Loud hum when amp connected to AVR (with amp turned off)

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jdeecraigslist
jdeecraigslist Posts: 15
edited April 2022 in Basic Hookup/Wiring Questions
I am having an issue that I can't figure out how to solve.

I have an AVR (Marantz SR5015) with my Polk 703's connected to the outputs. I have a separate integrated amp with nothing connected to it, in or out, except the power cord. When I connect the RCA pre-outs from the AVR to the input of the integrated amp, I get a very strong hum through the speakers - even with the integrated amp turned off! If I unplug the amp from power, the hum goes away.

I tried moving all the wires, touching both units all over in an attempt to find a way to ground them, no luck. I'm sure this is related to grounding but don't know what or where to ground. I also can't figure out how an amp that is turned off can be sending feedback to speakers that aren't even connected to it.
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  • pitdogg2
    pitdogg2 Posts: 24,579
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    What are you trying to do here?
    Are the U-bolts still connected to the integrated amp?
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  • jdeecraigslist
    jdeecraigslist Posts: 15
    edited April 2022
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    pitdogg2 wrote: »
    What are you trying to do here?
    Are the U-bolts still connected to the integrated amp?

    Trying to send music from my AVR to my amp. I forgot to mention that the original configuration was the speakers connected to the amp. I was getting a loud hum that I couldn't solve so I put the speakers back on the AVR but it's still happening there.

    U-bolts??b7bd2kwk7z9z.png
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  • pitdogg2
    pitdogg2 Posts: 24,579
    edited April 2022
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    Integrated got pictures of said integrated. Front and back or name and model number
    U bolts connect the integrated amp to its preamp. In most you need to remove the U bolts so you're just using the amp section.
    Post edited by pitdogg2 on
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  • audioluvr
    audioluvr Posts: 5,437
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    Shoot a pic of the back of your integrated configuration. What @pitdogg2 is trying to say is are your cables going from AVR "pre-out' to your integrated "amp in" inputs? and if so are your speakers hooked to your integrated?
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  • BlueFox
    BlueFox Posts: 15,251
    edited April 2022
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    jdeecraigslist wrote: »
    U-bolts??

    They aren’t U-bolts. Just U shaped jumpers between the preamp output and the amp input. If you don’t see them on your gear then your gear doesn’t support that design.

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  • pitdogg2
    pitdogg2 Posts: 24,579
    edited April 2022
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    Thanks Bud. That is what I was referring to. Mine on my old integrated were actually all metal, no RCA or cable just a solid metal U.

    Jumper would be a more appropriate term. Did the same as above.
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  • gmcman
    gmcman Posts: 1,759
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    What is the relation of the receptacle for your integrated amp to the receptacle of your AVR?

    What's connected to the AVR inputs? Do you have a HDMI cable from your cable box? Sometimes the coax for the cable may not be properly grounded outside.

    Could be a ground loop hum, and something that comes to mind would be your integrated being on stand-by instead of being powered off. Does your integrated have a HT bypass function? If so, try turning that off.
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  • jdeecraigslist
    jdeecraigslist Posts: 15
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    Problem identified, it was a ground loop! I put the integrated amp on a 3-to-2 prong adapter and it's dead silent.

    Is it "safe" to run the system this way or should I ground it to something else?
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  • Clipdat
    Clipdat Posts: 12,608
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    Should be fine as long as you don't touch it while dripping wet and naked.
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  • pitdogg2
    pitdogg2 Posts: 24,579
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    Clipdat wrote: »
    Should be fine as long as you don't touch it while dripping wet and naked.

    Dang it !! How did you know that is how I prefer to listen to my music?
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  • Clipdat
    Clipdat Posts: 12,608
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    Because it enhances your microdetails, key word micro.
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  • pitdogg2
    pitdogg2 Posts: 24,579
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    Clipdat wrote: »
    Because it enhances your microdetails, key word micro.

    But bulbus....😂🤣🤪
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  • Clipdat
    Clipdat Posts: 12,608
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    ka80nv7ifuok.png
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  • jdeecraigslist
    jdeecraigslist Posts: 15
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    I isolated the issue to my cable TV connection. Cable coax from the wall going into my cable TV box, HDMI to my receiver, amp connected to receiver via RCA.

    Removing the cable TV coax stops the hum. Alternatively, using a cheater plug stops the hum.

    I'm getting one of these "Cable TV Coax ground loop isolators" and we'll see what happens: https://amazon.com/gp/product/B0070Q6URO/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
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  • pitdogg2
    pitdogg2 Posts: 24,579
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    You could save money and remove the ground from the cable box cable at one end too.
    30 min and done.

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