AMSynths AM8111 (2023–)

A Eurorack resurrection of Roland’s forgotten 100M prototype, reimagined with SH-101 grit and Monopoly warmth

Overview

You can almost hear the ghost of 1978 in the AM8111—a module that never was, now reborn in 16HP of modern Eurorack. Roland’s System 100M launched with a handful of core modules, but one prototype—the 111, combining VCO and VCF—never made it past the drawing board. A few hand-built units exist, relics of a road not taken. AMSynths didn’t just replicate it; they rewrote its DNA. Instead of cloning the original’s likely design, they fused the punchy triangle-core oscillator of the Roland SH-101 with the rich, resonant ladder filter from the Korg Monopoly. The result? A hybrid that feels both nostalgic and startlingly fresh—like finding a lost sketch from a legendary artist and finishing it in your own hand.

This isn’t a museum piece. It’s a working musician’s tool, built around two modern Coolaudio chips: the V3340 VCO and the V2044A filter, both SMD-based and densely packed onto a compact PCB. The VCO delivers the expected trio of triangle, sawtooth, and pulse waves, but with a twist: a dedicated sub oscillator output, one octave down, feeding directly into the mix. That sub isn’t just for beef—it normalizes into the VCF’s signal path, letting you layer it with the main waveforms for thick, harmonically rich tones right out of the gate. The filter, meanwhile, is a transistor ladder design modeled after the SSM2044, complete with Q compensation to prevent volume drop at high resonance—a thoughtful touch that keeps levels consistent even when you’re pushing the filter into self-oscillation.

What makes the AM8111 feel so immediate is its layout. It mirrors the Behringer 112 and 121 modules, so if you’re coming from a modern 100M system, it slots in like a factory upgrade. The illuminated slider pots for cutoff and resonance aren’t just pretty—they’re functional, with the resonance slider using a reverse log taper, a trick lifted straight from Roland’s own 100M filter design. The normalization scheme is smart: VCO outputs feed the VCF inputs, and the keyboard CV input routes to the filter’s first CV input, enabling key tracking without patching. It’s the kind of thoughtful integration that turns a module from a collection of circuits into a cohesive voice.

Specifications

Key Features

SH-101 Heart, Monopoly Soul

The AM8111’s VCO is based on the Coolaudio V3340, a modern reimagining of the CEM3340 chip that powered the SH-101. But AMSynths didn’t just drop it in—they refined it. The Alfa Rpar tuning method adds extra trimmers for precision, making calibration easier and more stable. There were hiccups in development: early prototypes showed a glitch in the pulse wave around 40% width, where the leading edge would collapse. The fix? A hysteresis circuit inspired by the CEM3340 datasheet, with a 1.2MΩ feedback resistor and a 10kΩ buffer. It’s a nerdy fix, but it works—pulse waves now snap cleanly, even at extreme widths. The sub oscillator isn’t an afterthought; it’s a core part of the voice, normalizing into the filter and giving you instant access to deeper, more complex timbres without a single patch cable.

Resonant Clarity with Q Compensation

The V2044A filter chip is where the Monopoly’s spirit lives. Unlike the OTA-based filters in Roland’s original 100M modules, this is a transistor ladder with built-in Q compensation—meaning resonance doesn’t eat your signal level. In practice, that translates to a filter that stays loud and present even when cranked, perfect for sweeping leads or aggressive resonance effects. The resonance slider is inverted-log, mimicking Roland’s original design for smoother control at lower settings. And yes, it self-oscillates cleanly from 16Hz to 20kHz, making it a second oscillator when needed. A 3.3nF capacitor between the signal inputs adds a subtle high-end sheen, giving the filter a slightly brighter character than the original SSM2044.

Smart Normalization and Real-World Integration

The AM8111 doesn’t just fit into a 100M system—it enhances it. The VCO’s three waveforms and sub output normalize to the VCF’s three inputs, letting you mix and match waveforms directly into the filter. The keyboard CV input normalizes to the filter’s first CV input, enabling key tracking by default. A slide switch lets you invert the third CV input’s polarity—crucial when patching in an ADSR with negative output. And the LED driver, while simplified from Roland’s original transistor-based circuit, uses low-current LEDs to avoid pulling down the +12V rail, which early prototypes showed could destabilize pitch. It’s these small, hard-won refinements that turn a good module into a reliable one.

Historical Context

The AM8111 is a ghost story. In 1978, Roland introduced the System 100M with eight modules, including the dual VCO 112 and the VCO/VCF/VCA combo 110. The 111 was meant to be a middle ground—a single VCO paired with a filter, possibly even a VCF-only variant. But it never went into production. The 112, with its dual oscillators and VCA, made it redundant. Fast forward to 2022, when AMSynths’ Rob Keeble stumbled upon photos of the prototype on Alex Ball’s website. Instead of cloning it as-is, he asked: what if it had evolved? What if it borrowed the SH-101’s oscillator—Roland’s most accessible monosynth—and paired it with the filter from Korg’s Monopoly, a synth known for its warm, vocal character? The answer was the AM8111: not a replica, but a reimagining. It arrived in a Eurorack landscape already saturated with 100M clones, yet stood out by offering something the originals never did—a hybrid voice with modern stability and deeper sonic character.

Collectibility & Value

The AM8111 isn’t vintage—yet—but it’s already a sought-after upgrade for Behringer 100M owners. Priced at £149 new, it’s positioned as a premium alternative to the stock modules, and owners report it delivers. The build quality is solid, with all components surface-mounted and densely packed, but that also means repairs require SMD skill. Common issues are minimal: early units had pitch instability due to LED current draw on the +12V rail, but this was resolved by switching control circuits to the +10V precision rail and using low-current LEDs. The VCO output levels are boosted to match 100M’s 10V p-p standard, so integration is seamless. Failures are rare, but the module’s reliance on Coolaudio chips means long-term availability could be a concern. For now, it’s in production and selling quickly—so if you see one, grab it. Used units trade close to MSRP, reflecting its reputation as a “must-have” for 100M builders. Check for clean slider action and stable tuning across octaves; if it holds pitch and the LEDs respond correctly, you’ve got a good one.

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