# Bridging a HEAD-UNIT



## lawrence131 (Oct 28, 2006)

I just bought a Kenwood KDC-HD545U head unit for my bro to use with JBL GTO 6.5" Coaxials (can run at 2 ohm or 4 ohm, $55 with Amazon 45% coupon) as a super budget system. The HU is listed as 22W RMS per channel - can I bridge the front and rears from the built in HU to power the front speakers? He's on a budget so I thought this would be an OK start before adding any amps.

If I just connected the rear left (-) and the front left (+) to the front speaker, what would happen?

I have an Infinity basslink all-in-one sub he can use so I wanted to see how it would do without adding any (other) amps.


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## benny (Apr 7, 2008)

dont do it, unless you want to buy a new headunit.


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## 89grand (Nov 23, 2006)

No it's not possible.


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## tanakasan (Sep 8, 2007)

lawrence131 said:


> If I just connected the rear left (-) and the front left (+) to the front speaker, what would happen?


Best case...no sound. Worst case...new HU!

You can get *very* inexpensive amps that will spank a HU's minimal power rating.

Robert


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## bumpinP (May 5, 2010)

lawrence131 don't do it.

Didn't Pioneer put out mosfet decks that you could bridge the rear channels on? If memory serves me right they were advertised as being able to drive two front speakers and a sub off the rear channels.


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## bumpinP (May 5, 2010)

http://www.diymobileaudio.com/forum/classifieds/85867-cheap-pioneer-amp.html


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## sqshoestring (Jun 19, 2007)

You can pick up old common/major brand amps for like $20-40 on ebay all day long that will trash a HU. Even an ancient 12v rated 2x30rms will since that is like 2x50 cea. HU amps are worthless and thats that.....to be used in desperation only.


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## jperryss (Mar 15, 2006)

bumpinP said:


> Didn't Pioneer put out mosfet decks that you could bridge the rear channels on? If memory serves me right they were advertised as being able to drive two front speakers and a sub off the rear channels.


Around 98-99 I remember Pioneer's big 'run subs off your Mosfet45 headunit' push but I don't think they ever suggested bridging it. This would've been right around when the diamond-plate subs were out and there was a free-air version also.


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## mayhem (Apr 13, 2010)

You can buy super cheap amps all day long. Post a wanted thread in the DIYMA classifieds section, you'll likely get dozens of hits from guys who just have an old 2 channel amp in the closet or holding up the corner of a coffee table or something that they'll get rid of super cheap.


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## sqshoestring (Jun 19, 2007)

A normal HU is already bridged, you just can't make over 18rms off 12 volts and there is no changing physics even though the marketing people try over and over. Near half an amp is power supply to create higher voltage than 12, it does not fit in a HU and makes heat. The best you could do is find really efficient speakers and take what you end up with.


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## shibbydevil (Jul 2, 2010)

Im in houston, and I have a 4 channel crappo sitting somewhere I can give you. Better than whatcha have...


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## Oliver (Jun 25, 2007)

Koac V3 Hot 

This one uses an IC for power, same as a head unit.

Koac V3 inside - Amp Guts



> KOAC V3 400 watt 2ch high powered Car Amplifier
> Please wait
> Image not available
> 
> ...


*There's a Fool born every minute . . . *


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## bumpinP (May 5, 2010)

Wow that amp is seriously lacking. That is the sort of thing that turned people off of car audio. It takes effort to make sure you are not getting ripped off.


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## lawrence131 (Oct 28, 2006)

thanks, i was being too lazy, but cutting corners for this is a bad idea  I was also curious what would happen just from a theory standpoint but i'd better take it safe.

i found a steal on the MB Quart 4125 replacement which was very well reviewed and benched above spec so I'm giving my bro a hand-me-down MB DSC450 which should still work wonders beyond the HU. BTW the MB Onyx 4.125 which is a direct replacement for the DSC4125 (running 125 X 2, 500 X 1 bridged and actually puts out this much power or more) is only $129 shipped from Sonic if you do "Make Offer."


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