AMSynths AM8105 Super-JX Filter & VCA (2015–2020)

A rare Eurorack module that captures the elusive analog warmth of Roland’s late-’80s flagship synths—using original IR3R05 chips pulled from decommissioned JX-10s and MKS-70s.

Overview

Plugging in the AMSynths AM8105 feels like uncovering a secret passage into the heart of Roland’s Super JX architecture—one that most modular users never thought they’d walk. This isn’t a simulation, a behavioral model, or a chip-accurate clone built from modern equivalents. It’s the actual filter and VCA circuit from the Roland JX-10 and MKS-70, transplanted into Eurorack format, and centered around the genuine Roland IR3R05 analog IC—the same silicon that gave those synths their thick, rounded, almost vocal low-pass character. When AMSynths launched the AM8105 in 2015, they weren’t just offering a filter module; they were resuscitating a long-dead voice in a new body, using original parts scavenged from vintage gear before they vanished entirely.

The IR3R05 chip is the soul of the operation. Found in only a handful of Roland’s late analog/digital hybrids—the JX-8P, JX-10, MKS-70, and MKS-80 REV5—it’s a mixed-signal beast that combines a 24dB/octave voltage-controlled low-pass filter, a fixed 12dB/octave high-pass filter, and a linear VCA on a single die. That integration was rare at the time and is nearly impossible to replicate authentically today. Most clones have to approximate the topology using discrete op-amps and OTAs, but the AM8105 avoids that compromise by using real, tested IR3R05 chips pulled from working vintage units. The result is a filter response that’s smooth, musical, and slightly softer than the aggressive resonance of a Moog or the clinical precision of a SEM—more like a warm blanket than a laser beam.

What makes the AM8105 special isn’t just its sound, but its scarcity. AMSynths didn’t mass-produce this module. Documentation and vendor listings confirm it was limited to a single production run of just 50 units. Each one was hand-assembled in the UK using original Roland chips, making it as much a preservation project as a commercial product. That exclusivity has turned it into a quiet legend among Eurorack collectors who prize authenticity over convenience. It’s not a “do-it-all” filter—no multimode switching, no digital control, no CV attenuation on the front panel—but it does one thing with uncompromising fidelity: it sounds exactly like a Super JX breathing through a modular rig.

Specifications

Key Features

The IR3R05 Chip: Analog Archaeology in a Module

The AM8105’s entire design hinges on the Roland IR3R05—a chip so obscure it never received a full public datasheet, and so tightly integrated that reverse-engineering it would be nearly futile. AMSynths didn’t try. Instead, they sourced original chips from decommissioned JX-10s and MKS-70s, tested each one for performance, and wired them exactly as Roland did. This means the filter retains the subtle nonlinearities, the gentle roll-off above 10kHz, and the way resonance increases warmth without turning brittle. Unlike later Roland chips that leaned digital, the IR3R05 is fully analog in the signal path, with OTA-based filtering and discrete VCA circuitry. It doesn’t self-oscillate, which some might see as a limitation, but in practice, it prevents the harshness that can plague overdriven resonant filters. The result is a tone that’s lush and forgiving—ideal for pads, strings, and basses that need to sit deep in a mix without fighting for space.

Fixed High-Pass + Linear VCA: A Complete Tone Stack

What sets the AM8105 apart from most Eurorack filters is that it doesn’t stop at the VCF. It includes the full tone-shaping chain from the original Super JX: a fixed 12dB/oct high-pass filter and a linear VCA, both fed from the same IR3R05 die. The high-pass isn’t voltage-controlled, but it’s essential for cleaning up low-end mud—especially when processing external signals or layered oscillators. It rolls off below 100Hz in a way that feels surgical without being clinical. The linear VCA, meanwhile, gives the module a full dynamic envelope path, eliminating the need for a separate VCA in many patches. Because it’s linear rather than exponential, it responds more naturally to control voltages meant for amplitude shaping, making it excellent for percussive plucks or clean amplitude sweeps. The integration of all three functions—low-pass, high-pass, and VCA—means the AM8105 can act as a complete voice processor in a single 14HP space.

