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

    Joined:
    Feb 21, 2015
    Messages:
    1,173
    Likes Received:
    746
    Location:
    Södertälje, Sweden
    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
     
    Crunchifyable likes this.
  2. Crunchifyable

    Crunchifyable Well-Known Member

    Joined:
    Oct 28, 2011
    Messages:
    662
    Likes Received:
    334
    Location:
    Georgialina, USA
    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

    Joined:
    Feb 21, 2015
    Messages:
    1,173
    Likes Received:
    746
    Location:
    Södertälje, Sweden
    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

    Joined:
    Oct 28, 2011
    Messages:
    662
    Likes Received:
    334
    Location:
    Georgialina, USA
    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

    Joined:
    Oct 28, 2011
    Messages:
    662
    Likes Received:
    334
    Location:
    Georgialina, USA
    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

    Joined:
    Oct 28, 2011
    Messages:
    662
    Likes Received:
    334
    Location:
    Georgialina, USA


    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

    Joined:
    Oct 28, 2011
    Messages:
    662
    Likes Received:
    334
    Location:
    Georgialina, USA
    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.

     
    RickyLee likes this.

Share This Page