# usb dac



## 00940

Browsing on diyaudio, I found this : http://www.overclockers.com.au/~mwp/dac3/

 it's using pcm2902 as usb receiver, dir1703 as spdif receiver, pcm1730 as dac and opa627's (6 of them!) as output stage. 

 it looks really interesting, main difficulties being you have to etch your own boards and solder those little chips.


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## guzzler

6xOPA627?? 
	

	
	
		
		

		
			





 ouch, thats £90 straight away! but it does look very interesting. Just for interest, HeadRoom are about to release something similar based on the TAH headphone output, no pics or specs as of yet though...

 g


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## A3rd.Zero

It is an interesting idea. However, having worked with a few computer audio devices in the pro arena I have noticed a general lack in quality USB devices, which can be attributed to the fact that they are USB devices. USB is not quite suited for the transmission of data for audio. It might be useful to do a search for pro audio input and output devices, the ones made by Digidesigns and MOTU are almost exclusively either Firewire or PCI. The one USB digidesigns device that I know of, the MBOX has had problems.

 milo


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## 00940

well, m-audio has decent usb soundcards (the sonica to begin with). Furthermore, zzz used such a chip to get spdif from an usb out and reported good results.

 Regarding the opa627, i guess cheaper opamps could perhaps be used, the opa134 perhaps ?


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## asdfeproiu9

Hm, so how would one go about getting high quality SPDIF from USB?


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## 00940

http://focus.ti.com/lit/ds/symlink/pcm2902.pdf


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## ingmarwa

aos is coming up with a dac daugtherboard for the ppa. i found this thread, and then a thought came up in my head! is there a firewire chip that does the same thing as this usb chip? puts out normal stereo audio, plug&play? if so, culdn't you place this in the stage before the dac chip in aos dac, and get a bitppa?


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## ITZBITZ

The issue is drivers as well.

 I use a Sonica, and it works well. But I need to figure out how to wire it up for a coaxial output (or add an optical input to my ART DI/O). I'm thinking the prior might be easier, but who's to say since optical stays TTY and coaxial isn't.

 Anyone know of a simple circuit to add a coaxial digital output to the Sonica chipset?


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## Wodgy

There are firewire chips, but they're much more complicated to implement. Also, the firewire audio interface supports copy protection, and if you want to be able to play back copy protected streams, you have to sign a license with the vendor (at least Burr-Brown makes you do this) before you can get the chips.

 As for the Sonica question, can't you just remove the optical transmitter, add a 75 ohm resistor to ground, and a coaxial jack?


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## aos

Wodgy is right, licensing makes Firewire as good as dead. And Sonica definitely has driver issues - it is certainly not plug and play. For example you don't have linux drivers - because what actually happens is firmware upload every time device is plugged in the USB port! That is also why you must install softwre first, before plugging in Sonica. There are more and more devices like this, completely defeating the plug-and-play concept.


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## Wodgy

To be fair, the firmware "upload" is from the onboard ROM to the PCM3200 on the Sonica -- nothing is transferred to/from the computer on power up/when you plug in the device. Linux drivers are possible but no one has gotten around to writing them yet. (It would have been better to support the USB Audio standard, but a big part of their marketing is the SRS processor implemented in the driver, making a direct USB Audio implementation impossible.) If you're running Windows, of course, none of this is an issue, and I have tested the S/PDIF output to verify that it is bit-perfect. It's almost impossible to DIY a PCM290x solution for the retail price of the Sonica unless you can make your own PCBs or feel like soldering directly to the pins of a SSOP-28 device (sounds crazy, but there's one guy over at DIYaudio who did this by bending every second pin upwards).


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## aos

I was attempting to build a HTPC (home theater pc) back when I took a week of vacation in November, and I ended up wasting a fair bit of money and precious time as I tried to build a linux one. Sonica was one of the things I bought and that's how I found out about drivers and firmware upload. I attempted all patches on the web at the time but even though I got it pass error messages so it all appeared to work, sound drivers still wouldn't connect to the card, so I just gave up. I haven't returned Sonica to the store, I have it still, but according to RMAA, DAC inside is nothing to write home about. However, since that time I am unable to get my Revolution 7.1 to work in 24 bit or anything over 48kHz.

 I kept it because of optical audio - so if you have your own DAC you can use Sonica with a laptop to get excellent sound. I don't have a laptop yet but maybe one day...

 But if you get a chip that works as standard USB audio, and outputs bit-perfect digital stream, then it'd be cool to add it to a good DAC.


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## Wodgy

Ahh, Linux driver issues. I feel your pain.

 If anyone's interested in measurements of the Sonica's analog output, go here:
http://www.io.com/~kazushi/audiocard/sonica
 Very good for the price, but not excellent. Most of the noise is >100db down, which is better than almost all sound cards at this price.

 The analog stage of the Sonica is a 10uF coupling cap, followed by a minor resistor divider, then a ceramic cap to ground (presumably to filter digital noise, though neither the data sheet and eval board for the AK4353 recommend one). Modders can bypass the entire output stage with coupling caps of their choice to RCA jacks. I've done this with my Sonica (2 uF AudioCaps bypassed with 100uF Elna Silmics) and the sound improved noticeably, especially the highs which were a bit grainy before. Definitely a recommended tweak for modders. It's a very listenable device.


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## aos

That's far better than I got - I got noise flor at 80 something dB, distortion, non-flat frequency response etc. I did of course disable the DSP processing - or at least I think I did. I guess installing Sonica drivers screwed up my Revo setup. Now everything gets resampled to 44 or 48kHz. It makes sense as I didn't belive Sonica would be quite that bad.


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## Jupiter

Does anybody have an opinion on which usb audio chip performs better? Or is the performance pretty similar?


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## Wodgy

The best analog all-in-one choice is the PCM2702. The PCM290x is markedly inferior to the PCM2702 for analog output, but the PCM2702 doesn't have a digital output.

 You can (of course) do better by using the S/PDIF output of the PCM290x and a dedicated DAC chip. The PCM3200 is too difficult for DIYers to implement and offers no advantages over the PCM290x if you're just looking for a digital out.


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## Jupiter

What about the PCM2704/5/6/7?

 Do you have a link for the PCM3200?


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## Wodgy

Oops, my mistake. I meant the TUSB3200.

 PCM2702 has better analog specs than the newer PCM2704/5/etc. Check the datasheets. All the members of the PCM270x series have much better analog specs than the cheaper PCM290x series.


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## aos

PCM2704DB looks like it has SP/DIF out pin, so one could presumably just link it up to any DAC. Higher pin count versions have digital out already decoded but they seem to be missing left/right latch signal without which it may not be possible to connect them to a DAC chip.


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## Jupiter

Wodgy and aos,

 Thanks for the help. 
	

	
	
		
		

		
			





 I'll give the PCM2702 and maybe some of the PCM270x a try.


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## Jupiter

I've been looking at the schematic for the PCM2702 evaluation board. Why an external low-pass filter when the PCM2702 has an internal low-pass filter?


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## Wodgy

The low-pass filter is "needed" for two reasons. First, the DAC's digital filter only has about -80dB of noise attenuation above the audio band. That's actually pretty good, and there is an argument for this being good enough, but some engineers would want to do better. (In comparison, the 290x series has a fairly crummy digital filter, pushing ultrasonic noise down only to about -60dB, which makes an external analog filter more of a necessity for hi-fi audio.) Second, this is an 8-times oversampling design, meaning _serious_ switching noise will be evident in the output signal at 176.4 kHz and beyond. Most people want to get rid of this, to reduce distortion in amplification components later on, as well as to protect tweeters, though there is a school of thought saying that it doesn't matter.

 If you only care about reason #2, you can make the analog post filter a very gentle one, far away from the audio band. If you care about reason #1, then the analog post filter will need to be closer to the audio band. This is one argument in favor of using real DAC chips, rather than these integrated USB devices, but personally -80dB of ultrasonic filtration is good enough to me, and I'd move the analog filter out to at least 90kHz or so.


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## aos

Actually only top of the line DAC chips have better than about 80dB of stop band attenuation in the digital filter. You can usually combine them with a standalone digital filter if you do wish to keep using the same DAC chip and yet get a better attenuation.


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## Jupiter

Thanks again 
	

	
	
		
		

		
		
	


	




 Then I'll just skip the low-pass filter for now. Maybe I'll add it later.


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## Jupiter

Quote:


 _Originally posted by aos _
*PCM2704DB looks like it has SP/DIF out pin, so one could presumably just link it up to any DAC. Higher pin count versions have digital out already decoded but they seem to be missing left/right latch signal without which it may not be possible to connect them to a DAC chip. * 
 

I had a look at the PCM2704/5/6/7 datasheet. The PCM2706/7 has I2S output in addition to S/PDIF. (Page 18 of the datasheet.)


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## 00940

just to revive a bit this post, an attempt to a very simple USB-DAC/headamp.

 Basically, it's just a pcm2702 with BG at the analog output right into a buffered cmoy, with discrete diamond buffers. It should run from 3 9V batteries. PS of the pcm2712 is regulated by reg102 and the headamp section is powered by +/-9V, spitted by a tl2426 buffered by a buf634.

 I just realized that there are no pads to fit a pot. There should be some room just before the output caps for that.


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## aos

Interesting layout, you seem to have done a nice clean job of having digital paths short and placing capacitors as close to chip as possible. I am thinking of including such an USB chip with digital out into one of my DACs as an alternate input.


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## Glassman

all those burr brown USB chips run of 4MHz masterclock I believe, they are generating clock signal at multiples of Fs with their internal PLLs, but I have some doubts regarding their PLL quality.. however it would be interesting to include KWAK-CLOCK circuit running at say 16MHz, divide it by four using some 74HCxx logic and feed it to PCM2702.. jitter is the one and only thing which I am scared about regarding USB chips..


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## 00940

Schematic, straight from the datasheet :






 Edit : I'm gonna change the layout of the analog section to make it evolve towards this :






 The amp section is from Sijosae, as well as the discrete rail splitter. (see butterfly on headwize).


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## aos

Some of these USB chips use Burr Brown's SpAct technology, same as with DIR1703E receiver, that claims to drastically reduce jitter. I.e. about 70ps for DIR1703E compared to about 200ps of the likes of CS8412 and AK4117. I have heard from professional engineers that measured output of modern multi-segment DAC (which is less sensitive to jitter) when using DIR1703E and they say that jitter is gone. Now, I don't know how much of those improvements went into these particular USB chips.

 One drawback with receiver chip is that is is very sensitive to quality of input signal - ironic, isn't it? My digital cable box with coax out doesn't work at all, while portable CDP from Sony with G protection on has frequent very loud popping sounds as it loses lock for short periods of time (sony has lots of noise on its output when it spins up and down its motor in G prot mode). However, in the USB, quality of signal is probably more tightly controlled by the USB standard and it hopefully always works.


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## ITZBITZ

I really think this is cool.

 But what about the software drivers required to use the TI part? Something is going to have to tell Windows that this is a sound device and all that jazz. Any thoughts?


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## tangent

Any device that complies with the USB Audio spec works without any special drivers. It's like USB keyboards and mice -- you don't need special drivers for them, either.


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## ITZBITZ

Well, OK.

 I'm in to build one, assuming I don't have to open the Windows DDK.


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## 00940

Second layout, slightly bigger (I could still fit 2 of these on an Eurocard). 

 Differences : 

 - Room for a pot
 - Less jumpers and shorter ones
 - Amp is now multiloop and not simply buffered
 - Use of 2 batteries instead of 3. 
 - Voltage of the amp down to +/-4.5V.
 - Use of two 2200uF/10V instead of four 470uF/25V for the analog supply.


 Estimation of the cost : roughly 75$.


 EDIT : layout withdrawn, very unsatisfactory


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## 00940

stupid question... do I need that pot or is the digital attenuation of the pcm2702 satisfactory ??


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## ITZBITZ

Would the digital attenuation need a controller of some sort or is that also part of the specification (USB Audio)?

 This project seems seriously SMD. Is there a plan to demonstrate construction using a toaster oven and solder paste? I can see my wife already wondering why I'm taking the toaster oven into the garage. And then I can see myself at the store the next day buying her a new one.


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## 00940

From the datasheet :

  Quote:


 Digital attenuation and softmute features are included, and are controlled via USB audio class request.

 Digital Attenuator: 0dB to –64dB, 1dB/step 
 

There are not that many smd parts. Of course, there's the pcm2702, that's a ssop-28. All the other ICs are so-8, like the ones used in a Mint. The other parts are full size.


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## ITZBITZ

The only other thing I could see that might make this a little sweeter is the ability to bypass the headphone output and just get the signal out of the unit to connect to another amplifier. I see this as an extra input to my desktop PPA amplifier that I would mount inside the case with a rear-mounted USB terminal.

 If the op-amps could be configured to work as the gain adjustment/digital filter as a preamp to the main amplifier, that would be sweet. I haven't read the datasheet, but on other DAC's I've used an active low-pass filter is done using an op-amp and some caps/resistors. There is an applet on the Analog site that helps you tune your filter values for a 96kHz rolloff, etc. to get the high-level noise out of the signal.


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## 00940

Here's the "definitive" layout.

 I scratched the pot, moved things around to get more room, added 2 more caps in the analog supply, made all the power distribution for the headamp by wires to avoid big power traces all over the board, added 2 pads to get the signal before the headamp.






 Edit : power consumption problem :

 This thing should eat at least 40mA for the DAC and Sijosae claims a 20mA consumption for the amp section. So, it gives us a 60mA total power consumption. On two rechargeable 9V batteries, with 200mA, it gives us about 6 hours and half of life. On 8 AA rechargeable batteries, at 2000mA, it gives us a more satisfactory 33 hours life 
	

	
	
		
		

		
		
	


	




 Another option would be to use the power the USB could give us. It'd take a 5 to 9V dc-dc converter and quite a bit of regulation to clean the power coming from the computer.


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## ITZBITZ

Just allow for a DC power connector and we'll worry about getting enough juice to it. 
	

	
	
		
		

		
		
	


	




 I'll probably power it off linear supply (LM317-style)...
 Or a simple wal-wart would suffice for many like the Audiophile USB.

 The evaluation board uses a 6.3V power supply itself.

 There is always Tangent's battery board with 10 AA batteries as well..


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## guzzler

thats looking nice 00940! however, I was wondering if shoehorning the diamond buffer into makes sense both sonically or practically:

 using a space for a monolithic buffer (say the HA3-5002, or BUF634) would take a lot less space, while at the same time leave the option of the discrete buffer open, as can be seen with sijosaes implementation of the Jung buffer on a piece of board not much bigger than a DIP chip, or by ppls superlative discrete buffer. The monolithic buffer will *likely* sound better than any cheap 2N3904/06 implementation as well, but that's by no means definite

 also, it means people would *have* to buy excess output transistors so they could be matched to minimise DC offset, which is going to boost up the cost, complexity, and patience level of those wanting to make it.

 this is your design, I know, but if you wanted others to construct it (and I'd build it either way), the DIP option is definately worth considering seeing as there are components on that side of the board anyway

*edit:* just another thought on this; how many people would use the DAC with the headphone amp on board, and how many would connect to a dedicated headphone amp?? If no one wants it to have an amp on board, you could gain a lot of space, reduce the cost, and crucially, reduce the power consumption!

 I'm also going to question the use of the discrete rail splitter (sorry!). I can see the big advantage in this design being all discrete in that all the parts are readily available (especially seeing as we're in Europe!), but the performance of the discrete rail splitter does not even come close to matching a TLE2426 unless, again, you use some serious hand matching and excess component purchasing and even then, an imbalance is still more likely to occur than with a laser trimmed resistor pair. 

 g

*edit2:* bit of housework


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## 00940

Quote:


 _Originally posted by guzzler _this is your design 
 

Actually, I could hardly consider it as "my" design. The dac is straight of the datasheet and the analog section copied from different designs Sijosae posted on headwize. And it was more like an homework to get my feet wet with eagle. 

  Quote:


 using a space for a monolithic buffer (say the HA3-5002, or BUF634) would take a lot less space, while at the same time leave the option of the discrete buffer open 
 

Well, if we're going the road of monolithic buffer, we could as well shrink the space. The builder would have to solder a difficult piece (the pcm2072 ain't big). He'll probably be able to solder so8 parts.

  Quote:


 just another thought on this; how many people would use the DAC with the headphone amp on board, and how many would connect to a dedicated headphone amp?? If no one wants it to have an amp on board, you could gain a lot of space, reduce the cost, and crucially, reduce the power consumption! 
 

Honnestly, I didn't intend this design to go commercial in any way or be widely built. I planned to build one for me because I could have a need for such a design. An integrated solution would be cheaper than an sonica+pimeta combo. I'm not sure the DAC alone would offer a better quality ratio than a sonica. However, swapping the headamp for an output stage could be interesting considering most diyers able to solder such a thing already have an amp or two or even three.

 So... I'm gonna play a bit more with this. I'm gonna suppress the headamp, implement a low pass filter, an output stage (perhaps just a pair of buf634, the pcm2702 outputs up to 3V !) and try to get the power from the USB port.


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## ITZBITZ

I would look at the schematics of the ART DI/O. It's an excellent DAC with a nice op-amp based low-pass filter and highly regarded sonics. Use that as an example to create a line-driver stage.

 If you are truly looking to make a "Sonica with nuts" then use some monolithic buffers with some rollable DIP8 op-amp sockets and room for a gazillion batteries.


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## 00940

actually, i'm looking at the evaluation schematic that TI released. There's a low pass filter just waiting to be picked up. 
	

	
	
		
		

		
		
	


	




 I'll probably swap the opa2353 they used for an AD823 : they're cheap, they're good and above all, they work from a single 5V !

 We could thus power the whole thing from 5 AA with a comfortable lifetime. A charger could probably be easily implemented.


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## guzzler

keep us posted 00940, i would certainly be very interested in building one of these, and i've got a UV exposure unit, so if you leave it single layer, i could run you off a couple from that. I might run off a bit of the digital section with the line out, and hook it up, see what comes out...

 all the best,

 g


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## jamont

That SSOP chip will be tough to solder! Otherwise, this looks like a great project. Keep up the good work.


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## 00940

Quote:


 _Originally posted by guzzler _
*keep us posted 00940, i would certainly be very interested in building one of these, and i've got a UV exposure unit, so if you leave it single layer, i could run you off a couple from that. * 
 

Thanks for the offer ! Anyway, I intended to keep it single layer. It's simple enough and single layer is cheaper to get from pcb builders like olimex.

 Here is btw the layout for a DAC only, powered simply by 5 AA batteries. Grid is half an inch :












 Now, I'd need some advice, I've 2 ideas for the supply :

 1- One option would be to build a 5 AA battery pack. As recharging 5 AA would be painful (not really standard), we could just integrate a small charger and add a DC jack. Battery life could reach near 40 hours. No need to change batteries, just connect the device to a small wallwart (9V should be ok).

 2. Another options would be too go for less batteries. With 2 AA, we get 2.4VDC. Add to this a DC-DC converter and we're quickly back to 5.5V. It would have an estimated battery life of 16 hours. It's not more boring than having a pcdp.

 What do you think ?


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## guzzler

i agree, 5 AA would be a pain since almost all battery holders are 4 or 6 capacity, although you could use a dummy cell in a 6 battery holder. But it's weighing up the advantages of using a DC-DC converter which tend to be a nuisance in the extreme, and fairly bulky, although Xin Feng Super Micro and HeadRoom use them to good effect! For the 2 AAs, you could by the looks of things fit them onto the board directly, so looking at the last layout they'd be going from the top of the screen to the bottom.

 5 AA : less complicated circuitry, possibly higher quality, cheaper, awkward to fit, reasonably large
 2 AA : smaller, light, DC-DC convertor expensive and complicated

 g


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## 00940

Quote:


 _Originally posted by guzzler _
*2 AA : smaller, light, DC-DC convertor expensive and complicated * 
 

Actually, smaller, light, cheap and easy.

 The MAX1722 I've in mind cost 2$. Add an inductor, 2 resistors and 2 tantalum cap, you're done 
	

	
	
		
		

		
		
	


	




 Total : less than 5$.

 Maxim claims that : 

  Quote:


 Built-in synchronous rectification significantly improves efficiency and reduces size and cost by eliminating the need for an external Schottky diode. All three devices feature a 0.5§Ù N-channel power switch. The MAX1722/MAX1724 also feature proprietary noise-reduction circuitry, which suppresses electromagnetic interference (EMI) caused by the inductor in many step-up applications. The family offers different combinations of fixed or adjustable outputs, shutdown, and EMI reduction. 
 

Here's the updated version :


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## guzzler

Quote:


 _Originally posted by 00940 _
*Actually, smaller, light, cheap and easy.* 
 

i stand corrected, said the man with the orthopaedic shoes 
	

	
	
		
		

		
		
	


	




 i take it thats the DC-DC converter in the top left? Does look very nice and compact for sure! the whole thing is about 4" by 2" so that leaves it nice and small. The USB port could be shifted a little to the right which would save space, and i'm sure we could fit something into the spare space on the right, perhaps some kind of power control circuit??

 g


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## Nisbeth

Quote:


 _Originally posted by guzzler _
*... i'm sure we could fit something into the spare space on the right, perhaps some kind of power control circuit??* 
 

 Where's the blue power LED?
	

	
	
		
		

		
		
	


	



 On a more serious note, some sort of "signal lock" indicator would be useful (at least I think so). Otherwise, keep up the good work lads 
	

	
	
		
		

		
		
	


	





 /U.


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## 00940

I'm trying to figure out the cost, prices are indicative and are coming mainly from digikey or newark :

*ICs :* 
 1X PCM2702 : 9.66$ 
 1X AD823AR : 5$ 
 1X REG103UA-3.3 : 2.36$ 
 1X REG103UA-5 : 2.36$ 
 1X MAX1722 : 1.96$ 

 subtotal : 21.42$

*Caps :*
 2X Black gate 10uF/16V : 2$
 3X Pana FC 100uF/10V : 1.41$
 2X Pana FC 1800uF/10V : 3$ 
 4X 0.1uF/50V ceramic : 0.64$ 
 2X 10pf/50V ceramic : 0.52$ 
 5X wima mks-02 0.1uf : 1$
 1X wima mks2 4.7uf : 2.1$
 2X tantalum 10uf/10V : 1.3$

 subtotal : 11.97$

*the rest :*
 1X inductor 10µH : 0.77$
 16X resistors 1/8W metal RN55 : 1.6$
 1X usb connector : 1.12$
 1X crystal 12mhz : 0.5$
 2X nimh battery : 5$
 1X blue led : 1$
 2X rca jacks : 3$
 1X spst switch : 2$

 subtotal : 15$

 Total without case and boards : 48.40$

 edit : corrected some errors


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## guzzler

Quote:


 _Originally posted by Nisbeth _
*On a more serious note, some sort of "signal lock" indicator would be useful* 
 

 hmm, interesting idea, unfortunately it would require a complete rerouting of the layout as that would be a digital function, and the whole analog section is in the way.

 00940, that price sounds very reasonable, although we'd have to add a little (or a lot!) for European prices, but I can't see it coming to much over £40-50 or so.

 g


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## 00940

Quote:


 _Originally posted by guzzler _
*00940, that price sounds very reasonable, although we'd have to add a little (or a lot!) for European prices, but I can't see it coming to much over £40-50 or so.* 
 

If we could order from Germany, the costs would be very reasonable, as schuro and reichelt have VERY good prices. 

 On that list, the only problematic items would be the black gates and the vishay dales resistors. But the metal film ones carried by Reichelt are actually pretty decent. As always, the shipping costs will be a significant part of this total cost. A small scale group buy could be interesting as this pcb not meant for tweaking.

 I don't know how much work such boards would require from you. 1 drilled eurocard, with single layer, silkscreen and solder mask cost 26$ from Olimex. If we don't mount the batteries on the pcb, we can fit 4 pcb on one card, making the cost 6.5$ a piece. 2 cards are 47$, pushing the price down to 5.9$.

 It's not a project i want to make money on. But if we can save each other useless costs, it'd be great.

 I'll update the board with provisions for the on-off switch and the led, there's room for that at the right. I'll then post the *.brd file.


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## guzzler

to my mind, the Vishay-Dales aren't essential, more a sort of icing thing but if you like. I use decent quality .4W .1% resistors made by TruOhm which sound as good as anything else I've used.

 $6.50 a piece is a great price, and I'd like to see an example of Olimexs board because I've been thinking of using them a few times but never got round to it!

 as for the Black Gates, there are a few places in the UK that sell them, although you'd get killed on the price and availability so it's probably not a viable option to buy lots at a time

 g


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## Nisbeth

00940, which parts would it be necessary to source from Schuro?

 As for anything from Reichelt, my next (substantial) order with them will most likely go out in 4-6 weeks from now. If the timing is convenient, I could probably buy some of the parts in slightly larger quantities if anyone is be interested then? (That would save shipping and COD-fees as I'll be paying those anyway 
	

	
	
		
		

		
		
	


	




)


 /U.


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## 00940

in fact, thinking twice about it, none. Schuro doesn't carry the good values in pana FC. 

 From reichelt, we could source :

 jack rca, tantalum, ceramic and wima mks caps, metal film resistors, usb connector, inductor, crystal, blue led, switch.

 In fact, everything but the pana FC, the black gate and the IC.

