JCM 900 4100 mod

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

  1. tschrama

    tschrama Well-Known Member

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    thx!
     
  2. tschrama

    tschrama Well-Known Member

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    Ghostman likes this.
  3. iron broadsword

    iron broadsword Well-Known Member

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    I peed a little.





    Ok that settles it.. bringing my amp home tomorrow and doing this. The stock amp can get sorta in the ballpark but cannot nail that. Any idea what sort of volume you had the master running in that modded clip?
     
  4. tschrama

    tschrama Well-Known Member

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    Loud enough to record, but nowhere near cranked or where power tubes come in to play. Mind you that those reamped DI's are stunningly played. That helps a lot and the down tuning makes it sound very brutal. But the gain is there!
     
  5. iron broadsword

    iron broadsword Well-Known Member

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    That's what I wanted to hear. I play in drop Bb so it's all good.
     
  6. Roadburn

    Roadburn New Member

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    The gain stages are before the first tube.
    The first tube is used for the EQ section.
    The second tube is used for the FX-loop.
    The third tube is the phase inverter (which practically is a gain stage, but not as we know it)

    So the pre amp gain for the clean channel is also SS.
    Strictly, the whole pre amp is SS.

    Not sure how your mods will make it a tube pre amp when the gain is done with OP amps solely...

    It will change the sound. It might even improve the sound.
    It will not make it a tube pre amp though.

    http://www.drtube.nl/schematics/marshall/cd0189-iss7.pdf


    P.S. not dissing the DR. It won the 2010 best amp competition by unanimous vote (incl. the biggest 900 haters around agreed).
    P.P.S. OP amps work in hi-fi situations though. Not sure why they wouldn't in a guitar amp.
     
  7. tschrama

    tschrama Well-Known Member

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    Not sure why ampmadscientist claims that you cann't have a clean signal comming out of the FX-loop. My 4100 clean channel start to clip at around 12h00. For some lower output pickups it might be 14h00.

    It's also perfectly possible to dial the master volume such that the output tubes will distort, and I do like the sound and feel of that.

    And, indeed that will mess up you timebased FX's like echo and reverb.

    Further more ampmadscientist explains perfectly well how you can change the V1 in to a traditional gain stage + CF like you find in typical vintage Marshalls. Thereby, in effect, making it more like a double boasted tube amp.

    Have you noticed that the first opamp of the lead channel is just an TubeScreamer with gain set to 12h00, and tone pretty much all the way up?
     
    Last edited: Feb 2, 2015
  8. iron broadsword

    iron broadsword Well-Known Member

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    Hey tsch, in the other thread you said this:

    Do you recommend I do this as well as what you posted in this thread already, or is that accomplished in a different manner/not necessary?
     
  9. tschrama

    tschrama Well-Known Member

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    Yes, I do recommend it, but best to do one thing at a time and determine yourself if you think you need it.
     
  10. iron broadsword

    iron broadsword Well-Known Member

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  11. Rokinroller

    Rokinroller Well-Known Member

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    Really not so ! Its very easy to turn the DR into a firebreathing Godzilla. Put it this way....I would NOT trade my 4100 for an 800 . Had a few 800's ..ya good but 1 trick pony and QUITE overhyped for what they are. :wave:
     
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  12. Rokinroller

    Rokinroller Well-Known Member

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    I just cant agree with this post even if I tried to force myself. Too bad Ken, you dislike a great,versatile 90's Marshall amp like this. Yes to each their own I guess. :cool:
     
  13. iron broadsword

    iron broadsword Well-Known Member

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  14. Ken

    Ken Well-Known Member

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    Yes, my 4100 may not even had the right tubes! And I have no idea of the bias either. I wasn't into all that stuff until I got the DSL. I'd try a 4100 again now that I know so much more about getting good tone from them.

    I must say, these mods are really good! I wouldn't have though the amp could be improved that much. I'd still take a DSL and avoid the hassle of modding it, but I was proved wrong: a 4100 can be made to sound like a real Marshall with some fairly simple tweaks.

    Ken
     
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  15. iron broadsword

    iron broadsword Well-Known Member

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    I'm still honeymooning with the mod but I think tschrama nailed it. The mud's gone and the EQ is what you'd expect from a marshall. Looking forward to trying it out live this weekend.
     
