:


  Originally Posted by *threepointone* 
_or better yet, couldn't we just make a virtual ground with the standard tle2426 circuit and avoid the decoupling caps even without an amp?_

 

I was just about to ask that....

 Would make life much easier.

 Rob.


----------



## guzzler

You could, but doing so would defeat the purpose of this design, ie, simple and portable. Putting in a railsplitter would require you to buffer it to drive the full current requirement of the PCM2702 and headphones, and you'd waste half the supply on just opamps.

 The Vcom pin, being simply generated by a resistor divider is not stable, and as Alf's measurements have shown, not necessarily balanced on both sides. I don't understand the objection to having to install capacitors _in this_ design


----------



## robzy

Quote:


  Originally Posted by *guzzler* 
_The Vcom pin, being simply generated by a resistor divider is not stable, and as Alf's measurements have shown, not necessarily balanced on both sides. I don't understand the objection to having to install capacitors in this design_

 

You make a good point. This is just a simple plug-and-play diy DAC (not that its a bad one mind you!). However if there is a simple tweak one could do to improve "performance" then why not?

 A TLE requiring buffers and opamps and all that jazz is, i agree, overboard for what this DAC really is. Can i just throw this suggestion into the air though? What if one used a TLE to create a reference for output ground only? Keep the PCM operating off the same voltages, but reference its Vout to 2.5volts as created by a TLE?

 (Of course, this does draw into question just how well the PCM "centers" its output)

 Rob.


----------



## doobooloo

A quick question -

 For C1, the range of values are 1uF to 22uF. Is there an "optimal" value? What kind of a difference can I expect with differing filter cap values?

 Thanks in advance!


----------



## robzy

I found 0805 ceramic capacitors to be quite expensive in that range, so i just went for the cheapest. 

 (I'm not really answering your question though)

 Rob.


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## doobooloo

Quote:


  Originally Posted by *robzy* 
_I found 0805 ceramic capacitors to be quite expensive in that range, so i just went for the cheapest. 

 (I'm not really answering your question though)

 Rob._

 

Actually... the Kemet Hi-cap range of ceramics are not that bad.

 22uF 6.3VDC X7R 20% (Mouser: 80-C0805C226M9P) $1.40
 10uF 10VDC X5R 10% (Mouser: 80-C0805C106K8P) $0.50

 Given that you only need two... $1.4 isn't too bad, I thought. 10uF caps are a dollar for two so that's even more reasonable.


----------



## doobooloo

Also, another quick question about C13...

 Can I use a 330uF Panasonic FM part here? The suggested values are 10~47uF, is it necessary to stay within these bounds?

 I'm a bit more "sure" about using the 330uF part for C23 although the suggested values are up to 100uF... but I'm not too sure about C13.

 Again, thanks in advance!


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## guzzler

C1 doesn't really have an optimum value unless you calculate all the parameters for the filters and coupling to USB line, 1uF will do fine.

 C13 just couples the internal "ground" to the real ground, no point in going larger than recommended here.


----------



## doobooloo

Quote:


  Originally Posted by *guzzler* 
_C1 doesn't really have an optimum value unless you calculate all the parameters for the filters and coupling to USB line, 1uF will do fine.

 C13 just couples the internal "ground" to the real ground, no point in going larger than recommended here._

 

Thanks for the reply!

 Regarding C13... 330uF is the ONLY value available for 6.3V and 6.3mm diameter for the Panasonic FM line which I would like to use... I thought that if there is no point (i.e. no harm done) in using the larger value that I just would use it... better than trying to get a lower value by going up the voltage rating.


----------



## guzzler

Just go up the voltage rating, you don't need to worry about long term stability. Or, just get the cheapest


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## doobooloo

Quote:


  Originally Posted by *guzzler* 
_Just go up the voltage rating, you don't need to worry about long term stability. Or, just get the cheapest 
	

	
	
		
		

		
			



_

 

Well - if the 330uF/6.3V part and the 47uF/50V part cost the same and are sized the same as well, is there really a reason to purposely step down in capacitance and use the 47uF/50V part?


----------



## Alf

C1 - I have not done any tests or any calculations in this respect. Feel free to play with it. A larger value might work better a little bit if you your DAC is USB powered. Otherwise it is a waste of money. I used 0.47uF in this position. It works fine. 

 C13 - TI suggest using 10uF here. I tried 33uF, 47uF, and 56uF. No difference. 