 It won't be easy to get the chips. I can't find the AD823 in small package, nor the reg102 nor the pcm2702 nor the max1722. This at RS-components, farnell or conrad. 
	

	
	
		
		

		
		
	


	




 There's always the option to get them all as samples.


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## Jupiter

Some of those parts I would order from Digi-Key. I think they have good terms for international orders.

 Check with Farnell if you can order Newark parts through them. In Norway companies can order Newark parts through Farnell and I assume DIYers can too.

 I would like isolated inputs, since I've had problems with computers and ground loops previously.


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## 00940

actually, I can't check. RS, Conrad and Farnell do not deliver to individuals in belgium, only to companies. 
	

	
	
		
		

		
		
	


	




 They don't even reply to me in fact.


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## Nisbeth

Farnell will sell to private individuals here, but I prefer to think of them as a secondary source, because it's hideously expensive 
	

	
	
		
		

		
		
	


	




 If it would be possible to buy from somewhere else, even in the US, that would probably be cheaper.


 /U.


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## guzzler

Digi-Key are terrible for shipping to Europe, something like a $50 handling fee, although there is a UK flag on the Digi-Key site that I've clicked and says Digi-Key UK but same prices etc... strange

 RS and Farnell will both ship to individuals here but both are expensive as Nisbeth points out, and Farnell UK don't stock any of the ICs we need but I'll give them a call on Monday see what they can do.

 RS only have the AD823 and only then in DIP, which is annoying!! They do have however more or less the complete range of Panasonic FC...

 I think our best bet of obtaining these is either contacting Farnell, which I can do on Monday, or using samples, and here I think is legitimate as we can't buy the parts we want


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## Jupiter

00940,

 Analog, TI and Maxim have samples programs if you want to do it that way. TI and Maxim are pretty generous from what I've heard.


 guzzler,

 When did you order from Digi-Key?

 According to Digi-Key's website they have a €13 handling charge for international orders under €100 and shipping is €18 (in most cases).


----------



## guzzler

it wasn't me, there was a someone who ordered from digikey to europe and by the time everything had been added up (handling, shipping, import tax etc) it had cost him 70 euros extra on top of what he had paid before...

 TI have a very good sample program, I've used it in the past and I think this is a legitimate use as for all intents and purposes, those parts are not available to us.

 g


----------



## 00940

jupiter : you have to add to those figures 10€ customs presentation fees and an import tax of 10%. The 50$ quoted by guzzler look right.

 Well, we'll try the sample programs then. 
	

	
	
		
		

		
			





 We won't make it an usal practice.

 To summarize, who would be interested ? A first run would be for 4 or 8 persons. I'm gonna try to check options around. Olimex would run at 6.5$ a pcb (but we have to pay by visa card and I don't have one 
	

	
	
		
		

		
		
	


	




 ). I just found a small Belgian online shop that makes pcb. I'll ask them a quote.

 Second problem is I only have the light edition of Eagle. It doesn't allow me to copy paste the layout all over the eurocard surface. We'll need to find someone to just do that copy-paste.


----------



## Nisbeth

Quote:


 _Originally posted by guzzler _
*by the time everything had been added up (handling, shipping, import tax etc) it had cost him 70 euros extra on top of what he had paid before...* 
 

 VAT/customs is probably the key here. AFAIK, European VAT ranges from 16% (Germany) to 25% (Denmark, Sweden). If they ship UPS or FedEx, this could be very expensive since you have to pay VAT of both the cost of the items and s&h. On top of that, UPS/FedEx will charge a mildly obscene fee for customs processing
	

	
	
		
		

		
		
	


	



 For orders from the US, USPS and inconspicous packages is the way to go
	

	
	
		
		

		
		
	


	





 /U.


----------



## guzzler

If you tell Olimex you want the design to be copied onto the panel they do it for you. I would think most PCB shops worth their salt will do that for you as well, just ask.

 I once ordered some Sony Neige minidiscs from the states, cost about £25 pounds or so, then I was charged £27 by Imports, most of that being the extra carriage even though it was only Royal Mail. Something to be avoided to my mind! 
	

	
	
		
		

		
		
	


	




 And I'd be interested in one definately!

 g

*edit*: typo


----------



## 00940

OK.

 So :

 ICs : 
 1X PCM2702 : 9.66$ - Sample 
 1X AD823AR : 5$ - Sample
 1X REG103UA-3.3 : 2.36$ - Sample
 1X REG103UA-5 : 2.36$ - Sample
 1X MAX1722 : 1.96$ - Sample

 subtotal : 0$

 Caps :
 2X Black gate 10uF/16V : ? - ?
 3X Pana FC 100uF/6.3V : 0.54€ - RS
 2X Pana FC 1500uF/6.3V : 1.5€ - RS
 4X 0.1uF/50V ceramic : 0.28€ - Reichelt 
 2X 10pf/50V ceramic : 0.8€ - Reichelt
 5X wima mks-02 0.1uf : 0.75€ - Reichelt
 1X wima mks2 4.7uf : 1.80€ - Reichelt
 2X tantalum 10uf/10V : 0.44€ - Reichelt

 subtotal : 6.11€ (+??)

 the rest :
 1X inductor 10µH : 0.36€ - Reichelt
 16X resistors 1/4W metal : 0.8€ - Reichelt
 1X usb connector : 0.26€ - Reichelt
 1X crystal 12mhz : 0.44€ - Reichelt
 1X blue led : 0.5€ - Reichelt
 2X rca jacks : 1.78€ - Reichelt
 1X spst switch : 0.82€ - Reichelt

 subtotal : 4.96€

 Total without case and boards : 11.07€ 
	

	
	
		
		

		
		
	


	



 Total with board : 16.07€
 Total with board and case : 20.02€ (26US$)

 And of course shipping and so on.

 Btw, I was thinking at this case : http://makeashorterlink.com/?F51821C77


----------



## Jupiter

I don't think I'll need a board, since I'll probably do things a little different.

 I might order a few things from Percy. If so I could order some Black Gates. Maybe you want to get the 22uf/6.3V NX HiQ instead of the 10uf/16V standard?


----------



## 00940

That'd be great ! They are at 2.25$ a piece and will fit nicely in there. They're only 5mm wide, I'll update the board for them. I also need to update it because the inductor at Reichelt are not axial but radial.


----------



## Jupiter

I'll try to place an order with Percy within the next few days. By the way, there's also a 47uf/6.3V HiQ NX at $2.50.

 00940, do you want 2 or more?

 guzzler and Nisbeth, do any of you need any Black Gates?


----------



## guzzler

jupiter... I'm building a PPA just now, so unless you want to order lots of extra stuff for me, I might just order some stuff from Percy's myself. I'd never really looked through the catalog until now, but it looks good! And thanks for the offer, I'll let you know ASAP

 00940, is there any chance you could order the parts you were going to get in Germany for me as well, apart from the film/ceramic caps, the jacks, the led and switch as they're easy to get here, but the rest I can't get from my usual place?? that would be great if you could!


----------



## 00940

Guzzler : I can't order in Germany for less than 50€ anyway. Problem is what I need from Reichelt is really cheap : less than 15€. So, I was going to accept the kind offer of Nisbeth to join his next order. However, if I were you, I'd check twice the price at reichelt and those you can get locally, reichelt is very cheap on some stuff. I'll ask a friend to order pana FC at RS for me.

 I hope to finalize the board and format it to the right files by the end of this week. Btw, here is how Olimex boards look like :






 Jupiter : I'll take 4. Do you have paypal ?

 Nisbeth : are you interested in a board ?


----------



## Nisbeth

00940: I'd like 2 boards if the cost is as low as you say (5-7$)

 Jupiter: Same question from me, do you have PP?

 Gus: If you're OK with a 4-6 week wait, I can order parts from reichelt for you 
	

	
	
		
		

		
		
	


	






 /U.


----------



## Jupiter

guzzler,

 I can order more parts for you, but there's a risk of double customs charges.


 00940 and Nisbeth,

 Yes, I have a Paypal account.


----------



## ITZBITZ

I'll take up to $20US worth of boards, so if they are $7 each I'd take three of them. I'm in the US, so if I decide I only need 1-2 of them I would offer up the other to any US folks that want to build one.

 Just let me know via e-mail what information you need.


----------



## 00940

Nisbeth : 2
 ITZBITZ : 3
 Guzzler : 1
 Me : 2

 We are at 8 boards. That's 2 eurocard from olimex.

 Jupiter : perfect 
	

	
	
		
		

		
			





 Would you please let me know by pm your account and how much I've to send you, including shipping towards Belgium.


----------



## Nisbeth

Jupiter: I'm in for 6 pcs. of the Blackgates needed here. Send me a PM with a price incl. shipping 
	

	
	
		
		

		
		
	


	





 /U.


----------



## guzzler

Jupiter, I'll order from Percy Audio myself, their prices are excellent and smoke where I was going to buy from! Thanks for the offer anyway...

 00940... the place I get most of my stuff from is great for "normal" items, but less good for more exotic things. The Euro exchange rate isn't too bad just now, so if you could i would really appreciate it!

 cheers,

 g


----------



## 00940

guzzler : let me know by pm what you'd need. If we reach with our commands the 50€ line, I can directly order from Reichelt.

 If you can't find what you're looking for due to the fact it's in German, I can help. I don't speak german but i know really well what you can find at reichelt.


----------



## jboehle

I'll take 2 of the boards.

 -Jason


----------



## 00940

I found this on diyaudio :

  Quote:


 _Originally posted by borisov57_
*PCM2702 sounds boaring with low pass filter build with operational amplifier ( like in datasheet ). I use it with only 2u2 foil cap to block DC. * 
 

I'm gonna try to contact this guy. If indeed he had very good result without the low pass filter, we perhaps should consider to drop it. It would increase the life on batteries too. What do you think ?


----------



## guzzler

it's worth thinking about i suppose. The battery life is looking good as it stands, so if we do go ahead with this change it would have to be for aural reasons. i do quite like the idea of fewer actives in the signal path, although the cap would have to be a good quality one such as a Black Gate or a Solen or something similar

 g


----------



## Jupiter

00940 and Nisbeth,

 I'll order the following:
 For 00940: 4 x 22uf/6.3V Black Gate HiQ NX: 9.00 USD + shipping
 For Nisbeth: 6 x 22uf/6.3V Black Gate HiQ NX: 13.50 USD + shipping

 I don't know the shipping weight, but here are some examples:
 Letter, priority, 100 grams: 2.15€
 Letter, priority, 101-350 grams: 5.10€

 Let me know if you prefer a different shipping method.

 I'll send you a PM with the total when I've shipped the parts. No need to pay in advance.


 guzzler,

 also check www.partsconnexion.com


----------



## 00940

that's ok Jupiter, keep us posted.

 Thanks a lot


----------



## Nisbeth

That's perfect, thanks! 
	

	
	
		
		

		
		
	


	





 /U.


 PS: Looks like the Norwegian postal service is as expensive as ours


----------



## 00940

funny, i just saw this : http://www.hbl.co.uk/product.asp?ProdID=1032


----------



## Jupiter

Quote:


 _Originally posted by Nisbeth _
*PS: Looks like the Norwegian postal service is as expensive as ours 
	

	
	
		
		

		
		
	


	


* 
 

I'm afraid so. I suspect parcel rates might be worse. 
	

	
	
		
		

		
		
	


	




  Quote:


 _Originally posted by 00940 _
*funny, i just saw this : http://www.hbl.co.uk/product.asp?ProdID=1032 * 
 

That might be a copy of the eval board. Anyway, should be more fun to build you own.


----------



## 00940

Quote:


 _Originally posted by Jupiter _
*That might be a copy of the eval board. Anyway, should be more fun to build you own. * 
 

From their comments, it indeed looks exactly like this


----------



## gavinbirss

Hello

 I thought that you guys might like to know that KECES of Taiwan has a complete product and PCB of the PC2702 DAC.

 The nice thing about the board is that it has the SSOP28 package soldered on the board already.

 Email me if you guys want the email link for the english contanct person or a possibe dealer in South Africa. (Where I am)

gavinbirss@mail.co.za

 The price for a board will be around $ 25 and shipping will be arppox $ 20.

 But you can order 10 boards and pay only approx $ 20 shipping.

 Here is two pics of the board :

http://space.150m.com/usb.html

 Gavin


----------



## 00940

I knew that 
	

	
	
		
		

		
		
	


	




 Problem with keces board is that it is main powered and big. Not very practical for a small usb dac. Furthermore, the parts count is much higher, making it more expensive.

 Btw, I received an answer regarding the low pass filter : the guy confirms that the lpf was pretty ****ty and gave a confused sound.


----------



## gavinbirss

Hello

 Sorry for posting redundant info.

 00940 :

 "Btw, I received an answer regarding the low pass filter : the guy confirms that the lpf was pretty ****ty and gave a confused sound."

 Are you referring to the USB to HIFI Converter from http://www.hbl.co.uk/product.asp?ProdID=1032, which uses the OPA2353 opamp.

 My thoughts on the LPF is that you are forced to have a power supply and large device since a good LPF needs to have power supply with dual outputs. I also don't like the 100uf electrolitic cap in series with the output. I though a DC servo might be used for DC correction.

 Good luck 

 Gavin


----------



## 00940

no problem. Actually, it wasn't posted earlier in this thread.

 No, I'm not referring to that device. I contacted a guy who build one for himself. There are a few posts about that on diyaudio. I found there the schematic of the Keces dac. They're using exactly the same LPF but with a pair of opa604 and more voltage.

 Dc correction is not easy to implement correctly. A small black gate won't harm much and is much easier to deal with. I think it's a relatively safe bet to scratch the LPF and just use a 22uf black gate NX.


----------



## Wodgy

Just to clarify, the purpose of the LPF has nothing to do with DC blocking. See my (much) earlier post in this thread explaining the purpose of the LPF. (I'm not saying you shouldn't leave it out though.)


----------



## 00940

You're right Wodgy, my post was very confusing 
	

	
	
		
		

		
		
	


	




 Another point : if we scrap the LPF, we can make the board smaller. If the board is smaller, we can put 6 of these on an eurocard. 6 on eurocard means it's cheaper a piece. Cheaper a piece means we could use double sided pcb. It'd still be at 4.33$ a piece. 

 I'm redoing the board (once more, I'm knowing this schematic from memory now 
	

	
	
		
		

		
		
	


	




 ) with a groundplane. It will be cleaner.

 PS : I'm not doing more than 2 eurocards, which means a total of 12 boards. They are all spoken for.


----------



## Nisbeth

Keep us posted on the new layout
	

	
	
		
		

		
		
	


	





 /U.


----------



## ITZBITZ

It would be nice to make the LPF part of the board, maybe using the AD797 or something. In the datasheet, they show a layout for using it as an LPF/buffer for a DAC output. That could have some value to allow the customization of the line-out value and the function of the LPF. Analog has a applet to help calculate the part requirements when using this as an LPF/gain item.


----------



## 00940

AD797 requires too much voltage for this application (at least 10V) 
	

	
	
		
		

		
		
	


	




 That's why I thought of the AD823 at first.

 I'm really hesitating on this.


----------



## ITZBITZ

AD8620?


----------



## 00940

I don't think the AD8602 is comfortable with a single rail voltage input as the AD823 is. The good thing about the AD823 is that it would allow us to use the analog supply of the dac directly for the LPF too.


----------



## ITZBITZ

I gotcha. I can't see your schematic anymore so I wasn't sure how the supply was being setup.


----------



## ukram

Here is my USB DAC project:

http://hepso.dna.fi/misc/pcm2902/PCM2902_usb_dac.html

 It does not have output filter. I have been using this for a few months now. The sound is good enough for human ears in my opinion. It has 10 ohm resistor separating PC ground and analog output ground. It has line out only. I'm not sure if it can drive headphones. I'm using it with my LM3886 amp, HD280 headphones and Magnepans.


----------



## Jupiter

I've been looking at the schematic for the PCM2702 eval board. Anyone know what Q001 is for?

 Also, anyone seen a schematic for cleaning USB power?


 ukram,

 Why did you use the PCM2902? Did you want the option of digital output?


----------



## ITZBITZ

I'm actually thinking of working up a 2704/1794 combo for higher fidelity and a lower noise floor. Thoughts? The 2704 can to i2s into the 1794, and has some incredible specs.


----------



## 00940

I've done my homework.

 Here's a single sided pcb, analog and digital grounds connected. Power supply traces are 40mil, signal is 16 mil. Clearance is 8mil. Grid is 1 inch. I hadn't a correct layout for the inductor, so I used a cap layout. 










 ITZBITZ : well, if you're willing to use a main-powered unit, it looks like a good path.


----------



## ITZBITZ

The new board looks great! You've truly done your homework.

 So we'll tombstone the inductor in the corner? That's fine.

 Did I miss something, or are we down to a single voltage regulator? Or are we only regulating the power to the 2702 and letting the op-amps get whatever is thrown at them?

 I'm guessing a schematic/parts-list update is in order?


----------



## 00940

Quote:


 _Originally posted by ITZBITZ _
*I'm guessing a schematic/parts-list update is in order? 
	

	
	
		
		

		
			



* 
 

Indeed, more homework to do 
	

	
	
		
		

		
		
	


	




 This is the version without opamps. We still have 2 regulators, one for the digital section of the pcm2702 and one for the analog section.

 I'll probably try to design a version with the LPF even if I'm less and less sure it's worth the extra cost, consumption and size.


----------



## ITZBITZ

So is it down to just being a line output for an external amplifier at this point? That's cool. With this part, the LPF may be unnecessary. However, I'd be curious how the digital filter can be configured -- steep vs. slow roll-off.

 I need to read more datasheets but I'm too busy this week.

 Looks great though, nice work.


----------



## Wodgy

There is only one digital filter in the PCM2702; you can't configure it for smooth or steep roll-off (and there's no interface for an external digital filter).

 As for the analog LPF, have you considered compromising and implementing a passive LPF? You'd escape the the power consumption and op-amp choice issues.

 (As I've said before, I don't think leaving out the LPF is necessarily a bad choice, since the PCM2702 digital filter is good.)


----------



## Jupiter

Quote:


 _Originally posted by 00940 _
*Indeed, more homework to do 
	

	
	
		
		

		
		
	


	




 This is the version without opamps. We still have 2 regulators, one for the digital section of the pcm2702 and one for the analog section.

 I'll probably try to design a version with the LPF even if I'm less and less sure it's worth the extra cost, consumption and size. * 
 

I haven't placed an order with Percy yet, but I can delay that until the board is final if you prefer.


----------



## 00940

there's no problem jupiter. We need those back gate anyway 
	

	
	
		
		

		
		
	


	




 I'm discussing layout and ground loops on diyaudio. Here's a new layout making use of a second layer as ground plane (i just notice I left the led out, i've to add it again).


----------



## Jupiter

OK, I'll place the order this weekend.


----------



## Nisbeth

Looks nice and compact 00940 
	

	
	
		
		

		
		
	


	





 /U.


----------



## guzzler

thats looking lovely!

 jupiter: how did you get in touch with Michael Percy? I sent two emails a week ago requesting a quote and I've not had a reply yet??

 g


----------



## Jupiter

guzzler, 

 I've ordered from Percy previously, but I haven't been in contact with him lately. He does have a reputation of being slow.

 If you need a more reliable supplier, I would recommend partsconnexion. They're the most professional supplier targeting audio DIYers I've dealt with.

 What parts are you looking for?


----------



## Jupiter

00940 and Nisbeth,

 By the way, I noticed Percy has the AD823 (in DIP package).


----------



## ITZBITZ

Quote:


 _Originally posted by Jupiter _
*I've ordered from Percy previously, but I haven't been in contact with him lately. He does have a reputation of being slow.
* 
 

I ordered from Percy for the first time Monday and he shipped the same day. I paid through PayPal, if that matters.


----------



## guzzler

I'm getting quite a few Black Gates for my PPA and some Cardas solder. I'm sure he'll ship quickly, it's just he's not replied to my emails yet, so I can't confirm the price and I explicitly said I would be paying by PayPal... I'll give it a couple more days

 g


----------



## Jupiter

I'll let you know if I hear from Percy.

 I'm also getting Black Gates for my PPA. I think I'll try the super-e-caps configuration, but I'm not sure how that will work.


----------



## guzzler

the L-cancelling pair won't work on this board, you need two identical non-polar caps in parallel with the longest leads opposing each other which is supposed to make the ESR even lower, and lower the inductance (??) in the pair as well

 g


----------



## Jupiter

I was thinking BG NX 1000uf/25V for C1 (2 needed), BG N 33uf/16V for C4 (12 needed) and BG NX HiQ 0.47uf/50V for C2 and C5 (18 needed). Obviously, I will have to fit two caps where the PPA board only has room for one.

 EDIT: I started a new thread on Super-E caps so we can stay on topic here.


----------



## ukram

2902 has both D/A and A/D, which is nice for RMAA loopback testing.


----------



## jboehle

Any update on this?

 -Jason


----------



## 00940

yep.

 I've finished (i hope so) the last version of the board. I had to change the drill sizes, change the usb connector and some other little things. And to be honnest I didn't have much time the last weeks. I still have to update the partlist and the schematic.


----------



## Glassman

I've just received my PCM2706 to play with in a future.. I plan to use it with low jitter oscilator instead of simply conecting a crystal to it.. also I choosed PCM2706 becouse of it's I2S output..

 however, can those USB controllers work with Kernel Streaming? and does they support 24bit? I really need bit perfect output.. I will check that with it's S/PDIF out or even by connecting external S/PDIF transmitter..

 good luck 00940!


----------



## ITZBITZ

Looking forward to the boards (and soldering those TINY chips).

 Hopefully my ETS tip will be here by that time.

 Once you get the chance, please post the latest schematic, PCB and parts list along with an ETA from the board manufacturer.

 Regards,

 Chris


----------



## Scoops

I can't wait... having an on-board USB dac in my tube amp will RULE!


----------



## jboehle

EDIT: Wow I'm stupid I've been pondering getting the Sonica too long and for some reason posted a dumb question like this wasn't a DAC but instead just a USB->digital out device, which it isn't. DOH! Sorry for wasting your time! 
	

	
	
		
		

		
			





 -Jason


----------



## Scoops

output of a digital to analog conversion perfect? I doubt it, but at least it will be better than what i usually get out of a soundblaster and is available as a seperate sound output in the computer system.

 I've been a musician for a really long time, and never remember thinking "man, i wish this were bit-perfect"

 it's all part of the experience.


----------



## aos

Kernel streaming doesn't seem to work with Sonica but its digital output looks very good to me, even in 24/96.

 I've also ordered some boards with PCM2705, to use as s/pdif source. I'm really interested to hear how it sounds.


----------



## ITZBITZ

I use KS with my Sonica with the 1205 drivers. Works fine and is bit-perfect trying to play DTS tracks to my HT amplifier.


----------



## aos

what are 1205 drivers? Just the latest from M-Audio or something 3rd party? I must admit that I haven't updated my drivers at all.


----------



## ITZBITZ

http://www.m-audio.com/images/global/drivers/

 Sort down the list and you'll see the Sonica_12xx_web.exe driver sets. Just pick the 1205 version. Be sure to completely uninstall the previous version and disconnect the Sonica first before installing the new drivers and subsequently connecting the Sonica.


----------



## Wodgy

AOS, you should download the 1.2.05 drivers even if you're using _more recent drivers_ (e.g. 1.2.20). It seems counter-intuitive, but the digital output from the 1.2.20 drivers is not clean. You can test this out by attempting to play back a PCM encoded DTS file into a home theatre receiver; on Windows XP with the 1.2.20 drivers, a few of the least significant bits get mangled, and you'll hear static rather than music, because the receiver can no longer decode the bitstream. This doesn't happen with the 1.2.05 drivers, which is why everyone recommends them.


----------



## 00940

Here we are :

*Schematic : *







*Silkscreen :*







*Top/pads (+ parts outline) :*







*Bottom (+ parts outline) : *






 A few comments on the parts.

 Chips on board : max1722, dc-dc booster from Maxim, REG102 (5V and 3.3V), low dropout regulator from TI, PCM2702, USB DAC from TI.

 Capacitors : C1, C2 are 10uF tantalum. C3, C9 are Pana FC, 1000uF/6.3V. C6, C12 are Pana FC 100uF/6.3V. C15, C16 are ceramic, 32pF. All the other caps are wima mks-02 100nF. 220nF would fit.

 Grid is 1cm. The board is about 3cm/6cm (1.2"/2.4").


----------



## guzzler

looks fantastic!! i'm definately still in for mine 
	

	
	
		
		

		
		
	


	




 g


----------



## ITZBITZ

Looks great, can't wait to get the finished product!


----------



## Nisbeth

Looks great! 
	

	
	
		
		

		
			






 /U.


----------



## guzzler

just a couple of quick questions:

 1. what's the diameter of each the electrolytic caps??

 2. how much space is available around the inductor for the dc-dc supply?

_edit: damn, TI are out of the PCM2702 and will be for another month! oh well 
	

	
	
		
		

		
		
	


	


_

 cheers,

 g


----------



## 00940

Quote:


 _Originally posted by guzzler _
 1. what's the diameter of each the electrolytic caps?? 
 

Pana 100uF/6.3V are 5mm in diametre, Pana 1000uF/6.3V are 10mm and the BG 47uF/6.3V are 6mm. 

