ALM Busy Circuits FIZZLE GUTS (2012–2022)

A filter chip from a forgotten Casio sampler, rebuilt as a Eurorack module from scavenged silicon. Raw and rare.

Overview

Plug in the FIZZLE GUTS and the sound is immediate: thick, slightly hazy, with a top-end fizz that doesn't clean up no matter how far you roll off the resonance. It's not pristine and it's not neutral. It's the filter IC from a 1987 Casio FZ-1 sampler, pulled out of its original home and wired into a 12HP Eurorack module. This isn't a recreation or a simulation. It's the actual analog filter chip, the MB87186, salvaged from dead or donor FZ-1, FZ-10M, or FZ-20M keyboards and put into a dual filter and VCA setup.

ALM launched the FIZZLE GUTS around 2012, and it wasn't trying to be practical. It was one of the very first modules the company ever produced, born from a DIY ethos and a fascination with obsolete technology. Only about 30 units were ever assembled by hand. It wasn't mass-produced. Technicians hunted down rare, aging ICs from decommissioned digital synths, and each module depended on the survival of a discontinued part. That scarcity makes it a collector's oddity, but the sound is what keeps it relevant: a filter character that no modern clone has perfectly captured. It's softer than a Roland SEM, less aggressive than a Moog ladder, and nowhere near as clinical as a state-variable design. The low end is rounded, almost velvety. The high-mids can turn nasal when pushed, and the resonance flutters just slightly as it peaks. That's a quirk, not exactly a flaw, like the warble in a tape head that refuses to align.

The dual architecture gives you two complete signal paths, each with its own filter and VCA, fed by a shared resonance control and modulation inputs. That makes it surprisingly flexible. You can run stereo signals, layer two different timbres, or patch one side as a modulator for the other. It does its best work on something dense: a gritty wavetable sweep, a lo-fi drum loop, or a detuned supersaw. It adds a kind of analog patina, like listening through an old console with slightly oxidized contacts. It's not transparent. It's opinionated.

Specifications

Key Features

The Casio FZ-1 Filter IC: A Silicon Relic

At the center of the FIZZLE GUTS is the MB87186, a filter IC originally designed for Casio's high-end FZ-1 sampler, a machine that used 16-bit sampling at a time when most competitors were still stuck in 12-bit territory. The chip was never intended for modular use. It was part of a closed system, buried deep in a digital architecture that prioritized clarity and dynamic range. Isolated and repurposed, it sounds warmer and more organic than you'd expect from a late-'80s digital synth. The filter's 24dB/octave slope behaves more like a vintage analog design than a clinical digital one, with a gentle roll-off. The resonance peak doesn't self-oscillate cleanly. It breaks into a soft, breathy squeal instead. Engineers who've probed the circuit note that the IC's internal op-amps and OTA-like stages respond unpredictably to extreme CV, creating subtle distortion and phase shifts that vary from unit to unit, depending on the health of the salvaged chip.

Dual Signal Paths with Shared Character

Many dual filters offer independent control over every parameter. The FIZZLE GUTS takes a more minimal approach. Both channels share a single resonance control, so you can't dial in a screaming lead on one side while keeping the other smooth and flat. That limitation pushes you to treat the module as a stereo processor or a dual-voice tone shaper rather than two separate filters. Each side has its own audio input, filter cutoff CV input with attenuverter, and VCA level control, so the modulation can still differ between sides. The VCAs are DC-coupled, which makes them suitable for modulating audio, LFOs, envelopes, or even slow random voltages. That opens up rhythmic gating or wavefolding when patched creatively.

A Module Built on Scarcity

The origin story is what sets the FIZZLE GUTS apart. Each unit depends on a functioning MB87186 chip pulled from a donor FZ-1 or FZ-10M, machines that were never produced in huge numbers and are now rare themselves. As those source keyboards degrade, the supply of usable ICs dries up. ALM released the FIZZLE GUTS design as open source in 2022 to mark its 10th anniversary, so hobbyists can build their own versions if they can source the chips. Even with schematics available, the bottleneck remains: without the original IC, you can't build an authentic FIZZLE GUTS. Clones like the moddict FZ-2F have emerged, but they still rely on the same rare component. You can't just order one. You hunt for it, trade for it, or get lucky on the secondhand market.

Historical Context

The FIZZLE GUTS appeared in the early 2010s, when Eurorack was shifting from a niche hobbyist format to a legitimate platform for professional sound design. Most new modules at the time were either faithful recreations of classic synths or novel digital processors. ALM took a different path. Instead of looking to Moog or Buchla, they looked to forgotten digital workstations like the Casio FZ-1 and the Commodore 64. The FIZZLE GUTS was part of a broader "guts" series that included the SID GUTS, based on the C64's SID chip, reflecting a fascination with repurposing obsolete consumer electronics for experimental music. By using actual vintage silicon, ALM challenged the idea that modern manufacturing could replicate the quirks of aging components. Competitors like Doepfer and Make Noise were building precise, repeatable circuits. ALM was building modules with warts and all.

Collectibility & Value

Today the FIZZLE GUTS is less a functional module and more a piece of Eurorack folklore. With only around 30 units ever made, it rarely appears on the market, and when it does, prices reflect its rarity. Units in working condition typically sell between £800 and £1,200 GBP, depending on provenance and included documentation. Non-working units, often listed as "for parts or repair," still fetch £300-£500, primarily because the MB87186 IC can be harvested for use in other builds. The biggest risk for buyers is chip failure. The MB87186 is sensitive to voltage spikes, and many original FZ-1s suffered from power supply issues that could have degraded the IC over time. Service technicians observe that failed filters often show up as a complete loss of high end or a constant low-level hiss that overwhelms the signal path. There's no reliable way to test the chip outside of the full circuit, so buying a FIZZLE GUTS blind is a gamble. Collectors recommend only purchasing from trusted sellers who can provide audio demos and proof of stable operation. Since ALM released the design as open source, some builders are creating their own versions using salvaged chips. These are not official units and lack the pedigree, and the premium price tag, of the originals.

eBay Listings

moddict FZ-2F ALM Busy Circuits Fizzle Guts Clone Casio FZ-1

$600

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