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Thread: 2 head units

  1. #1
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    2 head units

    Hi everyone

    I've got a problem that I can't seem to get an answer on,I tried google and I checked forum site and other sites that I had in my bookmarks.I'm hoping someone here has some knowledge on this!

    I have 2 head units and both are wired so that only 1 can play at 1 time and the rca's goto 2 amps(1 for subs and the other for front speakers) but what I want to know is if I put splitters on the rca out of both units to my amps,will it damage either head unit even if 1 is off and will it affect the sound in anyway?

  2. #2
    FLAC Jahntassa's Avatar
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    Yes, it will potentially damage the outputs of the headunits. The OUTPUTS of those HUs are not designed to take any sort of input signal, and over time, may destroy something internally. I'm sure someone will have a better explanation, but that's what I know..

    You'd be better off getting a switch or a small mixer to do what you want.

  3. #3
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    Quote Originally Posted by Jahntassa View Post
    Yes, it will potentially damage the outputs of the headunits. The OUTPUTS of those HUs are not designed to take any sort of input signal, and over time, may destroy something internally. I'm sure someone will have a better explanation, but that's what I know..

    You'd be better off getting a switch or a small mixer to do what you want.

    Typically audio outputs(RCA), by design, have very low output impedance, wheras Zinput is usually very high. So there is a strong preference for current to to take a wrong turn at the Y ... if there is a puth for current flow behind the connector. The Voltage source that is amplified or driven by the other electronics in the HU is probably off or an electrical open, but maybe not, and if this maybe holds true then you're pushing some sensitive electronics the wrong way to ground (there's a lot of data one one need to be sure, from circuit design to individual component datasheets). So to be sure I'd not do it that way.

    I'd set up a relay type switching unit (designed for audio signals) to switch based on which HU's remote is active. And set it up so that if both are active, then a predetermined HU has priority and keeps the switch to itself.
    It's been a while...

  4. #4
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    Thanks guys,I guess I'll have to install switches,I'm glad I waited for an answer here before installing.I'm installing the units on tuesday,I'll put up some pics and let you know how it went.Thanks again.

  5. #5
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    So everyone is saying that this setup

    has a very good chance of damaging the sources?

    Is there such a thing as a diode isolated RCA cable? It shouldn't be all that difficult to cobble one together.

    Spyderbyte

  6. #6
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    I think an auctioneered setup would show some problems. Those diodes need a certain forward voltage to turn on. Being that these are low level lines, that bottom .5V of the scale may equate to some clipping. But...I've never tried it.

    To clarify, I'm not saying its a very good chance. It may cause no problem at all. But without internal skimmys of the HU's, it's an uncertainty, and possible.
    It's been a while...

  7. #7
    Maximum Bitrate Dennis5587's Avatar
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    Quote Originally Posted by DrGadget View Post
    Hi everyone

    I've got a problem that I can't seem to get an answer on,I tried google and I checked forum site and other sites that I had in my bookmarks.I'm hoping someone here has some knowledge on this!

    I have 2 head units and both are wired so that only 1 can play at 1 time and the rca's goto 2 amps(1 for subs and the other for front speakers) but what I want to know is if I put splitters on the rca out of both units to my amps,will it damage either head unit even if 1 is off and will it affect the sound in anyway?
    Also, If you were to have two head units hooked up to the amps, and they didn't have the same line out voltages to the amps, then your gains are going to be set wrong... any idea as to waht you're doing for that?

    2006 Mazda 3
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    JL300/4 Focal 6W4311B Focal TN52
    JL500/1 JL10w6v2

  8. #8
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    Quote Originally Posted by Dennis5587 View Post
    Also, If you were to have two head units hooked up to the amps, and they didn't have the same line out voltages to the amps, then your gains are going to be set wrong... any idea as to waht you're doing for that?
    Good point.
    That's the most immediate concern, and that will occur. I always miss the common sense stuff.

    THe best way to fight that is with identical HU's obviously, or at least knowing the output voltages.

    Or how about having an rca out from 'slave' HU go to RCA in on the 'master' HU, and have only the master HU wired to the amps.
    It's been a while...

  9. #9
    Maximum Bitrate Dennis5587's Avatar
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    Why does the op want two head units to begin with?

    ...and if he really did still want to do this, I guess he could have line drivers on the head units to have closer voltages

    2006 Mazda 3
    Behringer DCX-2496
    JL300/4 Focal 6W4311B Focal TN52
    JL500/1 JL10w6v2

  10. #10
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    Quote Originally Posted by h3rk View Post
    ...Or how about having an rca out from 'slave' HU go to RCA in on the 'master' HU, and have only the master HU wired to the amps.
    This by far seems like the best path IMO.

    A positive would be that the 'Master' could match volumes - at least it works that way my my Pioneer/Premier head unit where I can adjust the gain for each input source (radio/CD/Aux input) in the head - before it goes out to the amp - one gain setting at the amp then works for all.

    Trying not to beat a dead horse, this is essentially the way I use my computer. I run RCAs from computer to head unit, and use the HU to match source signal strength, then send a single set of RCAs to the amp. A small plus is I don't need volume buttons on the computer screen, giving back a bit of touch screen real estate.

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