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Amp fart noise at turn on

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  • Amp fart noise at turn on

    Hi all,

    I have just fitted a 4ch amplifier in my car to drive the speakers and when I turn on the HU the amp power light comes on and after about 5 seconds only what can be described as a farting noise comes from the speakers for about 1 second then the all sounds ok.

    Details of the setup:-
    Car - Vauxhall Astra 2004
    Speakers - fronts are 17cm components with the woofer replaced with aftermarkets. rear door are standard - size unknown.
    Amp - Pure Power 600w (cheapo - but just needed replacement amp for HU with no amp built in)
    HU - Alpine CD/MP3

    I have tried it with RCA's connected to my ipod instead of headunit to eliminate slow RCA powerup on the HU and it still made the same noise.
    I've also moved the ground point for the amp and checked all connections.

    Anyone have any idea what might cause this ?

    Any help really appreciated!!

  • #2
    Is it like a pop?

    Comment


    • #3
      Originally posted by swift_gti View Post
      Amp - Pure Power 600w (cheapo - but just needed replacement amp for HU with no amp built in)
      my guess is right here.

      There is a reason why its cheap.
      Take my advice: Do not try to build a system that includes EVERY feature. Start with the basics, build it to a bug free state, and THEN add on.

      Comment


      • #4
        I wouldn't describe it as a pop, its varied it pitch - hard to describe, it sounds like 'ppwerrrp' starts low ends higher.
        Probably doesn't make much sense but its really hard to describe it

        Comment


        • #5
          Originally posted by Will Albers View Post
          my guess is right here.

          There is a reason why its cheap.
          I hear what your saying - I'm not expecting this thing to be kicking out shedloads of power or anything, but surely it shouldn't do this even if it is lower end of the market!

          Comment


          • #6
            Its the fact that it happens regardless of source that leads me to the idea. Are your gains too high?
            Take my advice: Do not try to build a system that includes EVERY feature. Start with the basics, build it to a bug free state, and THEN add on.

            Comment


            • #7
              No it seems to happen even with the gains turned right down (gain position doesn't make the noise any louder or quieter either)
              I have tried it with my car CD player and notice its picking up noise from the cd player - if i skip track etc it whirrs while seeking.
              Could the remote lead have any impact? I notice theres a small nick in the stereos remote output - Is it possible to test the amp by looping the +12 from the amp to the remote input also ?

              Cheers

              Comment


              • #8
                Your ground is goofy on your amp. Where is it grounded? It sounds like your amp is trying to ground through the ground braid in your RCAs.

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                • #9
                  I've tried two different ground points one a bolt coming through from the body work and now its on a factory ground point that has two original items from the car connected to it.
                  Is there any way to test out the ground ?

                  Comment


                  • #10
                    Does it still make the noise if you dissconnect the RCA's from the amp?

                    Comment


                    • #11
                      Just done some more testing -
                      Another amp works fine with the same power leads/grounding point/speakers/RCA's
                      My amp doesn't make the noise with only one speaker connected (one out of the four channels) If I connect two speaker it does a small fart so to speak
                      With all four speakers connected its back to a loud pperrrrp when you turn it on.
                      I have just tried with the amp grounded directly onto the battery terminal with a new lead - still the same.
                      Amp still makes noise with no RCA's connected.

                      Guess the amp is dodgy??

                      Comment


                      • #12
                        Is it possible to test the amp by looping the +12 from the amp to the remote input also ?
                        yes you can short the +12 lead to the remote input to turn on the amp, try this without the hu connected to the amp at all. then try this with just the rca's from the hu to the amp but not the remote wire and short it manually. also try it with the rca's not connected but the remote wire from the hu.

                        Comment


                        • #13
                          Yeh tested it with a multimeter and done what you said - it still gave the same problem.

                          Comment


                          • #14
                            You said with only one speaker hooked up it doesn't make the noise. Is that with the one speaker hooked up to any channel? or a specific channel?

                            Comment


                            • #15
                              Any channel - Also tried with one speaker on one of the two front outputs at the same time as one speaker on one of the two rear outputs, it still made the same noise.

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