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Patch Bay Configuration
For Audio & Video applications

Q. What are the differences between full normal, half normal, non normal/open/isolated, and parallel patchbay wiring?

A: All patch panels should be wired with the output of an upstream device (like a preamp) at the top rear and the input of the next device downstream (like an A-to-D converter) at the bottom rear.

Half normal
This is by far the most common patch panel configuration (even though it is the most complicated).

  • Use for: maintaining a default signal path, with the option to split or replace the signal.
  • Routing when no plugs are inserted in the front: The top rear and bottom rear jacks are connected whenever no plugs are inserted into either front panel jack.

    Example: a preamp (top rear) is by default connected to an A-to-D converter (bottom rear).

What happens when you plug in from the front:

  • Inserting a plug in the bottom front jack breaks the connection between the top and bottom circuits.
  • This allows you to replace the source signal (wired at the top rear) with an alternate source.

    (Example: rather than send preamp A to an A-to-D converter, send preamp B to that converter.)
     
  • Inserting a plug in the top front jack does not break the connection.
  • This allows you to split the input signal both to the output wired in the patch panel (bottom rear) and also to a secondary source connected to this top front panel jack.

    (Example: send a preamp signal to an A-to-D converter and also send that signal to a mixer, headphone amplifier, etc.)
  • By using both jacks, you can insert an effect into the signal path.

Full normal

This is similar to half normalling, but it is used more rarely because it is not as flexible.

  • Use for: maintaining a default signal path, with the option to replace the signal.
  • Routing when no plugs are inserted in the front: As with half normalling, the top rear and bottom rear jacks are connected whenever no plugs are inserted into either front panel jack.

    Example: a preamp (top rear) is by default connected to an A-to-D converter (bottom rear).

What happens when you plug in from the front:

  • Inserting a plug into either the top or bottom front panel jack breaks the connection between the top and bottom circuits.
  • Inserting a plug into the bottom front jack breaks the signal path and sends the signal from that plug to the destination.

    (Example: rather than send preamp A to an A-to-D converter, send the signal from the patched-in preamp B to that converter.)
     
  • Inserting a plug in the top front jack breaks the signal path and diverts the source signal to that plug.

    (Example: rather than send preamp A to an A-to-D converter, send preamp A to some alternate destination.)
     
  • As with half normalling, by using both jacks, you can insert an effect into the signal path.
  • Full normalling is useful for connecting sources that should not have more than one load. (Most audio devices take advantage of impedance mismatching to allow one output to be split to multiple inputs. However, a few devices, like dynamic microphones and electric guitars/basses, are not designed for multiple outputs [unless a transformer is inserted into the signal path].)

Non normal (i.e. open, isolated)

  • Use for: completely configurable signal routing (but with no splitting).
  • Routing when no plugs are inserted in the front: The patch panel never connects the top and bottom rear jacks.
  • This configuration allows for free routing of any path using front panel patch cables. However, note that signal splits cannot be made using this type of patch bay.

Parallel

  • Use for: sending one signal to up to three different destinations.
  • Routing when no plugs are inserted in the front: Connection is always maintained from the top rear and bottom rear jacks, regardless of any plugs inserted at the front. This allows both front panel jacks to be used as additional outputs/splits.
  • What happens when you plug in from the front: An additional output split is created.
  • Parallel patch panels are useful for connecting an output, which is normally connected to one input, to several different inputs at once. Both front-panel jacks can send the signal to places where it is needed.


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