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Thread: Car stereo wiring for an AV retard

  1. #1

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    Car stereo wiring for an AV retard

    Hi guys, this isn't for my MM but I guess it's general enough to go here.

    I'm restoring an E36 BMW as a gift for my wife. I'm at the accessories stage of the resto. I don't understand AV stuff at all. AT ALL. I'm happy with an AM radio and one speaker for baseball games. But my wife likes trance music and this is going to be her party wagon. So here's the deal.

    I got a pair of MTX 10" subwoofers in boxes for free. They take up too much room in the truck so might as well throw them in the car.

    I'm getting a new head unit because the OEM one has a cracked LCD. I'm looking at an inexpensive Kenwood KDC-155U that does iPod and all of that. The specs are 50 watts x 4 channels and RMS (I don't know what that means) 22 watts x 4 channels. The car came with 8 speakers: pair of 5.25" under the dash, pair of 2" in the door panels and a pair of combined 4" and 1" in the rear deck. The foam on the stock speakers is torn so I'm replacing them with El Cheapo eBay speakers.

    I know I need an amp to power the subwoofers. I found a matching MTX 2 channel TC2002 600 watt 200 watt RMS amp on eBay for about 40 bucks. The battery is already in the trunk in the BMW. I read the manual for the TC2002 but none of the sample wiring diagrams match what I'm trying to do. There was a bunch of stuff about capacitors, multiple amps, etc. that I don't understand or want to deal with.

    How do I wire this up so the lights don't dim and the windows go up and down? The alternator is the 80 amp stock unit that's now 20 years old. The car has power everything, locks, windows, sunroof. No fog lights.

    Please help me with ideas for a wiring diagram. Keep in mind I don't even know what crossovers are. Thank you!

    Back of the head unit:

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    Back of the amp, part 1:

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    Back of the amp, part 2:

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  2. #2

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    To power the head unit use the factory wiring - earth, permanent power and ignition source. Forget the extraneous stuff like multiple amps, capacitors etc as this will end with you clawing your eyeballs out. Running your amp and subs is a full no brainer. The stock alternator will keep up with the whole show with an 80 amp output. 8 gauge wire to power the amp (red and black for obvious reasons), an inline fuse holder (weather proof with a 20 amp blade type fuse will do the trick), about 3 metres+ of stereo RCA cable and a roll of blue light gauge wire (this is the remote power trigger wire that runs from the head unit to the amp - without it the subs and amp will play dead). Buy an aftermarket head unit adapter loom to suit the BMW as it will save you time and having to hatchet the wiring under the dash (you may need an adapter for the antenna lead too...I think) Something like this will do the job -
    http://www.ebay.com/itm/BMW-Radio-Wiring-Harness-adapter-Factory-to-Aftermarket-stereo-e32-e36-e34-e38-/351160083079?pt=Motors_Car_Truck_Parts_Accessories &fits=Make%3ABMW&hash=item51c2c5a287&vxp=mtr
    Match the colour codes from the aftermarket harness to the Kenwood loom and you can't go wrong. If the battery is already up back then this makes life easier to power the amp but you still need to go through running the RCA's from the back of the head unit along with the blue trigger wire to activate the amp. It is actually a pretty easy deal doing a full install but it is time consuming (I'd allow a full weekend to get all the gear in and have it operational) Be prepared to pull out plastic garnishes and lift carpet to run the connections to the amp - and use cloth tape to secure it down. If it were me I'd run all new wiring to the speakers and solder them directly to the connectors on the replacement speakers but this would do your head in if this isn't your forte.

  3. #3

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    Thanks. I'm pretty good with tinning and soldering so I'll do those solid instead of butt connectors.

    I'm amazed how inexpensive this stuff has become. 10 years ago I "helped" a buddy with a navi install. The head unit was like $1000. Now they have comparable Chinese units on eBay for $150.

    There's a nifty no-name Precision Power head unit with a 3.4" LCD for only $70 shipped! This one comes with a provision for a backup camera and since my wife is learning how to drive (at age 33!) I think it would be a good idea to add one.

    There's also an option to ditch the combo 4"/1" jobs in the rear deck, use an adapter and install 6x9s.

    Would it be a good idea to upgrade the amp to a 4 channel and power the subs and the 6x9s through it?

    Is there any issue with mixing direct connection for the front speakers and RCA in the rear?

    Also, how the hell does the amp take a line signal from the head unit and "know" how to raise and lower volume, if it's an unchanging signal? That's how RCA works right?

    I guess I'm nervous about doing this because I don't know how any of this stuff works.

  4. #4

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    "sounds" like you are still contemplating which components to install. my 2cents: match RMS output of amp & handling of speakers. basically RMS is the max continuous operable ability (watts is just what "could be" handled when that "Metallica" base note occurs without system damage). the extra battery in the convertible is for my amp only (headlights were dimming on base notes).
    Last edited by ragragtimetime; 09-06-2014 at 12:29 PM.

