JMP 2203 100W MV Problem..

Discussion in 'The Workbench' started by GibsonSgSpecial, Sep 17, 2020 at 12:44 AM.

  1. GibsonSgSpecial

    GibsonSgSpecial Member

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    So I just scored a Marshall JMP 100W MV and just got it today and I play guitar in my shed, I got this amp from a vintage guitar/amp shop from the UK, I live in the US but the dude said the amp tech serviced and replaced the tubes and all that, the house wiring runs from the main breaker box to my shed, the wiring runs about 80-100 feet maybe.. and I’m kind of thinking it isn’t getting enough power but I could be wrong, it could be the amp itself, the amp sounds like it’s at 15-20 watts with the MV and pre-amp cranked at FULL volume, it sounds amazing though but is it volume loss or no? I also have a Marshall Origin 50W combo out in the shed and I can crank it at full volume and I have no issues with it at all?
     
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  2. Matthews Guitars

    Matthews Guitars Well-Known Member

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    It should be incredibly loud. What's your speaker cabinet? Got any volume issues with that same cabinet with a different amp?

    If the amp's output is low, the first thing to check for is ensure that it's set for the right voltage. In the UK the mains voltage is 240 volts, and you HAVE to reconfigure the amp for 120 volt power assuming that you are plugged into 120 volts. If there's a line voltage selector on the back of the amp chassis, set it to 120 volts. (Your local line voltage.) If it was set to 240, that could well have been the problem.

    If there's no line voltage selector on the back, take it to your local amp tech and have him make the internal jumper wire change required to set it to 120 volts.
     
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  3. GibsonSgSpecial

    GibsonSgSpecial Member

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    The cabinet is a 4x12 with 2 G12-65s and 2 greenbacks making it 180 watts total I'm assuming, I don’t have any problems with it, it’s a brand new cab, I used it with the Origin 50W, but I don’t see no line selector for the voltage, there is a line selector for the ohms, is there any way I could just buy a line selector or take it to an amp tech like you said? As you can tell, I have no knowledge at all, haha. Thanks for telling me..
     
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  4. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Almost all Marshalls have a voltage selector on the back as well as an impedance selector. We need pics.

    7B800B46-14EB-4A06-AB00-4ABA7FC526B7.jpeg
     
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  5. GibsonSgSpecial

    GibsonSgSpecial Member

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    Mine has the pinhole style selectors, here is some pics.
     

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  6. Chris-in-LA

    Chris-in-LA Well-Known Member

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    That’s an old school mains selector, the thing that makes it adjustable is missing. The amp is probably hard-wired for 220. Your amp tech can wire it for 120. All the necessary wires are probably there inside.
     
  7. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Oh, your tech can probably also fit in a replacement selector, too, if that’s what you want.
     
  8. GibsonSgSpecial

    GibsonSgSpecial Member

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    Thanks man, I appreciate it, I messaged the seller asking if the amp has been hardwired by any chance, if not, then I can probably just order the adjustable selector thing lol
     
  9. GibsonSgSpecial

    GibsonSgSpecial Member

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    I also don’t have any amp techs close by to me which is bad because I live in the middle of no where lol, I’d probably have to drive like 100-120 miles to an amp tech.
     
  10. Chris-in-LA

    Chris-in-LA Well-Known Member

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    It has to be hardwired, the two selectors should both have that thing with the pins on it. That has to be there to complete the circuit. I’ve heard that they can fall out so some guys just solder the wires inside. It’s a simple fix for any tech who’s familiar with Marshall amps.
     
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  11. GibsonSgSpecial

    GibsonSgSpecial Member

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    Right, I’ve done a little soldering but don’t wanna risk tearing the amp all to hell, haha. I’m waiting on the seller to message back if it’s like that or not, I'd hate to drive so far to an amp tech to get something so simple to fix but I guess I’d have to get it over with lol
     
  12. neikeel

    neikeel Well-Known Member

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    Inside there will be a short wire link on the back of the selector from middle lug to the 240v lug (usually a violet wire) you need to move it to the 120v lug (which i am pretty sure is red -assuming the PT is original )
    Very easy to do and low risk of doing any damage.
     
  13. Matthews Guitars

    Matthews Guitars Well-Known Member

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    No, not "almost all" Marshalls have the line voltage selector plug. Based on the many replacement back panels I've sold so far, units without the line voltage selector have been outselling the ones with the line voltage selector about 5 to 1. Of my own Marshall collection, five heads, none of them has it.
     
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  14. AlvisX

    AlvisX Well-Known Member

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    Voltage selection on JMPs is internal, not switched from the back panel
     
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  15. GibsonSgSpecial

    GibsonSgSpecial Member

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    Hey, little update, I got a message from that seller and he also says that it’s internally wired to 240v, I'm also thinking about doing a little work later today to get it wired to 120v, thank you all for the help!
     
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  16. Chris-in-LA

    Chris-in-LA Well-Known Member

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    But OP’s seems to have the external switch according to the pics he posted.
     
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  17. Chris-in-LA

    Chris-in-LA Well-Known Member

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    If you want help with the wiring, post some pic of the insides, especially the area near the old mains switch and the power transformer.
     
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  18. StingRay85

    StingRay85 Well-Known Member

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    If you know how to solder more or less, I'm sure with the guidance of these nice people here on the forum you can do it by yourself. Its only a small job. Just provide the pics and you'll see that it'll be an easy fix. The heaters of your tubes dont see enough voltage so probably not so good to use the amp like this
     
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  19. GibsonSgSpecial

    GibsonSgSpecial Member

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    Hey guys I'm getting ready to start taking the chassis out, I just got home from work but I will post pics of what’s gonna happen lol so some of you can help me through it, I’ve only soldered several times in high school and soldered some on my guitars, that’s about it, so it may not be the best, wish me luck lol
     
    Last edited: Sep 17, 2020 at 7:42 PM
  20. william vogel

    william vogel Active Member

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    Once you get it running on 120 volts, you’re going to need a chin strap for your hat. It should be an easy wire fix.
     
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