The pupDAC is the newest DAC design from cobaltmute, the designer of the grubDAC and SkeletonDAC. The pupDAC is a design primarily intended for the finest possible sound from a USB-only-powered DAC. While DIY-friendly with a now forgiving layout, it is very compact and designed for the tiny Hammond 1455C801 metal case. We think you'll find the sound from the pupDAC worth the work.
Parts types are no different than what you have found on the AlienDAC, BantamDAC, grubDAC, and SkeletonDAC - TQFP-32, SSOP-28, SOIC-8, SOT-23-5, 1206 and 805 series parts. It's just that there's so many of them. Still, go slow and keep track of the parts and you should have no problem. The techniques are no different than on any of the DACs mentioned, with a small exception.
Because there are so many parts on the pupDAC, trouble-shooting the PCM chips later on can be a real issue as access quickly becomes limited as the rest of the parts are installed. Plus, if you botch those two PCM chips and are unable to fix them, then you've potentially ruined a significant investment in all the other parts you've installed afterwards. IMHO, the most important thing you can do to ensure a successful build with the pupDAC is stopping, cleaning, inspecting, and testing the installation of the two PCM chips - U1 (PCM2706/7) and U3 (PCM1794). Get these two chips right before moving on to soldering the rest of the parts and your build should be successful.
To many of you, SMD soldering is something new and perhaps a little bit scary.
However, with the right preparation and strategy, you may find it easier in some
respects than through-hole soldering. Like any Do-It-Yourself exercise, success
depends a great deal on proper preparation and tools. SMD has some special traits that make a few tools (one in particular) absolutely necessary.
Here's a list of things you need, with the first one an absolute necessity:
- flux pen
- helping hands
- small-diameter eutectic solder
- small-tip soldering iron
Tweezers cannot be over-emphasized. Without a good pair, I have trouble imagining how manual SMD-soldering can even be accomplished. Get a good pair! I use a pair of ESD-safe, bent tip tweezers that I bought at Fry's, but all the good DIY-suppliers have them in stock - Mouser, DigiKey, Allied, Newark, etc. Here's a pic that's similar to the pair that I use (I bought mine at Frys):
Another device that you may find useful is the flux pen. The flux goes down as a
thin liquid and gets sticky very quickly - almost sticky enough to hold a part in
place. The pen form lets you apply the flux where you want it, even on a very small
SMD PCB. I like Kester and stick with their products. The one I use is the Kester
#186. It contains regular activating flux that works great (no water-soluable or
no-clean flux for me).
This varies with the individual, but I use a Hakko 936 soldering station, set
at 375 deg.C. Yes, I've turned up the heat with the pupDAC. It has a rather large ground plane to the grubDAC or SkeletonDAC. I also use a 0.8D chisel tip for the Hakko: 900M-T-0.8D. This is a half-size chisel tip of the standard tip that comes with the Hakko 936 (900M-T-1.6D). Keep in mind that the temperature setting and my tip selection go hand-in-hand. If you use a larger tip at that same temperature, it could be that it transmits enough heat to burn. So be aware of this if you choose to use different stuff - this is only a suggestion/guide and what works for me.
Finally, solder is the same solder that I use for all my DIY stuff: Kester 44 eutectic, 63/37, 0.025" diameter. (As a matter of fact, I bought a 1/2 pound in 2006 and have been using it ever since - on every DIY project, not just DACs.) Larger diameter solder is too big for SMD IMHO, and smaller stuff breaks all the time. Again, I cannot emphasize too much the need for using eutectic solder at 63/37. I have repaired a number of individuals' DIY projects over the years now, and I always shudder when seeing projects that used old 60-40 solder. It makes a real difference in the quality of the joints and there's no excuse - even Radio Shack sells 63/37 eutectic solder.
Be sure to review the GrubDAC and SkeletonDAC websites and please check out Tangent's excellent tutorial on SMD soldering: Tangent's Tutorial 3 - SMD Soldering Techniques . I learned how to do SMD soldering with Tangent's methods and with a few exceptions (use of the flux pen), I've been using them ever since. There are a couple of other excellent tutorials that exist on the web:
Edited by tomb - 11/17/12 at 6:42pm