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Robrob quarter power switch, as a speaker cable

Discussion in 'Shock Brother's DIY Amps' started by jtcnj, Dec 17, 2018.

  1. jtcnj

    jtcnj Tele-Holic

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    For head / cab use.
    1/4" fir plywood stuck to pedal enclosure with kitchen / bath caulk.

    Works pretty well with the amp cranked up, but still louder than loudish TV volume for bedroom / apartment playing.

    Less effect with the amp at lower volumes but I suppose it helps a little.
    The knots in the cable are not the preferred method for strain relief, but is
    "good enough" here.

    [​IMG]
    20181215_133414.jpg 20181215_133833.jpg
     
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  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Why plywood? That kinda defeats the heatsink properties of those nice resistors, although I wouldn't worry about it too much with a 5E3.

    Could also just 1/4" jacks on each end of the box as well so you don't have to worry about the cable.
     
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  3. Outlaws

    Outlaws Tele-Meister

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    I just made one last weekend too as a gift for a 5E3.
    1/4 power is just enough to take edge off without squashing the tone.
    Used a flanged box so it could be easily screwed into the cabs wall.
     

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    Last edited: Dec 17, 2018
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  4. jtcnj

    jtcnj Tele-Holic

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    Yes, makes more sense that way in hindsight.
    I did consider the heat issue.
    On either the 5e3 or 18w TMB it is meant to be used with I figured it would be ok. The strip of wood I cut that piece from and the caulk were on one of my work benches, and it came together from what I saw I had on hand.

    I had the plugs on hand, but not the jacks.

    I thought the same thing about the jacks AFTER I ordered parts for my 6g2 build.
    I have one 3' speaker cable made up of the same wire and 2 jacks and could have just made another one.
     
  5. Uncle Daddy

    Uncle Daddy Tele-Afflicted

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    I used different value resistors to give around 1/10th power, which equates to a 50% volume reduction. Works pretty well.
     
  6. bender66

    bender66 Poster Extraordinaire

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    What value resistors would put it at that?
     
  7. Uncle Daddy

    Uncle Daddy Tele-Afflicted

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  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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  9. jtcnj

    jtcnj Tele-Holic

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    Bumping this to comment on my experience.
    This goes for both the 1/4 power and 10% versions.

    I got used to using these and never really A/B with and without cranked to compare tone suck. I usually need to play at lower volume in my home.

    Since I built the RR JCM800 1w micro, I have. Even at 1w it is too loud when others are home watching TV, etc. The Emi GB128 cab is like 102 db sensitivity, so there's that. Sounds great though.

    Using the power soak circuits noticeably cuts somewhere in the upper mids (cant quantify this exactly), not in a good way. More for the 10% version.

    I can EQ around with amp pots and EQ pedal, but still has a somewhat "wet blanket" effect.

    They do cut the volume considerably, and I still often use them, and consider them worth having, but at a price paid in coloring tone.

    The Micro sounds glorious; I may re-configure it to 2 EF80 output tubes just to try it.
     
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  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    @Outlaws, I tried to PM you but couldn't. I would like to use your 1/4 power box photos on the website with your permission. If yes, what credit would you like for the photos? "1/4 power box and photos by . . ."
     
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  11. Nickfl

    Nickfl Friend of Leo's

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    I'm dialing in a version of the EF 80 JCM 800 right now. Be aware that the EF 80 tubes really start to have problems with plate voltages above 300v, so if you built the 12au7 version that is running the tubes at 360-370v you may have trouble turning it into the ef80 version with the same PT.

    Also fyi, I'm not sure how much power the 12au7 version of it actually produces, but the EF 80 is putting out up to 5w on my scope so it isn't exactly whisper quiet.
     
  12. jtcnj

    jtcnj Tele-Holic

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    thanks for the info Nick.
    I really want to add an oscilloscope to my bench, but $$$.

    I am considering the EF80 more to try the pentode PP, not so much for the wattage. I ordered 4 tubes for under $20.

    I think I do have around 360v anode voltage.

    Can I tap the OT to anode voltage from B+2 or B+3, etc.?
    EDIT: Not sure how Rob numbers them, but farther down power nodes.

    I dont recall the actual voltages; not at home right now.

    I built my micro with 1 (hi) input, but now would like to add the non cascaded v1 triode option, maybe on a switch. The spacing of existing hole is problematic to make it 2 inputs.

    The reason is to hit a more Plexi setup.

    Maybe I build a Bassman Micro => modded more to plexi to use the EF80 and the torroid OT on Robs site.

    I would like to hear the EF80s first though.
     
    Last edited: Feb 8, 2021
  13. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    @robrob - do you think there's a good way to incorporate this into an amp with a multi-tap OT?
     
  14. Outlaws

    Outlaws Tele-Meister

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    Go for it. No credit needed really but appreciate asking. I got my share of value from your site. I can email the original photos if these are compressed from the forum.
     
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  15. robrob

    robrob Poster Extraordinaire Ad Free Member

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    "Also fyi, I'm not sure how much power the 12au7 version of it actually produces, but the EF 80 is putting out up to 5w on my scope so it isn't exactly whisper quiet."

    Wow! Now I know why the first builder of the Champ Micro EF80 said he had to run it on an attenuator.
     
  16. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I'm not 100% sure about this because I haven't tried it, but according to the Hammond spec sheet below we should be able to run an 8 and 15 ohm output jacks by using the #4 yellow wire as the ground wire for both jacks, then #2 orange for the 8 ohm jack tip and #1 black for the 15 ohm jack tip.
    [​IMG]
     
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  17. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Oh, I was just thinking more in-general than applying it to a specific amp.
     
  18. robrob

    robrob Poster Extraordinaire Ad Free Member

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    My bad, I thought I was in one of the EF80 micro threads.
     
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