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Balanced outputs

Discussion in 'Electronic Design' started by Dirk Bruere at NeoPax, Jun 4, 2008.

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  1. Looking for a buffer design to provide a balanced output from an
    AK4396 DAC. The latter outputs a differential signal.
    I found this page, which seems to provide a nice example
    http://sound.westhost.com/balance.htm

    Particularly, Fig. 5
    Any comments on suitability, or anything I might have overlooked in
    using something like this?

    Dirk
     
  2. Eeyore

    Eeyore Guest

    All looks way too complicated to me.

    Did you know that a balanced output doesn't require 'symmetrical'
    voltages on both its legs, merely matched impedance ? Honest.

    You can do it with a single op-amp.

    Graham
     
  3. Buffer each leg separately with a unity gain config?

    Dirk
     
  4. Eeyore

    Eeyore Guest

    No. In the simplest configuration, the output op-amp drives the + wire via
    say 100 ohms.

    The - wire is connected to the local ground next to the op-amp's feedback
    network by another 100 ohms.

    That's a balanced feed.

    There are even cuter ways of doing it involving taking that second 100 ohms
    into the feedback network too but that actually goes beyond being merely
    balanced. It's 'active sensing' and will drive an UNbalanced input with the
    same precision.

    You only need 2 op-amps if you need say +28dBu output level.

    Graham
     
  5. I just need unity gain.

    Interesting page
    http://www.dself.dsl.pipex.com/ampins/balanced/balanced.htm

    Dirk
     
  6. Eeyore

    Eeyore Guest

    The one I suggested above was Fig 3. The very simplest. That will do you fine
    although 5 can help fix other problems like driving unbalanced inputs.

    The active sensing one is Fig 5.

    If you REALLY want to learn from an expert find Bill Whitlock's article(s) on the
    subject at jensen transformers. Of course he's promoting the use of transformers
    but there's a lot of good stuff there and he blows a few myths away. I saw him
    present this at an AES meeting actually. Very good too.

    Graham
     
  7. I just want to drive some high quality audio direct from a DAC +/-
    outputs over about 15m of shielded cable. I think I'll maybe reduce the
    DAC outputs to single ended first using the recommended circuit and then
    do one of the above - maybe using Fig 3
     
  8. Eeyore

    Eeyore Guest

    What DAC btw ?

    Graham
     
  9. AK4396

    Dirk
     
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