  5. #5

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    The amp receives the output signal from the head unit - whatever volume is going into it is coming out of it. If you find the bass is overpowering the system dial the gain back on the amp controls. I'd think if you add 6x9"s up back you will find the bass will become overpowering. A 'good' basic install is a pair of 6" splits up front (6" driver with a separate mounted tweeter - this is where the cross over unit is installed. It separates the midrange speaker from the tweeter speaker so they speakers are getting the right sound frequencies pushed through them), 4" to 6" dual cone speakers up back (this is to give the system some rear fill) and the subwoofer in the rear of the car (normally facing towards the farthest rear corner away from the drivers position) You can see the inputs on the amp (power, earth, rem) the 'rem' is the remote trigger input that runs from the head unit (this tells the amp to turn on - it is a low power input so don't try to hard wire a 12v feed into it). Where you see the 'bridge' marked on the outputs, this is the recommended method to hook up the subwoofer (positive from one channel, negative from the other). The amp that you're using is designed only to receive 2 channels from the head unit and is only going to be used to drive the subs so you can't mess that up.

  6. #6

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    OK. No 6x9s. Do you have a recommendation for affordable speakers? The speaker wells up front take 5.25". The 2" speakers in the door panel are proprietary BMW and nothing else will fit flush so I'm stuck with those. What about the 4" and 1" on the rear deck?

    What do you think about this head unit? I like the simple looks of it. The backlight looks like it would match BMW amber reasonably well.

    http://precisionpower.com/store/prod...265bi-106.html

    Here's the back:

    http://cdn3.volusion.com/kplve.lockb...jpg?1399037042

  7. #7

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    They make 5.25" aftermarket speakers but you have to go hunting for them as most car/auto accessory shops don't carry them. I had a pair of Rockford Fosgate Punch 5.25"s but you don't need to go spending big coin (although those speakers had a killer sound to them - nice and warm due to the cones being paper fibre) And the 2" speakers in the doors? Those aren't just plastic grilles concealing the tweeters mounted to the door chassis? Look on ebay for the 5.25"s - there are plenty to pick from and some good brands up for cheaps. What speakers are already up on the back parcel shelf in the beemer? If you can get a dual cone speaker that will swap in without grief I'd go down that path (it will make life easier on you) And when buying a speaker - if you can get your hands on the set you're looking for check out the size of the magnets, the quality of the speaker chassis, the speaker wire connections and how flexible the speaker cones are - these are all indicators of their quality. E.g. - thin, pressed steel chassis, small magnet, speaker cone feels like a disposable plastic party cup and a nasty looking mount for the wires held on with a tiny rivet? You can bet it will be junk...

  8. #8

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    I looked in the back of the 2" door card speakers and you're right, they're just Nokia speakers glued into the plastic sheath.

    For simplicity, I want to get full range speakers, not component. I'm going to order online so what brands are good?

    Can you explain how ohm ratings work in speakers?

  9. #9

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    I'll have a chat with my insanely knowledgeable friend about the 4 ohm Vs 8 ohm speaker thing (I think 4 ohm speakers are used in cars due to the low voltage power source) I would "think" you could use 8 ohm speakers in a car as they have a lower current demand but I don't know if a car amp would like it. I'm pretty sure if you use a 4 ohm speaker in home audio gear it could roast the amp driving it (unless you bridge a pair of them together to create an 8 ohm load)

  10. #10

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    Now I'm changing my mind. Since I'm doing an honest to goodness restoration, I think I want to keep the original AM/FM tape deck because it matches and all of the aftermarket stuff looks out of place and it will keep wiring simple. The car came pre-wired for a 6 disc CD cassette in the trunk I can pick up on eBay for not very much.

    Now here's my OCD kicking in. Since I have the MTX subs and will get the MTX amp, I want to get MTX speakers all around. So it matches. Don't ask me why, it's just aesthetically pleasing to me.

    What do you think about puting these 5.25s in the wells and putting the tweeter in the door card...

    https://www.mtx.com/52cs-coustic-car-speakers

    ...and then putting these 4-way 6x9s in the rear deck...

    https://www.mtx.com/694c-coustic-car-speakers

    And then having the amp roll off very low so the sub doesn't interfere with the 6x9s? I like the idea of 6x9s because they have adapters and it's easier to find 6x9s.

    Would the stock BMW HU be able to drive the 5.25s, the tweeters and the 6x9s while letting the MTX amp drive the subs? Or should I get the 200W OEM Harmon Kardon amp (for the upgraded sound system my car doesn't have) amp for the coaxial speakers? The stock sound system came with just the HU, no amp.

  11. #11

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    I couldn't get the link for the 6x9"s to work but the head unit will be sufficient to run the speakers. It would make a vast improvement to sound quality if they were running off an amp. Does the stock HU have RCA outs for an amp set up or a remote power out to trigger it? I think the factory head unit is going to become a hurdle in your install. I haven't had any experience with MTX gear but I've had enough to know that most of Pioneer and Sony stuff is JUNK. Here's a trick for you to try out. Take a speaker model number and google it - see if you get any different hits other than the manufacturers' name on them. I found an electronics distributor here in Australia were selling their own brand of car audio speakers that turned out to be ...Alpine. Identical product, same speaker grilles. Only differences were the the "S Drive" logos were missing, along with about $30 off the asking price.

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