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      03-16-2009, 09:37 PM   #1
strokeZ
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After market HU questions

Have some concerns adding an aftermarket HU....hope someone can help..

Have Alpine HU with 3 sets of pre-amp outs.....also has 18 Watts/Channel rms if taken at the harness out. A few things dont make sense to me.

1. after market bezel and antenna are non issues.....available and seem to give reasonable fit.
2. after market harness hooks into head unit via HU harness....but should this not be attaching to the pre-amp outs? read several threads here and seems that going from pre-amp outs will work if you can tie into vehicle specific harness - not sure how to go from RCA to harness.....nothing on line available it seems. Going from HU amplified signal to vehicle amp seems dangerous and / or useless as there is nothing to reduce HU amplified signal to a line level signal. Any one have similar experience in successfully doing this?

I see using the after market HU at pre amp outputs very advantageous for the following:

1. can use sub pre-outs to separate amp (replace factory woofers in floor area and rear deck) and drive subs w variable crossover on new amp to optimize sound and volume (use same wiring as in vehicle, just clip it from factory amp for new amp in/output)
2. Can use hi pass filter on after market HU to minimize low frequenciees to mid and hi range speakers. This would also unload factory amp as no low frequencies would be amplified (even tho not used).
3. will maintain factory amp for radio reception.

I figure pumping 4 new 6" subs w a high quality (JL Audio or equal) 75 watt / channel amp will do the trick

Any flaw in my logic? any electrical issues with this set up? (BMW's are finicky).......

glad for any help or thoughts that anyone can provide
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      03-17-2009, 08:47 AM   #2
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well since you are using a new headunit, you will have to run new wiring from the new headunit to each speaker that you plan to run off of the HU. you cant just connect the harness since the signal from the stock radio is digital and goes to the amp first and then out to the speakers.

its not worth getting the aftermarket harness. i did and realized the only thing that you could connect is switched power and ground (and i think i have to redo the ground cuase i have some engine noise now when running 2 sets of rca's). constant power had to be ran to the fusebox. If i could do it again I wouldn't have gotten a harness.

as far as the rca's go, im not sure why you would use a harness/rca converter if you are using aftermarket amps? wouldnt you just purchase rca cables and run them from the HU to the amps? or are you talking about connecting to the factory amp with rca's?

even though the factory amp is "technically" bypassed because nothing is connected to it, you will still need to leave it in place because the antenna runs through the amp and you will not have any radio reception if you remove the amp.

hope this helps!
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      03-18-2009, 03:59 PM   #3
strokeZ
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it does and thanks.....the digital signal is the killer. Not willing to re-wire the entire car just yet......I will look to add a clean sweep, amp and 8" subs behind the driver/passanger seat instead.....still might be a lot of wiring tho from what you posted here. Appreciate the feedback.
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      03-18-2009, 06:03 PM   #4
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not sure if an 8 will fit to be honest. i just took measurements over the weekend of the space behind the sub and it's really very little even if you run a free air sub. definitely do some measuring before purchasing any subs because you might be disappointed if you cant get them in there.

to add about the cleansweep, the rca's would run from the HU to the cleansweep which again means no need for a wiring harness/rca converter type piece
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      03-24-2009, 04:46 PM   #5
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yep....cleansweep is the only way to go. think someone on another thread said it best....cant half ass this one.....its an all or nothing mod (HU, amp, speakers, subs, etc). Thanks for all the replies!
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      03-24-2009, 05:31 PM   #6
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Quote:
Originally Posted by nickpapa View Post
to add about the cleansweep, the rca's would run from the HU to the cleansweep which again means no need for a wiring harness/rca converter type piece
sorry, let me correct myself. the rca's would go from the amp to the cleansweep. not the headunit to the cleansweep since the stock headunit does not have rca hookups.
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