Sunday, 23 December 2012

Digitech Bad Monkey - Bufferless

Updated 21st January 2013

The Bad Monkey is a very popular low cost pedal which most people have assumed to be a simple Tubescreamer clone but is a little bit more than just a verbatim TS808.  It actually bears a lot more resemblance to the DOD Juice Box which is handy because the person who did the trace couldn't get a couple of the cap values and so they have been inferred from the Juice Box schematic.

The layout is simplified from the schematic, and all the FET buffered switching has been removed so it has been put together with true bypass switching in mind, and the input and output buffers have also been removed, so this can be thought of as a Bad Monkey Eternity if you like! :o)

The cap values that were unknown were the 51p and the 220p. The 51p will be fine and is a commonly used value for this kind of filter (increase if you want to soften the distortion more), but you may want to experiment with the 220p and so I'd suggest socketing that one and seeing what you come up with.

If you want a bit more gain from it, try increasing the 100K Gain pot.

Info from Digitech about the original:

The Bad Monkey Tube Overdrive gives your amp a boost just when you need it. It has been compared to the TS-808 but with having the unique ability to smooth out the distortion by use of the low and high EQ controls. Most overdrive pedals give you one tone control knob thus limiting your tonal options. You asked for a pedal that will maintain your guitar's distinct tone and DigiTech delivered! With its rugged design, separate mixer and amp outputs, and amazing tonal options, this pedal truly is a Bad Monkey. From Blues to Rock to everything in between, it will give you that amazing overdriven tube amp sound that will keep begging you to crank it up!






26 comments:

  1. Replies
    1. What voltages are you getting at the IC and transistor pins?

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    2. Actually I've spotted an error on the bottom right hand opamp channel. The link should go to pin 7 not pin 6, and the 5K resistor on the right should go from pin 6 not pin 7. I'll update the layout and post it in a moment

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    3. I've updated the layout but I rejigged the components and links a bit so the 5K resistor can keep a 7.5mm pitch between leads. But to fix yours use this version, it will mean less messing about:

      http://i76.photobucket.com/albums/j6/IvIark_2006/Layouts/Vero/DigitechBadMonkey-Bufferless-fix_zps60c34123.png

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  2. No luck, so far, with this one. Just getting clean boost. I'll go through it tomorrow to see if I've made any mistakes. Here are some readings to be going on with. If you could shed some light it would be greatly appreciated and would save my aching brain!

    C. 8.91v
    B. 4.33v
    E. 3.75v

    Top IC

    1. 4.44v
    2. 4.44v
    3. 4.44v
    4. 0v
    5. 4.45v
    6. 4.45v
    7. 4.45v
    8. 8.91v

    Bottom IC

    1. 4.45v
    2. 4.45v
    3. 4.40v
    4. 0v
    5. 4.44v
    6. 4.45v
    7. 4.45v
    8. 8.91v

    Cheers!
    YA(Mark)

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  3. Eureka! 2 components missing from the layout: 1k and 220n to ground from first op-amp. Made a crude bridge and it sounds lovely.

    Mark

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    Replies
    1. Awesome, cheers Mark. Don't know how I missed those?! Doh. I'll correct and tag it.

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    2. To err is human etc etc...... in actual fact I have learnt so much trying to figure that one out. I have a better understanding of how that part of a circuit operates. Had I copied a flawless layout parrot fashion I would have been none the wiser. Once again, to both of you, keep up the good work! Cheer

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    3. Soooo.. You're saying that you'll learn more when we make mistakes.. :) Suddently i don't feel so bad about my past errors anymore :D
      +m

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    4. Nor should you.....but I'm not suggesting you guys throw us curved balls to keep us on our toes!! If you do cock up then you can always Captain Mainwaring from the 70's sitcom "Dad's Army" ( don't know if you are familiar with it, Miro): " I wondered who would be first to spot my deliberate mistake"!!!

      Mark

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    5. Has anyone spotted the deliberate mistake in the previous comment, yet?!

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    6. At one point last summer i had a feeling that Mark was testing me with some layouts :)

      Now that i draw those myself - the errors are never deliberate. They are just too easy to make.
      +m

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  4. Well it definitely works as layed out above. I misread the schematic and connected the 220 n cap to ground instead, double doh!! It still worked, however. Guess you can now finally call this one verified.

    Mark

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    Replies
    1. Excellent thanks mate. Yes it could go to vref or ground and the results should be the same as your experiment noted. I was tempted to take it to ground anyway because it was 2 rows away and so better suited for 5mm pitch caps but decided I should follow the scheme.

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    2. Hi Mark, just noticed this hasn't been tagged yet. This layout certainly works so chalk it up :D

      The active EQ make this one a little different from most other overdrives so definitely worth looking at and tweeking. I'm trying to study the scheme to figure out how it all works. Any clues as to how to tune the gain and cut off points on this? Cheers!

      YA(Mark)

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    3. I was sure I'd changed that. To increase the gain, increase the value of the gain pot. To alter the frequency response of the High and Low pots socket the 47n and 470n caps respectively and experiment with those.

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    4. Thanks Mark, I'll take those out and put some sockets in

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  5. The Low and High controls on mine alter the volume quite a bit. The Low alters the volume throughout it's entire range, the further clockwise the louder the pedal gets. The High control gives a big volume boost when turned fully clockwise, not so much until the end of the rotation.
    Seems odd, is this by design or do I have a fault somewhere?

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    Replies
    1. I forgot to mention I did use a tantalum cap for the 470nf with the + side facing lug 2 of the LOW pot.

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  6. WOW.
    I put 18 volts into this and used OPA2604's and it is the best 'metal' tone in a 125b that I've.....built. The 'LOW' is in the grave low with a range of distortion from very light TS on 4 to a triple wreck maxed out. Cool.

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  7. This comment has been removed by the author.

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  8. Excuse me, is a schema shown on top of page the last and verified? I´ve built it, checked many times and still I´m unable to get it working. So I don´t know whether this "branch" version in comment is right, or this, directly on this page. Thank you!

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  9. My fault, flipped ICs. Works like charm now! Thanks for sharing!

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  10. This was the first pedal I built a few months ago, fired up first time, very exciting. I have a Digitech Bad Monkey but I wanted a version with true bypass. Sound very similar in my ears, my original one is back in the box for safekeeping, I love my bad monkey. Thanks for the layout!

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  11. Why you do not draw a NORMAL schematic???

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  12. The great people who run this blog spend a lot of their valuable time making these terrific layouts for us to use - free of charge, I might add, and the schematics they use are usually the property of others, so can't be published here.
    I don't mean to sound grumpy but this question or request seems to come up a lot.
    A simple search on google will usually get you the schematic you are looking for. Usually the layouts use schematics from either freestompboxes.org or DIYstompboxes.com. You do have to be a member to access and search for schematics on these websites but generally you would be successful finding the exact scheme used for a particular layout.
    All it takes is a little effort.

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