Do you think making a sound card is a complex and impossible mission? Then, you’d better think again…
If you use the IC PCM2702 from Texas Instruments, you will create a powerful and well-built USB sound card. The best thing about a DIY USB sound card is you don’t need to install any driver for Windows XP/Vista, as they are already built-in. Just plug and play it!
This construction’s central core is a 16-Bit Stereo Digital-To-Analog Convertor with the USB interface PCM2702, of course. You need several additional parts to work with the PCM2702, and it’s not complex as you’ve thought here. The sound card can be powered directly from the USB port (jumper W1) or the external power supply (jumper W3). Two power supplies, 3.3V (3V-6V) and 5V (4.5V-5.5V), are needed for PCM2702.
The fixed output voltage LDO TPS76733Q for 3.3V (IO2) and the adjustable output voltage LDO TPS76701Q for 5V (IO3) can be applied. The Output voltage of IO3 should be set to a little bit lower than the input voltage to allow LDO good stabilization (Set it to 4.8V for better performance), and it can be set by adjustable resistor R33.
Also, you have to place the small ferrite beads before all power pins of PCM2702 in Vbus and GND of USB, as these small beads reduce high-frequency hum. Remember to place the Low-pass filter in the output signal to reduce the sampling frequency as well. [source]