HELP!! Alternator whine w/ new setup

[Trambounet]

Hi everyone! I am in desperate need of advice to get rid of alternator whine on my new setup.

Like many others on this forum I was not overwhelmed by the sonic quality of the Bose system on my MS3 GT. I ditched the Bose amp, subwoofer and speakers and replaced all this by
- an Alpine PDX5 amp installed under the passenger seat
- Image Dynamics components for the front doors: one crossover is under the driver seat - where the Bose amp used to sit, the other one is next to the PDX5 under the passenger seat
- an old set of Polk DB570 coaxials for the rear doors (don't really care about the rear doors to begin with, but could use a little filler back there)
- don't have the sub installed yet, but planning on getting a Pioneer Premier shallow mount sub for my trunk.

I reran new speaker wires through the dreaded Molex connectors for all 4 doors using 16awg, and 12awg between the amp and the crossovers.

I ran a 4awg wire from the battery to the amplifier through the grommet behind the glove box, as exposed on this forum (that was great by the way!). The power wire is running on the right side of the car.

The amp is grounded on the cross beam between the center console and the right door, right in front of the passenger seat. There is a threaded hole there - where the Bose subwoofer was attached - so I sanded the painted area down to the bare metal and grounded the amp right there.

I tapped into the Bose plug on the driver side and drove RCA's through the center console to the passenger side to connect to the amp. The RCA's are not close to the battery power wire.

The problem I am having is that, when the engine is running and the amplifier is on (even if the head unit if not on), I am getting a buzzing/humming sound through all 4 speakers.

What I have tried so far:
- If I unplug the RCA's, the buzz is gone (so the amplifier is not the source of the buzzing/humming), so there probably is a ground loop somewhere in the system through the RCA's shield/-
- If I step on the gas pedal, the frequency of the noise goes up, so it is likely alternator whine that I am hearing
- If I plug only one of any of the 4 RCA's, I am getting noise on the corresponding speaker
- I ran a 14awg wire from the head unit chassis to the where the amp is grounded (again, right in front of the passenger seat) to try to kill the ground loop, that didn't make a difference at all. Does that mean that the ground loop is not between the head unit and the amplifier??
- I also removed the fuse for the Bose amp, so the former power wire for the Bose amp is de-energized now

I am running out of ideas... I am starting to think it could be either the FM antenna or the Sirius box that are not grounded properly, or maybe the aux input. I figured that anybody who modified their system likely had a similar issue? It just seems like I have been super careful, but somewhat still created a ground issue by accident.

Any suggestions are welcome! Thanks a lot for reading this!

 

[def_one]

I have literally the same exact problem as you. Different components, but same damn results. I think its been narrowed down to the Bose HU with an aftermarket amp. Why, I have no idea, or how to fix. I tried running the power wire 2 different ways, about 4 ground locations, 3 different sets of RCA cables, nothing.

I ended up tapping into the Bose sub signal and running the new separate subwoofer, but the main speakers I put back onto the bose amp. I just couldnt stand it.

The only thing I thought to try but didnt, was running new power and ground wires up to the HU, so that the amps and HU share the same power source, but somehow I doubt that would do it.

Good luck and if you figure it out, I'll paypal you $5 for a beer (cheers)

 

[car46999]

My experience with this is that the power wire and audio cables are ran too close to each other, the alternator is "noisy" or a ground loop.

It sounds like it is before the amp.
Here are some tips:
Try an ipod playing music in to the amp inputs with a headphone to rca cable.

Try a temp power cable that is ran outside the car (don't drive like that (cryhard) )

Try different ground spots.

One of these should show what the issue is. Start with what is easiest for you.


If I had to guess, I would put my money on that moving the power and signal cables will fix it.

One more thing, how and where are you getting the audio signal from the Bose headunit?

 

[Trambounet]

Alright alright, thanks for replying guys, I was starting to feel alone. I'll definitely call you up on that $5 for a beer.

