AMSynths AM8111 (2023–)

A Eurorack version of Roland's unbuilt 100M prototype, built with an SH-101 style oscillator and a Korg Monopoly style filter

Overview

The AM8111 is a module that never existed in 1978, now built 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. AMSynths didn't clone it. They took the triangle-core oscillator of the Roland SH-101 and paired it with the resonant ladder filter from the Korg Monopoly.

It's built around two modern Coolaudio chips: the V3340 VCO and the V2044A filter. Both are SMD parts, packed onto a compact PCB. The VCO gives you triangle, sawtooth and pulse waves, plus a dedicated sub oscillator output one octave down, feeding directly into the mix. The sub normalizes into the VCF's signal path, so you can layer it with the main waveforms. The filter is a transistor ladder design modeled after the SSM2044, with Q compensation to prevent volume drop at high resonance. Levels stay consistent even when you push the filter into self-oscillation.

The layout mirrors the Behringer 112 and 121 modules, so if you're coming from a modern 100M system, it slots right in. The illuminated slider pots handle cutoff and resonance. The resonance slider uses a reverse log taper, a trick taken from Roland's own 100M filter design. The normalization is simple: VCO outputs feed the VCF inputs, and the keyboard CV input routes to the filter's first CV input, so you get key tracking without patching.

Specifications

Key Features

SH-101 Heart, Monopoly Soul

The VCO is based on the Coolaudio V3340, a modern take on the CEM3340 chip that powered the SH-101. AMSynths used the Alfa Rpar tuning method, which adds extra trimmers and makes calibration easier and more stable. Development had hiccups. Early prototypes showed a glitch in the pulse wave around 40% width, where the leading edge would collapse. The fix was a hysteresis circuit inspired by the CEM3340 datasheet, with a 1.2MΩ feedback resistor and a 10kΩ buffer. It's a nerdy fix, but pulse waves now snap cleanly, even at extreme widths. The sub oscillator normalizes into the filter, so you get deeper timbres without a single patch cable.

Resonant Clarity with Q Compensation

The V2044A filter chip is where the Monopoly side comes in. Unlike the OTA-based filters in Roland's original 100M modules, this is a transistor ladder with built-in Q compensation, so resonance doesn't eat your signal level. The filter stays loud even when cranked. The resonance slider is inverted-log, mimicking Roland's original design for smoother control at lower settings. It self-oscillates cleanly from 16Hz to 20kHz, so it can act as a second oscillator when needed. A 3.3nF capacitor between the signal inputs adds a bit of high-end sheen, making the filter slightly brighter 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

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. It never went into production. The 112, with its dual oscillators and VCA, made it redundant. In 2022, AMSynths' Rob Keeble found photos of the prototype on Alex Ball's website. Instead of cloning it as-is, he asked what would happen if it had evolved. He 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 result was the AM8111. It arrived in a Eurorack market already saturated with 100M clones.

Collectibility & Value

The AM8111 isn't vintage yet, but it's already a sought-after upgrade for Behringer 100M owners. It's priced at £149 new, positioned as a premium alternative to the stock modules, and owners report it delivers. The build is solid, with all components surface-mounted and densely packed, which means repairs require SMD skill. Early units had pitch instability due to LED current draw on the +12V rail. That was resolved by switching control circuits to the +10V precision rail and using low-current LEDs. The VCO output levels are boosted to match the 100M's 10V p-p standard. Failures are rare, but the reliance on Coolaudio chips means long-term availability could be a concern. It's in production and selling quickly. Used units trade close to MSRP. Check for clean slider action and stable tuning across octaves.

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