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PCM2702 USB DAC Revision B

post #1 of 670
Thread Starter 
I always wanted to build PCM2702 USB DAC also known as Guzzler’s DAC. I contacted Guzzler but he was completely out of boards. I realized that the only chance for me to build the DAC is to order the boards myself. Guzzler has kindly sent me his Eagle files and has been very supportive. The original design did not fit my needs 100%. So presented with the opportunity, I took the liberty of making some minor modifications to the board layout and to the schematic.

The new schematic

The new board layout

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

Your comments are very welcome!
post #2 of 670
I'm not qualified to comment, but right on with the design changes...now bring on the 1 box mint/usb dac combos!
post #3 of 670
Nice job... mark me down for 5 of them when the time comes.
post #4 of 670
When everything is finalized and ready for a group buy, just remember to contact Jude, and a thread can be posted in the Group Buy Forum.

-Ed
post #5 of 670
Neat, though if you are going to do it, why not go all out? Use a pcm2902, take the digital output and give it to an AD1865 or pcm1704 and then do the I/V right (I'll leave what that means to others, though my preference would be to use a transformer) rather than using the I/V builtin to the chip. Just a thought. This would, of course, cause the project to cost about 6x more, so maybe that's not what you're looking for ...
post #6 of 670
Great initiative, Alf


/U.
post #7 of 670
I would like to see a design that feeds it to a higher quality DAC also, however since this is to be portable I doubt that was the design intent.

However if an alternate design could be fashioned I would be very interested in it to a upper mid/hi fi dac kit that doesn't cost an arm and a leg.
post #8 of 670
The DAC is looking pretty good, but are you still using the Maxim MAX1722 IC? That, along with the WIMA MKS-02 caps that were origionally used, are very hard to source here, so if you could design it with other parts in mind, that would be great.
post #9 of 670
I'm interested in a few once the OK for a group buy happens.

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

Nice work Alf.

Botch.
post #10 of 670
Certainly would be a good idea to replace the MAX1722 with something obtainable from digikey

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

And an idea I was thinking of was a better output circuit than what is there, like an active HPF with 12dB/oct, something that you can use high quality small film caps in it and not have to worry about what load it is driving, though then you'd need the split supply but if you are running it in the same case as an amp that is no problem, just if you aren’t that it gets tricky
post #11 of 670
nice job Alf, count me in when doing group buy!
post #12 of 670
I missed on the first one, hope I don't miss out on this one.
post #13 of 670
nice work, keep it up
post #14 of 670

MAX 1722

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

You can check that in he schematic.

Manuel
post #15 of 670
Thread Starter 
Thank you for the warm feedback guys!

Quote:
Originally Posted by cetool
but are you still using the Maxim MAX1722 IC?
Quote:
Originally Posted by DaKi][er
Certainly would be a good idea to replace the MAX1722 with something obtainable from digikey
Quote:
Originally Posted by MASantos
I spoke with Alf during this week about the project an dhe told me that he wasn't going to use max1722
I considered this. Guzzler suggested using TPS6107x and I even designed the first version of Rev B around it.

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

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

Quote:
Originally Posted by cetool
That, along with the WIMA MKS-02 caps that were origionally used, are very hard to source here
The caps are available from Farnell UK. If you prefer not to buy from them, I will be pulling together a few kits. Part selection should not be a problem then.

Quote:
Originally Posted by dsavitsk
Neat, though if you are going to do it, why not go all out? Use a pcm2902, take the digital output and give it to an AD1865 or pcm1704 and then do the I/V right
Quote:
Originally Posted by dsavitsk
I would like to see a design that feeds it to a higher quality DAC also
I am too interested in a high-end DAC design to complement my EMU0404 at home. However I am afraid that this is out of the project's scope.

Quote:
Originally Posted by DaKi][er
And an idea I was thinking of was a better output circuit than what is there, like an active HPF with 12dB/oct,
I think the DAC will be used primarily as a daughter card and placed in the same enclosure as the amp. There are better designs out there for standalone DACs.

Quote:
Originally Posted by grawk
now bring on the 1 box mint/usb dac combos!
I designed the board with MINT in mind. There is enough space left to add a small amp and fit it all in Hammond 1455C802.

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