my car got gutted and replaced the bose speakers with mb quart premiums/reference f/b; 2X10" w6; 300/3,300/2,500/1 jl amps. i kept the head unit for "stealth" reasons. but i got engine noise... there are 3 power inverters inline with the bose factory amp and the jl amps... according to the installer the radio comes grounded in 4 places through the chasis... can anyone give me any ideas as to what to look for...so we/i can fix this issue...i know that some of you would be thinking just get a head unit and problem be gone... i'm putting a hold on that tll i can get me a nice nav all in one unit....for now i need to deal with the noise issue....any suggestings would be appreciated....
gracias(thank you)!

 

I'm not sure what you mean by power inverters inline with the bose amp? Do you mean line output converters? Why is the Bose amp still in the car if you have the JL amps?

It sounds like your installer connected a line output converter AFTER the bose amp to all 6 channels. Your stock HU has 4 channel outputs (FL, FR, RL, RR). If you connect the line output converters to the HU output you can get rid of the Bose amp entirely. The inputs to the bose amp are speaker-level outputs and suitable as an input to a line output converter.

On my system the output of the HU from the line output converter is free of whine or noise and sounds great. You should have no problems getting clean output, but definitely get the bose amp out of there. It's totally unnecessary and is adding a needless amplification step which can only add more distortion to the otuput.

Also, try lowering the gains on your amps.

 

Yes, you are correct they are power inverters(used to minimize a high output signal?). I'm not too sure why the factory amp was left in place...i know that they had done this similar set up with other g 35's ...so i didn't question them..but it's good to know what you just told me... i'll take this info to them...

 

Another thing to check would be the gain or input sensitivity. You might try turning the gain down slightly which may get rid of the extra noise.

 

the gains were turned down, i think djrobx might be on to something...

 

I'm guessing your installer was unsure about whether or not the Bose amp could be pulled (on some cars the amps can't be removed easily), and went the safe route by leaving it in place. Let them know it can be removed. If you still have a whine, then it's probably between the LOCs and the amps. The usual troubleshooting methods of changing ground locations and ensuring that the RCAs aren't runing near power lines apply.

Just know that it's definitely possible to get completely clean output out of the stock HU with aftermarket amps. You do not need to replace the HU to be whine free. Also find out what kind of line output converters were used. I'm using the Peripheral Ven4.

-- Rob

 

what about tapping into the stock ground coming out of the stock HU. Then run that ground to the back and ground it with the amps.

This will completely eliminate the ground loop if that is what is causing the noise.



2004 G35 Coupe 6MT
Volk GT-7's/ TEIN Basics
Falken 245/35/ZR19 & 285/35ZR19
Kinetix Racing Camber Rods/ K&N Typhoon CAI

 

would i even need the LOC's between the HU and amps??

Does any one have the schematics for the HU????

 

Yes, you still need the LOC. The head unit does not appear to output "line level" outputs . The same outputs that go to the Bose amp inputs go directly to the speakers on systems without the Bose amp. So, it seems logical to assume that the Bose amp has a built-in LOC, taking speaker level inputs and re-amplifying them.

You shouldn't need to run a ground all the way back to the HU, it wasn't necessary in my system anyway. Fixing these ground loop issues can be very trial and error though, it may work. You might try using the Bose amp's ground wire from the harness for the LOC ground. Good luck!

 

Actually, you don't need an LOC if you have the right amp and if you use the signals from the HU before amplification at the BOSE amp. I'm using a JL 300/4 to drive my front speakers and am definitely not using an LOC, it sounds great. An audio shop that I went to told me that I didn't need an LOC with a JL amp since they have a high quality LOC built-in. Sounded like hogwash to me, but then I installed the amp myself and found out that the audio shop was right (now how often is that going to happen in my lifetime!)

 

Yep, many amps have built in LOCs. If you've got one there, you may not need to buy an external one. LOCs in the amp used to be very common, even in the cheapest budget amps. Some equalizers like the ones from AudioControl have them built in as well. I probably would have just bought the AudioControl EQS and used its line output converter, except I already had an Alpine ERE-G180 and found a 4 channel LOC for $20 shipped on ebay.

The point to the original poster though is that the head unit does not output a "low level" signal. You are going to deal with a high level signal, with or without the Bose amp in place. If his current setup going through the Bose amp needed converters, he's still going to need them without the Bose amp.

-- Rob

 

finally got rid of the damn noies, went from the radio to the jl amps with out an loc.. and no more noise.. system sounds pretty good. eventually i'll get a HU replacement but for now this will do. thanks for all the replies...