Noisy Signal from Head Unit when Amplified

  1. slothin49

    slothin49 Member

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    New Issue, New Thread.

    I originally thought my issue was with my fix86 and posted a thread on that. But after eliminating the Fix86 and just using a standard LOC, confirmed my Factory 7" HU is producing a constant noise (between the 2-8KHZ range) even with volume at 0 when amplified.

    Anyone else had this issue? Seems kinda unfixable. I wonder if it's a defect in my head unit or if it's just a universal problem.

    Let me know if anyone has experienced this or been able to fix it. Really appreciate the help this forum has provided.
     
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    slothin49

    slothin49 Member

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  3. shoegazer

    shoegazer assistant to the assistant manager

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    There's still an aftermarket amp in the chain, right?
     
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    slothin49

    slothin49 Member

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    Correct. Currently the chain is HU>LOC>Amp>Passive XO>Mids/Tweets.

    Maybe it's picking up noise from the wiring behind the HU? It's a little messy back there with all the wiring
     
  5. shoegazer

    shoegazer assistant to the assistant manager

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    In my experience, RFI sounds more like a low hum or (if it's digital), more of a chirping. If it still sounds like a constant hissing; my gut says gain staging or just a high noise floor from a class D amp. I know it's a pain; but if you can temporarily bypass the aftermarket amp, you may be able to isolate the amp as the issue.

    Did the noise exist when the setup was all stock?
     
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    slothin49

    slothin49 Member

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    As far as I know, it did not exist while stock. My thinking is that it didn't exit because the signal just wasn't amplified enough for it to be present but who knows.

    So you're suggesting trying to just run the the speakers unamped to see if that fixes it?
     
  7. shoegazer

    shoegazer assistant to the assistant manager

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    Since the point where you described it as a hissing sound; my gut feeling has always been the power amp was the cause. Either it was working too hard with a really low signal (gain stage); or it was just a noisy amp.

    If you disconnect the inputs to the amp and just let it run by itself; you'll get an idea of just what it's adding to the overall sound.
     
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    slothin49

    slothin49 Member

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    What do you mean run by itself? If I disconnect the rca inputs from the amp, the hiss go silent
     
  9. shoegazer

    shoegazer assistant to the assistant manager

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    Yeah. It looks to me like that amp turns on and off as it senses input signal. There doesn't seem to be any way to keep it 'on' manually.

    If you have a RCA to 1/8" cable; you can connect your smartphone to one of the RCA inputs and play a music file at the lowest volume level above zero. That would send a (low) signal and, I assume, cause the amp to turn on. In this case... the music would be very soft if not silent. But you could get an idea of the noise floor (the lowest level of hissing possible from the amp) that the amp is producing by itself.
     
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    slothin49

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    I guess I should rephrase what I said. When the rca's are unplugged it is virtually silent. If i put my ear right up to the tweeters I can hear a very faint hiss. So I don't think the amp is shutting off output when it doesn't receive input signal. I don't have an 1/8 to RCA cable handy, but could easily pick one up if you think it's still worth it. I just don't think the noise is being introduced by the amp
     
  11. shoegazer

    shoegazer assistant to the assistant manager

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    I hear ya'.

    And if your heart and gut are more focused on another direction; definitely go that way.

    The amp could have a noise gate or other muting feature that will just confuse things. That's why I was going with the alternate source idea for testing.

    Is the hiss still audible with the HU's volume at zero? Or at one?
     
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    slothin49

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    I'm definitely grateful for your suggestions and willing to try anything! Thats what weird hiss is still there at 0 volume. And even when I press the audio power off button on the HU. If I don't fix this soon I swear I'm gonna dump the sound system in the wifes car and giver her the civic lol
     
  13. shoegazer

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    Well... if the noise is still there when the HU's power is off; IMO it's gotta' be the additional amp. That's the only thing left that's running, right?

    If ya' want... take a couple of photos of the connections and the settings. Maybe we can see something that's not obvious.
     
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    slothin49

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    And that totally makes sense you're right. I have a second amp (same model amp though), I'll try swapping them out. I'll give you photos of the connections too. I'll work on it more tomorrow!
     
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    slothin49

    slothin49 Member

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    Good news, I got the hiss to an acceptable level.
    Bad news, it has to be the Head Unit causing the hiss.

    So, today I tried a number of things.
    First, swapped the amp. Not the issue and the hiss was still there just as strong.
    Second, I wanted to make sure it wasn't my "homemade" wiring harness (a cluster fuq of wiring so that I don't have to do any cutting into the OEM harness). So, I unplugged the harness and plugged the OEM back in, which put power back to the stock speaker wires. I tapped into those and connected them to my LOC. Got everything else hooked up... AND the hiss is still there.
    With that experiment I had successfully replaced every single component and/or wire in the signal chain up to and including the amp. So it has to be the Head Unit.

    Back to the good news. I was getting everything wired up back to how I wanted it (HU>FIX>AMP) and ready to quit for the weekend. Instead of calibrating the Fix at 23/40 I tried it at 30/40 and tuned the gains on the amp. To be fair I had done that before but for some reason it helped this time. The hiss was still there but not bad. Acceptable I'd say. And then I put a desirable EQ curve on the Fix, which helped the hiss even more.

    So, problem isn't eliminated but is cured enough for me to accept it. I still want to ask my buddy who also has a '19 civic if he'd swap head units with me to verify whether it's my HU or all of the 7" Touch Screen HU's that have the hiss. He doesn't plan on upgrading his sound system so he'd never even notice it. Maybe a handle of whiskey and 50 bucks and he'll trade me? lol
     
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