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PCM2903C: Doesn't output audio

Nick Trevethan
Prodigy 100 points
Part Number: PCM2903C

I am using the PCM2903C in the circuit provided in the datasheet to make a USB sound card. I am currently using a Diodes Incorporated PAM8302A amp for the output (the Adafruit breakout board) with a PUI AS02008MR-5-R speaker. The PCM2903C is recognized on Windows 10 and Linux (Raspbian Pixel running on a Raspberry Pi Zero W) but it doesn't actually output any sound. I know the amp is working properly because I can send PWM from a microcontroller or signal generator and get the expected tones out. I checked the both the left and right output lines on an oscilloscope and neither is outputting any signal. I manipulated the HID pins to test if the chip was actually working properly and they worked (only in windows). 

When I was playing sound on my Windows 10 machine through the speakers and then plugged in the PCM2903C circuit, windows automatically switched outputs but sounds still didn't come out. Just to be completely thorough, I tested an off the shelf USB soundcard based on a C-Media chip and that worked fine on both systems. The PCM2903C did show up slightly differently on windows but I think the icon was for an S/PDIF device which sort of makes sense considering the PCM2903C's S/PDIF capabilities but I was wondering if this indicated that I needed to do some extra configuration to get the analog outputs to work. 

Unfortunately I don't have and S/PDIF devices that I could use to test the S/PDIF I/O to see if that interface is working. 

  • 0
    TI__Guru 57800 points

    Hi, Nick,

    The PCM2903C is a simple device which does not require a specific configuration, once it is connected to the computer it should be recognized as a USB audio device and start playing audio content from USB, given the device is configured as the playback device for some application.

    Is it possible to share the schematic of the PCM2903C?, I would like to see if there is something that could be causing issues. Is there any signal at the output of the S/PDIF interface?.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 100 points

    Hi Diego,

    It looks like the S/PDIF output isn't working as it should. I will occasionally see a square wave at around 1.4/1.5 MHz but there seems to be quite a bit of jitter. The square wave seems to be present even if audio is being played or not and the jitter makes it difficult to tell if playing audio changes the waveform in anyway. Full disclosure, I have never worked with S/PDIF before so I may be missing something (a quick google search seems to validate the 1.4 MHz). I am using a 200 MHz scope so I don't think the jitter is a measurement error unless SPDIF uses a much higher frequency. 

    As for the schematic, I am doing this all on a breadboard using the same schematic as the datasheet. I realize breadboards are not ideal for high speed signals but I figured the USB signals would have more trouble than the audio signals. With windows properly identifying the chip and the HID keys working I was fairly confident the breadboard was not the issue. I can send a picture of the breadboard but its pretty hard to see anything due to all the wires. 

    Best,

    Nick 

  • 0 in reply to Nick Trevethan
    TI__Guru 57800 points

    Hi, Nick,

    Thanks for the feedback. As you mention, the breadboard is not the ideal environment, but the part should be able to at least stream some data. Can you please mesure the voltages on the power pins of the device? this will help to verify if the internal regulators are working as expected. Also, can you please confirm if the caps used in your design have the same values as the recommended for the device?.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 100 points

    Hi Diego,

    I checked the voltages and noticed few things. 1 there was a fairly significant voltage drop between my supply and the actual PCM2903C pins (I was reading around 3.15 volts). I also noticed (much to my chagrin) that I missed a connection (one of the supply pins had its capacitor to ground but no connection to 3.3v). The device now works for both analog audio recording and analog audio output on both windows and Linux. 

    Thanks for the help and patience.

    Nick

  • 0 in reply to Nick Trevethan
    TI__Guru 57800 points

    Hi, Nick,

    Thanks for the feedback, Glad to hear you found the issue.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer