Aux-In ground loop - Toyota Nation Forum : Toyota Car and Truck Forums
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#1 Old 10-17-2012, 04:46 PM
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Aux-In ground loop

Ok I know I'm not the only one with this issue, but yall know that humming when an ipod (or another device) is plugged into the aux in AND a a power source from the 12v outlet? Well the cause for that is a ground loop, in otherwords, the voltages at the radio/auxin/12v outlet are different, and that allows a small dc current to creep into the AC audio signal, ie the hum.

I've been trying to solve it for a few weeks now, but now I'm stumpt. I've been using a ground isolator (aka a small transformer) to break up the dc current in the signal, but I'm looking to fix the problem, not put a band-aid over it. They actually issued a TSB for the navigation equiped HL because of the hum. All they did was install an inline transformer to mask it. So here is where I'm at:

I'm trying to get everything equal to the radio main 12v+ and ground. So:

1) I disconnected the aux in panel 12v outlet power connections. I tapped into the main headunit 12v +/ground, and used a relay to feed that to that 12v outlet only when ACC is activated. So now that outlet matches radio voltage since they are technically the same wire.

2) I took a look at the aux's in signal sheild, and I have isolated the shield as the cause of the hum, I'm just having a hard time fixing it. Here is the circuit between the radio and aux in:



The top abbreviations (*1) are for nav units, the lower ones (*2) are for non-nav. This is for JBL systems:
AUXl: cable detection wire
ALl: Left + signal
ARl: Right + signal
ASGN: signal shield
AGND: shield ground


Now if you look at the circuit, the non-nav headunits ground the shield to the headunit it self. But for navigation units, the shield is grounded to an OEM ground on the chassis (and its not the same one as the navigation chassis ground). This is why only the navigation headunits had the TSB issued. So I took out my multi-meter to compare the radio ground and the shield ground to see if there were any issues, and there were. There is a 3.3 mV drop and a 17.4 ohm resistance between the two grounds, in theory, they should be 0 V and 0 ohm (or close to zero ohm). There is the source of your hum. Now I tried to ground the shield to the radio ground, but it actually made the hum louder. So I'm kinda scratching my head as to what to do now. If yall have any ideas, I'm all ears. This has been on my nerves for 2 years now and I'd like to fix it.

Click Here for the Full List of Mods Done to My Highlander ---->>> 2008 FWD Highlander Limited

Last edited by sweeneyp; 11-05-2012 at 09:08 PM.
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#2 Old 10-17-2012, 04:54 PM
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dude......
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#3 Old 10-17-2012, 06:59 PM
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Why not using the bluetooth connection and forget about this aux in?
The hybrid highlander does not exhibit this issue
Another band aid is to buy from amazon or crutchfield a small cable which I think will cut some of the high frequencies
If you search for ground loop isolater you ll find it
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#4 Old 10-17-2012, 08:00 PM
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Quote:
Originally Posted by Steven k View Post
dude......
, you obviously haven't seen my other posts. This is nothing.

Quote:
Originally Posted by cutienoua View Post
Why not using the bluetooth connection and forget about this aux in?
Because my ipod classic doesn't have bluethooth, nor does my headunit. Pretty sure Bluetooth audio is a 2011+ feature.

Quote:
Originally Posted by cutienoua View Post
The hybrid highlander does not exhibit this issue
Because like on the non-hybrid non-nav headunits, all hybrid headunits (nav or non-nav) ground the shield to the headunit. Why mine doesn't is just strange

Quote:
Originally Posted by cutienoua View Post
Another band aid is to buy from amazon or crutchfield a small cable which I think will cut some of the high frequencies
If you search for ground loop isolater you ll find it
Quote:
Originally Posted by sweeneyp View Post
I've been using a ground isolator (aka a small transformer) to break up the dc current in the signal, but I'm looking to fix the problem, not put a band-aid over it.
^ I did They hurt overall SQ, so I'm trying to fix the overall problem, not patch it

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#5 Old 10-17-2012, 08:27 PM
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Amazon Amazon

I was using this before in the hybrid,but cannot be sure will not have the ground noise in the regular highlander!
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#6 Old 10-17-2012, 09:42 PM
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Problem is with one of those, it doesn't eliminate my problem. I would have to have a bluetooth receiver for the radio side of the equation (and that receiver would draw from a 12v source), the voltage difference would still be there, and the hum will remain.

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#7 Old 10-17-2012, 09:53 PM
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Do you have the usb cable at the OEM unit?
Is that one making any ground noise?
At last you can always upgrade your unit! smile
seen some pioneer appradio2 nice screen!
or the new 8 inch ipad would be nice in the dash!!

Last edited by cutienoua; 10-17-2012 at 09:58 PM.
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#8 Old 10-17-2012, 09:57 PM
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no I don't have a radio usb. The 08-10 HL's don't have any of those fancy features you 2011+ HL owners are spoiled on

---------------------

After looking more into it, it appears the VA- wire should be ground as well, I'll test that (ground it directly to the headunit ground) and post the results.

Click Here for the Full List of Mods Done to My Highlander ---->>> 2008 FWD Highlander Limited

Last edited by sweeneyp; 10-17-2012 at 09:59 PM.
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#9 Old 10-17-2012, 10:34 PM
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http://www.vaistech.com/dev/home.php
these guys are really good!
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#10 Old 10-17-2012, 11:03 PM
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Originally Posted by sweeneyp View Post
After looking more into it, it appears the VA- wire should be ground as well, I'll test that (ground it directly to the headunit ground) and post the results.
And after trying that, just like the signal shield...the hum was worse than before

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#11 Old 10-17-2012, 11:29 PM
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I have a simple solution for you: buy a battery pack
http://www.ebay.com/itm/3400mAh-Exte...item2323f9dab2

you can power the ipod and no ground noise
I have a similar battery pack and is good for a very long time!!
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#12 Old 10-17-2012, 11:32 PM
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Could, but I'd forget to charge it. Again another band-aid fix

Good idea though.

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#13 Old 10-17-2012, 11:34 PM
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that means you'll never have a Nissan leaf, if you don't charge it...

they have solar ones too

Last edited by cutienoua; 10-17-2012 at 11:39 PM.
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#14 Old 10-18-2012, 02:26 AM
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Ok new idea. Instead of trying to eliminate one of the grounds in the loop by using clever wiring, I'm just going to remove the ground all together. What I mean is isolate that 12v outlet from the rest of the car. I'm getting a 12V DC to 12V DC isolated power supply for that outlet. That should (in theory at least) stop this. Oh well, it will take a few days to get here. I'll post if it works.

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#15 Old 10-18-2012, 06:03 AM
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One of the suggestions that I've seen in communications forums (when dealing with direct grounded speakers) is to add a capacitor in the audio line. However, that sill may be something you consider a bandaid over a fix, and also probably works better for communications radios since we are not looking for the same things that an audiophile is looking for. Just wanted to throw the capacitor idea out there though...

2012 Toyota Highlander Limited AWD, Blizzard Pearl (His)
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