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Thread: RFI Picked up by Amp

  1. #1
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    Default RFI Picked up by Amp

    Hi everybody, I have an amp-related conundrum that I've as of yet not found a solution for: when my HT-5R's effects loop is engaged, I get a very audible radio frequency interference (RFI) from an AM station here in Maryland. This happens even when I take the lead plugged into the FX loop "send" into the "return". The RFI is present at the same level whether or not a guitar is plugged in.

    I have tested all the pedals in the loop, the power source for the pedals, and replaced all patch cables and longer 1/4 inch cables running from the amp to the pedal board and back to the amp. I have purchased a Furman power conditioner, which did nothing to squelch the RFI. I have replaced the tubes. I have even brought it to an amp tech at a Blackstar approved shop. He examined the amp, found nothing wrong with it, and even demoed it for me--it was pristine and quiet even with all the pedals plugged in and the overdrive channel engaged.

    I'm at my wit's end, having tried seemingly everything. It could be a problem with the mains in my apartment, though the recommended remedy--the power conditioner-- didn't solve it, and I'm not sure what else I could try. Alternatively, it could be the amp, despite it performing normally at the repair shop. Is it at all possible that something in the amp is awry and makes it susceptible to picking up RFI? Would love some input! Thanks everyone.

  2. #2
    Super Toneologist VinceT's Avatar
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    Default Re: RFI Picked up by Amp

    How close are you to the nearest AM transmitters (radio-masts)?


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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by VinceT View Post
    How close are you to the nearest AM transmitters (radio-masts)?


    Sent from my iPad using Tapatalk
    A quick Google Maps search shows there's a tower only 2.5 miles away. Is there a way to shield the amp from picking up this signal? Also, why would it only be audible when the FX loop is engaged? Just seems so strange.

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    of the Forum PFDarkside's Avatar
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    Default Re: RFI Picked up by Amp

    What cables are you using for your effects loop send and return? How long are they? Does the issue disappear with nothing connected to the loop? (It seems you are saying a patch cable connected has the same issue, what happens with no patch cable?)

    I’d try using good, short, shielded cables to see what happens. I hope it’s not an issue with the amp itself.
    Oh no.....


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  5. #5
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    Default Re: RFI Picked up by Amp

    Another option is to build a setup without using the effects loop. This might involve getting another source for your distortion in the front of the amp.
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    Mojo's Minions devastone's Avatar
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    Default Re: RFI Picked up by Amp

    The loop part is weird, usually those kind of signals get amplified by the front end of the amp, not the loop, and wahs are usually the worst culprits. Sorry, I don't have anything useful to add except that it's interesting, maybe a Faraday cage around the house?

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    Default Re: RFI Picked up by Amp

    use a shielded guitar cable (separate shield)-not a regular guitar cable -but lift the shield from the TS 1/4" -that will fix it.

    to be clear -this is 2 conductor 24AWG to 18AWG sized PLUS separate shield/drain cable that you only connect to the 1/4" connector on ONE side.
    Last edited by NegativeEase; 11-21-2019 at 12:20 PM.
    “For me, when everything goes wrong – that’s when adventure starts.” Yvonne Chouinard

  8. #8
    Super Toneologist DavidRavenMoon's Avatar
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    Default Re: RFI Picked up by Amp

    You can try connecting a 150 pF capacitor between the signal and ground on the loop return. That should shut the RF to ground.

    This was happening with my amp for a while at our rehearsal space. When I switched to a different AC outlet it stopped. I don’t use the FX loop, and it seemed to be from my pedal board.


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    Mojo's Minions devastone's Avatar
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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by NegativeEase View Post
    use a shielded guitar cable (separate shield)-not a regular guitar cable -but lift the shield from the TS 1/4" -that will fix it.

    to be clear -this is 2 conductor 24AWG to 18AWG sized PLUS separate shield/drain cable that you only connect to the 1/4" connector on ONE side.
    Okay, so just put the Faraday cage on the cable, but where is the fun in that?

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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by NegativeEase View Post
    use a shielded guitar cable (separate shield)-not a regular guitar cable -but lift the shield from the TS 1/4" -that will fix it.

    to be clear -this is 2 conductor 24AWG to 18AWG sized PLUS separate shield/drain cable that you only connect to the 1/4" connector on ONE side.
    Not sure I follow exactly. How many components would I need to purchase to make this happen?

  11. #11
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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by devastone View Post
    Okay, so just put the Faraday cage on the cable, but where is the fun in that?
    ha.... well I have to solve this issue in the studio professionally all the time -so we don't beat around the bush -we just murder the RF and move on
    “For me, when everything goes wrong – that’s when adventure starts.” Yvonne Chouinard

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    of the Forum PFDarkside's Avatar
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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by NegativeEase View Post
    use a shielded guitar cable (separate shield)-not a regular guitar cable -but lift the shield from the TS 1/4" -that will fix it.

    to be clear -this is 2 conductor 24AWG to 18AWG sized PLUS separate shield/drain cable that you only connect to the 1/4" connector on ONE side.
    So basically balanced cable, tip to tip, sleeve to sleeve and drain to sleeve on one side?
    Oh no.....


    Oh Yeah!

  13. #13
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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by lukemh987 View Post
    Not sure I follow exactly. How many components would I need to purchase to make this happen?
    I will post a link,.... or make you one and send it to you if I don't find an affordable one
    “For me, when everything goes wrong – that’s when adventure starts.” Yvonne Chouinard

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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by NegativeEase View Post
    I will post a link,.... or make you one and send it to you if I don't find an affordable one
    Sure, post a link. That'd be great. Thanks!

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    Default Re: RFI Picked up by Amp

    An update, after a little more tinkering, I've found that the interference is also happening when the FX loop is not engaged. Not sure if this calls for a different approach.

  16. #16
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    Default Re: RFI Picked up by Amp

    Have you tried a different guitar by chance?
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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by Hsb View Post
    Have you tried a different guitar by chance?
    Yes, have tried with several different guitars. However, the RFI happens no matter whether the guitar is plugged in or not.

  18. #18
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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by PFDarkside View Post
    So basically balanced cable, tip to tip, sleeve to sleeve and drain to sleeve on one side?
    Basically
    “For me, when everything goes wrong – that’s when adventure starts.” Yvonne Chouinard

  19. #19
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    Default Re: RFI Picked up by Amp

    Quote Originally Posted by NegativeEase View Post
    Basically
    For reference, I replaced my old cables with these Planet Waves American Stage cables. They seem to be high quality, but I'm not sure if they're a culprit in this.
    Last edited by lukemh987; 11-23-2019 at 07:26 AM.

  20. #20
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    Default Re: RFI Picked up by Amp

    Does this happen with the effects loop connected by just a (good) cable...no pedals?
    Dave, Ambassador/Writer/Artist for Seymour Duncan

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