  16. BigMacFullerton

    BigMacFullerton New Member

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    I'm a very happy JCM 900 DR owner and this whole thread is so full of BS I can't believe it. Do people realize that 900 DR is used on tour by more pro players THAN ANY OTHER AMP ON THE PLANET!!! There is a reason! I got mine on craigslist for $350 dollars from some lady who had no clue. I then took it to Kruse Kontrol Amplification in Burbank ca. for new tubes(the right tubes make all the difference) and to have it modded with the same mod that all these pro players are getting. My guy Jenz(from Germany) does a special mod on the 900. He has done work for the likes of Slayer, Kiss and GnR just to name a few! He charged me $300 for the tubes and the mod. The amp totally screams and is totally warm and creamy. It smokes any dark dead sounding mesa and I only paid around $700 for it including gas money to his place in Burbank. When I play gigs I get a lot of...that's the best 900 I have ever heard! What did you do?. I say you have heard better you just didn't know it was a 900!The tubes---He put Ruby 12AX7 AC5 HGs in the pre-amp and they sound great. After hearing some buzz about the JJ12AX7803s high performance w/ gold pins for $25 I tried one in the V1 and it's killer! Power tubes are Russian made military tubes and I'm not sure who makes them. They have no brand name on them but they are fatter looking than most tubes with thick looking glass...not sure. The mod is awesome but I don't know what he did because he won't tell me. Bottom line is the amp is as durable as any amp ever built and there is a beast inside of it just waiting to be released. And yeah the amp still sounds better when it's cranked but sounds acceptable at bedroom levels for sure. I can now get good early VH to early Metallica and great punk tones out of the amp and if you drop tune it can do some modern metal although that is not the amps strong suit. I was going to get an Orange but I'm happy with my 900 so I just haven't had the motivation to spend a grand on one. Stock the 900 is average at best but when tubed and modded right it is a really great performer! Try it you'll like it!
     
  17. BigMacFullerton

    BigMacFullerton New Member

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    Me too....800's have to have a pedal to make good distortion and I don't like using pedals. I sold an 800 years ago and I prefer my modded 900 DR for sure!:hbang:
     
  18. ampmadscientist

    ampmadscientist Well-Known Member

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    "Not sure why ampmadscientist claims that you cann't have a clean signal comming out of the FX-loop..."

    I did NOT say that. You misquoted me.
    You are quoting me out of context, severely.
    THIS is what I REALLY said: (read it yourselves, above!)

    "You want the effects send to be CLEAN?
    Then you want the distortion AFTER the effects return?
    You can't do that."

    AND I AM 100% correct!

    In
    order to successfully modify the 4100...
    YOU have to LEARN what is there and how to work with it.

    Subtracting stages (or clipping diodes) may give you a clean effects send BUT...
    You have no means of overdrive / distortion AFTER the effects loop return.

    It's the way that the amp was built, SIR.

    So unless you rip the entire thing apart, end to end: (and re-design the layout...)
    YOU CAN'T DO THAT.
    The REALITY remains. It WAS built that way, at the factory!

    So, no matter how much you misquote what I said...
    It doesn't change the prevailing reality.

    YES- you can crank the master volume, overdrive the output tubes...
    but you can do that with ANY amp.
    And by doing this, you make the amp VERY loud. Too loud to use, in most situations.

    Introducing the need for an attenuator...to keep the Output Tube Overdrive loudness - at a tolerable level...
    BUT at the same time, KILLING the clean channel HEADROOM!

    Therefore, your "plan" does not work for a professional guitar player
    Who wants to balance the loudness levels of the CLEAN and overdrive channels.
    From the standpoint of the GUITAR PLAYER - it doesn't work.
     
  19. ampmadscientist

    ampmadscientist Well-Known Member

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    I'm happy that at least 1 person understands how this amp works.
    It's a solid state preamp.
    The only way to change that - is to gut the amp, and start over!

    As usual:
    Anything you do is a compromise, and there is NO perfect solution.
     
  20. ampmadscientist

    ampmadscientist Well-Known Member

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    YES
    you "can" use effects pedals, distortion pedals...

    But to many professionals - effects pedals sound awful,
    compared to distortion in (from) the amp itself.

    My modifications were designed for players who don't like effects pedals.
    And, I never use them myself - either.

    To me,
    distortion pedals are child's toys.
    I hate the way they sound.

    I want my distortion from the amp - not from some pedal.
    AND if the amp does not sound good by itself...time to get a different amp...that DOES sound good by itself.
     

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