Presenting the babyDAC
*loud applause and other self-congratulations*
Since the world hasn't ended, I thought I'd post this DAC up for comments. I had been thinking of doing this for a long time, but school loads are always heavy for me. Four months later, I had a chance to come up with this little number. It's a TI PCM2706(/7?) USB-to-I2S feeding a Wolfson WM8740. I initially tried to squeeze a dual differential configuration on the board, but I thought I'd take a smaller step before tackling that behemoth of a project. It's all pretty straightforward after that.
I separated analog and digital grounds, and I went with a simple crystal oscillator for the clock. I left footprints for the box-type caps used in the BantamDAC, and I still have to work out clearance for the two non-corner notches. I also want to rework the mini-USB plug since I just grabbed it from the EAGLE library, but I had bigger issues with getting the two chips to play nicely on the board. I tried to reduce the length of the I2S lines as much as possible (pins 5, 17, 18 and 19 on the PCM), but I think overall the delay is negligible at this size. Also, components are tiny at 0805, cuddling nice and tight since I was a bit paranoid about not having room since I started with a second Wolfson chip on board. Thus, if anything is too unrealistically close, let me know.
If you look kinda closely, you'll notice a lot of vias overlapping with SMD pads. I operated with the principle that this is fine and acceptable since I couldn't find any standard stating the opposite, but I wanted to double check that this is alright. Some vias are completely engulfed by pads.
Though the board is cut for a cableDAC-ing, I still want to make use of the Hammond 1455C80x enclosures. That's why there is so much clearance on either side for tall parts. The idea is to eventually pair this with a balanced headphone amplifier with the Carrie's footprint. That's why it's hooked up for bus-powered operation so that the computer will give the USB as much power as possible. I just thought I'd try my hand at DAC design first since I didn't want to let cobaltmute have all of the fun. :)
There's lots of room and time for wiggling and rearranging, so fire those comments my way. Don't hesitate to be specific. ;)