Ground Noise in COMAND AuxIn/TV (Att Steve)
06-07-2004, 09:03 PM
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'02 C240/6
Ground Noise in COMAND AuxIn/TV (Att Steve)
I have an Euro Comand installed by Steve a year ago. At time of installation I had a hard disk MP3 player (Empeg) feeding through aux in, but this magnificent piece of electronic generated ground loop noise with the COMAND. Had to inline a Ground Loop Isolator. No obvious noise, but the sound quality was not as perfect as would otherwise be from the Empeg. Steve said this was due to a faulty install of the Empeg with relationship to ground. I lived with it for 1 year plus.
Recently I replaced the Empeg with a Carputer featuring a profesional, audiophile sound card, using an RGB adapter. In this install I was careful to go by the book in the installation all the way. Good grounding and power (straight to the bolt that grounds the car's battery, and battery +), good connections, audio separated from power lines, etc. Still have the ground loop problem. I am sure the Carputer is installed correctly with regards to power and grounds. Again, I had to use a ground loop isolator, and again the quality of sound is subpar due to this (the same carputer with desktop powered speakers, or play ing through my living room audiophile system, sounds astounding).
I believe that it is my COMAND that is not properly grounded, or is it perhaps defective? Playing a CD or FM on the COMAND sounds excellent, so the COMAND is capable of producing good sound.
My problem is the grounding. Anyone know where the COMAND is grounded? Or how to diagnose that the COMAND itself doesn't have a problem? Has anyone been succesful in using the aux-in or RGB adapter sound input with an Euro COMAND, and get crisp pristine sound? Obviously, sound from self powered devices that do not feed from the car's power do not count - My unit sounds good if I connect an Ipod or Archos running on batteries to the aux-in.
will really appreciate some help. Thanks!
Recently I replaced the Empeg with a Carputer featuring a profesional, audiophile sound card, using an RGB adapter. In this install I was careful to go by the book in the installation all the way. Good grounding and power (straight to the bolt that grounds the car's battery, and battery +), good connections, audio separated from power lines, etc. Still have the ground loop problem. I am sure the Carputer is installed correctly with regards to power and grounds. Again, I had to use a ground loop isolator, and again the quality of sound is subpar due to this (the same carputer with desktop powered speakers, or play ing through my living room audiophile system, sounds astounding).
I believe that it is my COMAND that is not properly grounded, or is it perhaps defective? Playing a CD or FM on the COMAND sounds excellent, so the COMAND is capable of producing good sound.
My problem is the grounding. Anyone know where the COMAND is grounded? Or how to diagnose that the COMAND itself doesn't have a problem? Has anyone been succesful in using the aux-in or RGB adapter sound input with an Euro COMAND, and get crisp pristine sound? Obviously, sound from self powered devices that do not feed from the car's power do not count - My unit sounds good if I connect an Ipod or Archos running on batteries to the aux-in.
will really appreciate some help. Thanks!
06-08-2004, 02:38 PM
#2
hey jules,
i am also a fan of carputers and been wanting to install one for many years now, just haven't found the right equipment nor the time now.
i believe that your ground noise is not from the comand unit but form the device that you are attaching to the comand unit. the reason i say this is because i have the same issue when i (hard wired) my 3rd gen ipod to my comand unit aux port, although the ground noise is very minimal in my case, i can still hear some noise only when my volume is low but nothing too drastic whereby i need to use a ground loop isolator. if your comand unit is defective, you should then also hear ground noise while playing your FM radio, or the CD but from reading your post that wasn't the case. also you mentioned that when you plug in yoru ipod running on its own battery and not using the 12v power source, you dont hear the ground noise, this is because the unit itself is isolating the ground properly. i would almost bet that even if you had a different radio which also has an aux connection and you hooked up your carputer using the car's 12v source, you will still here the ground noise. i could could honestly say that its not your comand unit.
i am also a fan of carputers and been wanting to install one for many years now, just haven't found the right equipment nor the time now.
i believe that your ground noise is not from the comand unit but form the device that you are attaching to the comand unit. the reason i say this is because i have the same issue when i (hard wired) my 3rd gen ipod to my comand unit aux port, although the ground noise is very minimal in my case, i can still hear some noise only when my volume is low but nothing too drastic whereby i need to use a ground loop isolator. if your comand unit is defective, you should then also hear ground noise while playing your FM radio, or the CD but from reading your post that wasn't the case. also you mentioned that when you plug in yoru ipod running on its own battery and not using the 12v power source, you dont hear the ground noise, this is because the unit itself is isolating the ground properly. i would almost bet that even if you had a different radio which also has an aux connection and you hooked up your carputer using the car's 12v source, you will still here the ground noise. i could could honestly say that its not your comand unit.
06-08-2004, 03:54 PM
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'02 C240/6
Thanks for the comment. What puzzles me is that if I hook up the carputer to the car for power, ground, and video; but then hoop up the sound to headphones or anything else that is not powered by the car, the sound is pristine. (I unpluged the sound out from the carputer and plugged in headphones, unbelievably great sound).
So the carputer by itself, or feeding some external amplifier in a non-car environment, sounds great. The COMAND on its own (FM or CD) sounds great. Interfacing the two: terrible ground noise. Interfacing the COMAND with any sound provider that gets its power also from the car: terrible ground noise.