Here is what I have found out since posting this:
- The head unit (which by the way is made by Sanyo, not Bose) outputs balanced signals, which I confirmed with my meter. What that means is that audio +/- have the same impedance to ground, in particular audio neg is NOT car chassis. You might stumble onto articles that assumes that audio neg is ground (i.e. unbalanced system), but that is not the case with the Bose setup. Also the channels are isolated from each other, so FL - is not tied to FR -.
- For you electrical guys, balanced signals are much more immune to noise that unbalanced signals. There are also better for ground loops, because audio neg is not acting as a ground. The amp amplifies the difference between +/-, and in a balanced output those 2 are equally likely to pick up noise, so when taking the difference, the noise will cancel out. Plus a twisted pair helps in that matter. Throw a braided shield on top of that (that must be grounded to car chassis btw) and there should be virtually no EMI/RFI noise picked up on the RCA cable. This is a passenger car for crying out loud. I work in the heavy transportation industry where our alternators are putting out more than 2000Hp, with power electronics everywhere, 1000Hp+ induction motors and in that environment a balanced twisted shielded pair (as used in CAN communications for example) is damn rock solid. So I am not buying the EMI/RFI thing, not in a Mazda3.
- My Alpine PDX5 is compatible with balanced differential signals. If the amplifier isn't compatible and is expected unbalanced signals, you will run into serious issues.

Now I ran a wire to the plug where the old bose amp ground was provided, and the noise was very much reduced. So maybe I should ground my amp to wherever that wire is going (probably a ground stud somewhere). But I can't find that spot for the life of me. Do you guys know where the Bose amp was grounded??

I am also left with the possible option of an f'ed up alternator/rectifier. I am borrowing the office scope in a few minutes to double check that. I should a lot of ripple on the battery +/- if that is the case.

Thanks again for chiming in!

 

[Trambounet]

One more thing, how and where are you getting the audio signal from the Bose headunit?

I basically bought a mating plug to the Bose amp connector, bought a 4 channel RCA cable, cut it to length and crimp terminated the wires with the right pins. Nice and clean. The RCA cable is then running against the cross member in front of the driver seat, goes up the center console by the shifter, and then goes under the passenger seat where my amp is sitting.

 

[car46999]

If you get an o-scope, check the rca jacks also. You would see it there also. It could be the alternator/regulator, but I would lean more towards the rca cables.
Good luck.

 

[Trambounet]

Alright I am giving up and going the GLI way... I tried everything I could do, and I still get the whine.

I found the ground point of the Bose amp by the way - sort of. I could trace the wire up to behind the glove box, in a funny looking plastic bulb, along with 5 other wires that just end up there. They're all bunched up and pressed together. It's very weird. The head unit is grounded to a stud literally inches away, but those 6 wires are just bunched together and hanging in mid-air. An ohm-meter shows that they are grounded to the chassis though, so why not attach them to a solid ground stud???

Anyway, grounding my amp at that point made no difference in terms of getting rid of the whine.

In short I have tried all of the following to get rid of the whine:
- Grounded the head unit and the amp at the same point - Nope
- Grounded the amp at the battery neg - Nope
- Grounded the amp at the Bose amp ground - Nope
- Moved the battery power wire around - Nope
- Good quality RCA's with grounded shield - Nope
- Removed the FM antenna, AUX port and Sirius module - Nope
- Checked alternator output - Nope

I am stopping here. I took half of my dashboard apart for the nth time this weekend to troubleshoot, and I have the feeling that if I keep doing that my car interior will start falling apart. The cover for the a/c control module almost snapped in half already, the cigarette lighter plate won't come out anymore (almost broke it in half too), the H/U wouldn't fit in the dashboard anymore (took me almost 1hr to get it to fit), the a/c control module is somewhat loose now, so I had to foam-pad it. That's not counting the numerious fu/k ups courtesy of Mazda and their love for impossible-to-remove connectors (door connectors especially, and the ones at the back of the head unit too) and cheap plastic retention clips. That car interior is not meant to be taken apart!!

So I bought a GLI from Radioshack just to try and it did remove the whine (eventhough I can still hear a faint noise). I am not a fan of it because the leads are extra long and it's female RCA's on both ends - wtf. I am going with the PAC model instead.

I am kind of disappointed by having to go the GLI way, I feel like I am cheating my way out of it. But I don't way to spend any more weekends on this project. Plus like I said my car interior is starting to show scars of the battle, so it's time to throw the towel.

 

[Mid_Life_Crisis]

I am kind of disappointed by having to go the GLI way, I feel like I am cheating my way out of it. But I don't way to spend any more weekends on this project. Plus like I said my car interior is starting to show scars of the battle, so it's time to throw the towel.

As I pointed out in the other thread, when you mix the input/output types, you have problems. The balanced H/U signal cannot stay balanced when you connect it to most amps, which tie their negative inputs to ground. By using the GLI you are simulating the factory setup. The H/U output is allowed to float and remain balanced because the circuit is completed through the ungrounded transformer coil in the GLI. It isn`t cheating, it is a necessary component in converting from balanced to unbalanced.

 

[Trambounet]

The balanced H/U signal cannot stay balanced when you connect it to most amps, which tie their negative inputs to ground.

