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DC powersupply and huge groundloops, I'm sad :(

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  • DC powersupply and huge groundloops, I'm sad :(

    A few months ago, I had my laptop powered by a DC-DC powersuplly( http://www.trust.com/products/product.aspx?artnr=14129) and the first thing I noted was that when the powersupply was on, my monitor would have a shaky image, and phantom lines passing verticaly.

    I assumed this was an effect of the power supply, so I made a simple 12V regulator connected to the output of the Trust power supply.

    Problem fixed, image perfect, just an extra powersource, with some heat to dissipate.




    The real problem arrised when I finnaly hacked into my factory radio and connected my laptop sound line out directly to the radio's amplifying IC.

    I could know hear the full interference generated by my powersupply, especcialy when the harddrive was accessed.

    In fact, by just laying there, the laptop power supply generated almost as much noise as the laptops full volume in the line-out.

    When the powersupply was off, and the laptop running on baterry, only the ground-loop sound remained, the "alternator whine". This of course was no problem when the engine was stopped.

    I have since, significantly shortened the power supply cable to less than 10 cm's(it was almost 2 meters, i did not cut anything), tried diferent groundings(radio "line-in" ground to chassis, and to to radio harness, laptop line-out ground directly to DC ground) and the best I got was a slightly reduced noise

    I was already thinking of ways to finnaly embed the touchscreen to the car, organnizing my music, thinking of new things to do, when I am again right at the start, with no sound! I have been very sad because of this drawback

    Any one can think of ways to fix this? I'm really out of ideas, I'm going to a alarm-mounting garage later this week, to see if they can help me, and consult a few friends.

  • #2
    Have you tried grounding the laptop's chassis to the chassis of the car?

    Comment


    • #3
      The only laptop's ground I have acess is the powersupply's ground, wich is directly connected to the DC ground(0,6 Ohms). I will try that, I'm thinking a number of combination of groundings, tough I assume the best combination is all the grounding be on the car chassis?

      Comment


      • #4
        This my current setup:



        I found out 2 things today.

        Just powering the touchscreen, either by my DC PS, or directly on the car plug, gives an amount of noise and ground loop(alternator whine)

        Suplying the laptop with power, gives this huge snap, crackle pop sound, as loud as the sound output.

        Tried a lot of diferent groundings, nothing better than slightly reduced noise.

        No noise on headphones, so this is clearly a grounding issue.
        Could it have anything to do with my sound injecting hacking?
        Without powering anything, the sound is perfect, no noise at all, suitable for software volume control. I connected the signal ground, directly to the shared analog ground on the IC. If I free this ground connection, will it help?

        Please, my car is sick

        Comment


        • #5
          Are you running the car while you're messing with things? Sounds like your alternator might have a lot of noise...
          Where exactly are you grounding things? You may need to try grounding everything to the same spot or even run a wire directly up to the battery and see if that fixes things.

          Comment


          • #6
            When the car is off, off course theres is no alternator whine. I suspect the noise I get is not really the alternator, but fuel injector, but the effect is similar.

            I've read around that grounding to chassis is better than directly to the battery.

            And my car stereo is grounded to the ISO 12v connector. I will try to isolate the IC signal's ground, and ground everything to chassis, maybe that will work.

            Any more sugestions are welcome

            Comment


            • #7
              Justto test go buy a $10 ground loop isolator from Walmart or RatShack and see if it does the trick. If it does, then it is just some simple re-wiring needed. If it does not help, then there is a greater problem. Of course, you could just leave the isolator on there, but people around here frown on that, Honestly, I use one for my sirius input.
              Fusion Brain Version 6 Released!
              1.9in x 2.9in -- 47mm x 73mm
              30 Digital Outputs -- Directly drive a relay
              15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
              Buy now in the MP3Car.com Store

              Comment


              • #8
                Not sure if you want to go this way, but this is how my setup is done. I tried everything to get the whine out of my system with no success, until I found a kit at circuit city. It's a usb to 1/8" rca jack converter.

