Question for the wiring experts re: coax for "line-level" connection...

Discussion in 'Home Theater Projects' started by Jeff Pounds, Sep 1, 2005.

  1. Jeff Pounds

    Jeff Pounds Second Unit

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    I'm getting ready to start a project connecting my computer to my receiver by running the connection through the walls/attic.

    One problem: my computer doesn't have any line-level R/L outputs for the sound... it only has the small headphone jacks in the back.

    So, the solution that I thought of is this:

    1. Get one of those Y-adapters from RadioShack for a "line-level" output like this:

    [​IMG]

    2. Plug that into the computer and run some RCA-type connector cables and connect that to a face plate that accepts RCA-type plugs.

    (Here's the part I'm wondering about)

    3. Connect each "line" to a run of coax.

    4. Terminate each coax "line" on a face plate by my receiver.

    5. Connect that face plate to a L/R audio input on my receiver.

    6. Enjoy music on my computer through my receiver.

    The things I'm wondering about:

    * Not being true line-level pre-am signals, will I even be able to hear sound in the receiver without jacking it all the way up?

    * Will the coax cable carry the sepearte L/R channels?
     
  2. Wayne A. Pflughaupt

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    You plan will work, Jerry, but there might be a couple of caveats.

    The plug in the back of the computer is not really a headphone jack. Yes, it is the same type of jack you often see in audio components for headphones, but the computer industry adapted those connectors for other purposes – mic inputs, audio outputs, and I think even 5.1 digital outputs.

    There is probably no good way to connect coaxial a line (assuming you’re talking about RG-6 or [even better for this] RG-59) to those RCA connectors on the face plate. It would be better to use whatever cable they recommend.

    I would run some installation-grade mic cable, like this. One cable will carry the left and right signal (the shield can carry the signal [-] for both channels). It will cost you twice as much to pull two coaxial lines.

    If you want to use coaxial cable, you can terminate it with F connectors, and then use F-to RCA adapters.

    A problem I did have when I ran the cable to my computer: 60-cycle noise (a.k.a. a ground loop). Since it was only temporary I never bothered to trace down the problem, but the likely candidate was that the circuit the computer was on was on the opposite phase from the system’s dedicated circuits. Either that or the computer’s power supply wasn’t especially “clean.”

    Good luck, and let keep us posted. I intend to string a permanent connection to my computer in the near future, so I’d like to know how it turns out for you. [​IMG]

    Regards,
    Wayne A. Pflughaupt
     
  3. Paul Padilla

    Paul Padilla Supporting Actor

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    Strangely enough, I just replied to someone in another thread with a similar question and I linked to what looks like the exact same adapter.

    The only question I'd have is whether it's truly a headphone out or a stereo line output. If you can drive PC speakers with it then it is a line out. Headphone outs do have some small amount of amplification because headphones themselves aren't powered.

    Anyway...you're on the right track. I don't see any reason that two runs of coax shouldn't be able to do the trick. We're just talking about 2 dual conductor wires...speaker wire would work too as long as (for code purposes) it's rated for in-wall use.

    You're not going to get CD quality audio this way but for MP3s and such it should be fine.
     
  4. Jeff Pounds

    Jeff Pounds Second Unit

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    Paul and Wayne -- thanks for the responses.

    Follow-up question though...

    Paul -- you said that in-wall speaker wire would also work?

    Can you explain that... I guess my main issue is that I've never hooked up any kind of interconnect run to a RCA-type connector.

    Is there any easy way to explain how that hook-up would work?
     
  5. rob-h

    rob-h Second Unit

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    If these systems are in 2 diffrent rooms, this is a lot of work for nothing. Why not just put an FM modulator on the PC and tune the reciver to the freqency? X10 use to sell a kit that did this and included a remote to switch songs.
     
  6. Jeff Pounds

    Jeff Pounds Second Unit

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    Aren't FM modulators around $100? That would be significantly more than running speaker wire.