 C23, C33 - I would go for the larger value. I found that 120uF capacitors were a bit better than 47uF ones. There is no audible benefit of going over 330uF (for me). It is possible to use 8mm capacitors in this position. I used 560uF Panasonic FM in one of my boards.


----------



## robzy

How critical is it that C13 be ultra-low-impedance? (And to what extent?)

 Would Pana FM's be suitable, or should we be looking for less impedance.

 (RS have some very fancy Nichicon, iirc, super-duper-low-impedance caps for example)

 Thanks,
 Rob.


----------



## Alf

Quote:


  Originally Posted by *robzy* 
_How critical is it that C13 be ultra-low-impedance? (And to what extent?)

 Would Pana FM's be suitable, or should we be looking for less impedance.

 (RS have some very fancy Nichicon, iirc, super-duper-low-impedance caps for example)

 Thanks,
 Rob._

 

FM would do fine. I tried FM and OSCON in this position and found no difference. I would not pay extra for super fancy capacitors here.


----------



## MASantos

I believe we might have a problem:

 I was placing an order with digikey for parts and it seems that the berg usb receptable is an absolete part. It has been replaced with similar one from assmann electronics inc, but will it fit? I can't find the speec sheet in the manufacturers website.

 Please let us know if anyone finds something


----------



## Dark_Shadow

Quote:


  Originally Posted by *MASantos* 
_I believe we might have a problem:

 I was placing an order with digikey for parts and it seems that the berg usb receptable is an absolete part. It has been replaced with similar one from assmann electronics inc, but will it fit? I can't find the speec sheet in the manufacturers website.

 Please let us know if anyone finds something_

 

Here what i found so far :

http://www.usa-assmann.com/Specs/USB/

 You did not say what model exactly it was so have a look and let us know =)

 Francois "Dark Shadow" Gregoire


----------



## .: ZMN :.

I ordered 609-1039-ND and got it after some delay. It fits (pdf)

 Seems to be out of stock again though.


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## doobooloo

If anyone's interested, here's my BOM (without case) for the DAC in USB powered configuration.


----------



## Tedro

Quote:


  Originally Posted by *.: ZMN :.* 
_I ordered 609-1039-ND and got it after some delay. It fits (pdf)

 Seems to be out of stock again though. 
	

	
	
		
		

		
		
	


	


_

 

good, becuase I have a grip of those. Along with everything else to make at least 5 of them.


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## robzy

My digikey BOM for the DAC. A few things need double checking, but feel free to use it as a reference.

http://www6.head-fi.org/forums/showt...=1#post2249206

 Rob.


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## whiz

this is the second time i'm reading 32 pages! just to understand some things...am i crazy? 
	

	
	
		
		

		
		
	


	



 well my current job is to be in front of a monitor! so what else to do? 
	

	
	
		
		

		
		
	


	




 1)i'm very comfused with lots of things...and especially with *output capacitors!* 
 -which is best for alien dac when it is powered from USB? 
 -which capacitor is value for money? and what capacitance?
 -when we say good,bad, etc what do we mean? has to do with which cap gives better "color" to our sound,better frequency responce, low distortion?

 2)if we put 40uF output caps and our amp has input caps? what happens?
 we have a sum of capacitance?

 someone wrote some infos about these, but i had problem to understand them completely!

 3)so many people made that board...why don't you use RMAA to see the results in papers? perfection might be not audiable to our ears due to imperfection, but no one cares to test it and upload some diagrams? except Alf and maybe 1-2 more? if i had the board i'd definitly do it!


----------



## robzy

Quote:


  Originally Posted by *whiz* 
_-which is best for alien dac when it is powered from USB?_

 

What the DAC is powered from does not affect the output capacitors in anyway (except maybe in voltage requirements, but that will not be an issue here).
  Quote:


  Originally Posted by *whiz* 
_-which capacitor is value for money? and what capacitance?_

 

Okay, there are two issues here - capacitors value (as in, how many uF) and capacitor quality (how well "built" it is for lack of a better explanaion). This is not just specific to the Alien DAC or DACs in general - but with everything in audio. While i could give you a bare-bones explanation of how this words, can i recommend that you read http://tangentsoft.net/audio/input-cap.html first? If you have any questions about what you read though, feel free to ask. (I just get the feeling that that document will adress a fair few questions)

  Quote:


  Originally Posted by *whiz* 
_-when we say good,bad, etc what do we mean? has to do with which cap gives better "color" to our sound or better frequency responce?_

 

All caps add colour to the sound, and "good"/"bad" is a very _very_ subjective thing. As a general rule of thumb - film caps are good, electrolytics are bad. But film caps only come in smaller values (unless you want to spend hudnreds of dollars). That being said though, there are some not so great film caps, and there are some pretty good electrolytics.

