This article showases a sound card with an IC from Texas Instruments, PCM2704. Thanks to this circuit with all necessary features inside 28pins SSOP package maker was able to built a quite small sound card. The result is a sound card with size of gumstick.
This device is a fully functional sound card for PC. The main advantage of using PCM2704 is a much easier construction. As you can see on the block diagram it has built-in 5V and 3.3 voltage regulator, HID interface (MUTE, VOL+, VOL-), S/PDIF output. The circuit can be powered directly from USB port. Next advantage is that the outup DAC is able to drive directly 32ohms headphones, but the ouput power is only 12mW. For all details please refer to the PCM2704 datasheet.