  Quote:


 2. how much space is available around the inductor for the dc-dc supply? 
 

I plan to use an axial inductor, it's 4mm wide. There's more than enough space to put it vertically. Something a bit wider could fit.

  Quote:


 edit: damn, TI are out of the PCM2702 and will be for another month! oh well 
	

	
	
		
		

		
		
	


	



 






 I'm not in hurry myself but it's certainly boring.

 I can upload the *.brd file if anyone is interested.


----------



## 00940

here is the *.brd.


----------



## aos

Has anybody finished theirs? I made one with PCM2705 last week, and hooked it up to another DAC via its digital out. It works, and the cool thing is that you just plug it into USB and it is ready to play music in 10 seconds (that's first time, after that it's even faster). But there are some ground loop issues to be aware of. Unfortunately I think I burned the chip out trying to experiment as I connected the thing to 12V and those small regulators can only take 6-7. Other big chips survived but PCM2705 is toast. So I can't report much back as I wasn't able to do any meaningful measurements due to ground loop. It seems that most of PCM270x are out of stock with very long lead times, unfortunately.

pic 1
pic 2


----------



## guzzler

i don't think 00940 has the boards made up yet, but I'm looking forward to making mine!

*edit:* In off the red: TI shipped my PCM2702 today, should arrive sometime next week along with the regulators 
	

	
	
		
		

		
		
	


	




 g


----------



## andrzejpw

sent you a pm regarding the boards.
 Can you also use this guy as a standalone dac, with coax in?


----------



## 00940

it's my fault, mea culpa, mea magnissima culpa 
	

	
	
		
		

		
		
	


	




 I asked a quote from Olimex (actually 3 times) with my hotmail mail account and I just realized today that they don't accept such free webmails. I sent them a new quote using my provider webmail. It's eastern time though.

 Really sorry about that. I'll let you know in the middle of next week the result and we'll finalize the order.

 There's however always a good point in problems : the *.brd I posted earlier had a mistake. I saw that this morning too when checking the board once again before sending the quote. The ground and +5VDC were inversed at the bottom right.

 Guzzler : PCM2702 are back in stock ? The TI website still says "call". 

 Andrzejpw : no, there's no coax in. You would have to use the pcm2902 to get both coax and usb in.


----------



## guzzler

i put 2 into my Samples account with TI about a month and a half ago, and they've stayed in there, so I don't know if it's a back ordering type thing. I've ordered 2 of the PCM2702 and the REGs, so if anyone's stuck for a set, I'll ship them out to you for nothing

 g


----------



## nleahcim

any updates? *taps foot impatiently*


----------



## was ist los?

Any one want to start a group order for the boards of one of these puppies?


----------



## nleahcim

Quote:


  Originally Posted by *was ist los?* 
_Any one want to start a group order for the boards of one of these puppies?_

 

I'd be interested probably.

 So has one been built yet? How big is it exactly? Wouldn't it be possible to replace alot of the discretes with smt components? Does anyone know it's power consumption yet? And also - how sensitive would it be to being near other computer components? Reason I ask is that I have a single board computer that I'm in the process of turning into an MP3 jukebox and it's audio output is simply horrid - so I need to find a very small replacement for it's built in sound card.


----------



## guzzler

No one's built one yet, as no boards have been made up. Have patience, although 00940 was only going to make 12 boards, if there's more interest, i might be willing with 00940's permission to get some more made up, but bear in mind this is NOT a simple DIY project: the SSOP chip is an absolute nightmare to solder. As for replacing the passives with SMD parts, it might be possible but you wouldn't save much space, as most of the board space is taken up with electrolytic caps, and for good ones you have to go through-hole. The board is only 3cm x 6cm and powered by two NiMH cells, so it's not as if it's huge! Power consumption will be dictated by the PCM2702, with the 3 power supply chips drawing a small amount as well. Current draw for the digital section is 22mA, while the analog section takes 18mA, for combined 40mA for the PCM2702, so call the total draw 45mA or so. With 2000mAh batteries like I was going to use, this gives just over 44hrs of use from a single charge. I've also made up a charger based on the MAX712 as well, so there's no need to open the case at all. Placing it inside a metal box connected to ground will give more than adequate protection from RFI

 g


----------



## nleahcim

Quote:


  Originally Posted by *guzzler* 
_No one's built one yet, as no boards have been made up. Have patience, although 00940 was only going to make 12 boards, if there's more interest, i might be willing with 00940's permission to get some more made up, but bear in mind this is NOT a simple DIY project: the SSOP chip is an absolute nightmare to solder. As for replacing the passives with SMD parts, it might be possible but you wouldn't save much space, as most of the board space is taken up with electrolytic caps, and for good ones you have to go through-hole. The board is only 3cm x 6cm and powered by two NiMH cells, so it's not as if it's huge! Power consumption will be dictated by the PCM2702, with the 3 power supply chips drawing a small amount as well. Current draw for the digital section is 22mA, while the analog section takes 18mA, for combined 40mA for the PCM2702, so call the total draw 45mA or so. With 2000mAh batteries like I was going to use, this gives just over 44hrs of use from a single charge. I've also made up a charger based on the MAX712 as well, so there's no need to open the case at all. Placing it inside a metal box connected to ground will give more than adequate protection from RFI

 g_

 

Wait I guess I didn't look carefully enough at the schematic - so it isn't powered by the USB port? The SBC that I would like to put it in *only* has a 5V power supply - and I wouldn't want to run this off of batteries...


----------



## ITZBITZ

This doesn't use the "dirty" USB 5V power source at all. However, the regular chip I think would allow it if you air-wired it. You just would not get as good a signal quality.

 I'm not sure though, check with the maker.


----------



## nleahcim

Quote:


  Originally Posted by *ITZBITZ* 
_This doesn't use the "dirty" USB 5V power source at all. However, the regular chip I think would allow it if you air-wired it. You just would not get as good a signal quality.

 I'm not sure though, check with the maker._

 

Why not just clean up the supply a bit? I mean it seems very impractical to be using batteries when you have a power source available...


----------



## guzzler

please read all the thread, most of what you've asked has been brought up already. Anyways, it takes a lot more effort and space to regulate and clean the 5V from the USB than to use a simple, super clean battery supply. You'd have to wire in 5V lines directly to the regulators, missing out the switching supply and you'd also have grounding issues. So, if that's the main concern, this isn't the board for you

 g


----------



## guzzler

okay all, here's the deal. 00940 is busy with other things right now, so I've slightly redone the board to correct the error in version 7 and tidy things up a little. 

 Beware, R3 (the oscillator controller resistor) has been replaced with a 0805 SMD resistor. If these ever get produced, I'll supply this piece to builders 
 with the boards. 

 Holes added to the top corners for mounting into a case

 I've also designed a small MAX712 based battery charger for the NiMH batteries we were going to use, more to follow on that

 Schematics are as before, but here's the lastest version I've made up. I'll give someone a sweetie if they can find any mistakes in it. I'm fairly sure it's bullet proof, but please concentrate on the grounding of capacitors around the PCM2702. 

 In a couple of weeks time (hopefully), I'll get a small prototype run made up and ship out a couple to some of you guys (I'll choose who and will be in touch, don't ask please). If there's no probs after that, we can swing into production.

 Anyways, here's the interesting side:







 And the ground plane side:






 peace

 g


----------



## ITZBITZ

I was just going to ask what the status was on this project and you beat me to it. Glad to see you picking it up, I think it's going to be a slick little part and a great alternative to the Sonica.

 Regards,

 Chris


----------



## Nisbeth

Whoa, nice to see this thread kicked back to life. Great job on the board gus, keep us posted on progress 
	

	
	
		
		

		
		
	


	





 /U.

 PS: I'm sweating over my final project which is due on Tuesday, so I'm too tired to look for mistakes in the layout


----------



## guzzler

Here's the battery charging board. I'm very sorry, but I got carried away with Eagle3D 
	

	
	
		
		

		
		
	


	




 it's absolutely great!











 Power comes into the single jumper on the right, and the battery and load connect on to the double on the left. The top layer is extended to help dissipate some heat from the PNP pass transistor. With 2 cells and 6V supply, that dissipates about 6W so that extra copper is essential. With around 1A charging current, I decided to parallel the protection diodes as you can see. The current sense resistor is a 2512 package resistor which you can see on the bottom left, unfortunatly Eagle3D doesn't have them in it's libary. The electrolytics I want there are 10uF 16V Sanyo OS-CONs, but any cap with 2.5mm pitch and 6mm diameter will do fine. Picture the small yellow cap on the left of the board to be a WIMA MKS-02 and you're there 
	

	
	
		
		

		
		
	


	




 For schematic, see the MAX712 datasheet, it's the typical usage schematic

*PLEASE NOTE:* This board is *only* for 2 cells. If I find time, I might make it so you can change the number, it's only a matter of putting some jumpers in, but the MAX712 is the most obtuse chip in the world, it's so badly arranged. The BATT- and BATT+ pins are the prime example, opposite sides of the bloomin' DIP!!

 g


----------



## Nisbeth

Absolutely fantastic! 
	

	
	
		
		

		
		
	


	











 /U.

 EDIT: Whoa, I made 500+


----------



## guzzler

Quote:


  Originally Posted by *Nisbeth* 
_Absolutely fantastic! 
	

	
	
		
		

		
		
	


	









 EDIT: Whoa, I made 500+ 
	

	
	
		
		

		
		
	


	


_

 

 Congrats, and it gets better. Sorted out POV-ray (funny variable, 704 instead of 8 
	

	
	
		
		

		
		
	


	




) and we have the DAC:

 Top (note size of SSOP chip, tiny!):






 Side (notice in particular, MAX1722 at top left, it's small! 0805 resistor just to the right of the oscillator):






 The two yellow "ceramics" at the top left are really tantalums, all electrolytics are Panny FCs apart from the output coupling caps which I've left space for Black Gates. The inductor on the top left is missing, as is the USB connector on the bottom left). The two SO8 chips you can just see at the top are the REG102 voltage regulators!

 BOOM, time for bed 
	

	
	
		
		

		
		
	


	




 g


----------



## nleahcim

Quote:


  Originally Posted by *guzzler* 
_Congrats, and it gets better. Sorted out POV-ray (funny variable, 704 instead of 8 
	

	
	
		
		

		
		
	


	




) and we have the DAC:

 Top (note size of SSOP chip, tiny!):






 Side (notice in particular, MAX1722 at top left, it's small! 0805 resistor just to the right of the oscillator):






 The two yellow "ceramics" at the top left are really tantalums, all electrolytics are Panny FCs apart from the output coupling caps which I've left space for Black Gates. The inductor on the top left is missing, as is the USB connector on the bottom left). The two SO8 chips you can just see at the top are the REG102 voltage regulators!

 BOOM, time for bed 
	

	
	
		
		

		
		
	


	




 g_

 


 Looks very nice! Is there any reason the crystal is so large? Is there any benefit to ones of that size? Also am I the only one bothered by the size of the USB connector? To me it seems like it's a waste of space... With the rest of the board being so small - it would seem more logical to me at least to use one of those mini-usb connectors you usee on alot of MP3 players and an occasional laptop.

 Now as soon as I can figure out how to run this off of a USB power supply (with a *fairly* clean power supply) I'll be making one of these. Since it will be internal in a SBC system - I'm going to do away altogether with the USB connector - probably put in a really small proprietary smt connector or something.

 Now for my super newbish question (I think it is probalby fairly obvious that I know nothing about audio) - could the output from this be used as an input to a stereo system? Or would it not be powerful enough?


----------



## AdamZuf

come on, finish the god damn thing so i could get one!


----------



## was ist los?

I'd like to make a request on the board. How about putting in pads to let us wire in our own PS or wallwart.


----------



## guzzler

good day all.

 Oscillator - standard HC49 package, you'll easily get one that size. As for the height, that was just an arbitary value, you get them as small as 3mm height.

 Pads for the power supply - USB supplies 5V, so you'll have to bypass the first regulator for that and power direct for USB and leave the 3.3V regulator in place. I'll see what I can do on the supply pin front and get back to you. The only problem I see with using your own supply is that you need both 5V and 3.3V, and the battery life will be pretty good anyway using 1800mAh NiMHs, plus the charger board means you don't need to open it

 USB size - again, it's a standard design, and you can use normal USB-B cables, without resorting to proprietary things. It also leaves space for the switching supply just above it

 g


----------



## ITZBITZ

Has the parts list been updated yet? I have most of the IC parts in multiples, I just need to make sure I've got all the caps, resistors, etc. I was about to place an order with Percy for some other items so I thought I would double check at least about the black gates since those are hard to find at DigiKey/Mouser.

 Keep up the good work, the 3D board views are just sweet, FYI.


----------



## guzzler

been thinking about the alternative power supply question, there isn't any need for additional pads for supplies >5V. There are points you can connect straight into, for example, if you don't use the switching supply, >5.1V can be connected to the right hand end of R2 or the bottom of C2. If you have a 5V supply, I've put a pad in (+ALT) for wiring that straight in, but leaving the 3.3V regulator in place. By doing that, you bypass everything behind the 5V regulator.

 ITZ, I'll try and get a bill of materials together tonight after I've got some work done. Not any huge changes really, I'll provide dimensions as of packages as well so you can substitute, ala tangents site.

 btw, re the size of the reg, I looked at some watch crystals, they were only available in 32KHz, the one there is 12MHz. SMD crystals are just the HC49 package, but with SMD pads instead of through hole pins.

 will keep you posted

 g


----------



## ITZBITZ

Quote:


  Originally Posted by *guzzler* 
_been thinking about the alternative power supply question, there isn't any need for additional pads for supplies >5V. There are points you can connect straight into, for example, if you don't use the switching supply, >5.1V can be connected to the right hand end of R2 or the bottom of C2._

 

NOTE: The regulators can only handle a MAX of 16V, safely I wouldn't go over 12V. So don't plan on powering this from the same supply as a large amplifier without an external regulator to drop down the power first.


----------



## 00940

I've to address my thanks to Guzzler who took the relay for this projects and my apologies to the others for letting you so long without any news. I was rather busy those last weeks. Hopefully it will get better. That's my first post in here since about a month. As you can see, it's possible to fight Headfi's addiction 
	

	
	
		
		

		
			





 Guzzler, the boards looks great but I'm wondering if the film caps are not too close from each other. I'm affraid that you could get some capacitive coupling there, having all the // caps acting as one. I made a quick check of the boards and everything looks fine. The charger board is definitely cute


----------



## guzzler

good to hear from you 00940! I'll take that into account in the next revision of the board, they are absolutely packed together there, so yes it is possible they'll couple. Maybe add 4mm or so to the total board length. I've spent a wee bit of time changing the width of the traces on the SSOP, they were a bit big before, and so could have led to briding between pins unless VERY careful. Also added the +ALT pad in. I'll get round to seperating the caps sometime tomorrow hopefully.

 Meant to answer the question before, it is a line level output

 Parts list:

http://www.mellowparenting.demon.co....er/usbdac.html

 g


----------



## 00940

Another thing I forgot. I was adviced to put 330K resistors at the output (from signal to ground), to minimize thump at turn on. This can be easily achieved by putting the resistors right onto the rca or the minijack. No need to modify the board for that.


----------



## guzzler

okay, got bored of maths so did a bit on the board. Spaced out the caps a little, to about the same as the original board, only added 1mm to the length of the board which was satisfying! I've managed to squeeze in a couple of 0805 resistors from the outputs to ground so no need for hanging resistors. Here's the lastest board:






 note the pad just above the 5V regulator, that's +ALT for direct 5V input, the 2 0805 resistors on the bottom left, and the neater traces around the PCM2702. It's also a 3mm high oscillator, just to give an idea of the scale

 g


----------



## Nisbeth

Quote:


  Originally Posted by *ITZBITZ* 
_NOTE: The regulators can only handle a MAX of 16V, safely I wouldn't go over 12V. So don't plan on powering this from the same supply as a large amplifier without an external regulator to drop down the power first._

 

Easily solved with a 78L09 and two film caps on a piece of veroboard or stripboard. You can solder it directly on to the DC-jack 
	

	
	
		
		

		
		
	


	





 /U.


----------



## doobooloo

I've been following up with this project for a while - any updates? 
	

	
	
		
		

		
		
	


	










 Thanks!


----------



## guzzler

i've put the order in for 25 of the boards. I've checked and double checked them, but I'm going to build one myself, along with two other guys. If all goes well, and it should, then I'll sell off the rest of those boards. Cosmetically, they say "BETA-1" on the bottom side, but they'll be the same board so that's not a problem. It was going to be VERY expensive to order just 5 boards for prototyping, so I just went with 25. Currently, it's looking likely to be around $10-12 for each board, probably a wee bit less

 g


----------



## guzzler

meant to add, timescale is probably about 1 month until I start selling them assuming that everything is okay; the expected ship out date is the 8th of June, then say a week to reach me, and then a while to build them up

 g


----------



## taylor

How do you plan on soldering the SSOP-28 chips on?


----------



## guzzler

Quote:


  Originally Posted by *taylor* 
_How do you plan on soldering the SSOP-28 chips on?_

 

steady hands and plenty of flux! or the toaster method, if anyone's feeling up to it...

 couple of notes: the bottom resistor on the board (Vbus on the PCM2702) is jumpered as the layout stands. This is consistant with the typical usage schematic in the datasheet, but in conflict with the evaluation board, which populates it with a 22R a resistor. I can't say which is better, but when the boards are made, if you want to put a resistor in there, you'll have to cut the trace on TOP of the board. This was an oversight on my part; I should have left it open and allowed people to jumper if they want, but that's the way it is. If there is interest past the first 25, I'll fix that.

 More importantly, you should try and get hold of the PCM2702 now, as most suppliers, and TI themselves are back ordered. If you order now, it should arrive at approximately the right time. There're no problems getting hold of the REG102s, DigiKey stocks those. The MAX1722 appears to be harder to get hold of, if anyone knows a stockist of those, please let us know.

 g


----------



## was ist los?

I got my PCM2702s already!


----------



## taylor

i'm considering picking up a 2704 to make myself a SPDIF transport with built in DAC (Until i can get a standalone DAC). Is the DAC comparable to the 2702?


----------



## guzzler

it's outwardly similar, it uses the same architecture and digital sections (SpAct) and it's the same family of chips, so it should sound similar. The pin-out is different however, so this board won't take that chip. I can put you down for one of these boards as well, as the planned original run as been extended so there'll be more for sale.

 g


----------



## taylor

Would the board be easy to modify to add a SPDIF output?


----------



## ITZBITZ

If you want an S/PDIF output, but a Hi-Fi Link ($49US). It's cheaper and it has both coaxial and optical outputs.

 This board will easily cost $70-$100 to build, so it's not feasible if all you want is a digital output.


----------



## guzzler

Quote:


  Originally Posted by *taylor* 
_Would the board be easy to modify to add a SPDIF output?_

 

 no, it would be impossible. The output of the PCM2702 is purely analog. The PCM2704 will give you digital output, but you're on your own in that case

 g


----------



## taylor

Ok, thanks for the advice guys.


----------



## nleahcim

Quote:


  Originally Posted by *taylor* 
_How do you plan on soldering the SSOP-28 chips on?_

 

One technique I'm rather fond of is to simply cover one side of the chip with solder - then take off all the excess with solder wick. Works like a charm. I've soldered some very nasty looking chips with this method all with 100% success.


----------



## was ist los?

I use the same technique as nleahcim.


----------



## Glassman

that's pretty good idea I'd say, I should try it next time I'll be soldering some SSOP..


----------



## taylor

Thanks for the good tip.


----------



## aos

That does work well. Even better if you use some flux beforehand.


----------



## 00940

PCM2702 will ship again as samples the 7th of July. This for those not able to get them easily by another way.


----------



## ITZBITZ

We're also looking at putting together a parts bag for most of the small stuff to lower the cost and reduce the number of parts sources for people wanting to build the DAC. So far, it looks like we'll be able to have everything except the chips available to ship with the boards. That way, you only have to get the chips (via your preferred method, see above) and a suitable case. All the resistors, caps, crystal, header strip, battery plug, etc. would all be included at a pretty low cost too since we can get the 50+ discount on most of the items.


----------



## guzzler

I updated the parts list a couple of days ago for those interested:

http://www.mellowparenting.demon.co....er/usbdac.html

 As Itz said, we've been looking at parts bags, and the more I think about it the more it makes sense:

Stops 25 x shipping costs (at least, each board needs components from 2/3 different US suppliers)
Avoids part incompatability
Take advantage of pretty decent discounts over single prices: who wants to buy or sell *1* SMD resistor?
As things stand, the boards will cost £5.75 each without components, plus a little (60p or so) for shipping... The boards will arrive very soon, and I'll let people take a look at them when I get them...

 stay tuned...

 g


----------



## guzzler

I stumbled across this:

http://www.qbik.ch/usb/devices/showdr.php?id=69

*seems* to be Linux drivers for the PCM2702 which appears to be included in the kernel, so hopefully it's supported by default. Well, the more the merrier 
	

	
	
		
		

		
		
	


	




 g


----------



## guzzler

Okay folks, I got the boards today, and I just had to build one 
	

	
	
		
		

		
		
	


	




 well, to my delight it worked first time, on the computer at least. I've still got to get my Black Gates for the output coupling stages so it might not have produced any sounds, but it popped up straight away in WinXP so initial impressions are good! The board is actually smaller than I realised, took me about an hour to populate it after I found my snips (under a pile a paper). Bad news is my camera ran out of battery and is charging just now, and the only shot I could get was this rather blurred photo:






 for size comparison, that's a Siemens c45 phone, and that is a normal size Control key on a keyboard, so this thing is small. In fact it is even smaller than I anticipated..

 so folks, give us a week or two to verify the analog out and then I'll ship these out.

 Thanks to: 00940 (obviously), Nisbeth and ITZBITZ for agreeing to test the boards

 g


----------



## Nisbeth

Fantastic! 
	

	
	
		
		

		
		
	


	




 Any trouble soldering the PCM2702?


 /U.


----------



## 00940

Great news !

 Was it battery powered ?


----------



## guzzler

Quote:


  Originally Posted by *Nisbeth* 
_Any trouble soldering the PCM2702?_

 

 none at all, I bought some 28awg SMD solder, but didn't need it: used 21awg Cardas silver solder excessively then used a desoldering pump to take off the excess. Same as the solder wick technique, but I've never been any good at using desoldering braid. The worst bit was lining the little legs up on the right pads.

 The boards are very nicely made, I was recommended the manufacturer by aos and I can only say it was a good recommendation!

*edit:* yep, battery powered, a steady 5.00V from the first regulator. Didn't want to prod around too much with the multimeter to measure the switching output with big prongs, will do that soon though. I assume the 3.3V output was good as the PCM2702 powered up fine

 g


----------



## doobooloo

I _think_ I posted earlier requesting a set or two but I am not too sure; in case I didn't, is it too late to lay my hands on a few of these boards?

 Thanks!


----------



## guzzler

Quote:


  Originally Posted by *doobooloo* 
_I think I posted earlier requesting a set or two but I am not too sure; in case I didn't, is it too late to lay my hands on a few of these boards?

 Thanks!_

 

not at all, the more the merrier 
	

	
	
		
		

		
			





 we'll *probably* be sorting out parts kits minus the semiconductors, and a couple of other things as well.

 Did some more measurements, output from switcher is 5.47V, 5V = 5.00V, 3.3V = 3.28V so everything is good on the power side of things

 g


----------



## hashman

I am sorry if it is too late for me to ask for a board as well. I've been oogling this project for a while and was too lazy to register at head-fi. if possible please count me in for at least one.

 hashman


----------



## AdamZuf

why didn't anyone ask how it sounds


----------



## ITZBITZ

I believe that gz is waiting on the coupling caps before hooking it up to an amplifier.


----------



## AdamZuf

how about making another version of the board so we'll have a coaxial output? it is quite a useful thing to have.. i think that the Xitel can't transmit 44.1khz.


----------



## ITZBITZ

Quote:


  Originally Posted by *AdamZuf* 
_how about making another version of the board so we'll have a coaxial output? it is quite a useful thing to have.. i think that the Xitel can't transmit 44.1khz._

 

The part used in this project does not have a digital output. There are a number of designs that use the 2902, a part that has S/PDIF output.


----------



## AdamZuf

Quote:


  Originally Posted by *ITZBITZ* 
_The part used in this project does not have a digital output. There are a number of designs that use the 2902, a part that has S/PDIF output._

 

is anyone working on these designs ATM?


----------



## 00940

adamzuf : http://hepso.dna.fi/misc/pcm2902/PCM2902_usb_dac.html


----------



## guzzler

we've got the parts mixed up here folks... the PCM*2702* is what this board uses, it's the PCM*2704* has the S/PDIF output. I'll put together a layout based on that if folk want to see one, I won't be getting any made though

 g


----------



## ITZBITZ

More Pictures


----------



## ITZBITZ

Voltage test: 5V reg = 4.98, 3.3V = 2.99, output from Maxim IC: 5.51

 Connected to USB powered from 3x1.5V AAA batteries (what I had on-hand)

 Recognized by Windows XP, no drivers needed, sound device added. Setup Foobar to point to it, adjusted volume with control panel to max output level (no attenuation at the DAC). I guess I didn't fry the 2702. 
	

