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Monday, 1 July 2013

Mindbender Fuzz - Mojo layout

Really useful mods for the all-time classic, the Tone Bender MKII Professional. Mods add more volume and a trimmer for accurate biasing the germs among other things...

From Fuzzcentral:
Here is my modified version of the ToneBender MKII Professional, the MindBender. I decided to use NPN Germanium transistors for mine so that I'll be able to use a negative ground arrangement, which allows use of modern power supplies. You can use 2N388A, SK3861, AC127, and a few other part numbers. I made a few more changes to the circuit to enhance it's overall performance:
  • First off, I added a 1M pulldown resistor to the input of the circuit, which will prevent "pops" when using true bypass switching.
  • The second change that I made was to replace the 100K resistor on the collector of Q2 with a 47K resistor. This helps tighten up the sound a bit, making it less "farty", and it helps to increase sustain.
  • Third, I changed the 470-ohm resistor that's in series with the output capacitor with a 1K2 resistor. This helps to boost the output of the pedal so that I don't have to crank up the volume control so much.
  • Fourth, I changed the 1KB "attack" pot to 2KB. This change doesn't really have any effect on the tone of the pedal, but it does help to prevent Q3 from becoming saturated.
  • The Fifth change was to replace the 8K2 resistor on the emitter of Q3 with a 20K trimpot so that the collector voltage of Q3 can be adjusted to exactly 4.5V-5V.
  • The sixth and final change that I made to the circuit is the addition of a 1N4001 reverse polarity protection diode. This isn't necessary but it helps to protect the circuit components in case the power supply is accidentally reversed or if the battery is touched to the battery snap backwards. 
Here's the Mojoed layout. 21 colums, so you'll fit this nicely in B-box and you still have big axial caps on board.


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10 comments:

  1. Unknown1 July 2013 at 23:49

    what is there is no germs or id i want to switch between si and ge?

    ReplyDelete
    Replies
    1. mirosol2 July 2013 at 06:20

      I've read this comment a few times and i'm still not sure what you're asking...

      Transistors are NPN Germanium. To make them switchable between Si/Ge, you would need three 3PDT toggles, one per each transistor. Plus the bias would be off once switched.

      As those are NPN germs, you should get it running nicely with some low hFE switching Si transistors like 2N3903 or 2N2369.
      +m

      Delete
    2. Unknown3 July 2013 at 21:18

      sorry should of been clearer. so if i just want to put Si in place of the GE i would have to remove the bias pot?

      Delete
    3. mirosol4 July 2013 at 07:29

      You'd still want to have bias on the trimmer to tune it just right.
      +m

      Delete
  2. Equinox2 July 2013 at 17:14

    I'd really like to hear some clips. Sounds great!

    ReplyDelete
  3. Jimijam7 July 2013 at 00:10

    I finished this one up with some OC84s and it is really nice... I recommend using some good single core screened audio cable so you can shield it because if you don't it can have a some hiss unwanted noise. This pedal has some great fuzz to it and actually cleans up pretty well when I turn down my guitars vol if you set the pedal right : )

    Thanks for the layout mirosol!~ I will see if I can post some clips

    ReplyDelete
    Replies
    1. mirosol7 July 2013 at 13:31

      Awesome. Finally. I struggled with this one myself... It was gating as hell and i didn't have time to have a proper debug session.

      I'll tag it! Thanks Leo!
      +m

      Delete
  4. Jimijam13 July 2013 at 17:29

    Here is a couple pics of the GE version made.
    http://i145.photobucket.com/albums/r233/jimijam_photos/DSC_0079.jpg?t=1373730367
    and the guts
    http://i145.photobucket.com/albums/r233/jimijam_photos/DSC_0076.jpg?t=1373730268

    I may make another si version since I really love this version of the tonebender. Thanks again Mirsol for the great layout... Soon as a get a decent recording of this pedal, I will put it on soundcloud

    CHEERS

    ReplyDelete
  5. Andy Miller10 December 2014 at 13:07

    Nice. Built this with some Sylvania 2N229s, hFE 60ish for Q1 and Q2 and 115 for Q3. Sounds cool even through my bench amp. Nothing sounds cool through my bench amp.

    ReplyDelete
  6. Unknown7 February 2021 at 17:34

    Any chance of a gut shot... Have the board wired up, but not functioning. Output is lug2 Level? To jack or to 3PDT? and layout says 9V+, but this is NPN. Is that 9V-? Apologise for resurrecting a near decade old post, just trying to troubleshoot

    ReplyDelete