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Building A Dual 2204/1987 Preamp

Discussion in 'Building the Classics' started by Crunchifyable, Nov 28, 2017.

  1. johan.b

    johan.b Well-Known Member

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    Cool.
    9 volt is fine for 12ax7 heaters (in series). Just look at all the DSL's and 900 series amps out there..cathode stripping is not a problem for low power, indirectly heated cathodes.
    J
     
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  2. Crunchifyable

    Crunchifyable Well-Known Member

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    I guess I don't understand how or why Marshall used 9v instead of the usual 6.3v.

    I decided to go with the dual preamp layout for now. A little more creativity required, but more preferable to a half empty turret board.

    [​IMG]

    Some caps are too big. Some resistors too small. I realize I'm missing a cathode resistor.
     
  3. johan.b

    johan.b Well-Known Member

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    They rectify 6.3 vac into ~9vdc to reduce hum. In the first preamp tubes.i guess it was necessary with the pcb layout.
    Off board twisted wires would have worked to, but more labour building ta amps
    J
     
  4. Crunchifyable

    Crunchifyable Well-Known Member

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    I see. Makes more sense now that it's explained as an ac vs dc thing. Well it's good info in the event i need to use a 9v input.
    I'm hoping the desktop power supply works out instead.
     
  5. Crunchifyable

    Crunchifyable Well-Known Member

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    It lives!

    I may have a loose wire or something in my tonestack and a lot of noise from breadboarding it out and not having enough shielded cable...but for a broken amp, it sounded good to me.



    I'm using my Class 5 as a power amp (2k2 input resistance)

    As a side comment...using a PC powersupply is very handy. It has many 12v wires...and many ground wires too.
     
  6. Crunchifyable

    Crunchifyable Well-Known Member

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    Realized what my problem was, sort of. Layout I was using didn't include a .022uf on output like most 2204 layouts have. added that and it sounds as expected.

    But bass control does nothing. Wiring seems ok.
     
  7. Crunchifyable

    Crunchifyable Well-Known Member

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    Ran it into a 100w amp (my bugera 333xl - EL-34 x 4) for the first time.

    No impedance matching used...so might have lost some high freq. The Bugera has a handy FX return level knob that I conveniently lowered all the way. But I still love how it sounds.

    I sense it has too much gain but I like the way it sounds.

     
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  8. Kelia

    Kelia Well-Known Member

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    I know this is an old thread but trying to understand what is the difference with a 2204 cascaded preamp and a Plexi with a one wire mod ?
     
  9. South Park

    South Park Well-Known Member

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    so What is it you don’t understand about the circuit .
     
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  10. Kelia

    Kelia Well-Known Member

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    Well I'm about to post a thread asking questions for guidance on building
    an amp to my taste but I'm no tech so I wouldn't do the job myself and I can't read a circuit yet
    but planning on lurning more.

    So my question is if there is a difference between a one wire more on a 1987 and a stock cascade 800 ?
     
  11. South Park

    South Park Well-Known Member

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    The cascade circuit has a pot to dial back the gain the ether is fixed . If want to build amps you need to go to school for this stuff. None of this stuff is easy or safe
     
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  12. stickyfinger

    stickyfinger Well-Known Member

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    The one wire mod has a lot more gain if wanted. Gain will very on what 4 hole amp you one wire mod. A Bass spec or a Lead spec amp and the power amp of those two amps will have more gain.

    Simply put the cascade Marshall 2204/2203 probably has the least amount of preamp gain on tap of any 3 stage pre amp circuit made by any manufacture. Probably why it sounds so good!
     
  13. Kelia

    Kelia Well-Known Member

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    Ok thanks !..that is exactly what I wanted to know !..............appreciate !
     
  14. cehuff3

    cehuff3 New Member

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    I know this is an older thread & I apologize.
    I have a question regarding a 2203/4 pre plus Lead/SLP pre in one amp. If I were to build something like this, I’d want to build the entire amp around the Marshall 50w EL34 power section.
    My question is, does anyone know of a source for a pre-drilled chassis & turret board for this amp?
    If I could get these two items, I already have most everything else I’d need to build out the complete amp. If anyone can help, I’d very much appreciate it.
    Thanks!
     
  15. neikeel

    neikeel Well-Known Member

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    Standard valvestorm chassis and circuit board for 2203/4
    [​IMG]
    My personal version of this is a 2204 without PPIMV and keep the presence on the front. I don't miss the PPIMV at all. It is just there for those that want NMV at lower volumes.
     
    Last edited: Jul 1, 2021
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  16. cehuff3

    cehuff3 New Member

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    Thanks Neikeel. I’ve haven’t had time for more than a quick glance over the layout so far, but this look like what I’m after. Thanks again Neikeel!
    Have a happy Independence Day everyone.
     

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