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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!