[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?