That's all well and good, but my Alpine PDX5 amp is [supposedly] compatible with balanced differential inputs. At least that's what the Alpine tech rep I talked to told me. I also checked with an ohmmeter, and the audio input neg is not tied to the ground reference.

 

[Mid_Life_Crisis]

That's all well and good, but my Alpine PDX5 amp is [supposedly] compatible with balanced differential inputs. At least that's what the Alpine tech rep I talked to told me. I also checked with an ohmmeter, and the audio input neg is not tied to the ground reference.

I`ve never trusted using an ohmmeter to check an input or output that way. There is just too much circuitry that can float until it is active. If you tell me you powered it up with a signal going through it and hooked it up to an o-scope, I`ll believe there is no ground reference. Until then...

 

[Trambounet]

I put two PAC ground loop isolators from Crutchfield - one for front left/right, one for rear left/right - and not only do they not entirely get rid of the noise (it's attenuated, granted), but they create a high pitch noise when close to the chassis' metal it seems. Although when I hung them in mid air while I driving, they did attenuate the noise. So that's cool. On the flip side they were very hurtful to sound quality. It was very obivous, the music sounded very tinny, it's like the mid bass was gone!!!

So now I have the choice between
- System with a lot of buzz, but good sound quality when cranked up above the noise
- System with less buzz - i.e. with the GLIs - (but still obvious), and crappy sounds quality when cranked up (Bose stock might sound better actually, I am not sure)

 

[Doozy]

two words. "bad ground"

reground EVERYTHING.

 

[Trambounet]

I have tried a half dozen ground points, from battery neg to the engine to any piece of bare metal I could see and the same problem happened. My current ground location shows 0.1 ohm to where the battery is grounded. What ground location do you suggest??

 

[twowings]

what about the vehicle grounding system itself ? I'd check/redo those first...

 

[car46999]

I might have found why you and others have noise. Today while installing my LOC, I noticed that it was not turning off its remote wire as it should.
My reason is that my non-bose head unit has a +6v dc offset on the front speaker leads (didn't check the rear yet) as soon as the car is turned on.

If you loc is passing this to your amp, your amp might amplify it as noise.

I forgot you are not using a loc, so if the bose unit does have a dc bias it might be on your rca's

 

[Mid_Life_Crisis]

I put two PAC ground loop isolators from Crutchfield - one for front left/right, one for rear left/right - and not only do they not entirely get rid of the noise (it's attenuated, granted), but they create a high pitch noise when close to the chassis' metal it seems. Although when I hung them in mid air while I driving, they did attenuate the noise. So that's cool. On the flip side they were very hurtful to sound quality. It was very obivous, the music sounded very tinny, it's like the mid bass was gone!!!

So now I have the choice between
- System with a lot of buzz, but good sound quality when cranked up above the noise
- System with less buzz - i.e. with the GLIs - (but still obvious), and crappy sounds quality when cranked up (Bose stock might sound better actually, I am not sure)

The one I used is from Radio Shack and worked fine. There are also sources for high grade pieces if you do a little searching.

 

[Trambounet]

I might have found why you and others have noise. Today while installing my LOC, I noticed that it was not turning off its remote wire as it should.
My reason is that my non-bose head unit has a +6v dc offset on the front speaker leads (didn't check the rear yet) as soon as the car is turned on.

If you loc is passing this to your amp, your amp might amplify it as noise.

I forgot you are not using a loc, so if the bose unit does have a dc bias it might be on your rca's

The signals coming out of my HU (Bose system here) seem to be +4V above ground (+ to GND is 4V, so is - to GND).

But since it's differential it doesn't really matter I guess.

 

[car46999]

The signals coming out of my HU (Bose system here) seem to be +4V above ground (+ to GND is 4V, so is - to GND).

But since it's differential it doesn't really matter I guess.

I would assume that some amps would not like that DC voltage. Which might be why some report no alternator noise, some do have it. I am sure alpine could shed some light on their amp for sure.

Good luck

 

[Trambounet]

Finally, problem solved!!

What I did is tap into the headunit harness directly at the back of the headunit instead of under the seat where the Bose amp is located, move the amp to the trunk and ground it to the left metal bracket (pretty obvious when removing the tool trays).

No need for a GLI or LoC or what have you. Sounds awesome, the whine is completely gone.

 

[kvndoom]

Man you coulda bought a JL amp and never had this problem in the first place. Not that I have one anymore (and as such I'm using GLI's), but I doubt I'll buy any other brand in the future. Differential-balanced inputs are a beautiful thing.