Wiring circuit

Creating a sound card is not more complex problems. If you use Great IC PCM2702 from Burr RED / Texas Instruments you can create a card USB sound fully functional. The sound card can be activated from the USB port and has one stereo output.


You do not need to install drivers for Windows XP and Vista, because the driver is already in the system, XP and Vista. So this series is really plug and play.

The core of this construction is a 16-Bit Stereo Digital-To-Analog Converter with PCM2702 USB interface.

PCM2702 only requires a few additional components to work. This scheme is not complex. The sound card can be activated directly from the USB port (jumper W1) or from an external power supply (jumper W3). PCM2702 requires two 3.3V power supply (3V-3.6V) and 5V (4.5V-5.5V). I use a fixed output voltage to 3.3V LDO TPS76733Q (IO2) and the output voltage is adjusted to 5V LDO TPS76701Q (IO3).

LDO Both are produced by TI, I use it because there in my drawer. Each LDO The same can be used. IO3 output voltage should be set to slightly lower than the input voltage to enable LDO stabilization is good, in my case the output voltage set to 4.8V. output voltage can be set by the resistor R33 is adjusted. In the case of low power supply, IO3 be shorted by the W3 jumper. Signalizes D3 LED power on.

Small ferrite beads are placed before all power pins on the PCM2702 and GND Vbus and USB. Small beads reduce high frequency hum. I have a problem finding SMD ferrite beads small local shops but finally I get some of them from the old hard drive. They are not really necessary, you can use zero ohm resistors instead of them.

Low-pass filter placed in the output signal path to reduce the sampling frequency. OPA2353UA dual op amp configured as two stereo-order low-pass filter. Led diodes D1 illuminates when the PCM2702 play audio data received from the USB bus. Diode D2 Led illuminates when the USB bus audio delay the transmission of data to the PCM2702.

This circuit works very well. I just had shorted crystal during soldering so that circuit does not work, but after removing the short noise, a sound card to work. I have been tested on Windows 2000, XP and Vista. The electronic circuit works in all the systems mentioned. Driver is in the operating system so that the sound card is ready within a few seconds after you connect the electronic circuit is with a PC / Laptop / Notebook you are in trouble with the sound card / sound card that.

During writing this article I have found that the PCM2702 is now not recommended for new designs, but TI offers a better solution. PCM2704, PCM2705 has the same functions as the PCM2702, but they include an output filter. They were able to push the headphones directly.

Volume and mute can be controlled via the SPI bus in PCM2705 or PCM2704 with pushbuttons in the case. PCM2704 and PCM2705 are in TSSOP28 package. PCM2706 PCM2704 and PCM2707 similar to PCM2705 but in addition they have the I2S bus. PCM2706 and PCM2707 are in a TQFP32 package. I recommend using the new chip (PCM2704 / PCM2705) for the new design an Operating System.