TC Electronic - MojoMojo Overdrive

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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UncappedOptics
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Post by UncappedOptics »

I finally caved and bought a MojoMojo to trace (also to test out, but mostly to trace). I knew it was the same overall design & PCB as the Dark Matter which I traced about a year ago so I figured I might as well give it a go to see what the differences are.

I also wanted to test a claim TC Electronic made. They say "...the fact that we use a special circuit that ramps up the voltage to more than 3 - 4 times the amount of your typical drive pedals", it turns out this is a lie. The whole circuit runs at just 9V, I have no idea why they're making this claim or what part of the circuit they could be referring to, maybe the doubled 4148 diodes that give more headroom and the slight attenuation before the clipping stage?

Either way, I'm a fan of the pedal and I hope the schematic may be useful to some people, either in re-creating the effect or taking inspiration from it.
TC Electronic Mojo Mojo.png
Changes from the Dark Matter:
  • Different voice switch action, this one alters the gain rather than the Dark Matter's which changed the bass response.
  • The Dark Matter only gives about +/-6dB of tone control but this pedal gives about +/-12dB
  • IC2B here is just a buffer whereas in the Dark Matter it adds gain
  • R27 is bigger giving more gain, probably to compensate for the previous stage losses
  • Finally, there's about 4dB of gain in IC2A vs it being a buffer in the Dark Matter
Something interesting to note is IC2B, this does nothing but act as a buffer, as such, they could have saved a cap and a resistor by making R21 a 0ohm link.

I do wonder is if they set out with the intention of making two similar pedals or if they designed one then tweaked it into the other.

I guess I now need to do the Paul Gilbert special edition to see if that actually includes a charge pump to up the voltage :D

P.S. I hope I posted this in the right place, I'm fairly new to posting here.

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roseblood11
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Post by roseblood11 »

Bump

Does anybody own the Paul Gilbert version?

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Lukasen
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Post by Lukasen »

Hopefully this will be my last overdrive (a week after purchase).
I just shorted diode D3 or D5 to make the distortion asymmetrical. It works, it doesn't sound so boring anymore, only when changing the gain it's good to adjust the bass and treble again.
And at lower gains, the switch helps, it really works perfectly.

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Lukasen
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Post by Lukasen »

I finally changed my mind. After the modification to asymmetric clipping, the sound was more wild, but at the same time some tones were masked by others or merged with them, and the equalizer did not help. I was inspired by a Reddit thread and replaced the original D3 (1N4148) with a BAT41 (I had it on hand). After the modification, it's a little dirtier than symmetrical clipping, and still Mojo Mojo retains the character of a brown-sounding overdrive, but mainly it's a bit sharper, it's more mid-focused and doesn't sound boring.

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