With Full-Speed Transceivers? Partially Programmable Descriptors? Adaptive Isochronous Transfer for Playback? Suspend Flag?
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This sound card can be powered from USB port and has one stereo output. This is really plug and play. The construction on the project web page inspired me to build this thing also. The schematic is not complex. PCM needs two power supply 3. Any similar LDO can be used. Output voltage of IO3 should be set to little bit lower than input voltage to allow LDO good stabilization, in my case output voltage is set to 4. Output voltage can be set by adjustable resistor R In case of low power supply, IO3 can be shorted by jumper W3.
LED D3 signalizes power on. These small beads reduce high frequency hum. I had a problem find this small SMD ferrite beads in local stores but finally I acquire few of them from old hard drive.
They are not absolutely necessary, you can use zero ohm resistors instead of them. Low-pass filter is placed in output signal path to reduce sampling frequency.
Realization: Bottom side single side PCB, made by standard etching method Assembled top side Assembled bottom side Conclusion: This circuit works very well. I have tested in Windows , XP and Vista. It works in all mentioned systems. Drivers are present in operation system so the sound card is ready in few seconds after you connect it.
During writing this article I have found that PCM is now not recommended for new design, but TI offer even better solution. They are able to drive directly headphones. I recommend using these new chips for new design look at the TI web page.
USB Sound Card with PCM2702