	
	
		
		

		
		
	


	




 Connected to PPA (the big-un') -> DT880

 Music comes out. Need to spend some time listening, but initial results seem favorable.


----------



## 00940

Quote:


  Originally Posted by *ITZBITZ* 
_Voltage test: 5V reg = 4.98, 3.3V = 2.99, output from Maxim IC: 5.51_

 

5.51 is a bit high, the regulator needs only 200mV to drop. Something along the line of 5.2 would be better and would save some battery life. It's just a matter of tweaking a bit the value of a resistor.


----------



## guzzler

looking good ITZ, still haven't got my coupling caps yet, I'll get onto the HiFi Collective about it, but I'm glad it works!

 I've finally worked out how to make it bus powered with a decent quality of supply, and (as always) it's so simple: jumper from a pad on R7 (which is otherwise unused) to the +ve side of the BATT connector. That way the 5V USB power gets stepped up by the switcher then regulated at 5 and 3.3V levels to provide a reasonably clean power source, though probably still not as good as batteries!

 g


----------



## ITZBITZ

Quote:


  Originally Posted by *guzzler* 
_I've finally worked out how to make it bus powered with a decent quality of supply, and (as always) it's so simple: jumper from a pad on R7 (which is otherwise unused) to the +ve side of the BATT connector. That way the 5V USB power gets stepped up by the switcher then regulated at 5 and 3.3V levels to provide a reasonably clean power source, though probably still not as good as batteries!_

 

I'll make a jumper that plugs into the battery connector tonight to see how it works out and report back. Right now, the background is dead silent on my PC that generates audible hum when using the Sonica. The Sonica picks up noise from the power supply on this really crap Dell at work. At home the Sonica is quiet so my high-end supply at home seems to be filtered better. So this will be a good test for me to try out as I have a very dirty PC to check it out on.


----------



## 00940

TI reported the arrival of new PCM2702 from July 7th to Aug 2nd. 
	

	
	
		
		

		
			





 I won't get mine soon


----------



## momerath

Quote:


  Originally Posted by *ITZBITZ* 
_If you want an S/PDIF output, but a Hi-Fi Link ($49US). It's cheaper and it has both coaxial and optical outputs.

 This board will easily cost $70-$100 to build, so it's not feasible if all you want is a digital output._

 

I've read several different places that the xitel Hi-Fi Link is only capable of outputting at 48K. Do you know differently or have a suggested product that doesnt resample. (and has linux drivers/supports standard usb audio)


----------



## PinkFloyd

Sorry.......... talking ***** hence edit.


----------



## guzzler

Here's a revised power plan for the DAC, remember the USB supply is as yet untested!






 R1, D1 and LM317 form a CCS to charge the battery. S1 is a DPDT switch that cuts power to the DAC on the right, and connects the battery to the DC supply on the left. The LED just confirms that DC is present. D1 prevents any back current if DC isn't connected, don't know if it's true but better safe than sorry. D1 is a 1N400x or equivalent. I recommend a charge rate of ~100mA to prevent overcharging. You could, of course, implement a charger with a controller chip on it, like the PPA board for example.

 S2 selects between battery power or USB. It should be an SPDT switch. D2 prevents a situation where DC is connected and the device is powered from USB, so no current flows TO the USB connector from DC.

 g


----------



## ITZBITZ

As mentioned by guzzler, I'm going to be handling the US distribution of the boards and parts. 

 The boards will be sold as a kit with everything except for the IC's included. A detail of all the parts is shown below. Estimated cost of the boards and parts is pending a final total from guzzler, but I'm guessing that it is going to be close to $30 (plus shipping).

 If you are interested, send me an e-mail (chris (at) campcreations (dot) com) so I can get your information on the list. First serve comes to those on the thread that expressed initial interest. To verify your identity, send me e-mail via head-fi so I can add your username to the list.

 All kits will be shipped USPS priority mail ($3.85) unless other arrangements are necessary.

 The US kit I'll be delivering includes all the following items:

 1USB DAC Board
 1Vishay/Dale 100K
 1Vishay/Dale 330K
 1SMD 0805 1M
 1Vishay/Dale 1.5K
 1Vishay/Dale 22.1
 2SMD 0805 MF 330K
 2Tant 10uF 10V
 21000uF Panasonic FC
 2NP0 ceramics 32pF
 8WIMA MKS-02 100nF
 2Sanyo OS-CON
 2Black Gate 47uF
 1Crystal Pad
 1C&D Radial 10uH
 1Crystal 12.0 MHz 32pF
 1Berg 61729
 1Molex KK 2-pin header
 2Molex KK pins
 1Molex KK 2-pin plug

 YOU WILL NEED to obtain your own PCM2702E, regulators and DC convertor.

 These are all the parts I used to build the prototype board and everything fit nicely and worked perfectly.

 Regards,

 Chris


----------



## Kenny12

hm.. intresting are there any australian distrobuters?

 also does this bypass the sound card? so you would just connect to pc and make it work?


----------



## guzzler

Quote:


  Originally Posted by *Kenny12* 
_hm.. intresting are there any australian distrobuters?

 also does this bypass the sound card? so you would just connect to pc and make it work?_

 

 no one in Australia, but I'd be happy to ship a board to you, minus the kit parts unless ITZBITZ can do them for you.

 It's plug and play in Win2K and WinXP, and comes up as a seperate sound device so you can A/B between your sound card and the USB device just in software. I'm interested to see if it works in Linux, as I saw it mentioned that were drivers for the PCM2702 in the kernel, but you need to move them from USB to Audio or something

 g


----------



## nleahcim

Quote:


  Originally Posted by *ITZBITZ* 
_As mentioned by guzzler, I'm going to be handling the US distribution of the boards and parts. 

 The boards will be sold as a kit with everything except for the IC's included. A detail of all the parts is shown below. Estimated cost of the boards and parts is pending a final total from guzzler, but I'm guessing that it is going to be close to $30 (plus shipping).

 If you are interested, send me an e-mail (chris (at) campcreations (dot) com) so I can get your information on the list. First serve comes to those on the thread that expressed initial interest. To verify your identity, send me e-mail via head-fi so I can add your username to the list.

 All kits will be shipped USPS priority mail ($3.85) unless other arrangements are necessary.

 The US kit I'll be delivering includes all the following items:

 1USB DAC Board
 1Vishay/Dale 100K
 1Vishay/Dale 330K
 1SMD 0805 1M
 1Vishay/Dale 1.5K
 1Vishay/Dale 22.1
 2SMD 0805 MF 330K
 2Tant 10uF 10V
 21000uF Panasonic FC
 2NP0 ceramics 32pF
 8WIMA MKS-02 100nF
 2Sanyo OS-CON
 2Black Gate 47uF
 1Crystal Pad
 1C&D Radial 10uH
 1Crystal 12.0 MHz 32pF
 1Berg 61729
 1Molex KK 2-pin header
 2Molex KK pins
 1Molex KK 2-pin plug

 YOU WILL NEED to obtain your own PCM2702E, regulators and DC convertor.

 These are all the parts I used to build the prototype board and everything fit nicely and worked perfectly.

 Regards,

 Chris_

 

I would pick one up *if* it runs entirely off of USB power.


----------



## guzzler

ITZ tried it off the USB supply, and whilst it does work it raises the noise floor to unacceptable levels, as I suggested earlier in the thread. Please, again, read the updates to the thread. You could run a trickle charger off the USB supply to a couple of AA/AAA batteries very easily if that would make you happier...

 g


----------



## nleahcim

Quote:


  Originally Posted by *guzzler* 
_ITZ tried it off the USB supply, and whilst it does work it raises the noise floor to unacceptable levels, as I suggested earlier in the thread. Please, again, read the updates to the thread. You could run a trickle charger off the USB supply to a couple of AA/AAA batteries very easily if that would make you happier...

 g_

 

Oh I looked at your picture that said something about the USB supply being untested - and so I assumed someone had figured something out. My problem is not so much the use of batteries - it's the size of them. I need something that is ridiculously small. The board alone is pushing my limits.

 BTW - would this circuit be able to act as a line out as well as a headphone amp?


----------



## guzzler

there isn't a headphone amp on board, the output is only line level. This is, AFAIK, the smallest USB DAC you'll find easily, and as such you'll have to either compromise on quality, or compromise on your design to fit batteries into place, after all 2xAAA batteries is not taking up much space

 g


----------



## nleahcim

Quote:


  Originally Posted by *guzzler* 
_there isn't a headphone amp on board, the output is only line level. This is, AFAIK, the smallest USB DAC you'll find easily, and as such you'll have to either compromise on quality, or compromise on your design to fit batteries into place, after all 2xAAA batteries is not taking up much space

 g_

 

Wow - I seriously suck at reading. 
	

	
	
		
		

		
		
	


	




 So this could drive the line in of a stereo system, or of amplified speakers?


----------



## guzzler

Quote:


  Originally Posted by *nleahcim* 
_Wow - I seriously suck at reading. 
	

	
	
		
		

		
		
	


	




 So this could drive the line in of a stereo system, or of amplified speakers?_

 

yes


----------



## Wodgy

Can anyone post RMAA measurements of this project?


----------



## ITZBITZ

My EMU-1212m should be here in a week, I'll create some measurements at that time and post them.


----------



## Kenny12

on the site it says 

 To power from USB: jumper from a pad on "R7" to BATT *** UNTESTED! ***

 anyone tried this?


----------



## ITZBITZ

Quote:


  Originally Posted by *guzzler* 
_ITZ tried it off the USB supply, and whilst it does work it raises the noise floor to unacceptable levels, as I suggested earlier in the thread. Please, again, read the updates to the thread. You could run a trickle charger off the USB supply to a couple of AA/AAA batteries very easily if that would make you happier..._

 

I'm going to try it out with an old Sony Walkman 4.5V wall wart to see if that provides decent power without raising the noise floor substantially. On batteries, it's dead silent playing a 0-bit track with the volume on my amplifier at max.


----------



## guzzler

Quote:


  Originally Posted by *Kenny12* 
_To power from USB: jumper from a pad on "R7" to BATT *** UNTESTED! ***

 anyone tried this?_

 

ITZ has tried it, it raises the noise floor substantially. Read the bottom of the last page of this thread for more info. I'll take that UNTESTED part out the docs...

 g


----------



## Kenny12

how many mil amps does it draw? and also could i used NiMh batteries without a worry? (ie 2.4V normal 3.2 peak)


----------



## ITZBITZ

I haven't measured actual current draw yet (I should probably do that here in the next couple of days), but it was estimated at 40mA. With a pair of 2300 mAh NiMH batteries (AA), you could easily get 50-60 hours before needing a charge.

 I'll measure the draw with two and three batteries as the DC-DC convertor will probably draw more current to get the higher voltage with only two cells.


----------



## guzzler

the whole point of the switcher was to allow you to use 2xNiMH cells 
	

	
	
		
		

		
			





 information page, which is being updated quite regularly is here:

http://www.mellowparenting.demon.co....er/usbdac.html

 all you need to know is there 
	

	
	
		
		

		
		
	


	




 g


----------



## ITZBITZ

Parts kits are in my hands. I just need to merge in all the US-sourced items and the kits will be ready for distribution. More to come as I just got back from vacation, but I expect to have everything in ready-to-ship bags by Wednesday.


----------



## Kenny12

anyone here compared this to any sound cards?


----------



## ITZBITZ

Quote:


  Originally Posted by *Kenny12* 
_anyone here compared this to any sound cards?_

 

I think I'm the only with a working unit, and I've compared it to the Chaintech AV-710 and the Sonica so far. I didn't do a solid listening test yet, however, as I shipped it to a set of good ears to give me his opinion. Hopefully he'll get back to me this week with his thoughts.

 I've found it so far to be very quiet (on batteries), solid bass, nice soundstage and smooth midrange. That's just straight out of Foobar using waveOut and no enhancements.


----------



## gastro54

errm, sorry if this has already been asked, but have orders for the kits already been placed? I reskimmed the thread and didn't notice anything. If not, when will we be able to place orders do you think, ITZBITZ?


----------



## guzzler

ITZ is open to orders now, give him a PM to sort stuff out, and be sure to look over the information page posted above 
	

	
	
		
		

		
		
	


	




 regards, and happy building everyone. I can't wait to see some pictures, and your hear your impressions.

 g


----------



## nleahcim

I know you keep on saying it won't work off of USB power - but has anybody tried putting a inductor and a capacitor on the power supply to smooth it out? This seems so impractical to use batteries...


----------



## 00940

Quote:


  Originally Posted by *nleahcim* 
_I know you keep on saying it won't work off of USB power - but has anybody tried putting a inductor and a capacitor on the power supply to smooth it out? This seems so impractical to use batteries..._

 

The USB power supply goes through 2 regulators (one switcher and a linear) and over 2000uf of capacitance. The problem is not to "smooth it". The problem is that your picking noise from the computer power supply.


----------



## Nisbeth

Would putting a ferrite bead/clamp on the USB-cable help or is there any other (potential) remedy for this? Just wondering, beause it would be somewhat more practical if this thing was powered by the bus (at least in some applications) 
	

	
	
		
		

		
		
	


	





 /U.


 EDIT: BTW, I also have a unit built & working and it sounds great!


----------



## guzzler

I've never said it won't work, it's just that it's performance drops when you power from the USB lines. If that drop is acceptable to you, then by all means power it from USB, but to me it defeats the purpose of the external soundcard, ie it provides audio seperate from the noisy computer supply. 

 Nisbeth, the ferrite would only block EMI from outside the computer, the real culprit here is the power supply inside the computer that is putting power down the USB line

 g


----------



## Nisbeth

Quote:


  Originally Posted by *guzzler* 
_Nisbeth, the ferrite would only block EMI from outside the computer, the real culprit here is the power supply inside the computer that is putting power down the USB line_

 

Oh well, back to the drawing board 
	

	
	
		
		

		
			






 /U.


----------



## Wodgy

Has anyone gotten around to doing RMAA tests yet? I might be interested in building this, but I'd prefer to see measurements first.


----------



## aos

I did some with PCM2702 but they're tough to make as grounds of DAC and the computer are connected because ground loops occur and measurements are pretty bad. In real life you're not plugging the out back to a computer but to a standalone device, hopefully with batteries. Anyhow I'd recommend using laptop running on batteries as the USB source when testing with RMAA, and another computer as measurement.


----------



## Nisbeth

I have just finished testing my finished usb-dac when powered from the usb-connection - it's dead silent! 
	

	
	
		
		

		
		
	


	




 I connected one of the R7 pads to the positive battery pad using a 1N4005 diode (to be sure the input voltage to the MAX1722 stays below the 5.5V maximum) and connected the dac (via a 5 m. low-quality cable) to my harman/kardon receiver. There is absolutely no noise a normal listening levels (-50 dB on the receiver with speakers and -25 dB with headphones). If I turn the receiver all the way up (+10 dB on the display) I can hear a very faint noise with my SR325's plugged into the receiver but playing this load would cause permanent damage to both speakers, headphones and ears and besides, the noise might originate from the receiver. Now, my computer (an old Powermac G4) might have an unusually quiet PSU, but it suggests that using the USB-connection as power source is possible at least in some configurations. Thinking about it, laptops should be OK as well since their 5V is generated from a battery. The capacitance and regulation on the USB board should be enough to suppress small fluctuations and most of the noise generated by the computer 
	

	
	
		
		

		
		
	


	





 /U.


----------



## tkerby

Quote:


  Originally Posted by *Nisbeth* 
_I have just finished testing my finished usb-dac when powered from the usb-connection - it's dead silent! 
	

	
	
		
		

		
		
	


	


_

 

Further to your ferrite comments, a ferrite on the outside of the cable will only protect against external noise but we could put ferrites over each of the power wires internally from the usb connector. This would mean lifting the connector from the board though which may not be preferable.

 Alternatively, we could use a shielded case and a mounted usb connector. That connector could have a small usb lead wired onto it forming an extension with small ferrites on the power wires at either end.

 The usb supply should also be decoupled as well as the regulated output

 Another thing to try may be these filtered usb connectors


----------



## ITZBITZ

I've e-mailed all the US folks directly that inquired about the kits. If you haven't gotten an e-mail from me yet, send an e-mail to chris @ campcreations (dot) com with USB DAC in the subject.

 The final kit price is $32 plus shipping and includes all the parts, minus the IC's. Again, if interested, e-mail me and I'll send you the same e-mail I sent the people who already replied.

 Regards,

 Chris


----------



## Kenny12

how's the non us order coming along?


----------



## guzzler

I'm out of boards at the moment, but I'm intending to do another run of boards with a few modifications. More within the week on that; nothing major just a few little things to tidy up and I'm working on the USB supply and a battery charging board. Stay tuned!

 g


----------



## doobooloo

PLEASE put me down for two of the upcoming second round of boards! 
	

	
	
		
		

		
		
	


	




 Thanks!


----------



## tkerby

Quote:


  Originally Posted by *guzzler* 
_I'm working on the USB supply and a battery charging board. Stay tuned!

 g_

 

If you want someone to look over any design ideas, I've got a lot of usb and emc experience.......


----------



## was ist los?

I'll take one.


----------



## ITZBITZ

Quote:


  Originally Posted by *was ist los?* 
_I'll take one._

 

If you are in the US, and want one of the kits, e-mail chris (at) campcreations (dot) com and I'll send you all the information.


----------



## ITZBITZ

The first few kits have shipped, you should have gotten a shipping e-mail from PayPal. The remaining kits will ship next week as Mouser was low on stock for the USB connector. The remaining items should ship Monday, I'll have them Tuesday and the remaining kits will be shipped.


----------



## ITZBITZ

Measurements using an Emu 1212m as the ADC with the USB DAC directly connected to the inputs (consumer -4 dBA setting).

 Overall, it seems nice and quiet. This is using batteries for power.

RMAA Results


----------



## jamont

Quote:


  Originally Posted by *ITZBITZ* 
_The first few kits have shipped, you should have gotten a shipping e-mail from PayPal. The remaining kits will ship next week as Mouser was low on stock for the USB connector. The remaining items should ship Monday, I'll have them Tuesday and the remaining kits will be shipped._

 

Any update on this? Still waiting for mine, thanks!


----------



## Wodgy

ITZBITZ, thanks for posting the measurements. Looks like you guys did a superb job.


----------



## DaKi][er

when will there be kits available to those outside the US? im interested in 2 or 3


----------



## guzzler

i'll be getting another run of boards done soon... will let you know when I do

 g


----------



## ITZBITZ

I'm still waiting on three of the parts from Mouser that were backordered until 7/26. They should have them in-stock by now but I need to call and double check that they aren't waiting for anything else before they ship.


----------



## Kenny12

any review on these by the people who already has them?


----------



## ITZBITZ

There are still a few kits remaining for those interested. I now have all the kits with all the parts, so shipping is within a day for new orders.

 Originally shipped to:

 Andrew D.
 Bryan F.
 John G.

 Remaining orders shipped today:

 John M.
 Douglas S.
 Christopher Z.
 Tom S.
 Val L.

 Those shipped today should arrive Tue/Wed of next week.


----------



## Construct

Quote:


  Originally Posted by *ITZBITZ* 
_There are still a few kits remaining for those interested. I now have all the kits with all the parts, so shipping is within a day for new orders.

 ...

 Those shipped today should arrive Tue/Wed of next week._

 

Thanks again for putting this together, 00940, guzzler and ITZBITZ!


----------



## guzzler

Quote:


  Originally Posted by *Construct* 
_Thanks again for putting this together, 00940, guzzler and ITZBITZ!_

 

 not at all, I hope you enjoy building it as much as I've enjoyed designing it! Please don't hesitate to contact me through PM, email, or this thread if you run into any technical difficulties or have questions regarding parts. I'm happy to answer anything like that, just no "the chip's too small?!" type ones 
	

	
	
		
		

		
			





 cheers

 g

 btw, finally finished mine (thanks to ITZ for the Black Gates 
	

	
	
		
		

		
		
	


	




 ) sounds great, really shows up the Audigy I've been using up till now. I'll finish putting the charger into the enclosure before I put up any pics


----------



## Suezo

Thank you to everyone involved with the project. 

 The DAC sounds very good from what I have heard of it. I have had it assembled for two days now and have had a chance to listen to it for only a few hours.

 I bought a Serpac case and will probably end up casing it up in the next few days.

 I was able to successfully solder all of the chips using my $20 soldering iron from radio shack along with some soldering braid. I also scanned the board when I was through and looked for bridges.

 For my third project (CMOY, PPA) this was quite enjoyable and I am very pleased with the results. (A plus: it worked on the first try)

 I probably won't be able to describe the sound too well, other than it is the best of what I have heard in the past. (Mid-range Kenwood and Sony CD players, and MP3 players, Karma and Nomad Jukebox 3, and the Audigy 2 sound card)

 I especially like the fact that the card outputs a line level signal and also enjoy listening to it on my stereo system.

 Also on a side note, I tried the DAC on a Linux system and can report favorable results. (no extra driver was needed)

 Thanks.


----------



## guzzler

Quote:


  Originally Posted by *Suezo* 
_Also on a side note, I tried the DAC on a Linux system and can report favorable results. (no extra driver was needed)_

 

 that's good news! I wasn't sure if it would work and there was no way for any of the testers to try it on a Linux system short of installing our own. What distro are you using out of interest? Or is it part of the actual Kernel?

 g


----------



## Suezo

I was running Knoppix v. 3.4 which includes Linux Kernel 2.4.26. It is a distribution run entirely from a bootable CD. When it loads it recognizes available devices. The DAC was recognized as a sound card from Burr-Brown Japan. I am not sure if it is in fact part of the kernel or not, but if anyone could tell me an easy way to check this, I would be happy to.


----------



## Nisbeth

Forgot to mention that mine works great on Mac OS X 10.3 
	

	
	
		
		

		
		
	


	





 /U.


----------



## guzzler

Quote:


  Originally Posted by *Nisbeth* 
_Forgot to mention that mine works great on Mac OS X 10.3 
	

	
	
		
		

		
		
	


	


_

 

 excellent. I'll add this to the documentation. My guess is that if your distro runs off a bootable CD, it will be kernel function as they wouldn't waste space on a single device that isn't that common (afaik)

 g


----------



## Kenny12

hm... anyone compared this to sound cards yet?


----------



## Construct

I just received mine. I'll assemble it later when I get the courage to solder that PCM2702 to the board.


----------



## nleahcim

so are any kits still available?


----------



## ITZBITZ

Yes, there are a few left. If you want more info, e-mail me @ chris (at) campcreations (dot) com and I'll get you all the details.


----------



## crayon

Just finished building mine, and looks like its supported under linux with the standard usb audio driver from the kernel. Sounds good, but I haven't spent alot of time listening to it yet.

 Thanks for putting together the kit, some of the components we're a tight fit, but all in all very nicely done.


----------



## walangalam

Finally got around to building mine. It took a few tries to solder the chip, as I was using a desoldering bulb, which didnt really work for me. I went back to my tried and true melt-the-solder-and-whack-the-pcd-edge-on-the-table technique, which worked really well.

 Its a lot quieter than my Turtle Beach Santa Cruz. Cant comment on the sound as I was listening thru a low resolution stereo system.

 Thanks to all who contributed and put together the kit. Great Job!


----------



## beamrider

Started to build mine today, everything went smooth as silk until I tried to solder the 1722. I got the first leg done, went to wipe it, and the damn thing dissappeared onto the floor somewhere. Nothing like trying to find a part the size of a small flea...........LMAO

 Dammit, I knew I should have ordered two of them.


----------



## guzzler

the second batch is being printed at the moment, will arrive the start of september with some slight modifications, nothing overly drastic though. All changes (really) involve the issue of powering from USB: I've put in space for an LPF with an inductor in series. Also, the two settings resistors for the MAX1722 are now 1206. All other resistors bar the input resistors are now 1206 to aid soldering. A small 0805 capacitor has been added as decoupling for the 3.3Vdc on the PCM2702 on the the advice of tkerby (thanks!)

 beamrider; sorry I don't have a spare 
	

	
	
		
		

		
		
	


	




 I suggest hoovering then going through the whole bag 
	

	
	
		
		

		
		
	


	




 seriously, if that's the only problem you've encountered you're doing well

 regards

 g

 btw, I've finished mine with the charger based around the MC33340 as per the PPA battery board. It's in one of those translucent Hammond cases that I swore never to use, but it happened to be a handy size and complements the gold RCAs nicely 
	

	
	
		
		

		
		
	


	




 I'll post pics as soon as my dad brings back the camers


----------



## beamrider

Managed to find the rogue 1722, and finish the board with no other problems.............Except one: I've got nothing working yet.

 Input voltage: 3.157
 Voltage across C1: 3.157
 Voltage across C2: 5.280
 Voltage across C3: 5.280
 Voltage across C9: 1.204

 Do these sound right?

 EDIT: Problem fixed - after re-checking everything again with a much better magnifying glass, found a loose pin on the 3.3V reg, re-wiped it, and it works like a charm. Sound quality blows both the Creative Live! and the Hercules GTXP out of the water, IMHO.

 I'd like to take this opportunity to thank everyone involved in the creation of this awesome device, and also thank the little voice in the back of my head this morning that whispered "No caffeine for you today!"


