Another 2204 Build

Discussion in 'Building the Classics' started by Matt_Krush, Oct 26, 2019.

  1. Matt_Krush

    Matt_Krush Well-Known Member

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    Well, my first JCM 2204 build, there are many like it, but this one is mine.
    It started as all stock then, well, you know how that goes...

    Deviations from Stock.

    1) 1st pair of Power Capacitors are 100uf (not 50uf)
    2) Added MojoTone Effects Loop
    3) Modified Tone Stack (see Pics Below)
    4) Added 120VAC Receptacle on back to power other crap
    5) Switchable Bright cap (on/off), Negative Feedback Resistance (100k or 200k), and V1b Cathode (10k to 5k)
    6) DSL 100W Power Transformer (in case I added other stages and needed the current)
    7) External Bias point and control, with capability to run EL34, 6L6, 6550, KT88 variants.

    Tone Stack Mod

    2204 tone stack.PNG
     
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  2. Matt_Krush

    Matt_Krush Well-Known Member

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    Circuit Board

    circuit board 1.PNG

    Other Guts

    7x.jpg

    8x.jpg
     
  3. Matt_Krush

    Matt_Krush Well-Known Member

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    Panel/Top

    1x.jpg

    3x.jpg 2x.jpg

    4x.jpg 5x.jpg
     
  4. Matt_Krush

    Matt_Krush Well-Known Member

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    [​IMG]
    Some Sounds if your interested..
    Cell Phone recording
    Gibson Studio, Dimarzio Super Distortion Pick Up
    1960B Cabinet.
    No other gear...




     
    Last edited: Oct 26, 2019
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  5. Joey Stockton

    Joey Stockton New Member

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    That thing is a beast! Tasteful mods and well executed. What effect does the increased filtering have on the tone?
     
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  6. Matt_Krush

    Matt_Krush Well-Known Member

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    Little no 'sag' when pushing really hard/loud.
    which for my type of music is what I want.
     
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  7. Matt_Krush

    Matt_Krush Well-Known Member

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    well, I couldn't leave well enough alone.
    Is it just me...or is really hard to put the soldering iron away and quit tinkering?

    Plate resistor for V1b: 220k from 100k
    Coupling caps 1st 2 stages: .047 from .022
    Removed Bright cap switch (no longer needed and that pot was acting flaky)

    Think I am done now (other than a head-shell and I guess a name)...really tamed the harshness, EQ more responsive, smooth distortion.

    I don't think an overdrive pedal is needed...LOL

    Ignore the white board mess..it was for a 4 channel preamp I built...
     
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  8. Exojam

    Exojam Well-Known Member

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    Looks very nice!

    I have to say I love the work bench and also that white board you have.

    I am trying to get the inside of my shed/workshop finished up and that gives me a few ideas.

    How long did it take you to bust it out?
     
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  9. Matt_Krush

    Matt_Krush Well-Known Member

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    Total Time...I don't know...started a month or two ago, get a couple nights...then it'd be a week or two before getting back at it.
    Which sucks, because I'm the guy that doesn't keep good notes...all in my head (until it isn't).

    I'd say it should be doable 5 days, 3 hrs at a time...

    The bench...it was a mess...whenever I do a just because build, it seems like a guitar or my gig rig has something crap out, then I get multiple projects scattered on the bench and parts all over. Scope and signal generator are in the left corner, and yes they are an indispensable tool for amp building.
     
  10. Exojam

    Exojam Well-Known Member

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    Like it!

    My 2204 clone took me awhile longer as it was my first build but it came out nice and love the sound of it.

    I just put the SIR #34 mod in it but I cannot stand the sound of it so it is coming out as soon I get some time to remove it.

    Correction: mine was a 50 watt clone build not a 2204.
     
    Last edited: Oct 29, 2019
  11. Matt_Krush

    Matt_Krush Well-Known Member

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    I am not familiar with the SIR #34 Mod...what I could find...looks like adding a .1uf cap in parallel to the 10k cathode resistor of the second stage?
    I experimented with a variety of caps there as well, but it sounded best (to me) without any filtering.
    I can say, with the changes i have made, I like I am getting!!
    I realize it may not be for most people, but it can be dialed back to the classic tones pretty easily.
     
  12. Amadeus91

    Amadeus91 Active Member

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    Great job, tailoring the amp to get what you want from it.
    What a rhythm chugging riff machine!!!!!
     
  13. South Park

    South Park Well-Known Member

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    Some mods work some don’t. Minor gain mods I think work best
     
  14. Exojam

    Exojam Well-Known Member

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    This was some information I had sent over to another member about it.

    These were the changes I found that make this change:
    The SIR #34 mod is pretty simple, IIRC -- according to my notes, it's a standard JCM800 with a

    470p cap across the V1b plate resistor, a

    100n cap across the V1b cathode resistor, and a

    680n cap across the V2a cathode resistor.

    What I found interesting is I also found other instructions for the #34 here on this forum that are as follows:
    .1uF over 10K cathode of the 2nd stage

    470 pf across the 100k plate resistor of the 1st stage (at least 500V cap)

    820 cathode resistor changed to 1k

    .47 over this 1k


    .68 on the presence

    150K resistor from the wiper of the gain pot to ground

    1n bright cap
     
  15. gldtp99

    gldtp99 Active Member

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    Nice job !!

    Here's a 2204 type build I did last year---- I also doubled the value of the first filtering stage filter caps---- also some moderate preamp gain mods and a fixed Resonance mod in the NFB loop.

    I used a higher mA/lower voltage rated Edcor PT and a stock type OT.

    My friend made this vid ---- he plays a modern Hi Gain style called Grindcore in his band so some of his playing style comes through even though he tried to make a Classic Rock/General Purpose type of vid.

    You can see how the EQ and other knobs are set in the vid:

     
  16. Exojam

    Exojam Well-Known Member

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    Can you PM me the mods you made?
     
  17. Matt_Krush

    Matt_Krush Well-Known Member

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    Modded Pre-amp Schematic:
    C3 & C7: .047uf from .022uf
    R7: 220k from 100k
    R6.2: 10k switched on/off via the master volume push/pull pot
    C10: 250pf from 500pf
    R15: 47k from 33k
    C12: .047uf from .022uf

    Negative feed back select-able between 100k & 200k via treble push/pull pot

    2204prem mods.gif

    Only other Mods is the MojoTone effetcs Loop.
    Oh and 100uf+100uf for the fist set of power capacitors.
     
  18. Exojam

    Exojam Well-Known Member

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    Thank you!
     
  19. South Park

    South Park Well-Known Member

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    A larger choke will lessen the voltage sag to
     
  20. Matt_Krush

    Matt_Krush Well-Known Member

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    I almost went with the jubilee tone stack.
    Next time...I will, and it'll likely be a lunchbox 20-30watter.
     

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