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PCM1793: differential output

george denno
Prodigy 70 points
Part Number: PCM1793
Other Parts Discussed in Thread: OPA1678,

I am looking to get a line differential output from this guy to go into an audio mixer. I would just like to confirm that I can throw a bipolar cap on each LOUT+, LOUT-, ROUT+, ROUT-, put some protection diodes in there, route to 2 balanced 1/4 inch jacks and be done with it. All the application notes have differential to single ended buffers and I would like to keep it differential. Thanks in advance for your patience, I am not an EE, I'm just a guy trying to build an audio transceiver.

  • 0
    TI__Guru 53573 points

    Hi George,

    That might work, but the reason this is buffered in most cases is that this can only handle a minimum output impedance of 1.7kΩ.  Meaning if too much current is drawn from the device there could be distortion.  In addition, if you have a low pass filter to attenuate the out of band noise (recommended) that R of the RC can cause a voltage divider with any load on the line.  So to an extent, this really depends on the input to your mixer.  One thought is that you can put a unity gain buffer on each output to keep it balanced (the OPA1678 is a good choice). 

    Let me know if that answers your question, and feel free to post your schematic for review.

    Thanks!

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 70 points

    So this is the basic idea you propose if I am not mistaken. from the data sheet it seems I can but zero crossing VIN +-800mv PP in this guy and get the same thing out with a much lower Z.

  • 0 in reply to Paul_Frost
    Prodigy 70 points

    it did not put the picture in the first one for some reason.

  • 0 in reply to george denno
    TI__Guru 53573 points

    I'm not sure I follow that last comment, but your schematic looks reasonable - I would still have the RC low pass filter between the PCM1793 and the amplifier.

  • 0 in reply to Paul_Frost
    Prodigy 70 points
    Thanks Paul, you're a winner. The comment is just me double checking that I can AC couple everything with no common mode voltage and get that 2V RMS signal I'm after.