What Makes The JCM800 Magic?

Discussion in 'Marshall Amps' started by Brad O'Dell, Aug 25, 2019.

  1. john hammond

    john hammond Well-Known Member

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    I, hot damn john lee hummer, am here to help you.
     
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  2. pedecamp

    pedecamp Well-Known Member

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    I recall demoing an MA and thinking the clean channel sounded glorious and very 3D and the gain channel sounding terrible (seems to be the general consensus). I'd go with an OD or distortion pedal in front of the clean channel if you have to use the MA but why bother, just use your 800 and ditch the MA.
     
  3. neikeel

    neikeel Well-Known Member

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    Sorry, thanks for that, I looked at your pics and could see the PI and output tubes and only the reverb and loop schem pics on my phone. I can see the preamp now.
    Marshall played it pretty safe with the preamp but of course there is lots of padding and switching going on. That and the small transformers make me wonder where the 'magic tone' is potentially being lost.
    Good luck with your endeavours, I will be fascinated to see if the mods get you where you want to be and would love to hear some before and after clips.
     
  4. BowerR64

    BowerR64 Well-Known Member

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    Why before clips? no one likes the way it sounds stock.

    I kinda like the different things this amp has with the boost and the blend control
     
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  5. Brad O'Dell

    Brad O'Dell Member

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    The MA100H was sold with a 4x12 crappy-speaker & particle-board cabinet and Chinese tubes.
    The 1936 2x12 and JJ's tubes catapulted it light years ahead of the terrible reviews IMO.

    What I am trying to accomplish here is more about fine tuning the amp instead of using pedals.
    I think I am on the right track, especially with cadorman's 500k pot idea to adjust negative input.
     
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  6. JAC

    JAC Well-Known Member

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    I think it is cool you took an MA100 and improved on it. Those 800s are awesome. I dig JMPs also.
     
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  7. Crikey

    Crikey Well-Known Member

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    My 1985 JCM 800 ( 2210) sounds awesome through a mesa cabinet with black shadows. The magic of the Jcm 800 is that it has amazing attack and dynamics. Its simple unlike other amps with a gazillion knobs and switches.
     
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  8. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    Well with my $150 MA50h the thing came with fresh tad tubes in both the power, and preamp positions, so I can't attest to the original tubes sounding or not sounding good.

    Boost the front end with a tube screamer, and turn the gain down. And volume up some.. It tightens the amp up, and removes the buzzsaw gain.

    Here's the thing with mine. I only have $150 in it..and you say you're getting close to $500 into yours?..I don't think I'd go that deep on the ma..not that you can't get them to sound ok with some fiddlin, but there are without a doubt better amps in that price range...And the way these ma's get smashed on the internet you'll be lucky to get $250 out of it selling it if you ever decide to do so..just my 2 cents on that.
     
    Last edited: Aug 29, 2019
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  9. neikeel

    neikeel Well-Known Member

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    Mainly to hear what the new tubes and better speakers do to improve things over stock. If same riffs and recording set up to minimise confounding factors.
    Never know it may make the MA a hidden gem and we can all pick one up cheap for trashy gigs!
     
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  10. Brad O'Dell

    Brad O'Dell Member

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    You will have to settle with a comparison of my MA100H and My JCM800 thru the same cabinet once the mods are all done.
     
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  11. Brad O'Dell

    Brad O'Dell Member

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    For all of the MA100H haters out there...
    How awesome would your favorite tube amp sound with these stock MA100 tubes in it?
    I would sell them cheap, especially if you dont mind the "dandruff" on the inside.
    WP_20190829_06_19_50_Pro.jpg WP_20190829_06_19_59_Pro.jpg
     
  12. JCMDOUG

    JCMDOUG Well-Known Member

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    I have been away for a few days. The 3H choke is what I use in all my amps and for Neg feedback I have settled on 133k.
    I installed these mods on my JVMs and then I put it in almost every amp I have. I was looking at Bogner amps and found they all have chokes, even the alchemist my 1st all tube amp. When they made the JVM100 JS Marshall installed a choke its all about the feel.
     
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  13. Brad O'Dell

    Brad O'Dell Member

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    What do you think of using a 500k pot instead of the 133k? I figured I would add a knob to the front of the amp to dial it in on the fly.
     
  14. JCMDOUG

    JCMDOUG Well-Known Member

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    The 500k pot is or 250k is a good why to go. I installed a switch and made a small test rig. I cut the wire coming from the output transformer and installed different values in line with the current value so I put a 33k inline with the 100k to get to my 133.
    after a few amps i stopped installing a switch to take it back to stock and just cut the wire and add what I need to get to 133k
     
  15. Brad O'Dell

    Brad O'Dell Member

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    I ordered the 133k resistor first, and it will be here before the rest of the stuff. Maybe I will throw that in and see if it does what I want. In your experimenting, what would too much or too little negative input sound like? Is it worth having a knob to sweep it to the extremes?
     
  16. pedecamp

    pedecamp Well-Known Member

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    Exactly this. A fun experiment but its getting expensive unless money is no problem.
     
  17. Brad O'Dell

    Brad O'Dell Member

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    $250 MA100H
    $100 New Tubes
    $45 Choke (Arguably you could get one for $20)
    $6 500k Pot
    $3 Knob
    $1 Wire and Solder
    ----------------
    $405

    1936 2X12 $300

    $705 (or $685) seems legit to me for a 100W for a peanut-shell-floor-bar-rig to stand in for my JCM800.

    My B-rig guitar is a Gibson LesPaul CM, for all of the same reasons.

    I got it for $400, so basically I have $1100 worth of stuff that might get damaged when I play a gig. Especially like the one in the pic, where people could touch my stuff if they were inclined to do so.

    Believe it or not, the drummer and bassist did not bring their "A" rigs either.

    I would like to add one more time that this thread was about figuring out what parts could be changed in the MA to be more like the JCM. The rest of these comments are just watering down the good information here. delme.jpg
     
  18. thunderstruck507

    thunderstruck507 Well-Known Member

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    Never tried the MA, wouldn't mind to. I also like to tinker around with things.

    But for $500 or just over you can likely find a deal on a TSL 100 watt if you look around. Or a little more will get you a nice Carvin.
     
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  19. JCMDOUG

    JCMDOUG Well-Known Member

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    133k would be fine. what I would do to reduce the number of times you put heat to the board is attach two long wires and put the 133 in line. when the pot comes in you can just cut out the resistor and attach the 500k pot.
     
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  20. JCMDOUG

    JCMDOUG Well-Known Member

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    having a way to sweep the range is a good idea to find your happy place and you can take it back to a stock value.
     
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