  Quote:


  Originally Posted by *whiz* 
_3)so many people made that board...why don't you use RMAA to see the results in papers? perfection might be not audiable to our ears due to imperfection, but no one cares to test it and upload some diagrams? except Alf and maybe 1-2 more? if i had the board i'd definitly do it!_

 

We are audio DIYists, perfection is not what the intruments tell us - its how it sounds  There is only so much you can tell of graphs and the like. (That being said though, they do come in handy sometimes)

 Rob.


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## whiz

thank you Robzy! you saved me from spending time searching for the best cap! 
	

	
	
		
		

		
		
	


	




 as i understand the perfect output cap is the one that colours music the way i like it! right?! (so if i want to play with different capacitance and brand i'm free to go ahead!)

 i want to go up to Farad! am i free? 
	

	
	
		
		

		
		
	


	










 someone to answer my question #2 please?


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## robzy

Quote:


  Originally Posted by *whiz* 
_thank you Robzy! you saved me from spending time searching for the best cap! 
	

	
	
		
		

		
		
	


	




 as i understand the perfect output cap is the one that colours music the way i like it! right?! (so if i want to play with different capacitance and brand i'm free to go ahead!)_

 

Sure. But keep in mind, generally the less a capacitor cost the worse it will perform. And the lower-value cap you go, the more bass you will be missing out on.

  Quote:


  Originally Posted by *whiz* 
_i want to go up to Farad! am i free? 
	

	
	
		
		

		
		
	


	








_

 

Hrm, to be honest im not sure whether you are joking here or not  1 Farad would definetly be overkill, and it would not sound good at all (any capacitor thats made out of material that offers 1 farad will not have great sonic qualities). Also - the output of the PCM2702 might not like absurd (yes, im sorry, 1 farad is a value considered absurd ) amount of capacitance.

 As for question number two - I'm going to let someone else field what the effects of input/output capacitors in series are because I am not 100% sure.

 Rob.


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## doobooloo

Quote:


  Originally Posted by *whiz* 
_thank you Robzy! you saved me from spending time searching for the best cap! 
	

	
	
		
		

		
		
	


	




 as i understand the perfect output cap is the one that colours music the way i like it! right?! (so if i want to play with different capacitance and brand i'm free to go ahead!)_

 

For the output caps though, given that even the BlackGate NX Hi-Q parts cost only a few bucks each, I see no reason to go down in cap quality unless one just wants to experiment...


----------



## whiz

Quote:


  Originally Posted by *robzy* 
_Hrm, to be honest im not sure whether you are joking here or not _

 

looooooooool! 
	

	
	
		
		

		
			




















 NO WAY you believed that!!! 1 Farad cap is like a bottle of water! i can't image having this for portable use even if it was the perfect cap! (useful though for other needs in car audio)

 am i offtopic?!?!


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## doobooloo

Quote:


  Originally Posted by *whiz* 
_NO WAY you believed that!!! 1 Farad cap is like a bottle of water! i can't image having this for portable use even if it was the perfect cap! (useful though for other needs in car audio)

 am i offtopic?!?! 
	

	
	
		
		

		
		
	


	





_

 

Yes, he could have very well believed that because very small >1F capacitors do exist...

 Click here for some available on Digi-Key: http://dkc3.digikey.com/PDF/T062/1091.pdf

 You _can_ get a 70F (seventy!) capacitor, its dimensions are only 18mm x 50mm.


----------



## Alf

Quote:


  Originally Posted by *whiz* 
_3)so many people made that board...why don't you use RMAA to see the results in papers? perfection might be not audiable to our ears due to imperfection, but no one cares to test it and upload some diagrams? except Alf and maybe 1-2 more? if i had the board i'd definitly do it!_

 

The link has been posted earlier in the thread V1.0 vs Rev B


----------



## whiz

Quote:


  Originally Posted by *doobooloo* 
_Yes, he could have very well believed that because very small >1F capacitors do exist...

