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Moamen Ayman
Moamen Ayman
Associate III
November 17, 2016
Question

Connect DAC to subwoofer

  • November 17, 2016
  • 5 replies
  • 912 views
Posted on November 17, 2016 at 15:51

Hello I'm working on an audio system, I have stored audio files as binary data on an external EEPROM and using STM32F407VGT6 I'm taking this data and send it through DAC to external amplifier and then speaker. now I want to add the possibility to connect an external available on market subwoofer (which used with PCs) and it should take the audio data through 3.5 audio jack, should I connect the audio jack directly to DAC or to the amplifier? I'm afraid if I connect it directly to DAC it may put overload on it!

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    5 replies

    Moamen Ayman
    Moamen AymanAuthor
    Associate III
    November 18, 2016
    Posted on November 18, 2016 at 13:01

    Could some help? and thanks in advance

    Christopher Pappas
    Christopher Pappas
    Senior II
    November 18, 2016
    Posted on November 18, 2016 at 14:28

    If you are referring to the on-chip 12-bit DAC, all you need is a DC-Blocking capacitor in series with each DAC output pin. Also make sure your Binary data is offset by 2048, so that the output can swing peak-to-peak.

    The max output of the on-chip DAC is 3.3 volts peak-to-peak, which is a bit on the high side to drive a line-level input such as those on PC powered speakers, but I have never run into a case where I have destroyed an amp or mixer input channel by applying the DAC output directly.

    As far as overloading the DAC, just make sure to enable the DAC buffered output when you initialize the DAC. I have driven 32-ohm headphones directly from the DAC. with just a drop in voltage swing only. Just avoid running the DAC into a dead short circuit!

    Moamen Ayman
    Moamen AymanAuthor
    Associate III
    November 21, 2016
    Posted on November 21, 2016 at 14:03

    is 0.22uF 

    DC-Blocking capacitor a good value?

    Christopher Pappas
    Christopher Pappas
    Senior II
    November 21, 2016
    Posted on November 21, 2016 at 22:32

    If you are driving a sub-woofer, I would use a larger value. 10 uF or 22 uF are good values to drive the sub-woofer's line input, assuming the input impedance is greater than 1k ohms. This will give less lower bass rolloff, and pass the full level bass signal to the sub-woofer amp. 

    Moamen Ayman
    Moamen AymanAuthor
    Associate III
    November 24, 2016
    Posted on November 24, 2016 at 10:25

    Thank you so much!

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