I *hope* its not the COMAND. But what is generating the ground noise?
So the carputer by itself, or feeding some external amplifier in a non-car environment, sounds great. The COMAND on its own (FM or CD) sounds great. Interfacing the two: terrible ground noise. Interfacing the COMAND with any sound provider that gets its power also from the car: terrible ground noise.
I *hope* its not the COMAND. But what is generating the ground noise?
06-08-2004, 04:17 PM
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Is your AUX cable completely shielded? It could pick up noise through induction.
-s-
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06-08-2004, 04:21 PM
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'02 C240/6
It is the glove box mounted aux cable that Steve puts in as an option with his installs. I believe its an MB OEM part. I suppose it is shielded, but can't tell.
But the same thing happens if I feed sound via the RGB adapter's sound input.
But the same thing happens if I feed sound via the RGB adapter's sound input.
06-08-2004, 04:46 PM
#6
Hi Jules,
i found some info that might help you. just as i thought, i dont believe that our comand units or any comnad units for that matter employs a built in noise cancelling curcuit. i say this because -
Amplifier Input Circuits:
The input circuit (sometimes called the 'front end') generally employs a noise cancelling circuit which compares the signal on the center conductor (the audio signal) to the signal on the RCA shield (which generally has little or no signal and is only used as a reference) and amplifies the difference between the two.
our units were made so that a factory option unit such as an MB TV Tuner for example can be attached to this comand unit etc, thses optiona factory MB units will more than likely employ a noise cacelling units built into it ie: in this example the TV Tuner. now if you notice that the when MB made the optioanl AUX available, they only provided the headphone jack in the glovebox, by plugging in ipod to this headphone jack we will never hear the ground noise whatso ever also because we are not using the car's 12v source. when we install a unit to our AUX port and that unit doesn't employ its own noise cancelling circuitry, we will definately hear the ground noise. I hope i'm making sense, it's easy for me to visualize but hard to put it into words. anyways, i would try this as a test, power your carputer using the ac powersupply connected to house curent 110v and just plug the output sound to the AUX unit on the comand and see if you still get ground noise, i dont think you will hear any ground noise anymore. overall, what i'm trying to say is that i am pretty sure that all factory optional MB accessory that attaches to the comand unit have themselves a built in noise cancelling crcuitry, hence why we dont here any ground noise using a factory TV Tuner etc. even though those devices are powered by the car's 12v source. in yoru secnario, i beleive it has somehting to do with your DC card to power your carputer motherboard, and i dont think that the dc board has any noise cancelling circuitry. i could be wrong but after careful thought, it is the only conclusion that i can think of.
sorry for the very long post, only trying to help
would like to find out how the test i sugessted turns out for you.
i found some info that might help you. just as i thought, i dont believe that our comand units or any comnad units for that matter employs a built in noise cancelling curcuit. i say this because -
Amplifier Input Circuits:
The input circuit (sometimes called the 'front end') generally employs a noise cancelling circuit which compares the signal on the center conductor (the audio signal) to the signal on the RCA shield (which generally has little or no signal and is only used as a reference) and amplifies the difference between the two.
our units were made so that a factory option unit such as an MB TV Tuner for example can be attached to this comand unit etc, thses optiona factory MB units will more than likely employ a noise cacelling units built into it ie: in this example the TV Tuner. now if you notice that the when MB made the optioanl AUX available, they only provided the headphone jack in the glovebox, by plugging in ipod to this headphone jack we will never hear the ground noise whatso ever also because we are not using the car's 12v source. when we install a unit to our AUX port and that unit doesn't employ its own noise cancelling circuitry, we will definately hear the ground noise. I hope i'm making sense, it's easy for me to visualize but hard to put it into words. anyways, i would try this as a test, power your carputer using the ac powersupply connected to house curent 110v and just plug the output sound to the AUX unit on the comand and see if you still get ground noise, i dont think you will hear any ground noise anymore. overall, what i'm trying to say is that i am pretty sure that all factory optional MB accessory that attaches to the comand unit have themselves a built in noise cancelling crcuitry, hence why we dont here any ground noise using a factory TV Tuner etc. even though those devices are powered by the car's 12v source. in yoru secnario, i beleive it has somehting to do with your DC card to power your carputer motherboard, and i dont think that the dc board has any noise cancelling circuitry. i could be wrong but after careful thought, it is the only conclusion that i can think of.
sorry for the very long post, only trying to help
would like to find out how the test i sugessted turns out for you.
06-08-2004, 05:01 PM
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'02 C240/6
I had tried the test you suggested. makes no difference. Terrible ground noise using brick ac-dc adapter (AC also has a ground, this is different than running on batteries). An ipod will probably produce ground noise as well if it is being charged via AC.
I do not have an MB device such as a TV tuner to tell is that will not cause ground noise.
It might be that the reference ground for the COMAND is different than the chasis or negative pole in the battery.
Now I'm looking into getting a better quality ground loop isolator to see if the sound improves. There is no distortion, its just that it introduces an undersired equalization where the mid range sounds funny.
I do not have an MB device such as a TV tuner to tell is that will not cause ground noise.
It might be that the reference ground for the COMAND is different than the chasis or negative pole in the battery.
Now I'm looking into getting a better quality ground loop isolator to see if the sound improves. There is no distortion, its just that it introduces an undersired equalization where the mid range sounds funny.