----------



## 00940

believe it or not, I've only begun today to build that thing


----------



## Nisbeth

Quote:


  Originally Posted by *guzzler* 
_the second batch is being printed at the moment, will arrive the start of september with some slight modifications, nothing overly drastic though._

 

Can you post a picture of the new layout?


 /U.


----------



## 00940

you know what ? Mine is finally done 
	

	
	
		
		

		
		
	


	




 It's running from the PS i'll be using for a gilmore dynalo (pi regulation with massive caps and LM317/337), then 7809, then finally it goes into the reg102-5.

 I was in hurry to check if I didn't burn the pcm2702 (bad soldering job : big glob of solder + desoldering braid, worked like a charm) and just wired a mini jack and fed it straight into a pair of KSC50. Recognized easily by win98, very clean sound at low volumes (it's clearly only a line out). 

 I'll post the beast later, when the gilmore it will be feeding will be over. I'm happy to see a project launched at the end of february taking form 6 months later 
	

	
	
		
		

		
		
	


	




 PS : Guzzler, I hate you. I lost one of those 0805 resistors and it took me half an hour to find it back. When I think I had never soldered something smaller than dip8 till today... More seriously, thanks a lot for making the boards.


----------



## guzzler

Nisbeth, sure:






 R10 and C17 are the LPF. The inductor will connect between R7 and V+ as an axial component. Notice also the small diode just above the USB connector as well as polarity protection. The 0805 capacitor is just to the left of the PCM2702. I've also added polarity indicators to all relevant components, bit of an oversight before 
	

	
	
		
		

		
		
	


	




 beamrider; glad to know you got it fixed and like it 
	

	
	
		
		

		
		
	


	




 00940; it's good for the eyesight, if not for the nerves! And thanks to you for most of the design 
	

	
	
		
		

		
		
	


	




 g


----------



## Nisbeth

Thanks for the layout Gus 
	

	
	
		
		

		
		
	


	




 One thing though: If the diode is just reverse biased across the battery terminals (looks that way to me), shouldn't it be able to withstand the (rather high) short-circuit current of the batteries? Getting SMD-diodes ith that current rating is difficult, isn't it? Just thinking out loud here...


 /U.


----------



## guzzler

Quote:


  Originally Posted by *Nisbeth* 
_Thanks for the layout Gus 
	

	
	
		
		

		
		
	


	




 One thing though: If the diode is just reverse biased across the battery terminals (looks that way to me), shouldn't it be able to withstand the (rather high) short-circuit current of the batteries? Getting SMD-diodes ith that current rating is difficult, isn't it? Just thinking out loud here..._

 

 yes, you're right, only a 1A diode will fit in that position which is unfortunate but will provide protection briefly enough to protect the rest of the circuit (I hope) before you realise the mistake. Hopefully the new polarity markings will help in that case as well. I couldn't put in series as the voltage drop would be too high, even with Schottky diodes (which are huge relatively). In the end, you can omit it, fit it, or if you have enough voltage to spare wire a diode in series with the supply

 g


----------



## Nisbeth

OK, just needed to clear that up. 
	

	
	
		
		

		
		
	


	





 /U.


----------



## beamrider

Quote:


  Originally Posted by *00940* 
_ Recognized easily by win98_

 

So I take it that you didn't have to load any drivers for it on your W98 system, then?


----------



## 00940

Indeed.


----------



## guzzler

here (finally) is a couple of pictures of my DAC:












 the "cut out" for the USB cable isn't terribly good but it looks fine when the cable is inserted. I did just with a drill bit in a dremel to try and make it roughly the right shape and it's nice and tight for the relevant end of the cable. As you can see, it's a snug fit for everything in the box with batteries, charger, and DAC

 g


----------



## jamont

Looks good!

 How did you secure the DAC board on the side without mounting holes? I'm still trying to figure out haw to do this...


----------



## guzzler

simple answer is I didn't 
	

	
	
		
		

		
		
	


	




 It's secured by the two screw holes using push on threads so the bolts don't go all the way through so it sits nicely and looks good. It's very stable with just those two, even more so if you cut the USB socket carefully and tightly so the actual connector itself serves to hold the board in place. The average USB connector is a bit longer than the socket, so this extra space serves almost like a bolt to hold the board firmly to the case.

 just for a note, those are AAA batteries, giving roughly 16 hours of playtime between charges

 g


----------



## NotoriousBIG_PJ

Is there a dac/amp version in the works?

 Biggie.


----------



## guzzler

Quote:


  Originally Posted by *NotoriousBIG_PJ* 
_Is there a dac/amp version in the works?

 Biggie._

 

no, I can't afford it basically unless someone else wants to take it on, although I could do a run of 5 or something, but the cost per board would be pretty high. Jamont is currently putting his together with a MINT which you could take a look at. If there are five people desperate for a version with a built in amp, I'll consider doing it

 g


----------



## jamont

Quote:


  Originally Posted by *guzzler* 
_no, I can't afford it basically unless someone else wants to take it on, although I could do a run of 5 or something, but the cost per board would be pretty high. Jamont is currently putting his together with a MINT which you could take a look at. If there are five people desperate for a version with a built in amp, I'll consider doing it

 g_

 

Putting guzzler's board together with a MINT is a reasonable way to go, the main issues are with power requirements. You need to provide +12V and -12V (or whatever) for the MINT and +5V or whatever for the DAC board, all relative to a common ground.

 But it would be cool to have a single board that combine DAC and headamp. With so many people using computers as sources, it seems like there would be broad interest in such a project.


----------



## NotoriousBIG_PJ

I'd be interested in one with an ra-1/cmoy type of amp built in to the same case.

 Biggie.


----------



## ITZBITZ

I still have three kits left, ready for immediate shipping.


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## jboehle

YGPM!

 -Jason


----------



## JCTW

YGPM


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## flecom

any idea when kits for the new revision might become available?


----------



## guzzler

still waiting on the boards to be shipped from the manufacturer *sigh* It was supposed to be 3rd of September, but I'll give them another couple of days before I start getting annoyed... I'll keep everyone posted. I've not discussed kits with ITZ yet for this, principly because I'm leaving home fairly soon for university and won't be able to afford many of the parts up front, although that's not to say we/I won't do kits as it is very helpful. If we/I don't decide to do kits, I'll be happy to help people on an individual basis

 g


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## nleahcim

What exactly is different in the new revision? 
	

	
	
		
		

		
		
	


	




 edit: and what are you drawing the schematics and boards with? Very professional looking!


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## Nisbeth

See post #277 for guzzlers comments on the new version 
	

	
	
		
		

		
			





 I believe the boards are made with Eagle (from www.cadsoft.de). Not sure about the schematic though? 
	

	
	
		
		

		
		
	


	





 /U.


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## nleahcim

Quote:


  Originally Posted by *guzzler* 
_the second batch is being printed at the moment, will arrive the start of september with some slight modifications, nothing overly drastic though. All changes (really) involve the issue of powering from USB: I've put in space for an LPF with an inductor in series. Also, the two settings resistors for the MAX1722 are now 1206. All other resistors bar the input resistors are now 1206 to aid soldering. A small 0805 capacitor has been added as decoupling for the 3.3Vdc on the PCM2702 on the the advice of tkerby (thanks!)

 beamrider; sorry I don't have a spare 
	

	
	
		
		

		
		
	


	




 I suggest hoovering then going through the whole bag 
	

	
	
		
		

		
		
	


	




 seriously, if that's the only problem you've encountered you're doing well

 regards

 g

 btw, I've finished mine with the charger based around the MC33340 as per the PPA battery board. It's in one of those translucent Hammond cases that I swore never to use, but it happened to be a handy size and complements the gold RCAs nicely 
	

	
	
		
		

		
		
	


	




 I'll post pics as soon as my dad brings back the camers 
	

	
	
		
		

		
		
	


	


_

 

so will you be making these available as a kit? Or are we going to have to seperately buy all the components ourselves? It definitely sounds like the newer revision would be better for me...


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## guzzler

as I say, I've not decided on kits at the moment, I'll have to check my account sometime in the near future.

 As Nisbeth says, board is done in Eagle, and the schematic I don't actually know, 00940 did the original and I've just worked off that, the TI reference design, and just extra checking all the traces to make sure it makes sense, it's fine for a board that's not terribly complex, just getting grounds to the right pins is the main problem

 g


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## nleahcim

Quote:


  Originally Posted by *guzzler* 
_as I say, I've not decided on kits at the moment, I'll have to check my account sometime in the near future.

 As Nisbeth says, board is done in Eagle, and the schematic I don't actually know, 00940 did the original and I've just worked off that, the TI reference design, and just extra checking all the traces to make sure it makes sense, it's fine for a board that's not terribly complex, just getting grounds to the right pins is the main problem

 g_

 

Well if you make a kit that is similarly priced to the original kit - count me down for one


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## 00940

On Guzzler's webpage, the first schematic has been drawn with expresssch. I was discovering eagle and didn't link the schematic to the pcb. I actually prefer the way the battery charger schematic looks. what did you use for that guzzler ?


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## guzzler

I used Eagle for the charging arrangement (which I need to update...). I did, however, try to draw in schematic for the DAC itself in Eagle which looked abysmal due to the layout of the symbols which meant I had traces crossing each other all over the place, it might be an idea to create a sort of libary of bitmap symbols and create the public schematic using those in an image editor. HeadWize do that for the articles and it looks really nice IMO. I'll draw up a nicer schematic shortly

 g


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## 00940

I'm currently considering a more serious USB dac design. The first little pcm2702 is pretty cool but we can push that further.

 It would use a pcm2707 to provide an I2S output, feeding it into a dac which could be this one : http://www.diyaudio.com/forums/showt...=&pagenumber=1

 It uses a tent clock for reclocking, a tda1543 DAC and a dc-coupled discrete I/V stage.

 This DAC would be AC only and cost quite a lot more than the small pcm2702 we're using now.


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## guzzler

Interesting... Would it perhaps be simpler to provide an S/PDIF output from the USB port, to allow people to connect their own DAC afterwards? That means that the really expensive part would be completely down to the end user, whereas we'd just provide a cheap, simple USB->S/PDIF converter.

 BTW, just been in touch with EuroCircuits, they've been busy and expected shipping date is 18/09 
	

	
	
		
		

		
		
	


	




 g


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## ITZBITZ

Stick with I2S and you avoid any and all jitter problems as everything is on the same clock.


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## 00940

I planned to do directly pcm2707 - dac chip in order to scrap the spdif stage and the jitter induced problems BUT the pcm2707 has an onboard clock you can't disable and they advice in the datasheet against the use of an external clock.

 That's why i'm thinking about that dac circuit with decent reclocking of the I2S lines. Tent clock aren't very expensive.


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## 00940

other option i'm considering is a pcm1794 followed by the pass D1 I/V stage.


----------



## ckunstadt

Quote:


  Originally Posted by *guzzler* 
_Interesting... Would it perhaps be simpler to provide an S/PDIF output from the USB port, to allow people to connect their own DAC afterwards? That means that the really expensive part would be completely down to the end user, whereas we'd just provide a cheap, simple USB->S/PDIF converter.

 BTW, just been in touch with EuroCircuits, they've been busy and expected shipping date is 18/09 
	

	
	
		
		

		
		
	


	




 g_

 

This sounds like a great idea! Especially if it had a female conector that could stick right to the back of any DAC. I'd buy one (can't build it).



 .


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## 00940

spdif output from the USB port is useful but doesn't make sense in terms of performance. It's by getting direct I2S that we can avoid the jitter problems induced by spdif treatment.


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## ckunstadt

so even if the SPDIF portion is less than a couple of inches long, it's not a great benefit? hmm, okay.


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## guzzler

Jitter isn't caused by trace length, although I would imagine dodgy routing could contribute (someone like to say yes or no to that?), but is rather an artifact of timing differences between components. In the original version of this DAC, the PCM2702 has something TI call the SpAct architecture which generates a rock steady clock from an external oscillator. However, if you took S/PDIF from a chip, like the PCM2707 to a DAC with a seperate clock, the two clocks wouldn't match precisely so you get timing errors in bits. Using the I2C bus like 00940 suggests means the whole system from USB decoder to DAC operates on the same clock so jitter is eliminated

 g


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## 00940

I've been reading a bit on diyaudio the last days. Found some nice ideas. 







 The caps for decoupling are missing of course and so are the LPF after the I/V stage or the balanced to unbalanced convertor.

 The PCM1794 is the hot chip right now on diyaudio. Well, why not to give it a try ? http://focus.ti.com/docs/prod/folder...t/pcm1794.html 
 20$ a piece at digikey.

 The pcm2702 is the coolest chip from the TI in our application since it offers a direct I2S output. No need to care about another good clock either since the SPACT system seems quite good . http://focus.ti.com/docs/prod/folder...t/pcm2707.html
 7$ a piece at digikey.

 According to this post on diyaudio, the Belcanto DAC2 uses the THS4130 as I/V stage. Quite simple. Well, we all know that it doesn't prevent the DAC2 to shine. http://focus.ti.com/docs/prod/folder...t/ths4130.html 
 7.2$ a piece at digikey.

 All those chips are smd of course. SOIC8 (big) for the THS4130, SSOP28 for the PCM1794 (small)and TQFP32 (in between) for the PCM2707.

 Power supply and decoupling needs to be defined. Probably a few REG101UA from TI. One for the PCM2707 supply, one for the triggers on the PCM2707, one for the digital section of the 1794, 3 for the differents analog supply of the 1794. They're at 2.4$ each at digikey.


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## ITZBITZ

Now we're playing with POWER. 
	

	
	
		
		

		
		
	


	




 Is the THS4130 dual channel? What about power supply? There was a lot of talk last time about how we should have made it USB powered from the git-go. If they can make the Emu1212m dead silent inside the PC, what's the chance of getting the same from a USB device?

 Also, we need to focus on making it easy to connect to a PIMETA/MINT/PPA without any problems with power supply, etc.


----------



## 00940

1. If I go further with that DAC, it's clearly not for a portable device. Our little PCM2702 had to beat the sonica. With this I want to attack anything under 500$. That means wall supply for the DAC and the output stage. The integrator opamp will probably be an OPA627 and those don't really work nicely on portable or low powered stuff. Regulation of the output stage will be by Sulzer regulators, one pair (+ and -) for each channel.

 2. On this basis, noise from the computer is absolutly not an issue. As it is now, there's still a ground connection between the USB port and the rest. If I make the PCM2707 bus-powered, I can limit the connection between it and the PCM1794 completly neutral, just 4 digital lines. I'll change that. The PCM2707 has an onboard 3.3V regulator that should be just fine for digital stuff.

 3. The THS4130 isn't a dual. It is a differential opamp. That means that it takes inverting and non-inverting inputs and outputs both amplified.


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## ITZBITZ

Okay, now we're really talking... 
	

	
	
		
		

		
		
	


	




 I would considering using an external AC->AC wall-wart with internal rectification/regulation. Nice to keep the transformer out of the case and makes it easy to go international that way. Or a simple switch using a design similar to the STEPS. If you want to go uber, consider a dual voltage design that I can't remember the name of but is talked about all -the time. For the low voltage parts, 3.3V is often enough. But for the output stage, you want +/- 15V to get the OPA627 hopping. You'll also want enough current to bias the output stage well into class A.

 Sounds like a fun project. I'll build one just to hear it sing.

 Even though I swore off SSOP28 after the last project!


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## 00940

The external transformer is nice to avoid any transformer noise. Sadly, it doesn't help much for making the thing international : the most powerful external AC/AC converter I can find in Europe is something like 15VAC/1A. In the US, you can get a far more interesting 24VAC/800mA. But it's 120VAC in only 
	

	
	
		
		

		
		
	


	




 From this point of view, the easiest thing would actually be to use Talema toroid for PCB. A simple jumper will change the input voltage. The 25VA 2X18VAC should be nice for this.


----------



## 00940

That could be the rectification-LM317preregulators board. Voltage values are just for example. The board allows 2X2200uF (panaFC) by rail. Two rails for the output stage, one for the digital section, one for the analog section of the DAC. All these to be further regulated on the dac board. It would require a transformer of 2X15VAC (or 18VAC) for the output stage and a 2X9VAC transformer for the PCM1794.


----------



## ITZBITZ

Make sense to me, the STEPS uses those transformers and they work very well.

 Might consider 4x1000uF instead of dual 2200uF to reduce ESR and take a look at the STEPS for a nice line filter setup that Tangent put into that. Very nice work.

 Might also consider 2x transformers, one for the high voltage and one for the low voltage to avoid burning off too much excessive voltage in the regulators. Probably not required, but who knows (not me).


----------



## 00940

Quote:


  Originally Posted by *00940* 
_ It would require a transformer of 2X15VAC (or 18VAC) for the output stage and a 2X9VAC transformer for the PCM1794._

 

 Quote:


  Originally Posted by *ITZBITZ* 
_Might also consider 2x transformers, one for the high voltage and one for the low voltage to avoid burning off too much excessive voltage in the regulators._

 

Looks like we are in agreement 
	

	
	
		
		

		
		
	


	




 I've been thinking about those talema. There are three problems with those I could see compared to classical toroids. 1/ They ask for bigger PCB. Thus more expensive ones. 2/ I'm stuck with the free version of Eagle. Their professional version costs too much for a student. The Transformer are eating almost all the space allowed. 3/ Since they have to be PCB mounted, they restrict your choice when it comes to implementation. Difficult for example to put them in another enclosure.

 The thing is that this possible (it's still a very hypothetical project) DAC will cost more, will be more difficult to implement than our small PCM2702. It will be only built by experencied diyers who could like some flexibility. I was thinking (due to space constraints in Eagle) to design it in a modular fashion. A preregulator board, a digital board with the pcm2707 and 1794 and their regulators, an output board with the opamps and their regulators. So one could improve on the output stage for example. 

 Regarding the line filter. I'm planning to use a filtered IEC jack. I will implement some kind of noise filter on the ac line after the xformers though.


----------



## 00940

Quote:


  Originally Posted by *ITZBITZ* 
_Might consider 4x1000uF instead of dual 2200uF to reduce ESR_

 

Thing is, the 2200uF/35V from the Pana FC line is the best compromise between capacity, size and cost.


----------



## guzzler

It seems a shame to spend all this money on a DAC that is only being used for USB input. It should be possible to take an external S/PDIF signal to the PCM1794 with a switching array of some kind. The jitter-free advantage would be lost using the external S/PDIF, but retained with the USB input. 

 I like the idea of modular boards, as 00940 a project like this would only be built by experienced DIYers, so they'd be able to choose what they want easily enough. So, if we were going modular, the Jung Super Regulator would be a great choice for the preregulator and/or the actual regulated stages. Also, this method would allow one person to concentrate on one section, so we could end with a top-notch design. Count me in for some more designing action 
	

	
	
		
		

		
		
	


	




 g


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## 00940

if we want to switch the I2S inputs, we need a daughterboard with : a receiver (cs8412 ?) and a clock (XO module ?). Plus their supplies of course.


----------



## AdamZuf

Anymore comments about the sound??
 How quiet is this thing? I'm considering using it to feed a strong power amplifier directly and to save the preamp on the way. Has to be really quiet..

 Thanks
 Adam


----------



## 00940

I couldn't stop myself fooling around with Eagle 
	

	
	
		
		

		
		
	


	









 soic chips are reg101. SMD parts are 0805 resistors and 0805 ceramic caps.


----------



## Voodoochile

Quote:


  Originally Posted by *00940* 
_If I go further with that DAC, it's clearly not for a portable device. Our little PCM2702 had to beat the sonica. With this I want to attack anything under 500$. That means wall supply for the DAC and the output stage. The integrator opamp will probably be an OPA627 and those don't really work nicely on portable or low powered stuff. Regulation of the output stage will be by Sulzer regulators, one pair (+ and -) for each channel._

 

I like the sound of those plans a lot!


----------



## Nisbeth

Maybe this could be the perfect match for the M3 (sorry morsel 
	

	
	
		
		

		
		
	


	




) amp?


 /U.


----------



## 00940

For the DAC and the USB chip, I'm thinking that LM317 followed by low noise reg101 regulators, with proper bypassing (oscon for digital, pana fc for analog, + smd ceramic) will be good enough. In the above layout, there are two reg101-3.3, one for each chip, powered from the same LM317 and three reg101-5, powered from another LM317.

 Btw, the DAC chip can be the PCM1798, which is pin compatible but far cheaper (6.5$). Specs are good.

 I'm currently thinking at the output stage. We have here a dac with differential output and it doesn't support passive conversion.

 1st question is thus : are we keeping balanced out or do we convert to unbalanced ? Of course, unbalanced out can always be taken between ground and non-inverting output. But it's far of being optimal. 

 2nd question : If we rule out tubes for I/V (I think we can agree on that), we have basically two choices : opamp or discrete. Opamp output stage is easy. We have the datasheet, we just have to adapt resistors and caps to the desired filters values and output voltage. Discrete I/V can be fully differential, like the passlabs D1 stage or be composed of 2 I/V stages for each channel. In my view, it doesn't make much sense to use a discrete I/V if it's to convert it to unbalanced with an opamp afterwards. 

 3rd : Of course, cost has to be taken into the equation. Assuming the use of opamp, we need 6 of them. OPA627*6, heavy bill. OPA132 could be an ok alternative. Discrete can be cheaper. The passlabs stage only uses few parts and relatively cheap ones. But beside the actual stage, there's also the PS cost. For example, the supply used in the 5000$+ Passlabs D1 was just a pair of 7815/7915. But we could go further and use Sulzer or even Jung regulator. Sulzer is ok pricewise, Jung cost a bit more (due to the more expensive opamp used). And do we regulate each channel or do we use a pair of regulator for each channel ? 

 Size is a factor. I can easily put an opamp output stage with its regulation on the board. That will be harder with a discrete output stage.


----------



## 00940

guys... have a look at the first page here : http://focus.ti.com/lit/ds/symlink/tpa6120a2.pdf

 And people at Diyaudio have begun to use the chip as preamp, reporting results superior to buf634+op627 in multiloop. THD goes down as load goes up. That could be our perfect output buffer/differential to single ended converter


----------



## guzzler

I've been thinking some about this, and regards my earlier suggestion of including S/PDIF input. Considering how many people now use their computer as their primary source, a high quality dedicated DAC is a sound idea. I'm now converted.

 1. Unbalanced, I would say. Using balanced outputs puts this into the realms of serious expense when you factor in amplification and headphones/speakers. For the short cable run most people use, balanced doesn't provide that much benefit to justify the extra expenditure.

 2. I quite like the sound of a discrete output. Again, if it were to be modular the end builder *could* choose between discrete or opamp. However, the target builder will have the necessary experience (we hope) to implement the discrete output properly. 

 3. Going discrete would, I think, cut the cost compared to using a high end chip like the OPA6x7 (6xOPA627AP = £90 
	

	
	
		
		

		
		
	


	




 ), perhaps not against an AD8610 or similar. Another consideration would be the LM6171, although as many note it is quite a touchy opamp and the layout would have to be carefully considered. Regards the Jung, it's actually not terribly expensive to build with the AD825; the actual 'Jung' part minus the transformer, filter caps etc, only cost me about £10 excluding PCB which was about £3.50 or so. If people aren't willing to stretch to that, a good LM317 (or similar) implementation would suffice. Personally, I would like a seperate pre-regulator (ie, Jung) for the digital and analogue stages. That would mean two; I think 4 would be overkill. (Although who ever said that was bad 
	

	
	
		
		

		
		
	


	




 )

 Regards size, I reckon we could get an SMD I/V stage in there quite happily, especially after the layout is squashed down. I also like the idea of the TPA6120, it removes a lot of circuitry into a convinient package (minus the heatsinking...), but would IMO negate the use of a discrete I/V stage. Also, I'd like to have a good listen to it before it was implemented here.

 g


----------



## 00940

We have a right channel and a left channel. Up to here everyone follows me. 
	

	
	
		
		

		
		
	


	




 The PCM1794 provides for seperate analog supplies for the L and R channel. The pcb layout (I draw it mostly for fun) feeds seperate supplies into those analog supplies. Would it make sense to provide the opamps of each channel (L and R) their own supplies ? It makes thus 4 regulators (+ for R, - for R, + for L, - for L). They could be fed from a common preregulator (LM317).

 A solution "in between" in performance and pricewise is the sulzer with ne5534.


----------



## guzzler

I suspect, but I don't know, that following a Jung (or similar) regulator with something like a REG102 removes the benefit of the Jung regulator. I'd be happy enough to run with the LM317 regulator and use 4 tried-and-tested REG102s afterwards to provide as much seperation between power supplies as possible. The cost added is fairly small...

 g


----------



## 00940

oops, sorry I was (very) unclear.

 Reg101 have pretty good specs. But they only go up to 5V. What I offered was to use Rerg101 for the chips (preregulated by LM317) and the Sulzer (or Jung) for the opamps (or transistors) of the output stage.


