JCM 900 4100 mod

Discussion in 'The Workbench' started by quiksilver98, Mar 21, 2012.

  1. Ken

    Ken Well-Known Member

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    This kinda sums up my experience with the 4100. I like plug and play amps, especially for the distortion tones and I just couldn't get the stock 4100 to sing at a reasonable volume. These mods sound quite good from what I can tell, regardless of how the signal path happens to be going.

    I'm not as anti-pedal though. Lots of pros have used (overdrive) pedals and sound really good too. If I were playing Zeppelin songs and I had to follow the cleanish Heartbreaker with the mega overdriven Lemon Song, I'd definitely use a pedal. My amp (DSL) in the highest gain settings compress way more than a pedal does for a similar amount of overdrive and some songs sound better with less compression.

    Ken
     
    iron broadsword likes this.
  2. Anickyan

    Anickyan New Member

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    Hey tschrama.

    What do you mean by "470k-47k", and what is the post-eq attenuator called ("R n")?
     
  3. tschrama

    tschrama Well-Known Member

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    The '-' sign means connected in series; '//' means connect in parallel.

    Stock, there is a 470K-470K-Gnd. That's a 6dB attenuator.
    The mod describes 470K-47k-Gnd for a 20dB attenuator (or about).
    More easely accomplished by piggybacking a 47K // the stock 470K.
     
  4. Anickyan

    Anickyan New Member

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    You also say to remove the 220k resistor around the tube. What is the number of that resistor? (e.g. R42, R34, etc.)
     
  5. tschrama

    tschrama Well-Known Member

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    I don't say that at all. I don't! I leave it in.
     
  6. Anickyan

    Anickyan New Member

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    It says so i 4] in the post i quoted before.
     
  7. tschrama

    tschrama Well-Known Member

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    " I don't believe that sounds much better "

    Leave it in..:slash: .. and you really should read a schemo
     
  8. okgb

    okgb Member

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    I had a silver Jube before I knew it had diodes and still liked it,...... Hey !

    I bought a jcm 900 high gain dual reverb [ for a reasonable price ] with plans to gut the preamp and rewire it , as it turns out I have too many projects so thought
    I'd fix the bad pot and sell it , when looking at mods on the interweb , and the pcb on mine I notice resisters where the pcb designates caps and the opposite
    on mine , C35 = 82K Resister C36= 4.5K R 58 = CAP C27= 4.7k , the amp works & sounds ok , not great was this a common manufacture problem ?
     
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    You should post pictures w/ plenty of light, cause we need to see what the PCB is...
     
  10. okgb

    okgb Member

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    photo bucket is extorting me to pay them so next best way to post the pix here ?

    Can I email you the pix to post ?
     
    Last edited: Jul 24, 2017

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