The Lastgasp Art Laboratories Green Monster Septic Fuzz (GM2) is a fuzz pedal described as an effect to create a septic distortion, characterized by a dirty, broken and rotten sound1. It is a discontinued circuit, summed up by the Guitar FX Layouts blog as "Discontinued circuit with noise for days"1. The pedal is no longer made, so today it survives mainly as a stripboard project for builders rather than as a product on a shop wall.
What it does
The Green Monster is the second version of the circuit, and the four knobs are the headline change. The layout write-up puts it this way: "GREEN MONSTER is back with four knobs! There is an easy to use sound which the first GREEN MONSTER (ultra fuzz) was neve..."1. The first Green Monster, an ultra fuzz, could not create an easy to use sound, but the write-up notes the sound is still putrifying1. In other words, the GM2 keeps the rotten character of the original while making it more manageable to dial in.
The controls are:
| Control | What it does |
|---|---|
| LEVEL | Output level2 |
| SENS.1 | Sensitivity control2 |
| SENS.2 | Sensitivity control2 |
| SENS.3 | Sensitivity control2 |
Analog Man's listing for the pedal gives the control set as "controls : LEVEL, SENS.1, SENS.2, SENS.3"2.
The circuit and the DIY layout
The DIY layout for the Green Monster was found from the DEFX files, as the layout blog's Mark explains: "Found this circuit from the DEFX files and thought this to be quite interesting"1. Builders who have put it together report mixed results. Commenter plasmid noted in April 2023 that "there should be a link between row 1 and row 3 to the left of the IC," calling it an error in the original layout, and said that bread-boarding it with that link sounded like the video1. Another builder, Vitamin, who built it with the mod switch, reported that shorting row 1 and 3 to the left of the IC made it "sort of work" but not really loud, that the pots act very strangely, and that the mod switch makes no sound difference1.
Two details from the layout matter to anyone building it:
- The 1N5817 in the layout is a protection diode and can be substituted1.
- The circuit uses an LM741 op amp. One builder substituted UA741s, writing "I used ua741's instead of lm741's but I am not sure that this is relevant to the problems I am encountering"1.
Builders report an error in the original layout. Commenter plasmid wrote in April 2023: "I think there is an error in the original layout - there should be a link between row 1 and row 3 to the left of the IC." In the modded layout, that link is performed by the switch. The same builder bread-boarded the corrected version and reported it sounds like the video1.
Not every build report is a success. Commenter Vitamin, building with the mod switch in December 2024, reported that shorting row 1 and 3 to the left of the IC made it "sort of work but not really loud", that the pots acted very strangely, and that the mod switch made no sound difference1. If you build one, expect the corrected row 1 to 3 link to be essential and the results to vary.
Where it sits in the Lastgasp range
Lastgasp Art Laboratories is a Japanese builder of experimental fuzzes, and the Green Monster belongs to a line of circuit-bending designs. The maker's later and current fuzzes include the Super Oscillo Fuzz, the 46 Sooper Fuzz, the Gomorrah, the Octavella Upper Octave Fuzz and the Lluna Oscillo Fuzz Drive. The Green Monster predates the current dealer availability of the line and is not part of it.
Videos
Dennis Kayzer
Joel Gilardini
Grinding Mass
Questions
What does the Green Monster Septic Fuzz sound like?
The Green Monster Septic Fuzz (GM2) is described as an effect pedal to create a septic distortion, characterized by a dirty, broken and rotten sound. The second version added four knobs, and the maker said it offered an easy to use sound that the first Green Monster ultra fuzz never had, while the sound remained putrifying. One layout source summed it up as a discontinued circuit with noise for days.
Is the Lastgasp Green Monster Septic Fuzz discontinued?
Yes. The Guitar FX Layouts write-up of the circuit, published in December 2022, describes the Green Monster Septic Fuzz as a discontinued circuit. The pedal is no longer in production, which is why the circuit circulates among builders as a stripboard layout rather than as a current product.
Can you substitute a UA741 for the LM741 in the Green Monster?
One builder who reproduced the layout used UA741s instead of LM741s, but reported that the build did not work properly at first and that the pots acted strangely. That builder was not sure the op amp substitution was relevant to the problems encountered, so the substitution is reported but not confirmed as trouble-free.
Is the 1N5817 diode needed in the Green Monster Septic Fuzz?
The 1N5817 in the layout is a protection diode, and the layout notes state it can be substituted. It is not part of the fuzz's tone-shaping circuit, so a builder has latitude in what fits that position.
Where did the Green Monster Septic Fuzz layout come from?
The Guitar FX Layouts blog traced the circuit to the DEFX files and published vero and tagboard layouts for it in December 2022, including a modded version with a gain switch. Builders in the comments later identified an error in the original layout involving a missing link near the IC.
Sources (2)
- Guitar FX Layouts: Lastgasp Art Laboratories Green Monster Septic Fuzz, Guitar FX Layouts (tagboardeffects.blogspot.com), 2024-12-26
- effect pedals, Analog Man (analogman.com), 2006-06
