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Is this really what you'd expect from an audio balun

Discussion in 'Electronic Repair' started by Bob F, May 5, 2013.

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  1. Don Pearce

    Don Pearce Guest

  2. Bob F

    Bob F Guest

    Will this design eliminate ground loop problems? My concept of baluns was that
    they isolated the two ends by placing them on opposite windings of a
    transformer. I am no expert, which is why I asked.
     
  3. Don Pearce

    Don Pearce Guest

    That is a different thing. You need a transformer to kill a ground
    loop entirely, but yes, provided there is enough inductance in the
    coils this will still make a good job of getting rid of hum from a
    ground loop.

    The downside of the transformer method is that lower bass response is
    usually somewhat compromised.

    d
     
  4. Will this design eliminate ground loop problems? My concept of baluns was
    that
    they isolated the two ends by placing them on opposite windings of a
    transformer. I am no expert, which is why I asked.[/QUOTE]

    It will stop ground loop problems for the range of frequencies where the
    transformers work. It's not clear what that is.

    Transformers have a limited working range of frequencies. The ones you
    posted have DC to MHz passthrough but limited common mode blocking. The
    other wiring of isolators blocks DC to MHz common mode but only passes
    through maybe 50Hz to 15 Khz; more or less depending on the quality.
    Isolators can do weird things to the impedance too.

    If this is pro-audio, the absolutely best fix is using balanced cables
    with balanced connectors. The audio quality will be superior to any
    other hack.
     
  5. Don Pearce

    Don Pearce Guest

    No, because of the way the windings are arranged their inductances
    cancel each other out for the audio signal, but not for the induced
    hum.
    Effects strat becoming apparent well before you hit the 3dB point.

    d
     
  6. Bob F

    Bob F Guest

     
  7. Bob F

    Bob F Guest

    The windings being on a transformer arranged so that common mode noise cancels,
    and the signal doesn't?
     
  8. I was going to get involved in this conversation, but have decided not to. All
    I know is that the schematics don't make much sense (primarily because there
    doesn't seem to be "proper" isolation between the bal and the un.
     
  9. Bob F

    Bob F Guest

    Which was exactly why I posted the question. At the least, there is a DC(/LF)
    path from one end to the other.
     
  10. I was going to get involved in this conversation, but have decided
    Which seems to kill the whole reason for baluns, does it not?
     
  11. Don Pearce

    Don Pearce Guest

    That's it. The windings are wound in the same direction on the two
    sides. That means that the forward and reverse signal currents on the
    two windings are always in opposite directions magnetically. So the
    signal doesn't see any net inductance.

    d
     
  12. Don Pearce

    Don Pearce Guest

    Isolation is not implied in the function. As long as the signal on the
    output is of equal amplitude and opposite phase on the two ports, the
    job is done. This circuit satisfies that perfectly.

    d
     
  13. Don Pearce

    Don Pearce Guest

    Nope, nothing to do with it - unless you require performance down to
    DC, which of course audio doesn't.

    d
     
  14. Bob F

    Bob F Guest

    Is this design going to avoid ground loop problems? Those signals would just be
    on the one side, so would they be canceled?
     
  15. Don Pearce

    Don Pearce Guest

    The ground loop is fixed by the inductance presenting a huge series
    impedance to the hum current, which only passes along the ground wire.
    There is no equal return current in the signal wire to cancel the
    inductance.

    d
     
  16. Don Pearce

    Don Pearce Guest

    Spidey sense is not always very useful.
    Construction of these transformers doesn't have to follow the normal
    rules. They don't need good linearity, so very high permeability
    ferrite can be used for the core in order to get a high inductance
    value. This is because the audio doesn't have to pass through the
    ferrite, it bypasses it.

    d
     
  17. Construction of these transformers doesn't have to follow the normal
    ?????????????????????????????????????????

    I know of no transformer type in which the signal "passes through" the core
    material.
     
  18. Don Pearce

    Don Pearce Guest

    Nit-picking the terminology? In a transformer, the core is used to
    couple the signal from the primary to the secondary. In this sense the
    signal "passes through" it. In the series balun the only signal that
    interacts with the core is the unwanted common mode or single sided
    signal. This is generally of such a low value that it has no chance of
    causing sufficient field strength to cause non-linearity.

    d
     
  19. Bob F

    Bob F Guest

    Doing a little research, I found the following page. It seems these baluns are
    "current mode" baluns.

    http://vk5ajl.com/projects/baluns.php
     
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