[Help!!]Marshall sv20H hiss(white noise) when plug in treble input

Discussion in 'Marshall Amps' started by Jay-Deco, Feb 22, 2021.

  1. Jay-Deco

    Jay-Deco New Member

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    I just got my brand new marshall sv20h, but I notice there is noticeable noise when I plugin to treble holes. (both jumping cable or use treble individually) but the normal channel is dead quiet.
    I use 2 greenback speakers, 25 watt each.

    1, when I unplug-in any cable, it is silent.
    2, when I just use normal channel, it is quiet.
    3, when I plug into treble channel, the hiss (white noise) starts at volume 1.5, increases with the volume up to 4 and then will not increase much when volume is over 4.
    4, Treble, mid, presence can affect the noise level a little bit.

    here is the video link:


    So, the question would be, is it a common situation on this amp? If not, how can I solve it?
     
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  2. Shane Stevenson

    Shane Stevenson Well-Known Member

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    This is not normal for the SV20. I’ve had this problem with other amps and it’s been tube related if I remember right. Others here will shoot you in the right direction. I’m no authority on the tech stuff but I’m a complete pro at giving my opinion. Hang around and you will find the fix. Good luck!
     
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  3. scozz

    scozz Well-Known Member Gold Supporting Member

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    Ive heard a few people complain about this, but only a handful. And the amount of hiss in your video sounds like something is not right with the amp,

    Like my buddy @Shane Stevenson said, people with more knowledge than me/us, will check in to help you out before too long.

    Welcome to The Marshall Forum.
     
    Last edited: Feb 22, 2021
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  4. Jay-Deco

    Jay-Deco New Member

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    thank you for replying!
     
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  5. Jay-Deco

    Jay-Deco New Member

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    yeah, I also read some of them, they have similar problem as mine, but I just want to make sure the problem is exactly what I am thinking about. Thanks for replying.
     
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  6. Gene Ballzz

    Gene Ballzz Well-Known Member

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    @Jay-Deco
    First, :welcome: to the forum!
    Did you buy it online and get it shipped to you or did you pick it up at a store? If locally picked up, take it back to them, show them the issue and check another identical unit to confirm or deny that its not normal. Offer them the choice of trying a new tube to fixit, or giving you a reolacement unit.

    If you bought it online, offer them the option of first sending you a new tube to try, or exchanging it for one that doesn't hiss.

    It's hard to tell from your demo. When you cranked the NORMAL volume up and down the HIGH TREBLE channel was all the way down. But when you cranked the HIGH TREBLE volume up and down, the NORMAL volume was also already up at about 50%.

    With all that said, the nature of the circuit design makes a certain small amount of "hiss" on the TREBLE channel fairly common. How does the amp actually sound, other than the hiss? And if you're going to own a tube amp, it's a good idea to have at least a new preamp tube on hand to swap in and out of the three positions, for testing just this sort of issue.

    Best Of All To You,
    Gene
     
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  7. Jay-Deco

    Jay-Deco New Member

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    Thank you for replying.
    I bought this though a friend and he contacted the Marshall amp agents in my country to get this brand new. I sent the vid to the agents but they claimed that this amp does not have a problem. So it means that I don’t think they would change one for me.

    I read Marshall sv20h tech spec, it shows:
    2* ECC83, 1* ECC83 (phrase splitter) 2* EL34

    Does that mean I need to buy three exactly the same ecc83? (I read in other thread, they say it is a pre amp problem so I don’t want to spend more on power tube)
     
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  8. Jay-Deco

    Jay-Deco New Member

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    Here is the update.
    I put a clean boost in the effects loop and turn the volume level down, and the noise nearly disappears even the two channels with maximum volume......:shock:
     
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  9. Chris-in-LA

    Chris-in-LA Well-Known Member

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    So, the hiss might be from the preamp. You don’t have to buy 3 new tubes, only 1 to test. Have you tried moving your current preamp tubes to different positions?
     
  10. Ufoscorpion

    Ufoscorpion Well-Known Member

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    The Marshall Astoria custom nails the page tone .
     
  11. Jay-Deco

    Jay-Deco New Member

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    Thanks for relpying.
    I am new to this type of amp. I used to play small fender tweed, so I haven’t tried moving the preamp tubes to different position. I will try when my new tube comes.
     
  12. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Try it now, if it doesn’t work use the new tube.
     
  13. ken361

    ken361 Well-Known Member

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    good chance its the v1
     
  14. BatmansMarshall

    BatmansMarshall Well-Known Member

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    When you touch the strings of your guitar does it go away? If so then dirty power. You need a power conditioner like a Furman. If the noise is still there then try replacing the pre amp tubes one by one. As stated you only need one new one to slot in and out.
     
  15. tallcoolone

    tallcoolone Well-Known Member

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    Swap preamp tubes—as said, it’s prob v1
     

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