2 headunits

I'm looking to install a second head unit into a 2007 Nissan 350z. It's double din so there is room to put it in. I was just wondering if anything need to be fabricated to support it?

The OEM bracket should be enough, assuming it has holes to ISO mount the second unit.

Are you going to hook the audio outputs up of the second unit?

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Kevin Pierson

Yea right now there is a 7" flipout monitor and the deck is going under it. The speaker outputs of both units are going to be hooked up.  The only reason I'm doing 2 headunits is the guy already has the flipout but the rest of his set up is alpine so he wants an alpine deck. I've already le him know that he cant have them both on at the same time. I haven't checked it out yet so I don't know if it has an iso mount or not.

You can't just hook the speaker outputs together to the same set of speakers - at least not safely, as you're likely to blow one or both HUs that way.  You need to use a selector switch or use one device as an aux input to the other.  Never connect amplifier outputs together.

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as long as both hu aren't powered on at the same time, i wouldn't think there should be a problem.

That is NOT a good idea (simply telling him to turn one off before turning the other on).  Eventually he will turn them both on somehow and damage something.

I would suggest using relays on all the outputs that are triggered by the remote wire of one unit.  Whenever that unit it is on it will energize the relays and switch the speakers to that unit.  Something else you could do is use one relay to energize a relay that cuts power to the 2nd unit.  I like the first idea better though, as it will allow you to safely have both units on, and we all like as many lights in our dash as possible!

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Kevin Pierson

I think I may just talk him into getting a 4 channel and running split rca's.

h4rdc0r3 wrote:

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as long as both hu aren't powered on at the same time, i wouldn't think there should be a problem.

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No, that is not necessarily true.  Even if one amp is on and the other one is off, the amp that is on is also connected to the output stage of the one that is off.  The operating amp is being loaded not only by the speaker but also by the output impedance of the other amp.  This can cause the operating amp to blow.

To use two different amps on one speaker, you must either be able to bridge the amps together (which you cannot do with HU amps) or you need a physical switch between the speaker and the amplifier output.  I like the relay idea, but you couldn't simply trigger them from the remote on lead as that might still allow both to be on at the same time - or both to be forced off.  You need a mechanical selector switch.

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h4rdc0r3 wrote:

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I think I may just talk him into getting a 4 channel and running split rca's.

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And how will that help if you are still trying to power a single set of speakers from different channels of the amplifier?  Same issue as with the HU amps.

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With running the amp if he has both hu's turned on all that will happen is the amp will recieve the signal from 2 preout sources. i didn't mean to say split rca's because what i would be doing is combing the rca's. the FR of unit 1 with the FR of unit 2. FL of unit 1 with the FL of unit 2. RR of unit 1 with the RR of unit 2. RL  of unit 1 with RL of unit 2. then just run those into the FR FL RR RL channels of the amp.

DYohn] wrote:

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p>I like the relay idea, but you couldn't simply trigger them from the remote on lead as that might still allow both to be on at the same time - or both to be forced off.  You need a mechanical selector switch.

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Can you elaborate on this a bit?  How could it allow both to be on?  The NC (87A) and NO (87) contacts of a relay can NEVER be connected, so how could the two seperate outputs ever be connected?

If you add an external amp you would need to isolate the relay control circuit from the common remote line that both head units would share, but other then that there shouldn't be a problem using the remote turn on lead and a relay for each wire (or a couple 4PDT relays).

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Kevin Pierson

If you used one 4PST on the output of each amp then they could still both be on or both be forced off.   Use a single 4PDT relay and then only one could be connected at a time, but if you turned both on whichever activated the relay would be the only one on.  You would not be able to select the alternate HU and leave both on.  I still think a manual selector switch is far more flexible and secure.

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DYohn] wrote:

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f you used one 4PST on the output of each amp then they could still both be on or both be forced off.   Use a single 4PDT relay and then only one could be connected at a time, but if you turned both on whichever activated the relay would be the only one on.  You would not be able to select the alternate HU and leave both on.  I still think a manual selector switch is far more flexible and secure.

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You could install an inline toggle switch to the remote wire that triggers it.  Then you would have a "priority" set up with a manual over ride.    :)

You could eliminate the remote wire from the picture all together and just use a toggle switch by itself.  There are many options, all up to the installer.

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Kevin Pierson

Absolutely, and using a toggle to control a relay is what I would do.  Like I said, a manual selector of some sort.

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