Aftermarket Stereo + Stock Amp - Loud 'pop' When Turning Stereo On/off Or Changing Stations

wild.coast Jan 31, 2020

  1. wild.coast

    wild.coast Test Drive

    So I installed a Pioneer head unit using the Metra 70-7551 harness, which uses the RCA outputs on the radio and uses the stock Rockford F amp.

    I'm getting a loud 'pop' whenever the head unit turns on or even when changing modes or radio stations. Did a bunch of research and this forum and elsewhere and sounds like, if I understand correctly, it's an issue with the blue/white wire coming out of the head unit into the 'amp turn on' (blue wire) on the Metra Harness. Specifically, that the head unit takes a second longer to cut power which causes the amp to build up a charge and release it - hence the noise.

    I've heard of people installing group-loop isolators on the RCA outs to avoid this (thread). I've also seen a post where someone installed a Relay on the blue/white wire to get it to cut out instantly (link). Does anyone know which is the better/proper way? After some reading, sounds like the ground-loop isolators are more of a 'mask the problem' solution - and significantly reduce the sound quality?

    Any chance this pop is due to some bad ground? This website seems to suggest some fixes: Engine whine and ground loop fixes... take two

    With regards to grounding, I know best practice is to ground everything off a single point. There were several wires that needed to be grounded:
    • Metra harness ground wire (black)
    • Metra harness amp ground (black/white)
    • Stereo (head unit) ground wire (black)
    I just connected all the together to a single wire and ran that wire to some bare metal behind the stereo for chassis ground. Interestingly, simple connecting the 3 wires listed together in the harness was fine - everything worked fine. So I'm guessing the head unit is somehow being ground already?? Via the antenna plug? If that's the case, would grounding it twice cause any of these 'subtle' issues?

    I don't have any background in electronics or automotive wiring, so just researching various threads but don't have any framework to evaluate what's right/wrong, and there seem to be a lot of conflicting opinions. Would love some expert help!! Thanks in advance!

    Pic of my wiring:
  2. meisanerd

    meisanerd Bought an X

    Edmonton, AB, Canada
    You need a ground-loop isolator. It has no effect on the sound quality.

    The popping is related to grounding. Not necessarily a bad ground, just a different ground. The stereo and the amp both need to know what a signal of 0 is relative to the rest of the electronics. However, the 0 is affected by the resistance in the grounding, which can be affected by the quality of the ground wire, as well as the distance to the battery/alternator. Since that 0 is different between the head unit and amp, the amp sees a small signal when the head unit is saying it needs to be silent. A ground-loop isolator breaks the ground signal between the head unit and amp (which is not needed at all in an audio application), this fixing the popping.

    You could fix this by running a ground wire to the same ground wire that the amp uses, or just throw an isolator in there and leave things as it is, which is much simpler.
  3. wild.coast

    wild.coast Test Drive

    Hmm, interestingly enough I actually do have the amp ground connected to the radio ground wire (I think).

    Here is my wiring for reference:

    Top left, you can see 3 wires joined together which all go to chassis ground. The three wires are:
    - ground wire coming out of the stereo
    - ground wire (black) coming out of the harness - this is supposedly the stereo ground as well? Not sure...
    - ground wire (black/white) coming out of the harness - this is the amp ground apparently?

    Really curious if my assumptions are right?

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