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Running Audio on Cat5 -- Possible???

Discussion in 'Electronic Basics' started by Ringo Langly, Feb 4, 2005.

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  1. Ringo Langly

    Ringo Langly Guest

    Hi all,

    I'm looking at wiring up my home with Cat5, and I have some rather odd
    questions. First every room will be wired with two pairs of Cat5 cable
    -- one definately for ethernet but the other I'd like to keep open for
    other applications, which is the purpose of this email.

    First... I want to run two phone lines on the Cat5 -- which will
    eat-up two pairs and leaves me 2 more pairs. Is it possible to run
    audio over those other two pairs? By audio, I mean wire-up a standard
    Left and Right (RCA) jack to either pair for stereo audio. Is this
    possible? I'll have a patch panel each cable will run to, so wiring-up
    some audio cables shouldn't be too difficult. I'm just technically not
    sure if audio will even run over a small gauge of wires for this length
    -- which I'm looking at 50-60 feet. Also I'm not sure if there'll be
    interference with two phone lines and two sets of audio cables running
    through the same Cat5 cable -- given the cables can support the audio.

    Thanks in advance for any ideas or suggestions. I'm just trying to
    make wiring my home both easier and as simple as possible. Take care,

  2. Dave Platt

    Dave Platt Guest

    First... I want to run two phone lines on the Cat5 -- which will
    What you are seeking to do is possible, but how well it works will

    If you simply RCA-terminate the two audio lines and go right into your
    audio components, I predict horrible problems with crosstalk, and
    especially with hum. You'll probably end up with a severe ground loop.

    A better approach is to use a "balun" (balanced to unbalanced audio
    transformer) at each end of each audio pair in the cable. A 1:1 audio
    isolation transformer is really what you want... connect an
    RCA-plug-terminated audio coax cable to one winding, and the RF-45
    wire pair to the other winding. Using such a device will have two

    - It'll prevent ground loops, by providing galvanic isolation of the
    grounds in the two rooms. Ground currents can't flow across the
    insulation between the transformer windings.

    - It'll probably reduce hum and crosstalk, by using each twisted
    pair in a fully-balanced mode.

    You can buy commercial audio baluns (
    is one such), or try homebrewing your own using audio isolation
    transformers (e.g. Radio Shack #273-1374) and connectors and casing of
    your own choosing.
  3. It's possible. For line level signals, there will likely be
    some discernable cross-talk, especially near the high
    end of the audio range.
    Not a problem unless you are driving speakers thru those
    wires or hoping to get microphone input levels thru them
    without some noise pickup.
    Interference (aka "cross-talk") would be my only concern.
  4. John Hines

    John Hines Guest

    Possibly, but if your on the phone, you shouldn't be as worried about
    the audio on the stereo.
  5. Mike Barnes

    Mike Barnes Guest

    What you want is entirely possible using a KAT5 transmitter and

    Although the KAT5 units are primarily for video, they convey an
    audiophile-quality stereo signal. The wiring is as follows:

    Blue (4&5) Left Audio
    Orange (1&2) Composite Video/S-video Luma
    Green (3&6) Right Audio
    Brown (7&8) 2nd Video Circuit/S-video Chroma/Digital Audio

    You can connect the audio pairs and leave the others unconnected. That's
    what I do, and it works perfectly. Alternatively you could use SPDIF and
    get *two* stereo signals down your two pairs.
    I can't tell you about phone lines, but FWIW I have about 10 metres of
    cat5 fixed wiring conveying KAT5 audio and ethernet in the same cable.
    [To the structured wiring police: yes, I know, I know.] At each end
    there's a specially-wired dual-RJ45 wallplate, with one outlet labelled
    "LAN" and one labelled "Audio" going to the KAT5 unit. I've detected no
    interference. To ask about phone lines you could contact Keith Doxey,
    the KAT5 designer:
  6. It is possible to run normal line level audio signals through
    CAT5 wiring together with other signals. I have personally
    done this, typically with video signal on the same cable.
    But there shoudl not be any problem with telephone on the same
    wire either (some crosstalk from rign signal and pulse dial possible).

    There is on "secret" on running the audio signal through CAT5 wiring
    successfully: the signals must be balanced.
    Balanced signals can be transported nicely through twisted pair
    cables without considerable crosstalk or without picking much
    noise on the way. The CAT5 twistred pair cable is not a suitable
    medium for transporting unbalalanced audio signals (the
    signal transfer method used n consumer audio RCA connectors and such).
    If you wire unbalanced signal source to CAT5 UTP, you will
    get considerable crosstalk between the signals on different pairs
    and the signal will very easily pick up humming noise.

    Balanced signals are available directly from professional audio
    equipment and can be directly wired to CAT5 UTP. One audio
    signal takes one wire pair. For left and right audio you need two
    wire pairs.
    If you want to connect equipment that do not have balanced
    connections on them, you need to use audio transformers on the
    both ends of the CAT5 UTP cable to perform balanced-unbalanced
    conversion (from unbalanced RCA to balanced on signal source end and and
    back from balanaced to unbalanced in the receiving end).
    In addition to signal balancing such tranformers will provide
    galvanic isolation on the audio interconenction
    (without isolation many times conenctions from one room
    to another will pick up humming noise).
    Ground currents can't flow across the insulation between
    the transformer windings.
    Audio transformers are available as separate components
    and there are also commecially adapters that can convert
    RCA audio to CAT5 wiring and back.
    You need to wire those audio transforemers to your circuit as well
    between your RCA and wire on the wall. You just can't just patch-in
    the cable from the hifi equipment to your patch panel.
    Line level audio will run though this wire this distance quite well.
    Been there, done that. I have one system at my home where I run
    the audio and video trough CAT5e wiring from my computer room
    to my living room TV/hifi system. Cabling distance is about 15 meters.
    No problems. The adapters are homebuilt (my own design).
    The audio adapter part is built out of one of those RCA stereo audio
    signal isolators sold or solving ground loop problems.
    Basicly have opened one the device (it includes two audio transformr),
    cut out the original signal out cable, disconnected the audio
    transformer secondaries from original wiring completely and
    soldered to two pairs on the CAT5 wiring. Works very well,
    is easy to build (if you know how to solder), and cost
    is very reasonable (those RCA isolators cost around 10-20 USD).
    Just build two of theose adapters, one for each end of the connection.
    Or go to a shot and buy a ready made box at considerably higher price.
    There is potential for some interference, but it could work
    well acceptably for you.
  7. I expect the 'phone circuits, now or in the near future, may be
    carrying an ADSL carrier for broadband internet.
  8. Randy Howard

    Randy Howard Guest

    It'll be far from ideal anyway.
    Or you could go a simpler route, and know that it will work, with
    off the shelf components. Check out the exstreamer and instreamer
    products from Very cool, interesting developer community
    working on bolting them into various home automation systems.

    All you need is normal CAT5 (or higher) plugged into your network
    switch wherever you want to run audio.
  9. I went the ready-made route and got two of these:

    They transport the A/V from my PC across a distance of ~30 meters to a
    stereo A/V modulator that merges the signal with my cable TV. It works
    very well indeed. :)

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