Super Chump: Unnecessarily Complex Single Ended Amp

Discussion in 'Shock Brother's DIY Amps' started by shortcircuit, Mar 30, 2020.

  1. shortcircuit

    shortcircuit Tele-Meister

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    What has 2 gain stages, 2 cathode followers, single ended output, and a bunch of switches? Super Chump!

    Mockup:

    01 Mock Up.jpg

    There's something seriously wrong here. Something I'd never done. Any guesses?

    Schematic:

    SC.jpg
     
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  2. DADGAD

    DADGAD Friend of Leo's

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    You could simplify it a bit by connecting the filament supply center tap to the cathode of the output tube, for some positive bias.
     
  3. shortcircuit

    shortcircuit Tele-Meister

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    There's going to be 160V and 180V on the cathodes of the 6C4 tubes. It's below the 200V Vhk limit, but I want to play it safe.
     
  4. FenderLover

    FenderLover Poster Extraordinaire

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    Not complex enough. I'd add another pot in the EQ bypass loop to form a divider with the Gain pot in bypass. That way you can simulate anywhere between EQ loss to full bypass and have variable variable boost.
     
  5. shortcircuit

    shortcircuit Tele-Meister

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    I drew it out a bunch of different ways, and I can't figure out a way to do it without a bunch of mixing resistors, which would defeat the idea of a plain raw switch.
     
  6. FenderLover

    FenderLover Poster Extraordinaire

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    Yeah, it wouldn't be full bypass either but I never found the huge boost with a bypass switch too usable as a performance feature.
     
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  7. tubelectron

    tubelectron Tele-Afflicted

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    Why not ? Yes it's quite complex, but you may be surprised by the result and the versatility...:)

    -tbln
     
    Last edited: Mar 31, 2020
  8. Danb541

    Danb541 Tele-Holic

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    What language are you guys speaking? I don't understand a damn thing. I'm thinking I don't belong here.
     
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  9. David Barnett

    David Barnett Doctor of Teleocity

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    What do the switched networks from the cathodes of the cathode followers to the split plate loads do?
     
  10. FenderLover

    FenderLover Poster Extraordinaire

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    If you have Merlin's book, it's figure 6.19. Basically it's a bootstrap circuit, where the the follower unloads the previous gain stage and the gain realized is close to the actual mu of the split-load triode. In this case close to an amplification factor of 100.
     
    Last edited: Mar 31, 2020
  11. shortcircuit

    shortcircuit Tele-Meister

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    Chassis drilled and painted. Waiting for the paint to harden before proceeding.

    02 Chassis.jpg

    Everything I'd ever done, I'd stolen from Merlin. However, since I have both of his books, I don't feel bad.:p
     
  12. BigDaddy23

    BigDaddy23 Tele-Holic

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    Subscribed!! Love your builds :lol:
     
  13. David Barnett

    David Barnett Doctor of Teleocity

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    I don't have the book, but apparently I need it...

    Looks like a form of positive feedback?
     
  14. elpico

    elpico Tele-Holic

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    I wouldn't either, anything you can say about tubes was already written by the 1960s. Heck, 99% of it was already written by Langford Smith in the 50s in RDH4. The rest of us are just rewriting what those great engineers figured out back when this stuff was worth spending engineers on :D
     
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  15. FenderLover

    FenderLover Poster Extraordinaire

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    Not really, bootstrapping effectively increases the load impedance, creating less 'drag' on the output and allowing higher output amplitude.
     
  16. shortcircuit

    shortcircuit Tele-Meister

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    Heaters and power supply done.

    03 Heaters and Power Supply.jpg

    Again, there's something that is a bit off.
     
  17. Mexitele Blues

    Mexitele Blues Tele-Holic

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    Will your volume pot be forming a variable high pass filter with the preceding coupling cap?
     
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  18. shortcircuit

    shortcircuit Tele-Meister

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    Ah fart! I thought I'd be ok with the 0.1uF coupling cap as I'd still have the full guitar frequency range down to 20k. What I overlooked was that 20k is half way on a 250k audio pot. Gotta put the output on the wiper and add a 2.2M resistor between the input and the wiper.

    vol.jpg

    I can drop the coupling cap to 0.047uF.
     
  19. shortcircuit

    shortcircuit Tele-Meister

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    Criminy, what was I thinking? I would only need the 2.2M resistor if it was fixed bias.
     
  20. tubegeek

    tubegeek Tele-Afflicted

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    While this is definitely true, Merlin has a knack for explaining things clearly and thoroughly, and for answering questions by running tests. It's from a useful guitar amp perspective that is a valuable service to numbskulls like us. His examination of the grid current compression in a Fender Bassman cathode follower is absolutely riveting* and I'm actually not sure whether the explanation of how to analyze a cathode follower <IS> in RDH4? I'll have to take another look. If it is, I must've fallen asleep when I was reading that part.


    *for numbskulls like us.
     
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