 Click here for some available on Digi-Key: http://dkc3.digikey.com/PDF/T062/1091.pdf

 You can get a 70F (seventy!) capacitor, its dimensions are only 18mm x 50mm._

 


 Nice dooboolooo! you've right! they are known but rearly used...so i forgot them!


----------



## doobooloo

Quote:


  Originally Posted by *whiz* 
_Nice dooboolooo! you've right! they are known but rearly used...so i forgot them! 
	

	
	
		
		

		
		
	


	


_

 

I wonder if they'll be any better than putting a battery in the signal path, though...


----------



## whiz

I hope someone can answer this...
 i understand that the crystal loading capacitors keep the crystal
 to the frequency we want. What happens if the loading capacitors
 aren't the correct value? what are the consequences to the operation of the alien dac?

 I'm talking about "frequency pullability"

 Thanks!


----------



## whiz

Quote:


  Originally Posted by *whiz* 
_I hope someone can answer this...
 i understand that the crystal loading capacitors keep the crystal
 to the frequency we want. What happens if the loading capacitors
 aren't the correct value? what are the consequences to the operation of the alien dac?

 I'm talking about "frequency pullability"

 Thanks!_

 

anyone kindly enough to answer my question please?


----------



## dakotart1984

Still off topic whiz, but commonly higher value caps are seen common, one typical example is in the original xbox, in wich i believe it holds "cmos" type settings. More specifically its a 2.5v 1F Powerstor cap, wire a few of them in parallel and you can make some neat projects. I recall this link I read on hackaday.. http://www.hackaday.com/2005/12/06/supercap-9v-battery/


----------



## stevodude

Woot, got pcb's, 

 Not sure if this should be posted here, but trying to organise a bom for australia supplier.

 Farnel au does't seem to stock the pcm2702e's neither does Radio Spares in au...

 or is there an equivalent I can get here in this backwater place called australia...

 I wouldn't mind ordering from a maximum of 2 suppliers, but so far I can't find 1 that stocks the dac, which is the main component I need, neither the REG101UA-3.3 or REG102UA-5, or the buf634 ( which I will probably have to build a custom buffer anyway, so thats not a worry).

 cheers, stevodude.


----------



## Andrew*Debbie

Quote:


  Originally Posted by *guzzler* /img/forum/go_quote.gif 
_C1 doesn't really have an optimum value unless you calculate all the parameters for the filters and coupling to USB line, 1uF will do fine._

 

Why is a C1 a high capacitance ceramic? ESR is kinda high at frequencies over 100MHz for a typical one. 

 Would a low value high frequency part be better here? One that has low ESR up to at least 1GHz. I'm thinking about using something like a muRata ERB21 or GQM21 at 50-100pF.

 My 'scope only has a 60MHz bandwidth, so I have no idea what kind of high frequency noise is on the USB power lines.


 ERB ESR graph


----------



## picklgreen

What other DAC chips is the Alien DAC compatible with? I am curious if there are benefits from using any of the other PCM270x family chips.

 Nevermind..I see the pinouts are all different.


----------



## cutun1217

hi everybody, im new in this forum. i want to ask whether i have any chance to get this board or do u guy have to eagle file or board layout so i can etch the PCB for myself?
 thanks so much.


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## GregVDS

Hello,

 I would like to know if the alien dac is working under mac os x? Is there something to instal, like asio driver or something else, or everything is recognized without any problem, or full incompatibility?

 Many thanks,

 GregVDS


----------



## achina

With at least 10.3 and 10.4 it is plug and play. Shows up as an additional sound device. Haven't tried it with anything older.


----------



## GregVDS

Thanks, I should definitely try to build this one. I plan to use is as source for a SOHA I already finished (with crossfeed, custom built output buffers and Epsilon12 protection). Can I simply join the outputs of the Alien DAC to the RCA inputs of the amp, without fussing with input switch, or the Alien DAC will have a bad influence when not used on the RCA signal? I mean the CL/CR could play for both system, right? I don't remember if the SOHA has DC input protection, I should check that. What is the best choice for CR/CL (discussed at libitum, I know, but a resumé of all the thread would be nice) if I have to put them in? As I understand, the Alien DAC is producing DC offset that has to be blocked, internally, or by the amp, right?