                It only requires a simple driver install and basically works like this...plug the usb in to the computer, use the supplied ground isolator and run your wiring to the radio....no more "whine"

                I have multiple high powered toys in my truck, and no matter what I did the whine wouldn't go away, until I used this kit. Works like a charm! I even tried those ground loop isolators from the roadshop...didn't do the trick. This kit was in the computer department...I forget what it was actually called though.

                I'm in the process of re-doing a lot of electrical in my truck, I am running a 2nd battery with an isolator kit to power my computer and my stereo when the truck is off. Hopefully it all works out for the best!

                Good luck with your wiring.

                Comment


                • #9
                  2k1Toaster, I'm thinking of trying the ground loop isolator to see if it really fixes something without killing the sound quality.
                  You say if the GLI solves the issue, some rewiring will solve the problem? As I have practicly tried every possible grounding. Theres not much room for signal wiring, as I have connected the line-out directly to the amplifying IC.

                  Unfortunatly, I could be hard form to get a GLI around here, but theres allways ebay.

                  truckman87, do you mean a usb soundcard?
                  That kit seems like USB soundcard + GLI.
                  And yes, I've tried using a USB soundcard wich gave an even worse noise


                  Wouldn't a ground isolator for the power supply be more efective, without the ineherit sound quality degradation if used in the line ground?

                  Comment


                  • #10
                    Originally posted by MoDu View Post
                    2k1Toaster, I'm thinking of trying the ground loop isolator to see if it really fixes something without killing the sound quality.
                    You say if the GLI solves the issue, some rewiring will solve the problem? As I have practicly tried every possible grounding. Theres not much room for signal wiring, as I have connected the line-out directly to the amplifying IC.

                    Unfortunatly, I could be hard form to get a GLI around here, but theres allways ebay.

                    truckman87, do you mean a usb soundcard?
                    That kit seems like USB soundcard + GLI.
                    And yes, I've tried using a USB soundcard wich gave an even worse noise


                    Wouldn't a ground isolator for the power supply be more efective, without the ineherit sound quality degradation if used in the line ground?
                    walmart has ground loop isolators under their name "Scosche" or something like that. Ground loop isolators by nature clip the sound. I dont know if that is the correct word but the regular meaning does what I am thinking. Basically a ground loop is just the power signal convoluting with the audio signal. THe ground loop isolator, looks for signs of this, and filters it out. Filters are not perfect. Even the top of the line filters, loose parts of the audio signal. The simplest explanation would be if you have taken basic math. A non-continuous signal does not exist in the real world. The parts inbetween are "clipped" so to go from allowing the signal to blocking it it goes from the audio level and ideally it has to go to 0 in 0 time. Impossible. At best maybe 1 clock cycle. Even then, it still allows a bit of the whine through. And then to get now from nothing back up to audio, you lose another chunk as it is ramping up.

                    I dont know if that makes sense, but here is the dumbed-down version in case somebody needs it: Ground loop isolators will distort your audio. That is why they are frowned upon.
                    Fusion Brain Version 6 Released!
                    1.9in x 2.9in -- 47mm x 73mm
                    30 Digital Outputs -- Directly drive a relay
                    15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
                    Buy now in the MP3Car.com Store

                    Comment


                    • #11
                      No it isn't a usb sound car, it's a cable that plugs into the usb port. then it is converted to the normal 1/8" jack, then it goes through this filter block...sort of like a ground loop isolator. Then i have an 1/8" plug converted to RCA's to the aux in on my head unit. The only difference between using my cd player in the radio and playing mp3's from my computer is about a +5 difference in volume level. Once I turn it up just a bit, it sounds just like i was playing a cd.

                      Here's a link to a cnet review on it

                      http://images.google.com/imgres?imgu...%3Den%26sa%3DN

                      Comment


                      • #12
                        Did you mean a shotsky diode? That would make no sense :P

                        I'm studying electronics, and had lots of classes on comunications, but I did not understand your explanation.

