Shouty Cat

Restive Filter Effect Module

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.

Notes

• 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.

Parts List

• 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

Demo:

https://youtu.be/6ITLHbkJ7C4

Not required or expected by any means, but if you like it you can use the Sponsor button to buy me a beer!