Origin 20H Hum when powered on

Discussion in 'Marshall Amps' started by progrockabuse, Feb 18, 2020.

  1. progrockabuse

    progrockabuse Member

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    Just a quick one, is it normal for the amp to hum loudly powered on? Not a hum from the speakers, just hum from the amp itself. Seems louded than most other amps I've owned.
     
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  2. ampmadscientist

    ampmadscientist Well-Known Member

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    Is the guitar cable UN-plugged when it hums?
    Is all the effects UN-plugged when it hums?
    If the output tubes are out of balance it will make a hum also.
     
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  3. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

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    Where’s your volume knob at power up ? If it’s on zero there will be a bit of hum, if it’s up at your playing level it will be more intense !!
     
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  4. Ken Underwood

    Ken Underwood Well-Known Member VIP Member

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    He has said that it is not coming from his speakers so positioning controls would not make an iota of difference.
    Its remotely possible that the output tubes could be causing the problems but i would be more inclined to suspect the mains transformer or choke, or at a pinch the OT
     
  5. Chris-in-LA

    Chris-in-LA Well-Known Member

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    I have at least one head that makes an audible hum when it is switched on. I believe it’s the power transformer powering up. Don’t think it’s a problem. The hum goes away before the tubes are even warmed up.
     
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  6. RCM 800

    RCM 800 Active Member

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    Ive never noticed any audible noise coming from either of my 20h's.
     
  7. Deerhunter1972

    Deerhunter1972 Active Member

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    My DSL20HR hums with nothing plugged into it and in standby. Guessing its the transformer...
     
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  8. ampmadscientist

    ampmadscientist Well-Known Member

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    Take out the first preamp tube, which is closest to the input jack.
    Did the hum go away?

    OK
    after the amp has been turned on 5-10 minutes:
    feel the output tubes and check the temperature, if one tube is cold and the other is hot it's probably a bad output tube.
    When the output tubes are out of balance it can make the amp hum.

    A broken input jack. Broken solder connection at the input jack.
     
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  9. Deerhunter1972

    Deerhunter1972 Active Member

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    Thanks for the advice I'm away from home tonight. I'll try your advice tomorrow. It has hummed since I bought it knew a little over a year ago. I did replace all stock power and preamp tubes with JJ's and still got humming.
     
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  10. ampmadscientist

    ampmadscientist Well-Known Member

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    If you can look inside the amp, sometimes parts can break off the circuit board when the amp is shipped. Look for anything that's come loose from the board.
    Once in a while, a capacitor lead wire might break off because of shock and vibration....rarely but it's happened.
    Or if you are not sure, you could always take your amp to a technician.
     
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