The Evil Twin


This was my first totally original circuit that does anything beyond being a simple gain stage. It is a crazy beestard, it is noisy and chaotic, and that’s the kind of different I like. It’s not something everyone is going to find useable, but some will, and that’s enough.

I’d originally had the idea of doing a series of JFET boosts/ fuzzes/ etc. using on JFET gain stage from the Wee Fettle Boost as the first gain stage then add other elements after to tailor the sound. So! Obviously the first – and most logical – thing to try would be to double up, so I put two Wee Fettle Boosts on one breadboard in series.

I realised this was a fair starting place, but it felt a bit ‘cheap’ just having two of the same pedal in one enclosure, so I started experimenting.

The first bit of experimenting I did was to try jumpering various parts of the circuit with caps, resistors, diodes and jumper leads. After getting a simple feedback loop with a single jumper, the whole thing started to oscillate, when I turned the guitar volume down the pitch changed. I found that the pitch also changed when I played with the pedal gain and volume knobs.

A couple of years ago I totally botched an early experiment with an op amp (which became known as the useless Gett), I got a similar effect going, but I couldn’t control those oscillations, and I thought if I could get this under control and expand its function a bit, it’d be pretty fun. I liked the idea of turning the guitar/ pedal into a whole new instrument.

That was the starting point for the Evil Twin. After playing around with more switching combinations and a bunch of diodes I found the Evil Twin was capable of:

  • oscillations and drones (you can control the oscillations with the knobs, and the controls on your guitar, you can also get drones that you can play through to varying degrees depending on the settings).
  • You can get a kind of resonant filter sound going on which is really screechy and feedbacky.
  • A bizarre pseudo tremolo going on where the tremolo speed changes based on the frequency of the notes
  • A glitchy suboctave sound, sometimes it changes the notes you’re playing too

All of the sounds are pretty chaotic, and depending on the setup you may or may not get some oscillating drones in the background. If that chaotic noisiness isn’t up your alley, you can always just use it as a double boost. or buy a Fettle Boost. or two.

The key to the evil is in the three vertical switches:

top switch – crazy on or off

middle switch – adds a wee bit of red LED craziness

bottom switch toggles between:

  1. germanium diode pair craziness
  2. blue LED pair craziness
  3. silicon diode pair craziness

With 3 added switches for craziness, I decided to simplify and differentiate the two boost sections to keep the layout a little bit cleaner. The boost on the right has gain and boost, but the volume is an internal trim pot. The boost section on the left (or sinister) side has gain and volume but the boost is always on.

For the first two small runs of The Evil Twin the top toggle has been a three way switch:

  • left – one kind of crazy (the second switch also adds crazy, the third does nothing)
  • middle  – no crazy (the two switches below do nothing)
  • right – a different kind of crazy (the two switches below add a load of crazy)

I decided to simplify this for future runs so:

  • left – no crazy, just double boost/ distort-o-fuzz
  • right – crazy (more crazy found in the second and third switches)

The Evil Twin seemed like a good and logical name, even though it broke from my tradition of using Geordie words and slang.


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