Assembly

If this is your first SMD project, you may want to check out the following links first to get more familiar with SMD soldering techniques:

Add PCM2702

The very first component you need to put on the board is PCM2702. This chip comes in a tiny SSOP28 package. It may be intimidating first time and it may take up to a couple of hours and a couple of PCBs to solder it down correctly. But with a good technique and some experience you will be able to accomplish this task in a few minutes.

There are many ways to skin this kitten. Here is the one I prefer. While it works for me, you may be more comfortable with other techniques.

After you installed the chip, you should examine the pins for undesirable bridges. They are difficult to spot. You may need a microscope or a magnifying glass. Alternatively, look at it holding against a bright light. You should see any bridges immediately. If your soldering looks OK, use a multimeter to do the final check. If you have unsteady hands, this may be difficult.

Add SO8 Chips

After PCM2702, soldering S08 packages is a breeze. First populate IC2.

You have two options with the IC3 position:

If you are going to power your DAC from a virtual ground amp, solder IC4 too. Otherwise, leave it out.

Add SMD Capacitors, Resistors, and Ferrites

I prefer soldering top side component first and then the bottom side. You can do it in any order you like. It is not really important. While populating the board, you should plan your actions ahead and follow two simple rules "smallest to largest" and "inside to outside". This is to prevent locking yourself out inadvertently.

There are two positions for C32. Here is what to do with it.

It may be a good idea to solder C1 after you have soldered the USB receptacle. This would give you easy access to the receptacleís pins. Alternatively, you may want install the receptacle after you populated all top side SMD components but before you started with the bottom side.

Be careful when you populate R14. Do not apply to much solder. It may flow down into the X1 pads and you will have to clean them later.

If you plan not to use CL and CR, do not populate R15 and R16.

Add Through-the-Hole Components

Now add LED, crystal, USB receptacle, and electrolytics. The order is not important. I use the "smallest to largest" rule while I do it.

You may have noticed that the board is designed to accept only electrolytics for CL and CR positions. Why is that? The answer is to make the board as compact as possible. Anyway, with a bit of creativity you can mount other capacitor types too. These are your options:

If your amp (or any other device you are going to connect your DAC to) has some input DC protection, do not populate CL and CR. This way you avoid all sorts of problems with coupling capacitors selection and mounting.

Wiring

Power supply. I will refer to the S1 pad nearest to the USB receptacle as S1a and to the other one as S1b.

Output connectors.

Test the DAC

Step 1. If you populated IC3, connect a battery or an external power supply. Do not connect your DAC to your computer just yet. Check the voltage at 3V3 and 5V pads. If you are not happy with the result, fix it before you proceed to the next step.

Step 2. Connect your DAC to your computer with an USB cable. Re-check the voltage at 3V3 and 5V pads. Meanwhile your computer should recognize a new USB device. If it doesnít, you have some debugging to do.

Step 3. Connect your amp to the DAC. Do not plug in your headphones yet. Switch on the DAC and the amp. Check the output DC offset of your amp.

Step 4. Plug in your headphones (you should switch off your amp while you do it). Select the DAC as the output in your music player. Enjoy the music!

Maximize the performance

Give your DAC some time to break in. The sound signature changes a bit within first 10-15 hours.

If you use Windows, install an ASIO driver. I recommend ASIO4ALL v1.8. There is a more recent version of the driver but it works quite unpredictably.