50 watt lead/bass spec in one amp?

Discussion in 'Amps and Cabs' started by How, Mar 22, 2015.

  1. How

    How Supporting Member

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    I'm sure this has been asked before but a search did not bring anything up. Is it possible to have a 50 watt Marshall that is both lead and bass spec in one amp? I know the different components used in each but is it possible to hook them up to be able to switch between the two?
     
  2. JoeB63

    JoeB63 Supporting Member

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  3. wyatt

    wyatt Member

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    It's not impossible. But you would have to switch a lot of components.

    Cathode bypass caps
    Coupling caps
    Tone stack components
    Bright caps
    Etc.

    Many amps have taken to changing various combinations if these (most noteably cahotde bypass caps)...but known I know switch all of them.
     
  4. Polvo

    Polvo Supporting Member

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    If your talking superlead and Superbass specs, yes look into the retro rockitt forums I amps and cabs, someone has altered theirs to those specs, one channel is lead and one channel is bass, with still the option to jump. Maybe fusion bear did the mod, I don't remember
     
  5. Kenny Blue

    Kenny Blue Supporting Member

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  6. Optimus Rhyme

    Optimus Rhyme Member

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    PRS HX/da is exactly what you're talking about.
     
  7. How

    How Supporting Member

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    I guess I should have mentioned that I have a bass spec amp I built and would like to have a lead spec also. I would like to do the conversion if the directions are readily available. If not I guess I will build another. Not the worst thing as I find I enjoy building Amps. JTM45 was the first. 50 Watt bass spec the second. Probably looking for an excuse for the third.
     
  8. Geetarpicker

    Geetarpicker Member

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    The differences are in the preamp, the tone stack, the phase inverter coupling, and the feedback loop. This would take some complicated switching to pull off completely. Even Marshall's own "LEAD BASS" JMP 50 model doesn't truly combine both circuits.

    Most mods that claim a "lead channel' and "bass channel" are typically only preamp changes which is really not the complete picture. That said, you can fake quite a bit of it right there EQ wise BUT the tone stack changes make the controls operate at difference frequencies, and the feedback loop changes affect the breakup characteristics considerably. A mod to fully give you a 100% lead spec sound on one input, and 100% bass spec sound on the other would probably take some complicated relays and switches to pull off. Like I said it's way more than preamp changes if you really get picky about it.
     
  9. tonyhay

    tonyhay Supporting Member

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    I have a '74 Marshall 50w Lead & Bass. I think that pretty much does it.
     
  10. bbaug14

    bbaug14 Supporting Member

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    I built one. I've compared it to actual Lead and Bass amps and the differences are very negligible (IMO). I didn't switch the feedback or PI couplers. Since mine is a 68 spec, the feedback didn't matter too much and I found a middle ground on the couplers. The rest is on a rotary switch. Works great.
     
  11. DICKIE C

    DICKIE C Member

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    Rockytop Amps had a model that included both JTM45 and '68 plexi 1987 tone stacks (you can switch between the two). Don't think Rockytops are in production anymore and I don't know how 'authentic' the tone of the amp was as I never played one. Apparently it can be done, though.
     
  12. big mike

    big mike Moderator - EL34 Emeritas Staff Member

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    It's not a big deal to do.
    You have compromises in NFB and plates capacitors, but really, it's close enough IMO.

    Do a split/shared cathode on v1. Then you just do a lead / bass tone stack switch. A 4pdt switch could likely do both at once, but I like them seperate.
    Google both those terms and I'm sure a layout will present itself.

    Depending on the amp, the bass spec pi plate caps may give you some low end the amp could be lacking.
    My main JMP I use the .1 caps just to get a little more low end happening.
     
  13. mixn4him

    mixn4him Supporting Member

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    The cool thing about this amp is you can mix and match the specs with the switch settings...
     

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