    Also, it's actually quite easy to run wires at my house. I already have hole for the wires from when I ran CAT-5 cable for my DSL connection to the computer, and my reciever shares a wall with my garage, so it's very easy to run wires straight down from the attic and through the wall to the receiver.
     
  7. rob-h

    rob-h Second Unit

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    You can get a modulator from radioshack for quite a small amount of cash. You dont get the control over the music though.


    x10's system is 49.95 right now:

    http://www.x10.com/products/lola_sg1.htm

    Lola Wireless Direct Connect Music System
    Everything you need is included:

    Lola Software for WindowsList Price
    $99.99
    Lola Wireless Remote Control$69.99
    USB Transceiver$49.99
    Direct Cable Pack$19.99
    FREE FedEx ShippingAlways free!

    You Save $189.97 (79%)
    NOW ONLY $49.99
     
  8. Paul Padilla

    Paul Padilla Supporting Actor

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    If you're not equipped to install connectors on the wire yourself, then pre-made coax might be easier and using the F-connector to RCA adapter like Wayne mentioned. I simply meant that two runs of speaker wire would give you the same number of conductors...two each for left and right. You should be able to find crimp on, or preferably solder on connections to terminate the wire with RCA connectors if you're feeling industrious.

    I'm a little intrigued by rob's wireless suggestion. I was well aware that this could be done but I've never looked into any of these products. I use lots of X-10 for lighting myself. However, it does prompt the question as to how you were planning to control the music from the other room. [​IMG]

    The $49 Lola system doesn't include the wireless capibility with the exception of the remote control. The $99 system comes complete with wireless capibility.
     
  9. rob-h

    rob-h Second Unit

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    Thanks Paul, I must have misread there!
     
  10. Wayne A. Pflughaupt

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    Jeff,
    You do not want to use speaker wire for a line level signal run. Speaker wire is not shielded, and will be highly susceptible to picking up interference with a low level signal. Not to mention, whatever connection scheme the in-wall RCA panels have probably will not accomodate large gauge wire.

    Again, if the RCA panel you’re going to use have screw-down terminals for connections, or are set up for soldering, the mic cable suggestion I offered is the simplest and cheapest route.

    Regards,
    Wayne A. Pflughaupt
     
  11. Leo Kerr

    Leo Kerr Screenwriter

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    Another possibility you might want to consider is that if your receiver will support it, run a digital line.

    It might require a ~$50 sound card for the PC, but then the analog circuits in most PC sound cards - especially integrated on the mother-board cards - is generally horrible. If, on the other hand, you get a cheap Soundblaster type card with an RCA SP-DIF connector on it, then you run one wire, and don't really have to worry about ground hum. (Note: You DO have to worry about ground differentials, 'cause you might end up with a pretty serious voltage difference between devices, which might be bad for one, the other, or both pieces of equipment.)

    Also, then you can use your PC for AC-3 and DTS playback... and some games will do at least quasi-AC-3 encodes...

    Leo
     
  12. Jeff Pounds

    Jeff Pounds Second Unit

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    Thanks for the tips, Wayne.

    I'll be starting this project tomorrow.

    I'll let everyone know how it turns out... [​IMG]
     
  13. Jeff Pounds

    Jeff Pounds Second Unit

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    Well, I finished this project last night.... it now works like a charm! [​IMG]

    Here's what I ended up doing...

    1. I used the Y-connector from above to split the line level signal into the L/R RCA outputs.

    2. Went ahead and ran two runs of coaxial cable as the interconnects between the computer and receiver.

    3. For termination, I used Wayne's suggestion of using and F-connector and then a male RCA adaptor.

    4. For the wall plate, I used this from RadioShack:

    [​IMG]

    The back of the RCA terminals will accept a male RCA plug, so I simply plugged the male RCA end from the interconnect/coax.

    So that's it! It actually works really well.

    Thanks to everyone who provided the tips! [​IMG]
     
  14. Wayne A. Pflughaupt

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    Congrats, Jeff. [​IMG]

    Regards,
    Wayne A. Pflughaupt
     

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