Saturday 2 January 2021

MXR Blue Box w. mods

 Couldn't resist to add another layout for the Blue Box since there is a bunch of mods online...

  • Octave switch that toggles between stock two octave down setting and one octave down setting.
  • Treble boost switch that lifts up 10nF low pass filter cap before the Output control. Should result in an overall brighter and louder tone.
  •  Both potentiometers is increased from 50k to 100k. This is supoosed to increase the overall output.

 One untested mod that could be fun to try out would be replacing 330ohm resistor that sends voltage to the CD4013 IC with a small value potentioeter for a starve control since those chips can behave quite funnilly at different voltages.

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15 comments:

  1. Alamondm27 January 2021 at 20:18

    Tried building, can’t get it to work, I don’t know enough about chips and such. Maybe someone with more experience may have luck

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  2. Alamondm27 January 2021 at 21:16

    The volume works, you can hear the tone switch doing something, the oct switch does nothing and the blend does nothing. I think I can almost faintly hear a fuzzy signal in the back ground but it’s hard to tell. Went through the typica trouble shooting first.

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    1. fuzzhead27 January 2021 at 21:35

      D1 seem to be in the wrong orientaion. Try flip it around.

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  3. Alamondm27 January 2021 at 22:00

    That’s money, flipping diode 1 worked. works great now, you can tag this one. I don’t recommend for bass though. The tracking from the 12th fret up is great but anything lower down the board and it doesn’t track worth beans, lol. I will box it up and give it to my guitar player, he will probably love it. Thanks for the help.

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    1. fuzzhead27 January 2021 at 22:06

      Awesome! Tagged.

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    2. Elijah-Baley28 January 2021 at 10:29

      What about the overall volume?
      I built some years ago the Sabrotone layout.
      I got a volume boost using a sort of LPB-1 booster on a daughter board in the end of the main circuit, how I saw in an alternative replica of this schematic. It worked fine, but maybe because all the wires I got, just a bit, of ticking noise sometime.

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    3. Alamondm29 January 2021 at 00:26

      with the blend maxed out either way volume is about unity. with blend set about center there is a slight boost above unity. I dont have a db meter so Im going by ear.

      Delete
  4. WTFiCanBuildMyOwnPedals12 May 2021 at 21:56

    Thanks for this layout! works amazing, I have some ticking too, but I think it's the nature of the beast. Volume was better than what I expected, considering reviews (never played an original), but I put an SHO after it anyway to never worry about it (I had to increase SHO input cap, because 100nF was cutting a precious amount of low end).

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  5. Chris Stelloh27 June 2021 at 23:11

    Hey! Had a question about the 47nf cap that goes to leg 6 of the JRC chip - in the old tagboard layout for this circuit, that cap is 4n7 not 47nf. Seeing as how that cap connects the output and the inverting input of the chip, could that higher value be the reason that my build of this circuit sounds as a Blue Box should, but has a ton of noise and won't gate at all no matter how low the input signal is? Either way - I'm going to build one with the 4n7 cap in that position and see what happens.

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    1. fuzzhead28 June 2021 at 08:32

      Hey Chris!
      Most of the schematics I've seen has a 47nF cap in that spot. Others has a 4,7nF. Most PCB makers sells the version with the 47nF cap. Not sure whats going on here since there is no factory schematic from MXR online...
      http://pedalparts.co.uk/docs/BlueFool.pdf
      https://www.pedalpcb.com/docs/Mantle.pdf
      https://effectpedalkits.com/wp-content/uploads/manuals/blue-box-fuzz-kit-building-manual.pdf

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    2. Chris Stelloh28 June 2021 at 09:09

      Gonna have to try both and report back. I'll let you know if the smaller value in that position cuts down on the noise, Anders!

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    3. Chris Stelloh28 June 2021 at 20:59

      Okay - 47nf it is. 4n7 worked but was way too quiet. Also - I managed to get my output control problems solved with a C taper 100K pot. It allowed for more synthy and gated sounds at lower volumes and still fuzzes out when maxed.

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    4. fuzzhead29 June 2021 at 08:16

      Thanks for the report. So what was the noise issue like? Those flip flop ICs can be noisy....

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  6. Chris Stelloh30 June 2021 at 04:49

    The first time I built, it had a really high noise floor and wouldn't gate at all like the blue box does. So I just made it worse and added a feedback loop and additional gain stage at the end to make it even louder and more musical and annoying.

    This time the build sounded as it should, tho.

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