JCM800ZW Noob

Discussion in 'Marshall Amps' started by Raleighred, Dec 7, 2019.

  1. Raleighred

    Raleighred New Member

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    I just bought a JCM800ZW and I'm running it into my Randall 4x12. I've set the amp to 16ohm to match the cab. I get sound but with the master and preamp at 8, I can talk over it. I've always heard how incredibly loud these things are, so either I've done something dumb in the setup or there's a problem with the amp.

    Edit: The Mains were set at 230V and when I changed to 110V, it's loud as hell at master volume at 2 but no gain at all. I was getting solid distortion with the previous mains setting...but I suppose that was due to the master volume being at 8. Hopefully I will be ok with an OD in front of it and a power soak. Any tips appreciated.
     
  2. WellBurnTheSky

    WellBurnTheSky Well-Known Member

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    Well, that's how EVH said he stumbled upon the whole Variac idea, and rock music was changed forever ;)
    Congrats on the purchase, and yeah, an OD and power soak will get you where you want !
     
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  3. Steve Smith

    Steve Smith Active Member

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    If you are running a British spec amp over the pond from 230 to 110 I strongly advise you get a qualified tech to check it out as it will most probably need rebiasing, just to be on the safe side. Not as simple as just changing the voltage selector switch IMVHO :)
     
  4. Steve Smith

    Steve Smith Active Member

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    The light dimmer story Ed now says was a wind up, and plain daft, unless you like burning valves and blowing the transformer
     
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  5. WellBurnTheSky

    WellBurnTheSky Well-Known Member

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    The story as he tells it now (which at least makes some sense) is, he inadvertently purchased a EU Superlead, and found out, just as the OP did, that he was getting very low volume and lots of saturation and compression. When made him think, he could use it to his advantage. Then he went to an electronics store, got a Variac and started experimenting.
     
  6. Steve Smith

    Steve Smith Active Member

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    Yeah I heard that as well dude. Ed took chances in the pursuit of tone, could easily have killed him or burned the house down ! No disrespect meant to your post dude :) Thanks
     
  7. Steve Smith

    Steve Smith Active Member

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    PS - JMP and TS9 does it for me without the danger :)
     
  8. ampmadscientist

    ampmadscientist Well-Known Member

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    Wecome to the forum Raliegh :cheers:.
    I think the wiring inside needs to be changed to run it on a different voltage.
    Not just the voltage selector.
    You should have a service center check the mains wiring and get it sorted, or if you can find the correct schematic.
    The primary winding(s) are in series for 230 volt, and wired in parallel for 120 volt. That's why it doesn't work correctly I'm fairly certain.
     
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  9. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Running a 2203 with the pre-amp at 10 should give you tons of gain no matter where the master is. You might need to get that amp checked out.
     
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  10. Raleighred

    Raleighred New Member

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    Really appreciate all the feedback and advice. The former owner did buy it as a Euro spec and changed the fuse, but never had anything else changed and it has never been in front of a tech. He had it for 9 months or so with no issues. However, I want it running at it's best and if there should be gain at 2, something is up bc there was none.
     
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  11. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

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    Welcome to the forum.
    Cheers to your new amp.
    Enjoy that beast !!
    But as said before take it to a tech.
    Mitch
     
  12. South Park

    South Park Well-Known Member

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    The variac trick is called a starved plate. You can drop the plate voltage and distort things . The problem is all the voltages drop . Tubes will short out. If dropped to much is the key thing. Variac should never be used with tubes.
     
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  13. marshallmellowed

    marshallmellowed Well-Known Member

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    It's my understanding that Marshall's equipped with the line voltage selector were designed to work, by merely selecting the appropriate line voltage. Say, you're a big rock star, and you take your amp to another country... While, in this particular case, checking the bias wouldn't be bad idea, I don't think it would normally be required, considering the power transformer is supposed to deliver the correct voltages to the tubes, regardless of the line voltage (assuming the correct line voltage is selected).
     
    Last edited: Dec 7, 2019
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