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  • Amplifier electrical interference

    I have a Fender HotRod amp which is picking up "static" interference from an unknown electrical source...Has anyone had this problem.....and if so what might be a resolution for blocking or masking the noise...

    Sincere81

  • #2
    Yes its something everyone deals with at one time or another.

    The problem is rarely the amp itself. The amp does what its designed to do which is amplify what you feed it. If you feed it noise it amplifies that too.

    The noise comes from what's going into the amp so you have to silence the noise at its source.

    Example one. Most fender guitars were designed back in the 50's to be an ultra budget instrument. Fender didn't even use shielded wire. They worked OK for clean tones so long as you didn't get the instrument near an electrical noise source and that's all he cared about. He also used single coil pickups that have no humbucking. Skip ahead to the present, and most fenders still have no shielding even though the cost of adding shielded wire costs nothing extra. They claim traditional tone as being the reason which is total BS. Shielding has no affect on the instruments tone, it simply lowers the noise levels.

    Add to this some gain pedals which preamplifiers the noise coming from an instruments poor shielding and the self noise, the hiss from transistors that amplify in those pedals, and inexpensive cables that usually have only 70% shielding compared to higher quality cords that have 95% or above and by the time the signal gets to the amp its a mess before you strike a single note.

    The way you determine it is the guitar cords and/or pedals is to simply unplug the amps input and turn the amp up with nothing plugged in. If the amp is quiet then you know the noise comes in on the guitar cord. If the amps noisy with nothing plugged in then you need tubes, and need them badly. Tube noise is quickly followed by tube failure. You should change them immediately. When tubes go bad they love to take out other components and then you have to pay big bucks to have them repaired.

    If the noise is external then there are several methods of modding the instrument to reduce noise. You can shield the wiring cavity with copper foil which you can buy. Its self sticking and you only need to solder a ground wire to it. You see a guitar wiring and its pickups act like an antenna to pick up any radio waves in the audio bands. The shielding captures all those magnetic waves around us coming from house wiring, telephone poles, electronic devices, Fluorescent lighting, dimmers, refrigerator compressors, you name it and grounds the noise before it gets to the hot signal wires in the instrument that carry the noise to the amplifier. Cheap cables let in a certain amount noise too.

    They also make metallic paint which can be painted inside the guitar cavity then grounded. Third you can replace single ground and signal wires with shielded wires which is usually the best because the shield is tight around the signal wire so there's no leakage of noise getting in.

    If you want to know more - Google up Fariday Cage. Fariday was one of the early inventors in electronics that developed shielding methods. Without him the chassis on an amplifier couldn't block all the magnetic hum around us. https://en.wikipedia.org/wiki/Faraday_cage

    As far as pedals creating noise goes, some of its unavoidable. Best thing you can do is first buy quality pedals that have low self noise.

    Second use realistic amounts of gain. Chances are what you dial up at low volumes is overkill for recording or live purposes. A rule of thumb I've always found useful is to turn my instruments volume down from 10 to 7 or 8. if it doesn't clean up completely, I have to much gains dialed up.

    Third, use a noise gate/hush pedal. Whet the pedal does is automatically detects the signal so when no musical notes are being played, it grounds the signal and silences sound. Its a gate that swings open when you play notes and swings closed when you stop. The noise is still there when you play notes but the amplitude of the musical notes masks much of the noise in back of them. When you stop, the envelope closes and the signal goes quiet.

    It usually requires a combination of all of these to get noise levels down.

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    • #3
      Originally posted by WRGKMC View Post
      ...
      The way you determine it is the guitar cords and/or pedals is to simply unplug the amps input and turn the amp up with nothing plugged in. If the amp is quiet then you know the noise comes in on the guitar cord. If the amps noisy with nothing plugged in then you need tubes, and need them badly...
      That is not always the case any more. Some modern amplifiers use switching jacks at the input with logic circuits that mute the signal in the later stages of the amp if there is noting plugged intonthe jack.

      I have found turning the volume control(s) on the guitar all the way down to be a better way to test than unplugging.
      As a human being, you come with the whole range of inner possibilities
      from the deepest hell to the highest states.

      It is up to you which one you choose to explore
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      • WRGKMC
        WRGKMC commented
        Editing a comment
        Have an example?

        With the guitar plugged in you still have the cord up to the controls. Bad cord or controls can make noise.

        But even if it was good, how is jack termination going to be any different then termination at the control besides a few feet of wire? Even if the termination is further along in the circuit, leaving it open doesn't help with anything, at least by removing the jack any termination back to the power amp should be quiet at least to the circuits normal noise floor. If there's circuitry before the termination that it would need to be signal traced.

    • #4
      No one mentioned the possibility that he's picking up EMI over the AC connection?

      Dirty AC can cause noise in an amp too.
      **********

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