                        I though ground loops were created by diferent voltage grounds, wich caused residual currents in the signal ground, wich finnaly tampered the voltage in the (signal - ground).

                        I could only imagine a ground loop isolator cutting out low and/or high frequencies, that could be over-compensated with EQ.

                        Been tampering with car radio, tried some heavy direct grounding to the chassis, and still, it could only atenuate the noise, and the whine was there.

                        If nothing is powered, the sound is perfect! If I power the monitor , I get some noise, If I power the laptop I get huge noise. I just don't see what's wrong!

                        Is someone with experience with this matter out there? I've built a car amp before, just for fun, but i can't seem to connect 2 wires straight! bah!

                        Comment


                        • #13
                          Originally posted by MoDu View Post
                          Did you mean a shotsky diode? That would make no sense :P
                          No thats not at all what I meant, and yes it makes no sense

                          Originally posted by MoDu View Post
                          I though ground loops were created by diferent voltage grounds, wich caused residual currents in the signal ground, wich finnaly tampered the voltage in the (signal - ground).
                          Yes that is one way to get ground loops. One is more of a hissing that goes up with the rpms and the other is more of a whine. The hissing is the power running too close to the audio signals, and the whine is as you put it.

                          Originally posted by MoDu View Post
                          I could only imagine a ground loop isolator cutting out low and/or high frequencies, that could be over-compensated with EQ.
                          No idea how you get EQ in any part of this, but yes it cuts out high and low frequencies meaining it sends it through a FIR filter. Basically an input signal is passed into the filter. It then convolves the audio signal with itself and 2 other signals at a certain equation that eliminates the ground loop. The audio that comes out of the ground loop isolator is actually "delayed" by a very small amount of time (not distinguishable by human ears) and for each sample point on the audio signal it compares it to some sample points both ahead and behind it and levels it out pretty much, eleminating the hissing. To get rid of the whine, it uses it the method I described last post.
                          Fusion Brain Version 6 Released!
                          1.9in x 2.9in -- 47mm x 73mm
                          30 Digital Outputs -- Directly drive a relay
                          15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
                          Buy now in the MP3Car.com Store

                          Comment


                          • #14
                            You know I just thought of something else....if you have any speaker wires, or signal wires you need to run them seperate from your power wires. Example if the speaker wires you run or that are already in your car are run on the driver side it is best to run the power on the passenger side to prevent cross talk. Especially with lower guage wires (thicker wires)

                            Other then that and grounding I can't think of anything else....Like i stated before...I still had a problem with mine, but it wasn't as bad as you are describing. I however have a ton of electrical and signal wires in my truck (8 speakers, and a 12inch JL sub, 2 amps, computer, monitor, radar detector, pa unit, aftermarket alarm, and a wiring selenoid kit for my 2nd battery.)

                            That usb grounding thing worked wonders for me.


                            good luck getting rid of the noise

                            Comment


                            • #15
                              Originally posted by truckman87 View Post
                              No it isn't a usb sound car, it's a cable that plugs into the usb port. then it is converted to the normal 1/8" jack, then it goes through this filter block...sort of like a ground loop isolator. Then i have an 1/8" plug converted to RCA's to the aux in on my head unit. The only difference between using my cd player in the radio and playing mp3's from my computer is about a +5 difference in volume level. Once I turn it up just a bit, it sounds just like i was playing a cd.

                              Here's a link to a cnet review on it

                              http://images.google.com/imgres?imgu...%3Den%26sa%3DN
                              As far as the usb connector goes, it's a plain old USB soundcard with "the HiFi-Link churns out audio that's matched to the sonic attributes of its cable".

                              Not sure how can a sound card even tell what's a cable's sonic atributtes, and how could it even do to help.

                              The filter block is what seems interesting, and as far you tell, it's really just a GLI. So it seems theres nothing special about that kit.

                              And besides, for 50$ it's, cheaper just buying a new stereo and use it's line-in(assuming it can handle and clear the noise).

                              Comment

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