----------



## guzzler

oh right, a *yes* to that one then. I've had a quick look at the Sulzer regulator, and the step up to the Sulzer-Borbely regulator. I think the S-B reg could be implemented with little extra cost, and as tangent mentions in his article, it's really a carefully selected and slightly improved version of the basic Sulzer

 g


----------



## 00940

edit 1 : oops, wrong picture

 edit 2 : fixed


----------



## guzzler

That would be the ultimate, brutal implementation..... I like it. For the Jung stages (or a S-B), we could cut out the LM3x7 pre-regs as they are part of the designs of each. One advantage of using Jungs is PCBs are already available for them, which cuts down on layout, but it would be very nice to implement it all one one digital and one analog stage. It would, to my mind, make it a complete project, not one that has been put together from what's available. I'll look into the advantages of the different regulators from ease of implementation, cost of implementation, and comparitive advantage points of view and see which would be the best for this one. Just as a note, discrete regulators are VERY touchy about layout.

 g


----------



## 00940

We could easily fit the chips, the output stage (assuming opamp filter) and all the regulator onto a single board. Even considering size restriction in Eagle. All that would be needed is a second board with preregulators. Pads could be placed for those wanting flexibility.

 There's an huge thread on diyaudio regarding the layout of Jung regulators.

 What do you think about the TPA6120a2 ?


----------



## niles

You really don't need all those sultzer/jung regulators on the output stage; two is perfectly adequate to supply the current. One positive one negative. You will not attain a significant performance advantage by using one reg/channel of the 1798 either; but I would substitute a 5V Jung regulator for the monolithics. That way you have three discrete regulators for the supplies that count the most. some would argue the merit of a Jung on the 3.3 line, but I think in this case that is overkill. 00940, have you come up with an answer about the system clocking issue yet from someone that knows more than us?


----------



## Nisbeth

Not sure if there's any inspiration to be had from it, but have a look at http://diyhifi.230v.dk/ (text in Danish but the schematics should be clear enough). 
	

	
	
		
		

		
		
	


	





 /U.


----------



## 00940

Niles : great to see you here.

 I've been speaking about clocking issues with an engineer on a french board. According to him, the system clock provided by the PCM2707 is perfectly able to provide the system clock required by the filter and the dacs of the PCM1794. Synchronisation should be ok.


----------



## Voodoochile

Quote:


  Originally Posted by *00940* 
_What do you think about the TPA6120a2 ?_

 

It looks great... this could be the schizz. I did see an error in the diagram regarding thepolarity of the B inputs of OPA4134, but I am relegated to finding bum nomenclature, it seems. Of course that 4134 could easily be replaced with something nicer as well, although having a dual package is good as far as tight matching is concerned. A quad is tight channel-to-channel, but thermal crosstalk might potentially have some adverse effects.

 Page 17 of the datasheet has some good layout considerations, also.


----------



## Nisbeth

Quote:


  Originally Posted by *Voodoochile* 
_It looks great... this could be the schizz. I did see an error in the diagram regarding thepolarity of the B inputs of OPA4134, but I am relegated to finding bum nomenclature, it seems. Of course that 4134 could easily be replaced with something nicer as well, although having a dual package is good as far as tight matching is concerned. A quad is tight channel-to-channel, but thermal crosstalk might potentially have some adverse effects._

 

Wouldn't using a quad op-amp limit the potential choices rather severely? There's the 4134 (in SOIC), the 4227 (in DIP/SOIC) and what else? Dual opamps seem to be the best compromise between form factor, performance and number of choices as far as I am concerned. 
	

	
	
		
		

		
		
	


	





 /U.


----------



## 00940

I agree with you on this Nisbeth. The only available quad usable here for TI are : opa4134, opa4132, opa4227, opa4228.


----------



## guzzler

Tangent noted the danger of using a single postive Jung in that if it drops out of regulation (eg, not starting correctly), you get the full unregulated voltage across it. This danger could be reduced by using the pre-reg set to a level that wouldn't cause damage, but it might be skimming the usable level from the Jung. In principle, I'm fine for just one, but that is something definately worth considering in that it could fry an awful lot of expensive hardware.

 Re quad opamps, the x227 isn't bad, but it's not too great either. We could go dual chips quite easily, and as they're not driving a heavy load directly, thermal crosstalk should be minimal


----------



## 00940

Quote:


 The diode on the error amp's output is now a 6.8V zener. This helps the regulator start up more reliably. It may be needed in difficult situations in the original Jung circuit, but Jung says it's absolutely essential in this new circuit. If you were to use a regular diode, the the error amp's output is likely to lock up near the negative rail on startup. 
 

taken from Tangent's website.

 shouldn't this take care of that problem ?


----------



## guzzler

I was just putting forward an example. There are other things like current variations on the output, I think, that can cause drop out. Have to check on that though. Also, for a 5V or 3.3V output, will that zener not need to be replaced with a lower value so the regulator starts up at all?


----------



## ITZBITZ

I'll throw in a few ignorant thoughts here myself:

 Could we use a transistor alignment like on the PPA to filter the power to each op amp channel, reducing crosstalk and avoiding having to use a billion regulators on the board? The 2N5486 (or whatever) running 14mA should be enough for an op-amp channel (or two if using something like an OPA2607). Just a though.

 And I would like to see two channel chips instead of 4 channel parts as they are more common and easier to roll. Even something like an LT1384 or whatever can be used if we provide enough pads for power supply bypassing that could be optional for easy-to-use op-amps.

 Clocking over I2S out of the PCM2707 is going to be plenty, anything more an you risk comprising the stability between the two parts I think. With I2S, the clock is part of the signal, so that's why no need for any reclocker.

 Any thoughts on how to control the sample rate of the 2707 from Windows? If I recall the last unit was 48000 KHz or 44100 KHz, not sure? How does it adjust based on source material, etc.

 Putting the transformers off-board is fine, and a line filtered IEC input is probably quite sufficient, keeping the AC basics out of the circuit to allow each country to make their own best choices.

 I'd like an LED to indicate power. Perhaps one to indicate PSU powered and one to indicate a bus-active state on the USB part. We need to be sure to properly mute when disconnected as well, if that's a consideration at all.

 Another option would be a rectification board that had the transformers, line filtering and schottky's to handle the switchover to DC with some phat filter caps allowing some customization (18mm spots to allow for audiophile cap usage) and some extra pads to allow hotwiring additional caps for the extreme (yes, YOU VOODOO) builder. 

 The last board was awesome with silence using batteries. Hopefully this power supply isolated unit will also be dead quiet.

 Has anybody mentioned that by using a differential output chip with an active I/V, there is NO capacitor in the signal path? Therefore the output is pure from the DAC. Very appealing to me!


----------



## 00940

pcm usb chips support in native 32-44.1-48 kHz. Depends of what your sending them. I think wodgy and AOS have been discussing that once,with comparaisons between linux and windows, i'll try to find the thread.

 I''ll have a look to the transistors. Grounding will be fun 
	

	
	
		
		

		
			





 And dual packages are for sure the way to go, no doubt about that.

 Power on led is trivial. Usb on too, we just need to tap the usb supply.

 Regarding the mute question, the datasheet says : The PCM2704/5/6/7 enters the suspend state after the USB bus has been in a constant idle state for approximately 5 ms. While the PCM2704/5/6/7 is in the suspend state, SSPND flag (pin 27 for PCM2704/5, pin 11 for PCM2706/7) is asserted. The PCM2704/5/6/7 wakes up immediately when detecting the non-idle state on the USB bus.


----------



## Voodoochile

Quote:


  Originally Posted by *Nisbeth* 
_Wouldn't using a quad op-amp limit the potential choices rather severely? There's the 4134 (in SOIC), the 4227 (in DIP/SOIC) and what else? Dual opamps seem to be the best compromise between form factor, performance and number of choices as far as I am concerned. 
	

	
	
		
		

		
		
	


	



 /U._

 

Yes, that's my concern. The datasheet shows a quad op-amp, but I think that a pair of duals is the way to go. The quads are just too tight, IMO.

 I'm a little surprised to see it suggested in the datasheet, but then again, I'm not too surprised. It always seems to be about making it as cheaply as possible.


----------



## Voodoochile

Quote:


  Originally Posted by *ITZBITZ* 
_Another option would be a rectification board that had the transformers, line filtering and schottky's to handle the switchover to DC with some phat filter caps allowing some customization (18mm spots to allow for audiophile cap usage) and some extra pads to allow hotwiring additional caps for the extreme (yes, YOU VOODOO) builder._

 

I do have a soft spot for 18mm caps pads. 
	

	
	
		
		

		
		
	


	




 It just opens the range up so dramatically compared to 16mm.


----------



## Nisbeth

Quote:


  Originally Posted by *Voodoochile* 
_I'm a little surprised to see it suggested in the datasheet, but then again, I'm not too surprised. It always seems to be about making it as cheaply as possible._

 

...and commercial designs are rarely built for "tweakability" 
	

	
	
		
		

		
		
	


	





 /U.


----------



## Voodoochile

What's a tweak?


----------



## 00940

something voiding warranty.


----------



## nleahcim

So are there any USB chips that support 4 channels or more? I would love to make my own surround capable USB sound card...


----------



## doobooloo

Kind of off-topic (but on-topic from about a few pages back) but...

 When is the second batch of the USB dac going to be ready for purchase?


----------



## guzzler

Sorry, the second batch is ready to go. I tried to post a Mall-Fi ad a couple of days back, but I've not heard anything from Jude since. I've posted the updates on the website, and the boards cost £5.25 each, including all passive SMDs. P&P is extra, but not very much.

 PM, or email to glelec at mellowparenting dot demon dot co dot uk

 g


----------



## 00940

you're right doobooloo, I'm gonna create a second topic for that USB dac bis.


----------



## nleahcim

Quote:


  Originally Posted by *guzzler* 
_Sorry, the second batch is ready to go. I tried to post a Mall-Fi ad a couple of days back, but I've not heard anything from Jude since. I've posted the updates on the website, and the boards cost £5.25 each, including all passive SMDs. P&P is extra, but not very much.

 PM, or email to glelec at mellowparenting dot demon dot co dot uk

 g_

 

YGEM


----------



## beamrider

Is this going to be available in kit form, as the first version was?


----------



## guzzler

Not complete kits (lack of time and money), but all the SMDs are included so you don't have to buy hundreds at a time

 g


----------



## nleahcim

Quote:


  Originally Posted by *guzzler* 
_Not complete kits (lack of time and money), but all the SMDs are included so you don't have to buy hundreds at a time

 g_

 

Hi I'm trying to figure out what else I would need to buy here.

 First you need the TI PCM2702E correct? (TI lists a number of PCM2702 chips - just want to make sure I'm looking at the right one) Then you need a TI REG102UA-3.3 (8 pin SOIC) and a TI REG102UA-5 (also 8 pin SOIC) and lastly for ics you need a MAX1722, and then these three:

 1 1 10uH radial inductor 
 1 12MHz CL=30pF
 1 USB type B connector 

 Is that all? Or are the capacitors not included? What about the parts listed in the suggested power supply? I only plan on using USB power for this circuit (I'd go through batteries at a ridiculous rate... so it is more economical this way for me) and I don't think I have the hearing to hear the difference anyways. Is there anything I don't need since I'll be using USB power?

 Also - can anybody advise on what specific parts to order from a US distributor (preferrably Mouser or Digi Key - as they're pretty much the only companies I order from). The problem is I can easily order a quarter watt 100K resistor - but now that it's for an audio application I don't have the slightest idea which to get... (I'm very inexperienced with DIY audio!)

 Lastly - anybody interested in putting together a kit with all the necessary components?

 edit: read this page more carefully: http://www.mellowparenting.demon.co....er/usbdac.html but I still am not sure on what I need to get!


----------



## guzzler

No, most of the resistors are now SMD, as I mention in the Revision A Additions sections. You only need to get two 22R resistors and a 1.5K resistor. You can get the Vishay-Dales if you like, but generics will work just as well as it's only on the digital lines. The other addition is the improved power supply for USB. I'd get a 10uH axial inductor, and a 47uF tantalum bead capacitor for those.

 You'll need to get yourself capacitors. I recall ITZBITZ saying it was hard to get WIMA caps in the States, or any other metallised polyester cap in 2.54mm pitch, which is a problem, I'll admit. If someone in the States would like to buy a quantity of boards off me, I should be able to get hold of the WIMAs to send as well, but it is a big financial commitment. I would very much like to offer kits, as it makes things a lot simpler for everyone, but I worked it out to around £350-£400 for the 25 boards with no guarentee of selling them all, and I can't afford that at this time.

 It's the PCM2702*E* that you want. The other options are packaging options, so they don't really affect us very much, unless someone wants to pick up the tab for 2000 PCM2702s? 
	

	
	
		
		

		
			





 edit: I've got some updates to make on the Suggested Power Arrangment, just skip that at the moment. Also, it's really for those wanting to implement USB and battery power into one box. I'm away until Wednesday, so I can't help you during that time. My apologies, and don't hesitate to get in touch

 g


----------



## ITZBITZ

These are all the parts/numbers I used to build the first round of kits. All were from Mouser/DigiKey/PercyAudio. Some parts have changed for the new board, so various changes will need to be made.

 USB DAC Board

 Vishay/Dale 100K71-RN55D-F-100K

 Vishay/Dale 330K71-RN55D-F-330K

 SMD 0805 1M

 Vishay/Dale 1.5K71-RN55D-F-1.5K

 Vishay/Dale 22.171-RN55D-F-22.1

 SMD 0805 MF 330K

 Tant 10uF 10V80-C320C220J1G 

 1000uF Panasonic FCP10199-ND

 PCM2702EPCM2702E-ND

 IC LDO REG 3.3V 250MAREG102UA-3.3-ND

 IC LDO REG 5V 250MAREG102UA-5-ND

 NP0 ceramics 32pF

 WIMA MKS-02 100nF

 Sanyo OS-CON

 Black Gate 47uF47uF/HiQ/NX/6.3V

 Crystal Pad

 C&D Radial 10uH580-17103

 Crystal 12.0 MHz 32pF520-HCU1200-32

 Berg 61729649-61729-1010B

 Molex KK 2-pin header538-22-23-2021

 Molex KK pins538-08-50-0114

 Molex KK 2-pin plug538-22-01-3027

 Eagle 2 AA Holder12BH325


----------



## doobooloo

A few questions -

 Do you know where we can get those WIMA caps? And also, is there any reason behind the specific choice of using Sanyo OS-CON electrolytics instead of the Panasonic FCs or FMs?

 Thanks for the info!


----------



## nleahcim

Quote:


  Originally Posted by *ITZBITZ* 
_These are all the parts/numbers I used to build the first round of kits. All were from Mouser/DigiKey/PercyAudio. Some parts have changed for the new board, so various changes will need to be made.

 USB DAC Board

 Vishay/Dale 100K71-RN55D-F-100K

 Vishay/Dale 330K71-RN55D-F-330K

 SMD 0805 1M

 Vishay/Dale 1.5K71-RN55D-F-1.5K

 Vishay/Dale 22.171-RN55D-F-22.1

 SMD 0805 MF 330K

 Tant 10uF 10V80-C320C220J1G 

 1000uF Panasonic FCP10199-ND

 PCM2702EPCM2702E-ND

 IC LDO REG 3.3V 250MAREG102UA-3.3-ND

 IC LDO REG 5V 250MAREG102UA-5-ND

 NP0 ceramics 32pF

 WIMA MKS-02 100nF

 Sanyo OS-CON

 Black Gate 47uF47uF/HiQ/NX/6.3V

 Crystal Pad

 C&D Radial 10uH580-17103

 Crystal 12.0 MHz 32pF520-HCU1200-32

 Berg 61729649-61729-1010B

 Molex KK 2-pin header538-22-23-2021

 Molex KK pins538-08-50-0114

 Molex KK 2-pin plug538-22-01-3027

 Eagle 2 AA Holder12BH325_

 

are you going to be putting together a kit for the new board? I can commit if the price is reasonably close to what it was last time. thanks!


----------



## doobooloo

Regarding the Black Gate output caps, I was thinking of subsituting the black gates for Solens. My assumption is that no matter how good and expensive those black gates are, they're not going to beat semi-decent polypropylene film caps like the Solens.

 Granted, the Solens will cost more but if it'll sound better I'm going to do it. Any advice would be greatly appreciated as Welborne labs' 20% sale ends soon!

 -doosik


----------



## 00940

I'm not sure solen are worth it compared to BG. Honnestly.

 Oscon are the "usual" pick on diyaudio for digital decoupling. Pana FC are preffered for analog decoupling. But if you want to use pana FC, it's ok.


----------



## pburke

Sorry to bust in with a question like this but I think there are a lot of folks who may not want to build a totally new DAC, yet are interested in hooking them directly to a PC.

 To be specific, I am looking for a way to add USB to a DAC that has the usual SPDIF input to a CS8412 chip, is reclocked, etc.

 Reading through this entire thread, I assume that I should be able to use something like a PCM2902 or 2707 to take USB and move it out as SPDIF, pass that on to the CS8412? (plus proper power for the chip, bypassing, clock, etc on the same daughtercard). 

 My question is: how good is that SPDIF connection going to be with this very short distance between source and receiver? I read somewhere on DIYaudio.com that long SPDIF runs (5 feet+) work much better. There are others who seem to have good success in modding the M-audio Traveler and adding that to existing DACs as USB interface - but I guess even those must be SPDIF interfaces. 

 Am I missing something here or am I on the right path? 

 Peter


----------



## niles

I've had mine built since mid September, and it worked on the first try after assembly (good job on the design guys.) My charger trickles ~65 milliamps. I am only getting a hour or so of listening before it pukes. I bought 2000mA/hr cells from Radiosh*t. Any suggestions? Anybody else having this problem? 

 Niles


----------



## doobooloo

Quote:


  Originally Posted by *00940* 
_I'm not sure solen are worth it compared to BG. Honnestly.

 Oscon are the "usual" pick on diyaudio for digital decoupling. Pana FC are preffered for analog decoupling. But if you want to use pana FC, it's ok._

 

Why do you say the Solens are not worth it? Are there any specific reasons?

 Thanks!


----------



## 00940

they're very bulky and the common grade doesn't sound any better than bg to my ears. The extra space is just waste IMHO.


----------



## tkerby

Worked firt time. I had to make a few component substitutions though. The 100uF caps are from an old power supply and rated at 25V, the 47uF oscons, now 100uF and the output caps are (unfortunately) the same tantalums used on C1 and C2. I also used a surface mount inductor as it was all I had. It does, however, sound fantastic though, even unamped on a pair of cheap headphones. The power supply noise is minimal when measured at the DAC although it can be clearly seen before the regulators. The 5V has a few spikes on it from the inductor switching, although they are such small pulses, I doubt they are audible.

 I'm thinking I may drop the output caps. Do they serve a particular purpose with the DAC or can they be dropped?

 My other suggetions for rev B (if there is one):

 - Connect the shield of the usb connector to the ground plane. It provides mechanical reliability and improved noise performance. I've scraped the solder resist off to do this
 - Place a via at any smd component ground connection. I noted some are routed topside to nearby through hole leads. Small vias will minimise ground loop area E.g IC1 gnd is connected to C17 ground pin. This should reduce switching noise
 - Get the manufacturer to stop the hole and cross method of soldering through hole to the ground plane. Each little lead acts as an inductor plus they are hard to solder. A large via is all that is required giving a 360 degree unbroken connection.
 - If possible, slide the crystal and caps towards the top of the board and the signal lines down. A 12MHz crystal is a large noise source as it has very sharp signal edges. Leads should be minimal in length so moving the caps and resistor towards the noisy usb side would be better


 Hope you dont object to my comments, this thing sounds absolutely perfect and I cant fault the measurements I've made on my scope so far. Its maybe last 0.5% improvements


----------



## guzzler

not at all Tim, it's nice to have a professional view of these things. I'll certainly consider this if/when I get round to working up another version. Glad the changes were an improvement as well....

 g


----------



## 00940

for the cross and hole thing, it's just the default setting in Eagle. I don't know if it can be changed; otherwise a few rectangles will cure that problem easily.


----------



## nleahcim

So I noticed that you're using a usb type a recpetacle for the usb connector on the usb dac. Doesn't this seem a bit impractical? I mean I've never even seen a male to male type A usb cable - as it's pretty much always the host that uses the type a connector, while usb devices normally use a sort of mini connector. Also - being that I think you've been trying to keep down the size of the board as much as possible - it seems like a complete waste of board space to use such a large connector. Well those are just my thoughts...


----------



## 00940

actually, it's the "standard" usb "b" jack. It's easy to find at any electronic supplier.

 You thus use that kind of cable which also is the official standard :


----------



## guzzler

Cross traces are easy to remove, it's just a parameter of the ground polygon. Easy as 3 clicks. Putting a pad round the USB connector is more of a problem, I tried to for the Rev A boards, but eagle would always eliminate the whole keep out zone for the hole, regardless of whether the thing covering the whole was a rectangle, trace, polygon etc.... I'll keep trying though

 nleahcim; I discussed this with you ages ago. Using a mini connector would introduce a proprietory part, which would be hard to find for some and so we'd get emails saying, we can't find this or that, and makes the project harder than it has to be.

 g


----------



## nleahcim

Quote:


  Originally Posted by *00940* 
_actually, it's the "standard" usb "b" jack. It's easy to find at any electronic supplier.

 You thus use that kind of cable which also is the official standard : 
	

	
	
		
		

		
		
	


	


_

 

Oops - I guess i looked at it wrong - I thought it was a type a! I have plenty of a to b cables lying around.

  Quote:


  Originally Posted by *guzzler* 
_nleahcim; I discussed this with you ages ago. Using a mini connector would introduce a proprietory part, which would be hard to find for some and so we'd get emails saying, we can't find this or that, and makes the project harder than it has to be.

 g_

 

I guess my memory must be fading in my old age... But I think there are fairly standard mini usb connectors - I mean I used the same USB cable for an MP3 player (MPIO), and 3 different brands of digital cameras (minolta, kodak, and canon) - no problems whatsoever. And that connector was like a 5th of the size of a type b connector! I mean type b connectors are HUGE!

 I dunno - I guess I just like things small - but I mean I really can't imagine one of these connectors being any harder to find than some of these wierd brand capacitors and whatnot...


----------



## flecom

Quote:


  Originally Posted by *guzzler* 
_Cross traces are easy to remove, it's just a parameter of the ground polygon. Easy as 3 clicks. Putting a pad round the USB connector is more of a problem, I tried to for the Rev A boards, but eagle would always eliminate the whole keep out zone for the hole, regardless of whether the thing covering the whole was a rectangle, trace, polygon etc.... I'll keep trying though

 nleahcim; I discussed this with you ages ago. Using a mini connector would introduce a proprietory part, which would be hard to find for some and so we'd get emails saying, we can't find this or that, and makes the project harder than it has to be.

 g_

 


 no there are standard mini connectors...

 a






 and b






 there is also a C iirc but its not common at all


----------



## beamrider

Quote:


  Originally Posted by *nleahcim* 
_Oops - I guess i looked at it wrong - I thought it was a type a! I have plenty of a to b cables lying around.


 I guess my memory must be fading in my old age... But I think there are fairly standard mini usb connectors - I mean I used the same USB cable for an MP3 player (MPIO), and 3 different brands of digital cameras (minolta, kodak, and canon) - no problems whatsoever. And that connector was like a 5th of the size of a type b connector! I mean type b connectors are HUGE!

 I dunno - I guess I just like things small - but I mean I really can't imagine one of these connectors being any harder to find than some of these wierd brand capacitors and whatnot..._

 


 However, the nice thing about using the current connector is that that's one less cable to carry around if I go to a friends house to show him this "cool magic music box." Never have to worry about leaving the correct cable at home when I travel, either. Nothing like traveling 4 hours to my fathers house, whipping out this cool box to blow his mind with, and then looking like an ass since I forgot the cable at home. Or perhaps the cable somehow got damaged in transit. I'm SOOL at that point.......hehe


----------



## nleahcim

so has anybody figured out an enclosure for this yet? Might a populated board be able to fit in an altoids tin?

 Also - what kinds of headphone jacks do you all reccomend?


----------



## ble0t

What would be decent substitute parts for the OS-CONs and the Black Gates? I'm having trouble finding those OS-CONS in particular


----------



## doobooloo

Quote:


  Originally Posted by *ble0t* 
_What would be decent substitute parts for the OS-CONs and the Black Gates? I'm having trouble finding those OS-CONS in particular 
	

	
	
		
		

		
		
	


	


_

 

I'll be putting in Panasonic FCs in their place. It really shouldn't make a big difference, I'll report my results soon (final pieces coming in today, will be able to build this weekend)...


----------



## ble0t

I was thinking about doing that for both the OS-CONS and the BGs...I don't want to order just 2 BGs from some place and pay $5 on shipping for $5 worth of parts 
	

	
	
		
		

		
		
	


	




 Thanks for the reply...I'll be interested to see how yours comes out


----------



## nleahcim

Quote:


  Originally Posted by *ble0t* 
_I was thinking about doing that for both the OS-CONS and the BGs...I don't want to order just 2 BGs from some place and pay $5 on shipping for $5 worth of parts 
	

	
	
		
		

		
		
	


	




 Thanks for the reply...I'll be interested to see how yours comes out 
	

	
	
		
		

		
		
	


	


_

 

the place that I found that sells the black gates had a minimum order large enough that we'd have to buy 10 black gates. I need 4 - would anybody else want to go in with me on them? Shipping from me to anywhere in the US should be like a buck - as I'd just put them in a padded envelope and ship them first class...

 edit: but I haven't been able to find a source for the os cons - so right now I'm planning on using the Panasonics that doobooloo is reccomending.


