This mod is based on the Rattle Crow pedal by Lastgasp Art Laboratories. It's been modified to work better with synths/toy keyboards and to be a bit simpler and more flexible.
- Based on how flexible the TL072 is, I expect this will work with a wide range of voltages. It definitely works at 9 and 12 volts as I was able to test with those with no issue.
- 4.5 volts wasn't quite enough, but you might get as low as 6-7 volts.
- I wouldn't go much higher than 12 volts but I think technically the IC can handle 18 if you're brave? I dunno what keyboard uses over 12 volts though so I figured it was a moot point.
- See schematic/PCB for different values for the "Cuts." These capacitors can filter/clip different frequencies to tweak the effect to better suit different applications. Cut 1 creates a kind of clipping effect, while Cut 2 is essestially a Low Pass Filter.
- I have added some additional solder points to the PCB to easily connect switches for connecting/disconnecting the Caps.
- Experiment, but I expect by using pots/crossing these points you could do some really wacky things.
- They can also be left unconnected to let all sound through. The original uses 58pF caps, but I didn't hear any difference with those caps and nothing during my testing.
- The "Scream" Frequency control feels much better with a Reverse Log pot IMO, but for cheaper builds a Linear pot works fine.
- The "Shout" Sensitivity control is adjusted for high input signals coming off of a synth/toy keyboard. Tweak this as needed for lower level signals like a guitar/line level input. (The original pedal uses a 50k pot for reference).
- The original pedal has a Level control that can be installed by connecting a 10k Log pot:
- Wire Output from board to Pin 2 of pot; wire Ground from board to Pin 1 of pot.
- TL072 IC
- 250k Linear Potentiometer
- 1k Reverse Log (audio) Potentiometer (Linear works too for cheaper builds, it just doesn't feel as nice)
- 2SC1815 Transistor
- 1N4148 Diode x 2
- Capacitors (film/ceramic):
- 0.1uF x 2
- 47nF x 2
- 6.8nF x 2
- Cut 1 Cap (see schematic) x 1
- Cut 2 Cap (see schematic) x 1
- 10uF electrolytic capacitors (any voltage rating 16v or higher) x 2
- Resistors:
- 100k x2
- 47k x3
- 2.2M x1
- 470k x1