Authentic Signal Path, Minimal Interface

AMSynths kept the front panel sparse by design. There are no knobs for input level, no resonance attenuation, no mix controls. What you get are three CV inputs (cutoff, resonance, VCA level), an audio input, and an output. This minimalism forces the user to treat the AM8105 like a component in a larger system, not a standalone effect. The lack of panel controls means it relies entirely on external modulation sources—ideal for modular purists who want precise CV control without onboard offset tweaking. The audio input is normalled, so patching a cable breaks the default path, allowing for easy signal chaining. The build quality is industrial: thick aluminum panel, gold-plated jacks, and hand-soldered through-hole components. There’s no digital firmware, no microcontroller, no hidden menus—just pure analog signal flow from input to output.

Historical Context

The AM8105 emerged at a time when Eurorack was shifting from boutique curiosity to mainstream synth culture. Around 2015, demand for authentic analog character was peaking, and manufacturers were racing to clone classic filters—Prophet, Moog, SEM, Oberheim. But few were willing to go as far as AMSynths in pursuit of authenticity. While others used modern equivalents or discrete rebuilds, AMSynths bet on scarcity and provenance. The IR3R05 chip had long been out of production, and Roland never released a datasheet, making it a black box to most engineers. By sourcing original chips, AMSynths sidestepped the guesswork and delivered a module that wasn’t just inspired by the Super JX—it *was* the Super JX filter, reborn.

The JX-10 and MKS-70 themselves were transitional machines—Roland’s last gasp of true analog design before fully embracing digital synthesis. They were overshadowed by the Jupiter-8 and later the D-50, but they had a devoted following for their smooth, polished sound. The AM8105 gave modular users access to that character without needing to lug around a 120-pound rack unit or risk damaging a vintage keyboard. It also arrived as the DIY and “skiff-friendly” movement was gaining steam, and AMSynths positioned it as a premium, limited-run alternative to mass-market clones. Its release coincided with a broader trend of “analog archaeology”—reclaiming lost circuits from dead synths—and it became a benchmark for how far a clone could go in capturing the soul of its source.

Collectibility & Value

With only 50 units ever made, the AM8105 is one of the rarest production modules from any Eurorack manufacturer. It’s not just scarce—it’s fragile in the long term. The IR3R05 chips, while robust in their original context, were never designed for the higher current loads or extended voltage swings common in modular systems. Service technicians observe that prolonged exposure to overvoltage CV or hot-plugging can degrade the chip’s performance, leading to increased noise, loss of resonance, or complete failure. Because replacements don’t exist, a dead IR3R05 means the module is effectively unsalvageable. There are no known modern equivalents, and no PCB redesigns from AMSynths.

On the secondhand market, the AM8105 trades quietly but at a steep premium. Units in working condition typically sell between $800 and $1,200, depending on provenance and included documentation. Those with original packaging or test reports from AMSynths’ build batch can fetch even more. Collectors prioritize units with verified chip history—some sellers even provide photos of the chip’s date code or test readings. Because the module was hand-built, there are minor variations in soldering and labeling, which enthusiasts use to authenticate genuine units versus potential clones or counterfeits.

Buying advice is simple: test it thoroughly. Check for noise floor on the output with no input, verify 1V/oct tracking across the range, and test resonance response at different cutoff points. Listen for any crackling, distortion, or dropouts—signs of a failing chip. Avoid units that have been modified or repowered, as the IR3R05 is sensitive to power rail stability. Given its irreplaceable core, the AM8105 isn’t a module to “fix later.” It’s a museum-grade artifact that demands respect—and if you find one that works, treat it like a vintage microphone or a NOS tube: use it sparingly, power it cleanly, and never hot-swap cables.

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