AMSynths AM8105 Super-JX Filter & VCA (2015–2020)
A rare Eurorack module that brings the sound of Roland's late-'80s flagship synths to a modular case, using original IR3R05 chips pulled from decommissioned JX-10s and MKS-70s.
Overview
The AMSynths AM8105 is the actual filter and VCA circuit from the Roland JX-10 and MKS-70, moved into Eurorack format. It isn't a simulation, a behavioral model, or a clone built from modern equivalents. It's built around the genuine Roland IR3R05 analog IC, the same silicon that gave those synths their thick, rounded, almost vocal low-pass character. AMSynths launched it in 2015, using original parts scavenged from vintage gear before they vanished entirely.
The IR3R05 chip is the heart of the module. It turns up in only a handful of Roland's late analog/digital hybrids - the JX-8P, JX-10, MKS-70, and MKS-80 REV5. It 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 approximate the topology with discrete op-amps and OTAs. The AM8105 uses real, tested IR3R05 chips pulled from working vintage units. The filter response is smooth, musical, and slightly softer than the aggressive resonance of a Moog or the clinical precision of a SEM.
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, which makes it as much a preservation project as a commercial product. That exclusivity has made it a quiet legend among Eurorack collectors. It's not a "do-it-all" filter. There's no multimode switching, no digital control, and no CV attenuation on the front panel. It does one thing, and it sounds like a Super JX run through a modular rig.
Specifications
| Manufacturer | AMSynths |
| Production Years | 2015–2020 |
| Original Price | $230 USD |
| Filter Type | 24dB/octave Voltage-Controlled Low-Pass Filter (VCF) |
| High-Pass Filter | Fixed 12dB/octave |
| VCA Type | Linear Voltage-Controlled Amplifier |
| Core Chip | Roland IR3R05 (original, salvaged) |
| Resonance | Voltage-controlled, non-self-oscillating |
| CV Input | 1V/oct tracking (filter cutoff) |
| Audio Input | 1/4" and 3.5mm compatible (normalled) |
| Audio Output | 1/4" and 3.5mm compatible |
| CV Inputs | Cutoff, Resonance, VCA Level |
| Module Width | 14 HP |
| Depth | Approx. 40mm |
| Power Requirements | ±12V, 100mA total |
| Weight | 380g |
| Front Panel | Aluminum, black anodized with silk-screened labeling |
| Mounting | Standard Eurorack M3 screws |
| Production Run | Limited to 50 units |
| Status | Discontinued |
Key Features
The IR3R05 Chip: Analog Archaeology in a Module
The whole design hinges on the Roland IR3R05, a chip that never received a full public datasheet and is so tightly integrated that reverse-engineering it would be nearly futile. AMSynths didn't try. They sourced original chips from decommissioned JX-10s and MKS-70s, tested each one for performance, and wired them exactly as Roland did. So the filter keeps 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. Some might see that as a limitation, but in practice it prevents the harshness that can plague overdriven resonant filters. The tone is lush and forgiving, suited to pads, strings, and basses that need to sit deep in a mix.
Fixed High-Pass + Linear VCA: A Complete Tone Stack
Most Eurorack filters stop at the VCF. The AM8105 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 cleans up low-end mud, especially with external signals or layered oscillators. It rolls off below 100Hz. The linear VCA gives the module a full dynamic envelope path, so many patches don't need a separate VCA. Because it's linear rather than exponential, it responds more naturally to control voltages meant for amplitude shaping, which suits percussive plucks or clean amplitude sweeps. With low-pass, high-pass, and VCA together, 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. There are no knobs for input level, no resonance attenuation, and no mix controls. You get three CV inputs (cutoff, resonance, VCA level), an audio input, and an output. That means the module relies entirely on external modulation sources, which suits anyone who wants precise CV control without onboard offset tweaking. The audio input is normalled, so patching a cable breaks the default path and allows easy signal chaining. The build is industrial: thick aluminum panel, gold-plated jacks, and hand-soldered through-hole components. There's no digital firmware, no microcontroller, and no hidden menus. The signal path is analog from input to output.
Historical Context
The AM8105 appeared when Eurorack was shifting from boutique curiosity to mainstream synth culture. Around 2015, demand for authentic analog character was peaking, and manufacturers were cloning classic filters - Prophet, Moog, SEM, Oberheim. Others used modern equivalents or discrete rebuilds. AMSynths bet on scarcity and provenance. The IR3R05 had long been out of production, and Roland never released a datasheet, so it was a black box to most engineers. By sourcing original chips, AMSynths sidestepped the guesswork. The module isn't just inspired by the Super JX filter. It *is* the Super JX filter.
The JX-10 and MKS-70 were transitional machines, Roland's last stretch of true analog design before it moved fully to 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 that character without a 120-pound rack unit or the risk of 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.
Collectibility & Value
With only 50 units ever made, the AM8105 is one of the rarest production modules from any Eurorack manufacturer. It's also fragile in the long term. The IR3R05 chips 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. Replacements don't exist, so 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, and some sellers 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 tell genuine units from potential clones or counterfeits.
Buying advice is simple: test it thoroughly. Check the 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 crackling, distortion, or dropouts, which are 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, this isn't a module to "fix later." 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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