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Hi there, welcome to my blog - La Revolution Deux. It's an odd name - but I like it! Here you will find all the info on my various DIY Guitar effects builds, amplifiers and guitars. Everything from a humble Ibanez tubescreamer to the holiest KLON Overdrive.

You may also find a few effects builds that I am looking to move on - usually in exchange for other effects/gear/cash. You can always check my ebay account to see what I've got up for grabs.

Have fun, enjoy the blog - Fred Briggs :-)


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Sunday, 15 January 2012

Mad Professor - Stone Grey Distortion

Here's another Mad Professor one. Here's the marketing stuff from the Mad Professor website:

"The new Mad Professor - Stone Grey Distortion (SGD) is a modern high-gain distortion pedal with unparallelled clarity and definition.

This pedal was developed for high gain applications and specifically for clarity at heavy distortion levels.

The Stone Grey Distortion is unique in that it has razor sharp dynamics and high gain intensity. It's ready for drop tuning, 7 string, and modern rock players who are seeking extreme gain with intense "string to string definition".

Play a chord and hear each note distinctly, instead of it turning to "mush" like many other high gain pedals.

With the gain turned down, the Stone Grey Distortion approaches overdrive-like textures and responds to the player's touch and dynamics like our other Mad Professor pedals do."

And a demo video too:

Well, it's been taken apart over at freestompboxes.org and here's the schematic (Thanks to RoseBlood11):

As you can see it's quite an interesting setup, with that opamp gain stage pushing a couple of CMOS inverter stages into clipping (they sound good because they've got Mosfets inside:-) 

[EDIT] Here's a schematic taken from a 1970's Japanese electronics textbook:

As you can see the structure is very similar but check out the control layout - "bias", "overdrive" and "amplitute", that dual gain control could work quite well. I think this circuit is worth exploring some more, I find I need a little less treble and more bass, I'm also interested in exploring that bias control... If anyone tries it let me know!

Here is his vero to go along with the schematic (Again, RoseBlood11's work):


  1. It works, and sound's great, but it have a hum, when I turn the vol. up! Like the 50hz's hum. What's the problem? Thanks, Marcel!

  2. hello, I've finished my project...I use TL071 instead of TL051, but it doesnt have distortion...I dont know why?

    any suggestion for replacement of TL051?

    greeting from Indonesia

    1. Try LF351 opamp. It works great to me, otherwise double on your pcb route or check your soldering. It may helps you :)

  3. The circuit definitely works with TL071... I used a OPA134 because I couldn't find a TL051, and they sounded exactly the same.


  4. Which Japanese textbook is that from?

  5. Guys! Ocassionally I made mistake and connected output from tl051 to output (bypass cd4069) - and it's a fantastic booster for high gain!

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  8. Woh! I always thought Craig Anderton invented the idea of using a 4049/4069 for distortion and everyone since red lamma has been ripping him off. Live and learn. Live and learn.

  9. Woh! I always thought Craig Anderson invented the idea of using a 4049/4069 for distortion and everyone since red lamma has been ripping him off. Live and learn. Live and learn.


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