Jcm800 2205 resonance mod help...

Discussion in 'The Workbench' started by Mark Simon Hell, Sep 12, 2019.

  1. Mark Simon Hell

    Mark Simon Hell New Member

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    Hey guys..
    I did the usual resonance/depth mod as I did many times on plexi and 2203/2204...
    But in this 2205 dosent work...
    instead of make more bass does more open sound.. more volume... i tried differents caps (4n7, 2n2.. 1n) but nothing..
    where am I wrong?
    Thanx
     
    Last edited: Sep 12, 2019
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor. free Mars!
    Can you post pictures?
     
  3. Mark Simon Hell

    Mark Simon Hell New Member

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  4. Mark Simon Hell

    Mark Simon Hell New Member

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    ..i find the solution... cut of R46 and all the D.I. wiring...
     
  5. Mark Simon Hell

    Mark Simon Hell New Member

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    ...nothing.... dosent work.... shit.. the depth effect is very "little" .... 0,0047.. 0,0022.. 4ohm, 8ohm, 100k, 47k..... it's the same or very little differences...
    what is? :wtf:
     
  6. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    What is the writing on that capacitor in the picture?
     
  7. RickyLee

    RickyLee Well-Known Member VIP Member

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    What is the year of this 2205?
     
  8. Mark Simon Hell

    Mark Simon Hell New Member

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    4n7 630v

    1988
     
    Last edited: Sep 14, 2019 at 6:58 AM
  9. RickyLee

    RickyLee Well-Known Member VIP Member

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    I was making sure you did not have the early version with the PPIMV. You do not have a PPIMV installed, correct?

    I did a resonance pot on my first '88 2205. I can not recall if I used a capacitor across the pot though. I am thinking due to the design and nature of this amp, you will not see drastic changes in the NFB loop tweaks. I am remembering getting a slight volume increase but nothing drastic.

    If you are looking to turn the amp into a serious monster, install a cathode bypass cap on that very last stage. 10uF -22uF and you will get a massive volume and bottom end increase. I tried it for a short time and then removed it. My 2205's are already at loud with just a nudge of the master volume from off to below 1.
     
  10. Mark Simon Hell

    Mark Simon Hell New Member

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    Ok forse ho risolto con una risoluzione di 39k resistor... 4ohm, 4n7 and 39k.. as a Soldano Slo100... Dosnt work great as in a JCM800 2203/2204 or as 5150, SLO100 and so on.. but is ok! Thanx Ricky
     
  11. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Why the 39k instead of the potentiometer?
    What value potentiometer did you use and did it have issues at lower resistances?
     
  12. South Park

    South Park Member

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    Set the depth control the same as 2204 and see what happens that might help try a different resistor. My jcm800 makes little differance
     
  13. Mark Simon Hell

    Mark Simon Hell New Member

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    no no.. also the pot .. 1M pot
     
  14. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Oh, gottcha. No 100k but 39k instead.
     
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  15. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    I see the difference with these amplifiers. With Marshall's 2205/2210 designs the early release has a more common PI circuit but with use of a PPIMV. The later designs eliminated the PPIMV but use a lower gain unbalanced PI circuit. That is going to affect the negative feedback operation.
    The key component changes from common PI are the 22k (instead of 10k) in the tail and the use of the 330k and 120k control grid loads instead of the dual 1M.
     
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