Lastgasp Art Laboratories Rattle Crow Restive Filter

The Rattle Crow Restive Filter is a filter pedal from Lastgasp Art Laboratories, listed by the retailer Analog Man with the controls LEVEL, FREQ. and SENS.¹ It sits in the filter family, but it is not a straight auto wah: the filter is affected according to the size of the input signal, so your picking strength drives the sweep, and the circuit adds a distorted, unstable character on top.²

What it does

As an envelope-driven filter, it follows the same basic idea as an auto wah: the filter moves in response to how hard you play rather than to a rocking treadle. What sets the Rattle Crow apart is its character. The Guitar FX Layouts write-up describes it as "a kind of auto wah, but it has hysterical and distorted qualities, a broken auto wah sound," and characterizes it as "a wild and sorrowful tone."²

The three controls cover the usual jobs:

• SENS. sets how strongly the filter reacts to the input signal. Per the Guitar FX Layouts write-up, "basically the sensitivity pot is just a volume pot at the front of the circuit," so it shapes both the drive into the filter and the reaction.²
• FREQ. sets the filter's frequency.¹
• LEVEL sets the output level.¹

Circuit and DIY notes

The pedal has drawn interest from the DIY community: Guitar FX Layouts published a stripboard layout for it on 19 December 2015, based on a schematic shared in a forum.² That write-up gives some detail on the original design:

• The layout was drawn for the 2SC1815 transistor (BCE pinout) and a TL072 op amp, with builders reporting BC169 and LM358 substitutions working.²
• The circuit uses diode clipping; the layout's author used 1N4001 diodes measured at 0.6Vf and reported it sounding like the demo.²
• The original pedal uses the third pole of the 3PDT footswitch to cut the 9V connection to the whole circuit, along with what the author calls "a funky LED setup."²

A commenter on the same page compared it to the MASF Biloma, calling the two similar circuits and asking for a comparison.²

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