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I recently replaced my refrigerator with a brand new LG model LTCS20220W. The fridge is silent, but when it is running, my guitar amplifier is picking up a 4,500Hz signal which is driving me crazy. I used a spectrum analyzer on the output from my amp to determine the frequency of the noise.

The noise seems to be coming over the power line, since it's still present even when nothing is plugged in to the amp, and the input volume controls don't affect the noise volume.

I've looked on line for power EMI filters, but they all seem to start down at the 150KHz level.

Does anyone have an idea on how to filter this noise out?

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  • 4
    Turn off the fridge when it matters.
    – Nick Alexeev
    Nov 27, 2016 at 1:26
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    Add a power line choke to help block signals on the power line. Then add a toroid choke at the amp audio input from you guitar, as audio cables can pickup external noise and send it to the amp. The amp has no way if isolating it. If the changes don't reduce it sufficiently you may have to add an audio notch filter.
    – Optionparty
    Nov 27, 2016 at 1:38
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    Modern refrigerators use inverters to provide variable frequency drive to the motor to provide high efficiency. I expect that the inverter uses 4.5kHz for the PWM frequency in the inverter. As others have said a line filter of some form is needed. I'm surprised that the audio equipment is so sensitive or that the interference is so great.
    – Kevin White
    Nov 27, 2016 at 1:44
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    Is it conducted noise, the. ac couple DC supply to the spectrum analyzer. Then use low ESR caps according to 500Hz and 50 Hz this will improve filtering. Most have filters to 10 Hz which allows excessive ESR broadband. look for lowest ESR 100uF and 10uF with 100mohm and 10mohm or less respectively. IF SA shows no 4.5kHz the it is a CM problem and your humbuck is inadequate,, heat big CM choke for the guitar in
    – Tony Stewart. EE since '75
    Nov 27, 2016 at 2:58
  • See if you can find another outlet, on another circuit breaker, for either the music or the 'fridge. That can mute the noise a little. I'd consider, too, whether the fridge, or the amplifier, are faulty.
    – Whit3rd
    Nov 27, 2016 at 6:49

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This sounds like it may be a grounding issue. The most common source of such problems is differences or changes in ground between components. If that fixes it, you might want to start looking in to the grounding situation in your house and see if something is not properly grounding somewhere.

If it is actually impacting the voltage levels of the house overall rather than it being power on ground, I'd probably talk to the refrigerator company about why their refrigerator is causing power conditioning issues for your whole house. It might also be worth simply trying a different circuit then as well, preferably one from the opposite side of the main breaker box if possible.

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