Approach to building a dual plexi/2203 preamp

Discussion in 'Amps and Cabs' started by LPV, Nov 8, 2018.

  1. LPV

    LPV Member

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    I would like to mod my preamp on my 2204 MK2 master circuit (that I built into my Traynor) to switch between an original plexi(ish) type preamp and current MK2 master in there now. I don't need both triodes on the plexi, just the bright and common cathode. The challenges are the voltage dividers and the cold clipper on v2 plus others so I know it can't be 100%. I'm just looking for an approximation of that crackle.

    Can anyone suggest a schematic of another amp that does something similar ?
     
  2. fusionbear

    fusionbear exquirentibus veritatem Gold Supporting Member

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    I built an amp like that for a friend. I used completely isolated signal paths. I used a relay right at the input jack and a relay right before the PI entrance to make it work. I used .047 couplers in the PI circuit.

    Basically, I used two 12X7's for the Plexi side. I paralleled the triodes fed to a volume control, then to mixer type circuit, then to a cathode follower to a bass spec tone stack. The output of the treble pot went to the relay then to the PI.
    On the OD side, I used two 12AX7's too. I experimented with the 2203 type preamp, but settled for a cascaded type plexi circuit instead. I named the amp "el machete". Amp sounded really awesome....
     
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  3. LPV

    LPV Member

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    Thanks Carl, I guess I'm trying to find a lazy way out so as not to have to add more triodes but I do understand why you would go that route. I was hoping to just skip a gain stage like the standard MK2 low sensitivity input but not lose so much gain to the rest of the preamp.
     
  4. JimSoprano

    JimSoprano Member

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    Look into Friedman Smallbox...
     
  5. gldtp99

    gldtp99 Member

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    Here's a couple versions of SDM's "2 in 1" Mod from the Valvestorm website:

    https://drive.google.com/drive/folders/0By1xsHfamQ8iVndqbzd3STVYd3c

    I've never used these mods but it sounds like they're what you are looking for----- A JCM 800 and a Superlead preamp in the same amp---- and a way to switch between them.

    I have a '78 JMP 2203 and a '73 Superlead so I just use them one at a time depending on which type of tone I'm looking for that day.

    Maybe I suffer from a lack of imagination ?

    I see your amp is a 2204 circuit built into a Traynor------ I'd think SDM's "2 in 1" Mod would work on a 2204 circuit as well as the 100 waters.
     
    Last edited: Nov 9, 2018 at 6:20 AM
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  6. LPV

    LPV Member

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    Thanks that's kind of what I'm looking for. I may give this a try.
     

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