----------



## ble0t

Are there any boards for this that are currently available? I sourced all my parts out and was going to order them tomorrow, but having a board for them would be a good thing


----------



## guzzler

Still a few boards left yes, give me a PM

 g


----------



## 00940

Here's what could be very well be my next USB dac. It won't see the light before june or july though. 







 PCM2707 => I2S => PCM1794 => Passlabs D1 I/V stage (minimalist, without the buffer)

 Regulation onboard for the pcm2707 and pcm1794. Outboard regulation for the gain stage. The output caps are outboard too. Balanced to unbalanced will be done by a dynalo that will double as preamp. Bypassing of the IC by 100uF oscon + ceramic (solderside). 

 Size is half an eurocard.


----------



## JHouser

so...Would this be a better D/A conversion than the one in my ADCOM GCD-700? Dual Burr/Brown 20bit D/A converters? Thanks

 Not the above DAC but the familiar board you all have built.


----------



## doobooloo

Wow. Keep us updated with the progress! Looks great.


----------



## tkerby

00949 - please please please dont split your groundplane. The signals crossing the bridge need a return path and thus will create more noise on the board. You have two options, either use a continuous plane and keep analogue and digital signals away as far as you can physically move them or, crate a bridge between the planes (and only one to avoid loops) directly below those signals.

 If return current cant flow beneath signal wires, it will only go elsewhere on your board and create noise


----------



## 00940

The grounding question is what I'm working on right now. I've read about anything and it's contrary on that topic. The only thing I'm quite sure of is that the DAC must be completly on the analog plane.

 Option 1 : one single groundplane 
 Option 2 : two, joined by a ferrite bead somewhere 
 Option 3 : two, joined by a trace under those resistors carrying the I2S signal
 Option 4 : two, joined at the power supply
 Option 5 : two, with the I2S passing through some isolating device such as the ISO150 (costly and big)
 Option 6 : two, joined by a pair of schottky's, back to back
 Option 7 : two, joined by a resistor

 Honnestly, for this, I'm still researching what's best. 
	

	
	
		
		

		
		
	


	




 The power supply will be made out of two transformers. One 2X5VAC for seperated supplies for the 2707 and 1794. One 2X30VAC for the I/V stage.


----------



## tkerby

Option 1 : one single groundplane 
 In my opinion, the best option. Just keep the analogue and digital traces as far apart as possible


 Option 2 : two, joined by a ferrite bead somewhere 
 Bad plan for digital signals. The I2S will lose its sharp edges and you will likely see jitter as the sample point moves. Your circuit should be designed to handle up to the 5th harmonic of a signal with minimal losses to get a good edge to sample. This rules out a ferrite connection. 

 Option 3 : two, joined by a trace under those resistors carrying the I2S signal
 OK option, but power supplies should be isolated for each board, or the power connections should also be made at or around the same point. The reason for this is that both ground and power can carry a high frequency signal. It doesnt care which plane it jumps to as it is ac

 Option 4 : two, joined at the power supply
 Bad idea, the return path will be a big ground loop that will run round the gap and transmit noise onto the entire board via the power supply. Also, very poor emc and esd protection as the high frequency created on one plane may just jump across the planes using the I2S wires and fry the chips

 Option 5 : two, with the I2S passing through some isolating device such as the ISO150 (costly and big)
 Good option, I suggest two boards are used with completely isolated power supplies or a single board with three islands and one psu for each. The ISO150 sits as in the middle island and only allows the I2S to hop. 

 Option 6 : two, joined by a pair of schottky's, back to back
 Bad idea, there is no low voltage DC return path. Noise will be created at a level equal to the voltage drop across the diode on each board. You will most certainly hear this on the output

 Option 7 : two, joined by a resistor
 Similar to option 6, we're looking to lower impedance, not create it


 What you have to remember is this - any signal will take the path of least impedance. Note that two ground planes near to each other form a capacitor, a length of track is a resistor (and inductor) and a via is a bigger inductor and little resistor. A signal will take the easiest path, wherever it has to jump. This will depend on frequency.

 The best board is a 4 layer board with central ground and power planes. This allows return current to flow beneath any signal thus giving the smallest possible loop area. By minimising loop area, we minimise coupling between signal lines. By keeping a distance, we prevent crosstalk at the signal decreases proportional to a power of distance from the track.

 I suggest the following

 1 - Use a 4 layer board (or 5 layer for two supplies, alternatively split only the power plane (2nd layer from base, make the ground the third from base and run all important signals on the top layer thus next to a complete plane)
 2 - Keep power and ground on central planes
 3 - Decouple the supplies next to each chip
 4 - Keep Analogue and Digital as far away as possible
 5 - Ensure separation between signal lines
 6 - Match the length and impedance of the I2S lines for the best signal quality
 7 - Place in a metal box, but only provide a single starpoint to the box for all grounds to avoid loops forming


----------



## 00940

wow, I didn't expect such a nicely detailled reply 
	

	
	
		
		

		
		
	


	




 Thanks a lot 
	

	
	
		
		

		
		
	


	




 - 4-5 layers boards : not an option for me, I need to keep everything on two layers because I'm using eagle freeware and because it'd be awfully expensive to produce in very low series. The project is intended to be purely a one-shot project. Perhaps two or three other boards done but that's it.
 - decoupling as close as possible : I'm trying to. For now, I can hardly do closer. What would you use for decoupling ? I'm planning 47-100uF electrolytic coupled to a 100nf ceramic.
 - I think I'll go with the common groundplane. Iso 150 are too much of a problem to get working


----------



## ble0t

Does anyone have a part # (preferably Mouser or Digikey) for a pad/cushion for the crystal used in this DAC? I haven't been able to find one on either site. Or is there a more DIY method?

 EDIT: Typical...right as I post it, I find the Mylar spacer in the catalog. For anyone else who is curious, the part # at Mouser is 520-700-9001.

 I guess I have a side question...what discernable difference would I see with/without something?


----------



## nleahcim

Quote:


  Originally Posted by *ble0t* 
_Does anyone have a part # (preferably Mouser or Digikey) for a pad/cushion for the crystal used in this DAC? I haven't been able to find one on either site. Or is there a more DIY method?

 EDIT: Typical...right as I post it, I find the Mylar spacer in the catalog. For anyone else who is curious, the part # at Mouser is 520-700-9001.

 I guess I have a side question...what discernable difference would I see with/without something?_

 

wait - is one even necessary?


----------



## ble0t

Well, I got my DAC assembled, but I'm having an issue and I was hoping someone had some ideas...

 If I use two AA batteries (i.e. 3.15V) I get 1.75 volts out of the MAX1722 and if I use the USB supply (~5V) I get 3.75V out of the MAX1722 . Obviously something is a miss at or before the converter. I did some measuring around the board and the voltage drop over R10 (10R resistor) is close to 2V when using batteries, which obviously isn't a good thing. I assume this would be the sign of a faulty or shorted MAX1722? It doesn't appear that any traces are bridged, but I wanted to get some opinions before I started desoldering it. Thanks in advance.


----------



## Jeroen

Quote:


  Originally Posted by *ble0t* 
_Well, I got my DAC assembled, but I'm having an issue and I was hoping someone had some ideas...

 If I use two AA batteries (i.e. 3.15V) I get 1.75 volts out of the MAX1722 and if I use the USB supply (~5V) I get 3.75V out of the MAX1722 . Obviously something is a miss at or before the converter. I did some measuring around the board and the voltage drop over R10 (10R resistor) is close to 2V when using batteries, which obviously isn't a good thing. I assume this would be the sign of a faulty or shorted MAX1722? It doesn't appear that any traces are bridged, but I wanted to get some opinions before I started desoldering it. Thanks in advance._

 

I had the same problem on the second one I build. It turned out that two pins of the dac were soldered together. Another option may be to replace the max1722, which fixed my first usb dac. Good luck!


----------



## Ozymand

Sorry for the thread necromancy, but I'm looking for some assistance in building one (actually two) of these. I am having a very difficult time finding a source for the 2.5mm pitch WIMA MKS-02 0.1uF capacitors and the max7122 converter. Mouser, Digikey, and Newark either have them out-of-stock or isn't a valid part number. Can anybody suggest equivilants that could be used in their place?


----------



## beamrider

Hehe, good luck with the Wima's. I got mine from Newark a few days ago, but there's a 17 day lead time on them; they have to ship them in from Farnell in England, and with the additional shipping cost, they ran me well over a buck apeice....


----------



## doobooloo

Quote:


 Does anyone have a part # (preferably Mouser or Digikey) for a pad/cushion for the crystal used in this DAC? I haven't been able to find one on either site. Or is there a more DIY method?

 EDIT: Typical...right as I post it, I find the Mylar spacer in the catalog. For anyone else who is curious, the part # at Mouser is 520-700-9001.

 I guess I have a side question...what discernable difference would I see with/without something? 
 


  Quote:


 wait - is one even necessary? 
 


 Does anyone have an answer for this? I've looked at some computer motherboards and various pc cards and only half the time the crystals have plastic pads underneath.

 What kind of performance benefits will damping pads bring to this specific application - or more aptly, how will the sonic performance be degraded by omitting it? I just built one without it and while I still can (haven't hooked it all up yet) I'd like to know if it's going to make a difference or not here.

 Thanks in advance!


----------



## guzzler

Quote:


  Originally Posted by *doobooloo* 
_Does anyone have an answer for this? I've looked at some computer motherboards and various pc cards and only half the time the crystals have plastic pads underneath.

 What kind of performance benefits will damping pads bring to this specific application - or more aptly, how will the sonic performance be degraded by omitting it? I just built one without it and while I still can (haven't hooked it all up yet) I'd like to know if it's going to make a difference or not here.

 Thanks in advance!_

 

No, it's not necessary and you won't notice any difference in performance. The sole purpose is really to isolate the X-tal from too much heat, and from mechanical strain. Nothing to worry about on this front. The only thing is, they're very cheap so I thought I'd just include them anyway. Certainly not worth paying 8p for one, and £3.75 for shipping!

 g


----------



## individual6891

Anymore boards available?

 There are a few parts that are kind of difficult to source for UK. Was wondering if it was possible to order some parts from guzzler?

 This includes:

 MAX1722

 the USB type B connector (although I can get USB-B PCB connectors from a different brand, I'm not sure if all of them are universal in terms of connection pins - any advice?)

 The blackgates for CL/CR - Does 47uF electrolytics have to be used? Or can you use polypropylenes in here?


----------



## Ozymand

For the MAX1722, your best bet (and I know this is going to open up a can of worms) is to see if you can source a part directly from Maxim themselves. I've been having issues finding a vendor here that has the parts and I'm now waiting on Maxim to approve my samples request so I can build a USB DAC. Maxim will ship it from their closest source (hopefully a company somewhere in the UK for yourself) as to minimize the shipping costs. I've heard the pro's and con's of using the samples for personal usage (so please don't derail this thread with it), and in this case I'm desperate for the parts that I'm willing to make an exception and take advantage of the samples program to finish this long-delayed project.

 Other options include puting in an order with a vendor and waiting the lead time for the parts to become available. Or maybe someone here might have some spare ones they may be willing to part with. Good luck with it!


----------



## individual6891

I looked at the other-brand USB connector again and compared it to the BERG used on this board- looks like identical pin configuration and spacing.

 I'll prolly use some polypropylenes to replace the blackgates.

 Just need to get my hands on a PCB


----------



## doobooloo

Just finished the casing for my USB DAC (rev. A):































 I had a Hammond case lying around from previous PPA projects, so I decided to use it for the DAC. I coupled the output Black Gate NX Hi-Qs with some Angela/SCR 0.33uF tin foil caps. This coupling quite significantly brought out the mids and highs, and I'm very pleased with the results.

 I currently have two amps connected from the DAC, I put three pairs of RCA outputs (paralleled) just because there was just enough space for three. I had the two amps previously connected with an RCA splitter, it should be better that the splitter is now eliminated from the chain.

 All internal wiring is 22AWG teflon sleeved silver. Battery holder is Bulgin 4xAA tray type, and they're connected in parallel (2 x 3V).

 Anyway, the DAC sounds excellent, a substantial improvement over my bypass/blackgate modded OptoPlay.


----------



## Syzygies

Your case work is stunningly beautiful. There was a general exclamation in our house, _You've got to see this!_.


----------



## DaKi][er

You certainly have the touch for making beautiful casework, I wish some of that would wear off onto my work 
	

	
	
		
		

		
		
	


	




 I got 2 of the 5 dac's working (havnt gotten around to the others) but they are only sitting on my bench with rca's hanging off them for now


----------



## Kenny12

ok i just made one of these, and i'm powering it off the usb, however i'm getting a highish dc offset, 300mV by the time it comes out of my pimeta.

 i havnpt put any of the rev A stuff in as i still need to buy it, but does this seem abnomral?

 also when the guide goes

  Quote:


 Using an axial 10ｵH inductor, connect one pad from R7 to the postive input. Ground is straight from the USB supply 
 

does this mean connect it inline from r7 to positive input?


----------



## Magsy

Wow, I'm looking to house mine atm and that one is truely awesome! Job well done 
	

	
	
		
		

		
		
	


	




 Did you cut that yourself?


----------



## nleahcim

Quote:


  Originally Posted by *Kenny12* 
_ok i just made one of these, and i'm powering it off the usb, however i'm getting a highish dc offset, 300mV by the time it comes out of my pimeta.

 i havnpt put any of the rev A stuff in as i still need to buy it, but does this seem abnomral?

 also when the guide goes



 does this mean connect it inline from r7 to positive input?_

 

Yup.

 doobooloo your work is beautiful as always.


 I just finished putting together one of my DACs. Now I need to finalize a layout for my headphone amp and I'll have a much much better way to listen to music with my laptop!


----------



## doobooloo

My USB DAC is sounding richer and fuller as it's burning in! Anyway, I have a question - is it possible to bypass kmixer with this DAC? I'm not too hopeful since it's using the system default driver, but maybe there's a hack that I'm not aware of that will allow me to bypass kmixer and get some cleaner results.

 Thanks in advance!


----------



## Mr.Radar

Quote:


  Originally Posted by *doobooloo* 
_My USB DAC is sounding richer and fuller as it's burning in! Anyway, I have a question - is it possible to bypass kmixer with this DAC? I'm not too hopeful since it's using the system default driver, but maybe there's a hack that I'm not aware of that will allow me to bypass kmixer and get some cleaner results.

 Thanks in advance!_

 

Have you tried Kernel Streaming?

 Also, has anyone compared this to any soundcards (AV-710, 0404, etc.)?


----------



## doobooloo

Quote:


 Have you tried Kernel Streaming? 
 

How would I do this? My primary music player is WMP.


----------



## Mr.Radar

Quote:


  Originally Posted by *doobooloo* 
_How would I do this? My primary music player is WMP._

 

WMP doesn't support KS. Try Foobar2000.


----------



## doobooloo

Hmm. I really like how all my albums are arranged in WMP... any way to do it in WMP?

 Meanwhile I'll give foobar a try...


----------



## Kenny12

ok the high dc offset on my pimeta wasn't the ubs dacs fault, however it does still have a offset of ~3mV straight out of dac which i think is ok.

 in foobar why does the dac make a strange sound b4 changing tracks?


----------



## Magsy

Right I've been busy and got a load of rmaa results on this! I've done a battery vs usb power comparison 
	

	
	
		
		

		
			





 I'm a RMAA n00b, but I think I got it figured. When I changed sample rate I also changed it in Patchmix to match. Everything seemed to work ok, even if it didn't it doesn't matter, it was the same for either the usb power or battery power tests so they are vaild to compare.

 I used the emu0404 to record with, I couldn't test loopback because I don't have enough adaptors..
 My dac has all the trimmings, the axial inductor and blackgates.

 First we have the battery power tests which are here!

 It doesn't look too bad to me, way better than onboard sound so I'm happy 
	

	
	
		
		

		
		
	


	




 I tired the test with two aa's but it didn't happen, voltage was too low to make the tests at 48khz work (white noise) so instead I used 4 aa's which measured at 5.25v. On 2 aa's (2.65v) the volume was considerably less than usb power or 4 aa's, I had to adjust 5db more in patchmix to get the level up for Rightmark.

Here we have results for usb power!

 It looks worse than it is and in listening it doesn't sound too bad, I couldn't really tell them apart to be honest apart from infrequent HD noise. That said it is a fairly big gap performance wise...I am wondering if I should go back back on my plans and use battery power now.

 I have a comparision of the two here so you can see the results side by side.

 I'll try to get some results via my laptop tomorrow to see if power is cleaner there.


----------



## Icy006

To jump back to a subject brought up earlier in this thread: a USB DAC with S/PDIF output. There is a great little USB soundcard made by Voyetra Turtle Beach called the Audio Advantage Micro.

 It has a single analog output (headphone amp claimed, but 3rd party reviews call it a bit lacking in power). The great thing is that it can do S/PDIF via a Toslink optical out instead of the analog jack (they use a proprietary adapter, included). $30 shipped from places like Amazon and Newegg.

 Could meld this into some DIY external DAC project and none would be the wiser


----------



## dsavitsk

Quote:


  Originally Posted by *Icy006* 
_There is a great little USB soundcard made by Voyetra Turtle Beach ... that ... can do S/PDIF via a Toslink optical out_

 

There are a bunch of USB cards with digital out. There are also some people now modding DACs by internally adding various flavors of these cards to them. Search the computer audio forum here for lots on this.

 -d


----------



## Kenny12

very nice sound. 
	

	
	
		
		

		
		
	


	




 what config should i use it in foobar? should i resample to 96k ? 

 also how does this usbdac compare to something else diy such as the nonoz III ?


----------



## robzy

(on which page can i find the schematic of the DAC all you guys are talking about? :S)

 Rob.


----------



## Magsy

http://www.mellowparenting.demon.co....er/usbdac.html


----------



## Ozymand

Hrrm... does anybody know of a substitution for the WIMA caps? I managed to aquire 8 of them (thank you, Guzzler!), but I don't want to have to put in a minimum order of 50 from Mouser to get the remainder for the second DAC. I thought for a bit I had found a cap that was a similar pitch, but now I can't find it anymore on the Digikey website (wasn't a box cap, but a radial lead poly disc cap... I think).

 But in other news, the first DAC is coming along well. Hopefully by Sunday I'll have it all assembed sans casework. You can guarantee I'll have pics by then.


----------



## doobooloo

Quote:


  Originally Posted by *Ozymand* 
_Hrrm... does anybody know of a substitution for the WIMA caps? I managed to aquire 8 of them (thank you, Guzzler!), but I don't want to have to put in a minimum order of 50 from Mouser to get the remainder for the second DAC. I thought for a bit I had found a cap that was a similar pitch, but now I can't find it anymore on the Digikey website (wasn't a box cap, but a radial lead poly disc cap... I think).

 But in other news, the first DAC is coming along well. Hopefully by Sunday I'll have it all assembed sans casework. You can guarantee I'll have pics by then._

 

I have three left over from my other two USB DACs - if someone else can supply you with the remaining 5, I can send you the three your way.


----------



## Magsy

I've been fiddling again!
	

	
	
		
		

		
		
	


	




 Got my Toshiba Tablet laptop out to give it a whirl with the USB Dac and RMAA. I got some intersting, if expected results!

 You can find them here

 Same as last time, input to the same pc with the 0404. I powered the dac via usb with the lappy plugged in, with the laptop on batteries and finally with it powered via 5.25v's worth of NIMH's.

 All the results are so close I doubt you'd ever tell! Certainly sounds the same! Its way better than when powered from my pc 
	

	
	
		
		

		
		
	


	




 I have a meaty main pc but I blew the good Antec psu up, so I'm on a no-name one at the moment. A new Truepower 430 arrives next week so I will also test on that just out of interest.

 Solves my dilema anyway, I'm building it into an enclosure with no batteries because I'll be using the laptop with it. I'll put a power jack on the outside should I ever need to use it on a desktop.


----------



## doobooloo

That's very interesting! I should build my second DAC with USB power and see how it performs. I was just hesitant because my bypass-modded OptoPlay had a pretty high noise floor.

 Thanks for the results!


----------



## nissenos

Im wondering...

 Is it possible to connect this device to the USB output of an Ipaq pocketpc? I have problems with the noise levels from the headphone out and I would be extremly happy if there was an alternative. Iwe understood that the Headroom bithead only works with cds or "wave out", so if a program would be installed to send this (wave) information through the usb, then it could technically work? 

 Daniel


----------



## Icy006

To my knowledge, the Bithead line and this DIY USB DAC are both a "Standard USB Audio Device". Any OS that supports things falling into this specification should support them (Windows, Linux, OS X...).

 I don't know if Palm or PocketPCs support this, but Google probably does.


 p.s. Nice avatar


----------



## nissenos

Quote:


  Originally Posted by *Icy006* 
_p.s. Nice avatar 
	

	
	
		
		

		
		
	


	


_

 

Thanks 
	

	
	
		
		

		
		
	


	




 Well it seems I was completely off with the wave and cd stuff, well at least when I checked with the bithead stats, so probably the same with 00940 and guzzlers usb dac (correct me if I’m wrong). I’m going to try this and hopefully I will have a new favourite portable music source in the near future.


----------



## Ozymand

Got it nearly done.. got all components soldered in except for C17. I noticed this was an addition but noted for if you were going to use the USB supply. Does it need to be in if you're going to use batteries? If it's not essential, I'll just add it later when I put in the next order of parts to Digikey.

 Otherwise.. it's almost there. Need to buy a USB cable, find a suitable case, and wire up the RCA jacks.


----------



## doobooloo

I have a question...

 Is it safe to connect four batteries in series? I am getting frustrated with the short battery time of connecting 2x2. I got a brand new pack of cheap alkalines and they lasted like three hours.

 With rechargeables it should be fine since 1.2V x 4 = 4.8V but with 1.5~1.6V it's going to be over 6V... Will this damage the switching trans?

 Yesterday I was watching Troy at full volume since the volume encoded in the movie was rather quiet... I had put in the batteries like half an hour before the movie started but towards the end of the movie the nasty white noise came out at full volume and I thought my drums were being blown out.


----------



## Nisbeth

Max. input voltage for the MAX1722 is 5.5V, so 4 rechargeables should be OK while 4 alkalines are probably too much 
	

	
	
		
		

		
			






 /U.

 EDIT: From the MAX1722 it actually looks like it works with input voltages down to 0.9V. How about using the 4 batteries in parallel instead of series/parallel?


----------



## Magsy

Quote:


  Originally Posted by *Nisbeth* 
_Max. input voltage for the MAX1722 is 5.5V, so 4 rechargeables should be OK while 4 alkalines are probably too much 
	

	
	
		
		

		
		
	


	





 /U.

 EDIT: From the MAX1722 it actually looks like it works with input voltages down to 0.9V. How about using the 4 batteries in parallel instead of series/parallel?_

 

In my case 2xnimh in series were barely powering it, as soon as they dropped to ~2.3v 48Khz playback became white noise.

 I've been running mine with 4xnimh in series and its been fine, you get much more output (volume) too, which you need because imo its too quiet on ~2.5v. My nimhs were measured at 5.25v's initially, it didn't blow up


----------



## 00940

I'm gonna check the datasheet of the maxim chip again, the number of batteries shouldn't matter much actually. I don't remember a graph input voltage vs output current. 

 But only 3 or 4 hours of playing is ridiculously low. Or your batteries are really of the lowest quality, or there's a problem with your dac.


----------



## Ozymand

Another option provided by the design is hooking up a supply greater than 5V after the MAX1722 (there are vias on the PCB to do so). The inputs on the REG102 devices are rated up to 12V (if I'm reading the datasheet right), so you could ideally hook up a 6 to 8 cell battery pack to your USB DAC (or a single 9V battery).

 Curious, what would happen if you attempted to hook up the GND and V+ of a USB DAC to the virtual ground and V+ of a Cmoy or any other split rail designed headphone amplifier? Could it be possible? Would it make sense? That way you could simplify the design to a single battery supply driving both units...


----------



## doobooloo

Woohoo!

 I took apart the DAC and connected four brand new alkalines in series. I didn't bypass the Maxim IC.

 It works! The battery pack measures 6.41V when connected but no problems.

 I am going to rewire my battery slot in series now. 
	

	
	
		
		

		
		
	


	




 Phew! Thank God it didn't blow up or anything.


----------



## Ozymand

Glad that the 4 batteries in series is working out for you, but I'd keep an eye on it. It may not blow up immediately, but I'd be kinda wary as it may cause premature failure of the device. This could be very akin to overclocking a computer, more voltage you put into it the faster it goes but also the faster it'll die (relatively speaking, I've had my Cel300A overclocked to ~500MHz for nearly 5 years now and it's still going.. outlasted 2 hard drives and a power supply).


----------



## doobooloo

That's true. I'm going to try to get NiMH cells as soon as possible, and I've got a dozen of half-depleted alkalines that will work well in this application too.


----------



## phobus

Hi. I've been looking but can't find it. Has anyone compared the usb dac with a Chaintech or Emu 0404/1212? I'm really interested in getting one, but would like to know approximately where it stands compared to the different sound cards.


----------



## individual6891

Just finished my USB DAC..

 Will be using LM317 to supply 6-7V into the 5V regulator
 Will be using LCR Audio-grade Polypropylene's for output caps..
















 Sound comparisons soon once it's cased up


----------



## individual6891

The guide at mellowparenting is wrong.. 

