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SLO-Nakid

Discussion in 'Shock Brother's DIY Amps' started by robrob, Sep 3, 2020.

  1. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    I've compared the schematic and the layout the old fashioned way. I printed them both :) I also checked out the original SLO schematic.

    I found some differences:
    1) The stage between the cold clipper and the cathode follower has a 220k plate resistor in the original.
    2) That same stage has a 1uF bypass capacitor which is missing in the layout
    3) The choke is current rating is 150mA on the schematic; on the layout it is 125mA.
    4) You removed the stage after the fx loop. This stage consists of a DCCF. Merlin somewhere says that the DCCF is very important for the overdriven sound. In his book he specifically mentions the SLO100 having two such circuits cascaded. I've never played a SLO100 and don't have much amplifier experience at all, but based on Merlin's remarks I would say you might change the tone of the SLO by removing the second DCCF.
     
  2. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Tom, thank you again for your very close examination and finding of errors.

    1) Yep, fixed
    2) Yep, fixed
    3) Already fixed on the current schematic and layout
    4) The important cathode follower is the one paired with Preamp 4, which is the primary distortion triode. I paired it with the tone stack buffer cathode follower so they will interact when overdriven. The SLO-100 FX loop dumps 99% of the guitar signal so the FX recovery triode and its cathode follower are never overdriven so its cathode follower isn't important for overdrive tone.
     
  3. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    Regarding 3): Then the pdf is out of date.
     
  4. robrob

    robrob Poster Extraordinaire Ad Free Member

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    It probably was an old pdf. It's updated now. Thanks again Tom.
     
    Last edited: Sep 5, 2020
  5. XTRXTR

    XTRXTR TDPRI Member

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    I like it, I like the adjustable NFB,. Looks like you can get some light to heavy distortion depending on how you adjust everything. slo building the distortion is cool. The amp on my bench has all the iron to make this, which is tempting. I gotta finish what I started though. Modding my 2204 with tube buffered FX loop your 3-way cold clipper switch and I might even add a very slow tremolo...get that Robin Trower Bridge of Sighs sound.
     
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  6. XTRXTR

    XTRXTR TDPRI Member

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    I like that you put the pinout numbers in the schematic too.
    1. Is the convention that V1A refers to Pins 123 and V1B to pins 678?
    I can't find anything about it, except the old data books refer to triode one as pins 678 and triode two as pins 123, so I guess that means V1A refers to pins 123 and V1B refers to pins 678. This makes more since in terms of sequencing A to the lower numbers and B to the higher numbers. There was one data book that called for a more favorable preamp triode using pins 678 aka V1B with regard to hum. Would you agree? Maybe refer me to some literature on the convention, not all schematics have the pinout and most only say V1A, V1B etc.

    And then Marshall has two schematics for a 2204 where one shows V1A as the cold clipper and one shows V1B as the cold clipper.
     
  7. robrob

    robrob Poster Extraordinaire Ad Free Member

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    XTRXTR, you are correct VA1 is pins 1-4, V1B is pins 5-8 (9 is joint heater pin). V1B is the quieter of the two triodes and is why Soldano used the B triode for the critical stages. He even uses the B triode for the phase inverter input.
     
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  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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  9. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    I'm diverting a bit, but you could use the unused triode and use a parallel input stage to reduce the noise.
    Might be more of a mod and might be unnoticeable with the 68k input grid stopper.
     
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  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    A parallel V1 is definitely and easy mod.
     
  11. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I added an optional "Power Amp Boost" mod. A switch bypasses the cathode follower upper attenuating resistor which eliminates the attenuating voltage divider for a 21% boost in signal into the phase inverter and power amp. This gives you more power tube distortion than a standard SLO-100.

    [​IMG]
     
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  12. XTRXTR

    XTRXTR TDPRI Member

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    Thanks for answering that, I'll stop trying to find that answer in a whitepaper or book now and take your information as truth and fact.

    Rather than me guessing can you explain how that reduces noise theoretically or in real terms? I'm trying to learn as I go.o_O

    The switch mod jumpers the 22k Resistor allowing a lower cathode resistance and boosting the signal - very cool. I love your switch mods. Is that something you would use RG 174 shield for? I have one more question what can you do with the third switch lug? :D
     
  13. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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  14. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Jumpering around the 22k resistor eliminates the voltage divider formed by the 22k and 82k cathode resistors so it boosts gain.
     
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  15. XTRXTR

    XTRXTR TDPRI Member

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    I might have to look up this book. Merlin's Preamp book.
    Another resource I have used in the past is the NEETS unclassified electronics I believe the US Navy created, they still update the newer stuff. It is a good way to learn some fundamentals or in my case relearn and remind. A good teacher once told me that you don't have to know everything but you should at least know where to find it.
    Thanks @Tom Kamphuys
     
  16. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Merlin's preamp book is my favorite tube amp book so I recommend it but I ask that we not start discussing how to learn electronics in this thread.
     
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  17. SKEsq

    SKEsq TDPRI Member Silver Supporter

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    Once I recover from my most recent purchases this is on my list. I've built a couple amps based on your website - stoked to see another interesting option.
     
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  18. XTRXTR

    XTRXTR TDPRI Member

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    Copy That Rob:) I'll try to stay within the design of your amplifier for questions or comments.
     
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  19. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The first SLO-Nakid 6V6 has been built. Here is a youtube clip:
     
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  20. kleydejong

    kleydejong Tele-Holic

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    Killer demo Rob, nice job on that circuit! I have yet to make a higher gain amp that I have liked, but there are some really great ideas that I need to implement in this schematic. Your website always makes it much easier to digest!
     
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