Alien DAC v1.1 Construction Thread - Page 58

I build a Alien Dac too, but I have some problems. When attaching it to my PC it says 'Unknown device (device might be broken)'. Does anyone have an idea what i might have done wrong?

well i haven't had to do much troubleshooting on this project, and this is the most obvious thing, but the first thing you should do is re-check EVERY joint on the PCM2702. it sounds like the computer is recognizing that a chip is there, but that the chip is either, a) not connected correctly, or b) fried.

if you have a multimeter with fine enough probes, i recommend going over the entire chip and checking the resistance between each pad and the upper part of the corresponding pin, to ensure that you have a good joint. i also checked the resistance between adjacent pins and pads, to make sure i didn't have any hidden bridges. if you do this, note that pins 13, 14, 15 and 16 are all connected to ground, so the resistance will be roughly zero between any two of them, if they're connected properly.

perhaps i'll still give those 0805 caps from Digi-Key a shot. unfortunately, i don't know that i'll ever use them again if the result isn't good, and Digi-Key makes you buy a minimum of ten . but... i guess i can forgo lunch one day and spend that $3.30 on caps instead .

Hi Chrizo! There are many discussions about this subject within this huge thread. I would encourage you to use the search feature and search for the word unknown. I'm positive you'll find some answers. Mostly, though, you'll find that the top things to check would be:
- is your board cleaned (flux can short some of the pins on the 2702)?
- is there any solder between the pins of the 2702?

As you can see, lots of items deal with the main chip on there. But there are lots of replies to those questions as well!

Welcome to Head Fi!

These are such standard values for decoupling IC's, that if you do any smt PCB's in the future, you will need much more than 10. I bought 100 recently. Of course, the NP0/COG are more expensive than the X5(7)R. Still, these are generally used all over the place in electronics (not just audio).

good to know - i no longer feel so bad about buying 10. don't think i'll jump on board and buy 100 like you just yet, though.

So I just finished botching the solder job on my 2nd alien PCB while trying to solder in the PCM chip.

On the first board/try, I took a toothpick and individually fluxed each pad. I then tinned a corner pad with a very small amount of solder. I slid the chip into place and soldered the first pin. I was going to solder each pin.. I got up to 4 pins done and then a bridge! So I tried to add some flux and sorta move the solder away from the chip but it really wouldn't move much. I tried a solder braid but that didn't pull much solder either. I then decided to try to add more solder and make sure my tip was clean and sweep it across, but I think the solder just flowed underneath and connected where I couldn't easily reach it with the braid or just to get it to separate with heat.

On my second board, I tried to get tricky and tin each pad with a very tiny amount of solder.. I set the chip into place and tacked the first pin. I then was pretty successful with all the pins and then on the other side, I added too much solder because some of the pins weren't setting to the pads and it went much like the first chip, only this time, the pins had kinda slid off the bump of the tinned pads and weren't lined up correctly!

So, I'll maybe order a third PCB and if I can't get it, I'll just use Jeff Rossel's excellent pre-soldered chip option but I'm pretty stubborn about doing things myself.. since it is a DIY project!

I was watching the very few youtube vids on SSOP28 and read some popular how-to posts on here about soldering these chips but I can't manage to get something usable (yet).

FYI - from my own experience, it seemed that to make the flood and suck work would require a too-hot iron. Like you, I found that the wick was less than optimum in pulling the solder from the pins - unless you turned the heat up and spent more time applying that heat, etc. - which can't be good for the PCM chip.

Instead, I used the method that Alf references on his website: applying a tiny bit of solder to the tip, while working horizontally across the rows of pins and wiping constantly as you go. It's sort of an action of putting a little solder on the tip, then wiping it off in a downward and away motion parallel to the direction of the pins. If you get a bit more solder, then continue wiping until the solder cleans up. You start it out with flux everywhere - the solder will only stick to the pins and the pads. A bridge only results if you use too much solder. The wiping minimizes that potential. Better to think you haven't added enough solder than to start out cleaning up blobs in the first place.

That seemed to work better for me, practically and psychologically. On the other hand, the flood and suck method seemed more one of "ruin it, then fix." Of course, IMHO and YMMV.

i made a bit of a hash of mine to begin with but continued to flux and wipe for about an hour till i got it done just give the chip time and dont let it get too hot.

ill post pics once i get the mountain of flux cleaned off the board!

I finally found time to put mine together. Messed up the soldering of the PCM chip the first time trying to do it with my old butane iron and no flux. After that I went down to Jaycar and bought an electric iron and a flux pen. 2nd attempt was a little more successful. (Having a glass of wine also helped - my hands were too jittery from too much coffee). I painted flux over everything, pinned the opposite corners of the chip. I was worried about bridging on the bottom corner, until I realised the pins were connected anyway. I tried the method where you run the iron down the edge of the pins, but I had too much solder so it bridged the lot. I used solder braid and my (hotter) butane iron - keeping the iron on one spot in the braid and moving both quickly down the line of the pins. Not sure if that's the proper technique, but it seemed to work. By some miracle everything worked and I'm listening to it now.

The one thing I have noticed is that with the amp turned up, I can hear noise that is influenced by mouse movement, graphics card and disk activity. I assume it's a common thing because pretty much every work PC I've used with ****** onboard sound has had real bad noise of a similar nature. Is this RFI that's being picked up by the DAC, or something like a power supply issue? (Currently unregulated USB) I've got it sitting in an unshielded plastic case until I find it something better.

That said, the noise floor is well below my threshold of hearing with my amp set at a reasonable volume. I'm really happy with this awesome little circuit! I'll build another when I get around to doing my headphone amp. Thanks heaps to everyone who worked on the design!

To check if it's a power-supply issue, just grab some batteries... three fresh alkaline AA batteries should get you somewhere between 4.5 and 4.8V, enough for testing your unregulated config. Tape them together and go. (Make sure it's not above about 5.5V or you'll start frying something... Also make sure that the switch S1 on the board is OPEN, otherwise you may send the battery's juice straight back into your USB port. It doesn't like that.)

hi,

i just build my alien dac.

i got the 3v3 but on my 5v i'm getting 1.47v.

where shld i look towards for debugging?

If you're building the unregulated USB version, did you jumper pads AV+ to 5V? If you used an adjustable regulator, have you got the correct resistor values?

i'm building from a kit i got from jeff.

so the resistor values shld be correct.

i'm guessing since the 5v isnt there i shld be looking at the regulator IC instead. Not sure what caps and resistor shld be populated if i'm building from the kit jeff packed. it be running from usb alone

its possible that you switched R31 and R32, as following the equation for choosing them,

Vout = ( 1 + R31 / R32) * 1.26

would give approximately 1.47 if you put R31 and R32 in the others position, so it could be a very minor issue, my math just so you don't have to do it for a 4.8v out

( 1 + 31k / 11k ) * 1.26 = 4.82

but

( 1 + 11k / 31k ) * 1.26 = 1.7