  Quote:


 To bypass switching supply (5.2V < Vs < 10V): connect +ve to the right hand pad of R2, Ground to right hand pad of R1, omit IC1, R1, R2, L1, and C1 
 

should be

  Quote:


 To bypass switching supply (5.2V < Vs < 10V): connect +ve to the right hand pad of R2, Ground to* left * hand pad of R1, omit IC1, R1, R2, L1, and C1 
 


 Also, I'm having problems with the 3.3V regulator, it's output is 1.93V
 (Using 6.64V into the 5V regulator, giving a good 5.0V output, going into the 3.3v regulator)

 Anyone got any suggestions?

 -Andy


----------



## individual6891

Ok, the 3.3V regulator was fried, replaced everything now and it's ok... but windows XP doesn't recognise the chip when I plug it in... is this fried too?

 (Unknown USB Device)

 Andy


----------



## Magsy

Quote:


  Originally Posted by *individual6891* 
_Ok, the 3.3V regulator was friend, replaced everything now and it's ok... but windows XP doesn't recognise the chip when I plug it in... is this fried too?

 (Unknown USB Device)

 Andy_

 

I had that in first plug-in to my desktop. Tried it on another port after a reboot and it worked ok. Worked first go on my laptop....


----------



## individual6891

Quote:


  Originally Posted by *Magsy* 
_I had that in first plug-in to my desktop. Tried it on another port after a reboot and it worked ok. Worked first go on my laptop...._

 

Well i replaced the actual dac chip, and way hay, "usb speaker" installed..

 But more problems:

 There's quite a bit of background hum with thew USB connected to my headphone amp on max .. Also when I change volume with the headphone amp, there's more scratchy sound.

 The headphone amp itself is fine with a different source.

 Any clues?


----------



## 00940

try to connect the casing of the USB connector to ground.


----------



## individual6891

Quote:


  Originally Posted by *00940* 
_try to connect the casing of the USB connector to ground._

 

Tried just now, still very fuzzy. The PCB is uncased btw.


----------



## guzzler

Have you measured all the voltages in the circuit, you should get almost exactly 5V and 3.3V from each the regulators. The voltage out from the MAX1722 should be pretty much 5.5V. Check connections from the PCM2702, and also the coupling capacitors.

 g


----------



## individual6891

Quote:


  Originally Posted by *guzzler* 
_Have you measured all the voltages in the circuit, you should get almost exactly 5V and 3.3V from each the regulators. The voltage out from the MAX1722 should be pretty much 5.5V. Check connections from the PCM2702, and also the coupling capacitors.

 g_

 

After replacing most of the chips (cos they fried the first time due to the +ve on the wrong pad).. I get 3.3V and 5.0V

 The PCM2702 pins seem to be ok, though one of the pads came off the PCB, but it doesn't connect to anything (definitely sure on this). I used a DMM to check for continuity between pins, but i'll double check later. It fuzzes quite a bit when you turn the headphone amp's volume knob - maybe an impedance issue?


----------



## guzzler

Yep, I was going to say it might have been an impedance issue. What's the value of the pot on the headamp? Sorry about the error on the page, I've changed it now. If it's a write off, I'm happy to ship you out another for free, as it's entirely my fault in that regard....

 g


----------



## individual6891

The pot is 50K, going into a standard MINT design.

 The boards only slightly damaged with some (useless) pins missing, but I'm not sure if it's something underneath the chip that I can't see - really shouldn't be, cos I doubled checked most of the parts which looked abused, and they seem ok. Not sure if a new PCB is needed or not, quite difficult to desolder the PCM2702! If you have a spare PCB, I could try it again I suppose, but it's up to you


----------



## dsavitsk

For those interested, I posted a review of this DAC at http://www.ecp.cc/gud.html. It is still a bit of a rough draft, and as such may get updates at some point.

 If anyone has a better picture of an assembled unit that I could use on the site, please let me know.

 -d


----------



## 00940

I'm curious about that problem of bit perfect output and resampling issue. Here is what the engineer of Grace replied when asked about the digital output of the pcm2902:

  Quote:


 I have not tried the asio4all driver yet but the tests I have done on the PCM2902 (the usb controller in the m902) with windows 2000 and xp pro as well as mac osx using the generic drivers that load automatically have all resulted in bit perfect data transfer. However, there are some situations I found in mac osx were the os does some sort of sample rate conversion and the data is not transfered error free. It is not obvious when this is happening unless you can monitor the data stream coming from the PCM2902 with a bit analyzer. As soon as I get a chance I will post all of the setup details for each os.


----------



## dsavitsk

Quote:


  Originally Posted by *00940* 
_I'm curious about that problem of bit perfect output and resampling issue. Here is what the engineer of Grace replied when asked about the digital output of the pcm2902:_

 

I seem to remember this guy http://www.wavelengthaudio.com/Cosecant.html claiming bit perfect output over USB from a Mac with simple settings in iTunes, though I am not seeing it on the site anymore.

 Interestingly, though, he is claiming that the volume should be at 50% on windows, With the guzzler usbdac, there s definitly stuff missing with the volume at 50%. Compensating by turning up the amp volume, I think it sounds flat, but maybe I am just imagining it?

 -d


----------



## 00940

No, you're right, turning down the volume kills the dynamic range. 

 Did you try to use asio4all ? It works well with the USB dac but I couldn't get a difference compared to the standard windows drivers, this with a gilmore and grado sr225.


----------



## Magsy

Hmm I've had the same problem.

 I am at this moment putting my mint and dac in a box, I put a OPA2227 on the mint in place of the previous AD8620 and its now pretty much perfect...


----------



## individual6891

Hmm I'm using an AD8620 with the fuzzing during volume change, do you think it's definitely the opamp to blame?


----------



## individual6891

Hmm still not working well at all..

 Guzzler, any chance you could send over a replacement PCB?


----------



## guzzler

YGPM

  Quote:


  Originally Posted by *individual6891* 
_Hmm still not working well at all..

 Guzzler, any chance you could send over a replacement PCB?_


----------



## Kenny12

how do u guys mount ur pcbs? semms very hard


----------



## z2trillion

Quote:


  Originally Posted by *Kenny12* 
_how do u guys mount ur pcbs? semms very hard_

 

Yeah, soldering the components was surprisingly easy, but i'm having trouble figuring out how to case it up. The square usb connector doesnt help.


----------



## dsavitsk

Quote:


  Originally Posted by *z2trillion* 
_ i'm having trouble figuring out how to case it up. The square usb connector doesnt help._

 

I used one of these http://www.datapro.net/products/1591.html


----------



## Magsy

hehe, the _hard_ part 
	

	
	
		
		

		
			





 I spent ageeeeeeees looking for a solution because my case does not have a removable lid.

 I bought some motherboard style 'posts' which had thin threads on the bottom and were long. I drilled two holes in the bottom of the case and put a nut on the bottom of the post. My case has two 'grooves' cut in the bottom of it, the nuts fit in this groove perfectly so the case has no protrusions. The board is then fixed to the top of the posts.

 I'll take some pics later to show you..

 THe problem i have is the usb connector is a little loose on the pcb, I couldn't get it mounted firmly.


----------



## DaKi][er

the usb pci backpane you get with motherboards came in handy for me - 





 just that usb A to A male cables are very rare so i got 2 regular cables and diy'ed them to get my A-A


----------



## jamont

Quote:


  Originally Posted by *z2trillion* 
_Yeah, soldering the components was surprisingly easy, but i'm having trouble figuring out how to case it up. The square usb connector doesnt help._

 

Just drill a round hole large enough for the connector on the cable on the end of the case. Then mount the PCB to the bottom of the case with nylon or brass standoffs. I screwed nylon standoffs to the PCB and fastened them to the case with epoxy. That way I could make small adjustments in the position of the board before the epoxy set to get it positioned just right.


----------



## iampivot

Where do you guys get your black gate caps from? Am looking for a source in the UK.

 Additionally, are someone using this DAC with a good headphone amp circuit? Am looking for something that will fit with the DAC in a nice metal enclosure.


----------



## Magsy

Quote:


  Originally Posted by *iampivot* 
_Where do you guys get your black gate caps from? Am looking for a source in the UK._

 


 Prepare the wallet for pain, then head to www.hificollective.co.uk


----------



## dsavitsk

I have been using one of the beta version of these for a while and it's totally quiet. I just build a "rev a" and I'm getting a bunch of computer hdd noise. Both are powered off the USB, and I am using the same computer.

 It's not burned in enough to compare overall sound quality, but the computer noise is odd. Anyone share this experience? I am using a different amp, the one with the silent dac (a Millett) uses a STEPS while this one (a Pimeta) uses a Velleman, so maybe since the computer is plugged into the same power strip, the Velleman is not able to filter out what the steps does?

 Edit: on closer examination, the noise is from the wireless nic (not the HDD.) I have winamp set to buffer ~ 20 seconds of tracks since I am reading the files over a wireless network. The noise shows up between songs as it is gathering the data.

 -d


----------



## individual6891

Ok, just got the replacement kit guzzler, and it's all sounding top notch. Thanks a lot for organising this!


----------



## cetoole

Are there any PCBs left?


----------



## ixeo

so how does this compare to, say, the EMU0404/EMU1212 ?


----------



## Magsy

It doesn't compare, it sounds good and as a second mobile sound card its great but its not an 0404/1212 replacement for the desktop.


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## Kenny12

i think it sounds roughtly the same as my av-710


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## Tohex

Hi, i'm kinda new....i've been reading up on this thing. As far as i know DAC stands for digital to audio conversion. So basically this little thing is a mini sound card via USB (as far as i've read)

 So to run say shure e2c's off it....would u have to add an amp after this thing...or?

 And where abouts on all the schemetaics/PCB things does the final 'output jack' go...if that is what it is designed to do....as i said i'm new....just wondering

 Sounds cool tho (looks like quite a number of u r using it)

 Thanks

 Alucrep


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## dsavitsk

I have been using a beta version of one of these for a while. I recently built a Rev A and I am having some issues. Every once in a while it makes some Bill the Cat noises and just shuts itself off. To get it back on, I have to unplug it and plug it in a few times. Rebooting seems to help, too.

 I thought at first that it was just a bad joint somewhere, but I resoldered anything that looked questionable, and no improvement. It is likely not the computer as the beta works fine. Also, when it is shut off, I can hear some hiss from it, so it seems to be getting power. Does anyone have any ideas on what to look for as far as troubleshooting?

 -d


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## individual6891

Quote:


  Originally Posted by *alucrep* 
_Hi, i'm kinda new....i've been reading up on this thing. As far as i know DAC stands for digital to audio conversion. So basically this little thing is a mini sound card via USB (as far as i've read)

 So to run say shure e2c's off it....would u have to add an amp after this thing...or?

 And where abouts on all the schemetaics/PCB things does the final 'output jack' go...if that is what it is designed to do....as i said i'm new....just wondering

 Sounds cool tho (looks like quite a number of u r using it)

 Thanks

 Alucrep_

 

You'll need an amplifier to amplifier the output of this DAC. Maybe it'd be able to power low impedance Shure E2Cs, but I'd still recommend a basic amp.

  Quote:


  Originally Posted by *dsavitsk* 
_I have been using a beta version of one of these for a while. I recently built a Rev A and I am having some issues. Every once in a while it makes some Bill the Cat noises and just shuts itself off. To get it back on, I have to unplug it and plug it in a few times. Rebooting seems to help, too.

 I thought at first that it was just a bad joint somewhere, but I resoldered anything that looked questionable, and no improvement. It is likely not the computer as the beta works fine. Also, when it is shut off, I can hear some hiss from it, so it seems to be getting power. Does anyone have any ideas on what to look for as far as troubleshooting?

 -d_

 

That sounds a bit strange, are you sure the pins under the PCM chip haven't come loose and shorted pins? Have you checked the regulated outputs to be +5V and +3.3V? I'd recommend you'd get a DMM and check if any adjacent pins have 0 resistance between them, indicating a short.


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## Tohex

Cool, i'd be happy to have a go at building a small Cmoy or something anyway...fun. 

 I see that dooboloo also has that post going about a small DAC and Amp together for USB. That would be cool...so i'm not sure whether to wait, or to build this and a small amp...i guess i dont mind either way.

 I'll have to get in contact with guzzler.


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## dsavitsk

Quote:


  Originally Posted by *individual6891* 
_That sounds a bit strange, are you sure the pins under the PCM chip haven't come loose and shorted pins?_

 

I'm sure of nothing 

  Quote:


  Originally Posted by *individual6891* 
_Have you checked the regulated outputs to be +5V and +3.3V?_

 

I've got 5.01V at one point and about 8.1V at the other. Straight across the batt tabs (from the USB) is 4.83V. I actually think that there is a short in the USB jack, as I have to jam the cable in pretty hard to get it to connect. Of course, since I epoxy'd the jack to the board, I may never know for sure.

 My other rev-a board and my beta board work fine.

 -d


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## dsavitsk

USB DAC built to match Grado RA-1












 -d


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## iampivot

I am trying to source the exact black gate caps and sanyo caps. The hificollective website doesn't have the Nx type, only the N type, and I've been unsuccessfull sourcing the sanyo OS-CON caps. Any links to sites in the UK that has them?

 Second, the website http://www.mellowparenting.demon.co....er/usbdac.html doesn't load pictures properly in other browsers than IE, because the img url's use \ instead of / for path separators. 

 I tried mailing Guzzler about it, but got no reply. I also think I remember seeing a different version of this website some time ago, with more information about each particular revision. Does anyone know any other website with more details on this DAC?


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## shiggins

iampivot,

 You can get the oscons from rapid electronics, 11-2522. 75p each. They're also doing free delivery this weekend and no minimum order. Nice. I didn't use black gates, instead got Nitais, also from rapid electronics. No idea on their relative quality, but dirt cheap and will get you going until you find black gates.

 BTW, Guzzlers pics load fine for me using Opera.


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## guzzler

iampivot, I thought I sent a reply to you? 
	

	
	
		
		

		
		
	


	




 It should work fine in Internet Explorer if you have such a thing. Sorry about that

 Anyways, I'm in the middle of two things at the moment

 1) Exams

 2) I'm almost completely out of DACs, so I'm going to be working on a new board over the next couple of months. 

 Scheduled changes are:

 a) including low voltage opamps and space for a 3.5mm jack for use as a proper portable source for travellers, and for people who want some more filtering for line stages. Current capabilities will, of course, be retained

 b) getting rid of the MAX1722 for something more easily available, or looking into buying small quantities

 c) Making the board a different shape (ie, square) with holes in each corner for easier mounting (possibly make it fit the Hammond 1455, maybe, they're a bit common!)

 d) making the socket stick out for easier panel mounting

 I'm not going to say much more about it at the minute, as I've really not got a bean of time just now, but I'll start on it the start of July and post some updates

 g


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## bg4533

Guzzler, 
 The pics work in Internet Explorer. They do not work in other browsers (Firefox for me).


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## jerb

I dont suppose there are any unused kits still floating around?


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## awagner

Just thought I'd chime in and express my interest in this project. If there are any of the previous versions of the kit available, I'd like to purchase one or two, and I'd also like to be a tester for the new version. 

 Since you seem to be reconsidering the form factor for the next revision, I think it might be cool to consider making the design expandable with daughter-cards for power supplies, headphone amplification and crossfeed, etc.

 So for non-portable use one could take something like per-anders' QRV07 design...

http://home.swipnet.se/~w-50719/hifi/qrv07/index.html

 chop it in half, flip the power supply half upside down and mount it under the amp portion, put the USB dac on top of these (3 cards total)

 For portable use, a NiMH battery board and maybe a board with a MINT amp with (jumpered, optional) crossfeed, and the USB DAC on top (again, 3 cards total)

 I'm not suggesting you should necessarily design all of these boards, but it might not be hard to make provisions for others to do so by choice of connector placement and jumpers for things like internal vs. external power, internal vs. external volume pot, availability of cases of varying heights for the width you choose, etc.

 Thanks!
 Drew


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## Dr_Skoobie

Hello all,

 I recently got my kit constructed, but am encountering problems. I'm using the dac in conjunction with tangent's "tread" power supply.

 As I can get a nice clean 5vdc from the tread, I have power running into the +5v (formerly +alt) pad, bypassing IC2.

 Like another poster, however, I'm getting closer to 1.5v from IC3, not the desired 3.3v. 

 Guzzler's site still refers to grounding a bypass PS with Vs = 5v to the *right *pad of R1-- which I did initially. I discovered after examining the layout that ground connects to the left pad (verified by testing continuity with the USB connector and DAC chip grounds), duh. Could I have damaged the regulators by having ground attached to the right hand pad of R1 when I powered up the first several times?

 I am also complicating my troubleshooting somewhat by having IC2 connected, as I soldered the SMDs before knowing what PS approach I would take. I did omit the LCR and C1-4 as suggested, but figured that having IC2 installed would be harmless as the +5v pad bypasses it-- am I mistaken?

 Any help in troubleshooting and determining next steps is welcome.

 thanks!

 dr_s


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## guzzler

Which version of the board are you using? If it's a Revision A board, there won't be a pad to the right of R1, except one marked >5V, so I'm not entirely sure where you've put the ground. Is there any chance of a picture (or even annotate the layout from the webpage) of where you put things? IC2 shouldn't have any impact on it as the input trace for it doesn't go anywhere if you've left out the switching supply parts. Really, I'm a little confused as to where you've put the ground, but after that we'll take a look

 g

 PS; regards website, I know what's happened there... I updated it over the easter holidays using the old version from home, and the changes were on the copy I've got here at uni so that's why thats changed. It'll be a couple of weeks until I can change that back


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## Dr_Skoobie

Hi Guzzler,

 It is the revision A board. There is no through hole, I was using the actual right hand solder pad for R1 (which is omitted in this case) for my ground connection.

 When I moved it to the left hand side, I chose the negative/ground through hole for C17 (which connects to the left hand solder pad of R1). As I don't need the L-C-R filter, this seemed convenient.

 I assume this is correct... kind of disappointed to hear that removing IC2 won't fix my problem, no silver bullet!

 With regard to the tread, I verified that the PS is putting out 5vdc relative to its own ground. Measuring from the +5v pad to the revA board ground, however, I get only 1.6vdc. I don't know if this is a symptom of a problem with my construction of the DAC, or a sign that I simply need to increase the voltage output from the tread, considering the load presented by the DAC circuit. I thought I would seek counsel here first so as to avoid damaging anything by guessing. 
	

	
	
		
		

		
		
	


	




 thanks!

 -dr_s


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## guzzler

You could try removing IC2, but it shouldn't do anything. You connected it backwards when you had ground to >5V, but now that you've disconnected that, that trace doesn't go anywhere so it's not like the IC is shorting to ground or anything. The TREAD is more than enough to supply the DAC. First of all, check you're soldering around the main chip with a magnifying glass. It does sound like a short to ground somewhere. Also, it might be a good idea to measure your current draw as this would confirm the problem. Let us know how you get on

 g


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## danko

Hello guys!


 Have anyone tried this PCM2702 DAC to work under linux?
 If it works good, then I think, it's time for upgrade my soundcard 
	

	
	
		
		

		
		
	


	




)

 guzzler, can you send me the EAGLE file-s of the board? 
	

	
	
		
		

		
		
	


	






 thanks in advance: Danko


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## dsavitsk

Quote:


  Originally Posted by *danko* 
_Have anyone tried this PCM2702 DAC to work under linux?_

 

It should work fine.


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## danko

thanks! I have found on www.linux-usb.org, that this chip works perfectly under linux. So, it's time to upgrade my soundcard


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## guzzler

http://www.mellowparenting.demon.co....r/2702RevA.brd

 Enjoy


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## danko

thank you, so much!!!


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## awagner

Thanks for providing such a great kit Guzzler! Here is a photo of one of my completed kits, all cased up. If you are using USB power, I highly recommend this enclosure; it machined cleanly (two holes), it seems bomb-proof, and it looks good (to me at least). It cost me about $5.

 The enclosure is aluminum die-cast with four phillips screws:
 BUD CU-123

 The stereo 3.5mm chassis jack is an MCM 27-655, I believe.

 The grommet is 3/16 x 5/16"

 The USB cable is a chopped printer cable, soldered directly into the board. 

 If you use solid core hookup wire and insulate the board/box with electrical tape, it fits snugly in one direction and is held in place by the wires in the other two directions. (wire = shock absorber)

 Don't forget to put the grommet in the hole and thread the cable through the grommet before soldering into the board. I also tied a knot in the cable to provide additional strain relief.


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## Mod_Evil

Hi friends. I will make a USB DAC with the PCM2704DB... What the differences of the PCM2704DB to PCM2702? The sound input? The sound quality is better than PCM2704? What drivers I use in PCM2704DB/PCM2702 ? 

 thanks.


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## dsavitsk

Quote:


  Originally Posted by *awagner* 
_The USB cable is ... soldered directly into the board._

 

Seems like such a simple idea, but it's a really good idea with this kit.


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## jboehle

I still have one of the original versions of this kit that I never built up. The board is labeled "BETA-1" on the back. I have a couple of questions:

 1) Is there anything wrong with the layout of the BETA-1 boards that would discourage me from building it up?

 2) Does anyone have instructions for building up the BETA-1 board (ie. what goes in each labeled hole)? I can't remember if it even originally came with instructions (if it did I lost them).

 3) Should I even bother building this kit up, seeing as how it requires AA batts and the later versions of this board and the new version Alf is working on are powered from USB (seems much more convenient)? Should I just wait for Alf's new version to come out?


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## Nisbeth

1) No.Other than an optimized power arrangement on the newer version of the board, they are identical.

 2) This should get you most of the way: 
http://www.mellowparenting.demon.co....er/usbdac.html

 3) The kit works fine and it doesn't have to be run on batteries. You might get a little noise, but it shouldn't be too much. 


 /U.

 PS: If you don't want to assemble the kit, I'm pretty sure someone will be willing to take it off your hand.


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## jboehle

So to run the BETA-1 board off USB power I make a jumper from one of the R7 pads to the BATT+ pad, right? Is that it or do I need anything in between (reading through this thread, I think someone used a diode to protect the MAX1722?)?


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## Nisbeth

It could be my post you've read because I'm using a diode on mine - just in case - but it shouldn't really be necessary 
	

	
	
		
		

		
		
	


	





 /U.


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## jboehle

So is the only extra connection to enable USB powered operation from R7->BATT+? Or are there other jumpers elsewhere?


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## Nisbeth

Quote:


  Originally Posted by *jboehle* 
_So is the only extra connection to enable USB powered operation from R7->BATT+?_

 

Yup, that's it 
	

	
	
		
		

		
		
	


	





 /U.


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## jboehle

Finally got around to building my BETA-1 board. The 3.3V and 5V outputs from the regulators measure fine. I think I may have a problem though. I have my meter hooked up to measure the output DC offset before I plug in the USB. I then plug it in, and the DC offset jumps to .25V-.5V and then after 30-60 seconds, settles down to ~1mV on each channel. I am measuring this from OG->OL, and get the same results on OG->OR. Shouldn't the DC offset be 0mV at all times due to the Black Gate output caps? I wonder what I messed up...


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## jboehle

Anyone got any ideas on how I should troubleshoot my dac?


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## guzzler

Did you get polarised caps, or non-polarised? Could you perhaps give us a couple of pictures as well?

 cheers


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## jboehle

Mine was one of the original kits put together by Itzbitz in the US. It came with everything needed to build the board (except for a case). I took some pics last night but they're blurry...I'll try to take some better ones tonight. As far as I can see, I haven't bridged any of the pins on the 2702, but then again I don't have a magnifying glass handy so I can't be sure.


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## J-Pak

Anyone care to rehost the schematic picture? Thanks


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## guzzler

they're still up; apparently FireFox doesn't like my code (not surprising, I don't like it!) Just copy the link to the large ones into your browser, and change the slash directions


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## J-Pak

Thanks working fine in Internet Explorer


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## MiRaCL

How is this DIY Usb Dac compared to a usb dongle soundcard? I've seen these cheapo usb soundcards priced at 10$,they have stereo out and some of them hace toslink out.

 Do these have the same audio quality as the one beeing discussed in this tread?


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## drbig

Hello, This is my first post. This looks like such a great project, but I am afraid to tackle it without a PCB because of the small smt's. does anyone know if PCB's are still available for this project?


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## iampivot

Does anyone have a copy of schematic site? It seems to be down at the moment.


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## jives

Quote:


  Originally Posted by *00940* /img/forum/go_quote.gif 
_Here's what could be very well be my next USB dac. It won't see the light before june or july though. 






 PCM2707 => I2S => PCM1794 => Passlabs D1 I/V stage (minimalist, without the buffer)

 Regulation onboard for the pcm2707 and pcm1794. Outboard regulation for the gain stage. The output caps are outboard too. Balanced to unbalanced will be done by a dynalo that will double as preamp. Bypassing of the IC by 100uF oscon + ceramic (solderside). 

 Size is half an eurocard.




_

 

Was that project ever continued or finished?
 I'm asking because I'm planning to build a similar DAC myself and now I'm searching for infos and ideas


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## picklgreen

Yes! They called it the Alien DAC.


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## jives

As far as I know, the Alien DAC implements the PCM2702 as a Decoder and DAC. But I meant a setup similar to that mentioned by 00904, with a dedicated DAC like the PCM1794.

 Edit
 Okay, found the right thread


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