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Thread: DAC Technical Question - Resistors inline with outputs

  1. #1
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    Default DAC Technical Question - Resistors inline with outputs

    This may belong in the Advanced Technical Discussion, however more DAC stuff shows up in this category.

    What are the resistors on the OpAmp outputs to the ILDA connector for? Are they for cable matching, current limiting, or filtering or what? For reference you can look at the bILDA schematic here: http://www.linux-laser.org/download/bilda/bilda-sch.png bILDA uses 75 Ohm resistors. I have also seen 22 Ohm used as well. Any help/hints would be appreciated.

    Thanks, Chris

  2. #2
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    Had the question answered not on the forum. They are there for short circuit protection so as to not draw too much current from the output op-amps. Thanks DrLava.

  3. #3
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    A few years back, I was experimenting with an op-amp filter circuit using signals from an audio card to drive it, and I
    recorded its output from the line input jack. Whenever I connected the circuit to the line input, it would latch up. In
    desparation, I got a wild idea to add a small resistor (22 Ohm) in series and it pulled the project out of the toilet- not
    sure why, maybe it was RF kickback or something.

  4. #4
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    Actually... These resistors set the output impedance of the DAC. Without them, the output op-amp can oscillate and/or pickup spurious EMI from the external cabling.

    It is normal to always have series resistors, just about every single audio op-amp stage does (typically 150 ohms).
    This space for rent.

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