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vm9512 jensen in dash hu


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csnut18 
Copper - Posts: 196
Copper spacespace
Joined: January 27, 2007
Location: United States
Posted: April 24, 2008 at 3:43 PM / IP Logged  

Ok everyone, this is my situation. I have a polk momo c400.4 and a c500.1    They are driving a mmc6500 up front and mmc650 in the back. I have a 12" polk sr sub as well. My head unit is a jensen vm9512. Previously I had the c400.4 biamping the mmc6500's. Everything was fine, but I like rear fill and the mmc650's need more juice than the puny wattage the hu was throwing their way. So yesterday I went out and spent a little while rewiring the system. I now used the original crossovers that came with the mmc6500's and wired them to the two front channels on the amp and then went ahead and hooked the rear mmc650 coax to the rear channels on the amp. I sealed up the speaker connection on the hu and hooked the rca's onto the rear preamps on the jensen. I adjusted the gains to make everything sound nice. Everything sounded great except I noticed some alternator noise in the rear right mmc650. The noise was only coming from that speaker, nowhere else. The noise is slight and with music playing or talk radio on i cant hear it but it is there and if i have the radio on really low and rev the car it gets slightly worse. If I turn the car off it disappears. If I leave the engine on and turn the stereo off and rev the car, its not their as well so I doubt the crossover is picking it up. Now keep in mind that the rca's run are knukonceptz krystal 4 channel ones which all 4 channels of rca are all combined in one wire so they are all run together and still only one speaker has the noise. I went ahead and unplugged the rca from the amp and turned the stereo on and the noise was not there either eliminating the amp as the source. My grounds are all good and everything is ground at the same spot in the back including the jensen and this worked great for awhile so i know thats not the prob. The rca's are not picking up the noise because it is one thick wire for all 4 channels so they would all pick up the source of noise equally but thats not happening. It is obvious to me now that the rear left rca preout on the jensen has a slight defect that is causing this. In all honesty, I didn't have the time today to continue to troubleshoot and switch the rca's on the back of the hu to see if the rca that leads to that speaker would still have noise if i plugged it into the fron channel for example but I am pretty sure that this the problem is the preout. I guess their is nothing I could do not other than to just get rid of this piece of crap jensen and have to settle for an ordinary headunit as I don't want to shell out the cash for a legit in dash video from the reliable brands. I know you guys will think I am nuts but I like rear fill so I want this to work. In any event, thanks alot in advance and hope to hear from people.

chillin420 
Copper - Posts: 236
Copper spacespace
Joined: March 27, 2008
Location: California, United States
Posted: April 24, 2008 at 5:22 PM / IP Logged  
i would honestly check the rcas also.  it could be a bad rca jack, so new rca's might be in order.  ir you switch them to the front and no noise to the rear speaks then it is deffinetly the rca in the deck.  you could take it apart yourself and try and fix the connection that is faulty, or take it into a local audio shop that has a repair service avail.  and see if they  can fix it .  otherwise you will have to et a new hu. 
you can do it....
advanced MECP, lol does it really matter....
patience is a virtue
csnut18 
Copper - Posts: 196
Copper spacespace
Joined: January 27, 2007
Location: United States
Posted: April 24, 2008 at 10:13 PM / IP Logged  

Yes I will troubleshoot it further tom. I will switch the rear speakers rca to the front prout and if the noise goes away which I seriousl think it will, we know what the problem is. It will not surprise me at all since this headunit came slightly faulty to begin with. The screen sometimes only comes out halfway and goes back in and many times the outside screen just goes dark and comes on itself after some time. The jensen is just not a quality piece. It has an insane amount of features for the price but I will not be getting another one again. Its a shame but you do get what you pay for.

Chris Luongo 
Platinum - Posts: 3,746
Platinum spaceThis member consistently provides reliable informationspace
Joined: May 21, 2002
Location: Massachusetts, United States
Posted: May 01, 2008 at 7:20 AM / IP Logged  
If you switch all the stuff around (left to right), one piece at a time, maybe you can isolate the problem.
That is, go to the amplifier, undo the left and right RCAs,and reconnect them backwards (left RCA to right amp input, etc), and see what that does.
Next, put those RCAs back to normal, and go behind the radio and switch them around there.
You could also switch the speaker wires coming out of the amp.
With a little trial and error, you should be able to figure out where the source of the trouble is.
Also, if you suspect the RCAs or their placement is bad, if you have a spare RCA cord, just temporarily run a new cord (don't install it, just run it through the car's interior), and see what that does.
Also, you could connect a small house speaker to the amplifier's output, to see if maybe it's the speaker's crossover that's picking up the noise.

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