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Finished modding my 76 JMP non-master volume. Clip inside

Discussion in 'Amps and Cabs' started by scottosan, Aug 16, 2005.

  1. scottosan

    scottosan Supporting Member

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    Before I get flamed for modding a vintage Marshall, when I bought this, the original PCB was just mangled by a previous owner and had none of the original tone caps and had incorrect values in many areas. So what I did, is I just removed the whole board and original Pots and have them in a plastic sealed bag incase I am going to put the original board back in. I put it a PTP board with my own circuit in it. I did not drill any holes or any intrusive mods to the chassis.


    http://home.comcast.net/~scottosan2004/76mod.mp3
     
  2. Rock Fella

    Rock Fella Member

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    do me a favour ok.

    do you have a boost pedal or simply an overdrive pedal , put it in front of that amp drive off and level 50% and over depending on how it sounds. and play me some lead tones please.

    that amp sounds positively bitchin , you have a killer rhythm tone thing going on there , id imagine that sound dont yield the screaming sustain that a clean boost pushing the front end will give ...............go on , do it !!

    what about a master vol mod , is there one of those or did you play that with the paint peeling off the walls ?

    good job
    jimmy
     
  3. Crazy Dave

    Crazy Dave Member

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    Belgium
    Holy Smoke! Great tone man. That thing roars like a wild animal.:dude
     
  4. scottosan

    scottosan Supporting Member

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    It has a master volume, the volume was at 9:00 very modest volume. I do have some pedals that i have built that I will try. I am currently messing with a switchable bright cap that definately gives it a kick in the pant's but the amp feeds back like a mofo at high volumes with the bright swtich on. I can solo for crap. I built and amp with the same circuit I put in this one and Brian H got to play it. I thought the single note stuff was awsome. Personally I thing it would sound better on the single note stuff through a vintage 30 cab. Thanks for listening.
     
  5. Rock Fella

    Rock Fella Member

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    from what i can hear in the clip , ADDING a bright cap wouldnt be something id be inclined to do. if it sounds right, dont fix it, and that amp sounds RIGHT !!

    you gonna put a level boost in front of her for me ? oh aye and please use a les paul if ya got one handy.:)

    jimmy
     
  6. scottosan

    scottosan Supporting Member

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    Ok, I've got an 808 clone and a Paul. I'll let you know. BTW, the tone controls were at 11:00, so cranking the mids and presence up a bit definately changes the tone.
     
  7. Buckeyedog

    Buckeyedog Supporting Member

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    Hey Scottosan, does your jmp have two vertical inputs?? I see these mid 70's jmp's that don't seem that high in demand. Wonder why?? I know it's your circuit you put in, but how about the stock circuit in these?? Thanks.
     
  8. Randy

    Randy Member

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    Sounds awesome! Crunchy yet clear with plenty of tight bottom end.

    I too would like to hear some single note leads with a boost - perhaps one that adds some low mids if you have such an animal.

    Do you do Marshall mods for others?
     
  9. scottosan

    scottosan Supporting Member

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    It was 4 input non-master volume when it was stock I am just using 1 input and plugged the other 3. It has the same circuit board as the mid 73-76. 76 was a transition year. The 2 input JMP's are master volume with a 2203/2204 circuit. Mine had the 1987/1959 circuit. It is my understanding that some of the first master volumes were slightly different in the preamp section.
     
  10. scottosan

    scottosan Supporting Member

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    I am always tinkering so that is a possibility. As for doing mods for others, I would really like to let some gigging folks in the area road/stress test the circuit at a practice or gig before I start doing something like that.
     
  11. Rock Fella

    Rock Fella Member

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    looking forward to hearing those boosted clips buddy.

    none of that scooped mids crap , plenty of juicy mids are the order of the day :D
     
  12. scottosan

    scottosan Supporting Member

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    I am reporting back with not so favorable results. I am already pushing these gainstages so hard the the boost is making almost no difference except more saturation. I used an 808 clone, so I don't actually have a clean boost handy.:(
     
  13. scottosan

    scottosan Supporting Member

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    OK, here is the guts. not the neatest, but functional

    [​IMG]
     
  14. pfrischmann

    pfrischmann Member

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    Interesting layout!

    Looks like Mallory caps and lot's of .0022's in a split cathode configuration?

    Have you tried Sozo caps?


    I just did a borad for a DOA '78 with .022's across the coupling caps etc and .1's in the PI section...splite cathode of course.

    What are you using for a slope resistor?

    have you tried a .68 presence cap with a 4.7K resistor in parallel...keeps the presence out of ice pick range..

    Thanks,
    Paul
     
  15. scottosan

    scottosan Supporting Member

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    I have an amp I built identicle to this one with sozo's. TO be honest, I like the Mallories better. They sound clearer to me. I know alot of folks like them, but I've AB's them extensively and at least for this circuit I like the 150's. For the slope I'm using the 56k/470pf
     
  16. Relicula

    Relicula Supporting Member

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    That amp kicks ass, play it.
     
  17. scottosan

    scottosan Supporting Member

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    Thanks for listening
     

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