 I never soldered SMD, but am reading all tutorials available. Is it ok to go unregulated USB power? What should I expect in comparison with the stock headphone output of my Macbook (sound quality point of view, apart from the SOHA influence)?

 All the very best,

 GregVDS


----------



## MASantos

Quote:


  Originally Posted by *GregVDS* /img/forum/go_quote.gif 
_Thanks, I should definitely try to build this one. I plan to use is as source for a SOHA I already finished (with crossfeed, custom built output buffers and Epsilon12 protection). Can I simply join the outputs of the Alien DAC to the RCA inputs of the amp, without fussing with input switch, or the Alien DAC will have a bad influence when not used on the RCA signal? I mean the CL/CR could play for both system, right? I don't remember if the SOHA has DC input protection, I should check that. What is the best choice for CR/CL (discussed at libitum, I know, but a resumé of all the thread would be nice) if I have to put them in? As I understand, the Alien DAC is producing DC offset that has to be blocked, internally, or by the amp, right?

 I never soldered SMD, but am reading all tutorials available. Is it ok to go unregulated USB power? What should I expect in comparison with the stock headphone output of my Macbook (sound quality point of view, apart from the SOHA influence)?

 All the very best,

 GregVDS_

 

Regarding the CL/CR, I have done some extensive testing with different caps( FM's, Elna's, Nichicon's, Black Gates) and the best IMO is the 4.7uf BlackGate High-Q Nx. It takes some time to break in but gives the best sound. But if you have space in your enclosure and are willing to spend the money, you could go with some nice "boutique" film caps.

 Manuel


----------



## amb

Quote:


  Originally Posted by *GregVDS* /img/forum/go_quote.gif 
_...
 Is it ok to go unregulated USB power? What should I expect in comparison with the stock headphone output of my Macbook (sound quality point of view, apart from the SOHA influence)?_

 

I recommend using the REG101UA to regulate the USB power rather than unregulated. The computer's 5V line can be quite noisy. My own testing shows no tangible improvement with external power (over regulated USB power), even when that external power is a battery.

 The Alien DAC should be a nice upgrade over the onboard sound of virtually any computer, especially laptops. It could do only 16-bit and either 44.1KHz or 48KHz sampling rates, though; but that shouldn't be a big issue with computer audio.

 Btw, there is a dedicated Alien DAC thread with lots more info.


----------



## jasonhanjk

What gives with that battery?

 Without plugging the USB, this circuit won't work. Plug in the USB and the battery start to drain.


----------



## amb

Quote:


  Originally Posted by *jasonhanjk* /img/forum/go_quote.gif 
_What gives with that battery?

 Without plugging the USB, this circuit won't work. Plug in the USB and the battery start to drain._

 

The USB is plugged in, of course, but the Alien DAC I built has a switch that lets me select +5V power from the USB bus or from an external source.


----------



## Leoseller7

Hey Guys,


 New to this scene, wanted to know if I needed this DAC when using my Shure E530 with a Xin Reference Amp for use on my computer. I don't want to change the sound, hopefully want to improve it, can someone help?

 I know using an amp in the signal path does improve the sound, but I think I still wanted a good inexpensive DAC (USB) to use with my computer (X-Fi Extreme Music soundcard)

 Thanks in advance for your guys help


----------



## bubbamc119

^ I'd guess you would notice quite an improvement using this DAC, after all the source is the most important part of the signal chain. Soundlaster cards are generally crappy for music (cheap onboard DACs).


----------



## babbkutz@comcast

who is selling the latest revision PCBs?


----------



## MisterX

http://glassjaraudio.com/


----------



## eddiewalker

I'm afraid I killed my beloved bus-powered DAC. I built it a week ago and have been enjoying it while i wait for an enclosure. I brushed my hand against the back of the board, and one channel was gone. I fished around with my output wires to make sure they hadn't touched, and *poof* both channels are dead.

 I've rebooted, replugged in and I've checked both voltage test points. That's about the extent of my troubleshooting experience. Where else should I probe around or what else should I try? I'm really hoping I didnt kill the pcm2702 with static discharge. Help?


----------



## srwalker

I've also managed to kill one of my channels, I'm not sure how. The other works fine, my voltage test points are good and I've swapped the output caps round to make sure they're not the problem. From the look of the schematic I'm thinking there's not much else apart from the chip that I could have killed, anyone got any suggestions please?

 Thanks
 Simon


----------

