AMSynths AM8120 VCF & VCA (2023–)
A Eurorack module that resurrects a Roland prototype that never made it out of 1978—now with Jupiter-8 filter DNA and Q compensation that actually works.
Overview
You know that feeling when you patch in a filter and the sound just settles, like it was always meant to be there? That’s the AM8120. It’s not flashy, not over-engineered—it’s a quiet powerhouse that does exactly what vintage Roland gear did best: stay out of the way and let the music happen. This module is AMSynths’ reimagining of the Roland 100M 120, a prototype that never saw production, combining the VCF from the 121 with the VCA from the 130. But AMSynths didn’t just clone it—they upgraded it. The filter now pulls from the Jupiter-8’s 24dB OTA design, and the Q compensation is implemented smartly using half of an AS662 OTA chip, so you don’t lose level as resonance climbs. That’s the kind of detail that separates a faithful homage from a museum piece.
At 16HP, it’s not the slimmest module on the rack, but it earns every millimeter. The front panel is powder-coated in a subtle Pantone Mid Grey 5U with crisp white silkscreen—minimalist, yes, but with a tactile presence that feels more boutique than budget. The slide pots for cutoff, resonance, and VCA gain have a smooth, deliberate action, and the green LED indicators under each give just enough feedback without screaming for attention. It’s a module that looks like it belongs next to a vintage Roland System 100M, but functions like a modern Eurorack citizen. The normalized connection between the VCF output and the first VCA input is a thoughtful touch—patch cables are minimized for basic use, but full flexibility remains for complex routing.
Sound-wise, it’s warm without being muddy, sharp without being brittle. The 24dB mode has that classic Roland growl—think Jupiter-8 basslines or SH-101 leads with a little extra throat—while the 12dB mode opens up for smoother, more organic textures. The VCA, pulled from the Roland 130, offers both linear and exponential response, giving you the precision of studio-level amplitude control or the punch of classic synth envelopes. It’s not a “character” module in the way some boutique filters are; it’s more like a trusted tool—reliable, consistent, and always ready to do the job.
Specifications
| Manufacturer | AMSynths |
| Production Years | 2023– |
| Original Price | £220 (assembled), £150 (kit) |
| Format | Eurorack |
| Width | 16HP |
| Depth | 35mm |
| Current Draw | 120mA @ +12V, 30mA @ -12V |
| VCF Type | OTA-based 24dB/oct low-pass, 12dB/oct selectable |
| VCF Modes | 12dB, 24dB |
| Resonance | Voltage-controlled, Q-compensated, self-oscillation at maximum |
| VCA Type | OTA-based, linear and exponential response |
| VCA Inputs | 3 audio inputs, 3 CV inputs |
| VCF Inputs | 3 audio inputs, 2 CV inputs for cutoff, 1 CV input for resonance |
| Outputs | 2x VCF outputs, 2x VCA outputs |
| Normalization | VCF output → first VCA audio input |
| Filter IC | AS3109 |
| VCA IC | AS662D (half used for VCA, half for Q compensation) |
| PCB Design | Dual PCB: front PCB for jacks and pots, main PCB for circuitry |
| Front Panel | Grey powder-coated aluminum, white silkscreen |
| Mounting | M3 screws, included |
Key Features
The Filter That Roland Never Made
The AM8120’s VCF is a hybrid of history and hindsight. While the original 100M 120 prototype used the 121’s filter, AMSynths opted to base theirs on the AS3109 chip found in the Jupiter-8, giving it a slightly more refined character. The 24dB/oct slope is thick and authoritative, capable of everything from rounded pads to snarling leads, while the 12dB mode offers a softer, more vintage-voice kind of warmth—perfect for emulating string machines or early analog polys. The real magic is in the Q compensation: instead of the usual volume drop that plagues OTA filters at high resonance, the AM8120 uses the second half of the AS662 OTA to actively compensate, keeping levels consistent. That means you can crank the resonance into self-oscillation without the sound disappearing or distorting unpredictably. It’s a subtle but critical upgrade that makes the module far more usable in live or mix contexts.
Two-in-One Efficiency Without Compromise
Combining a VCF and VCA in one module could’ve led to compromises, but AMSynths avoided them. The VCA is a direct replica of the Roland 130’s design, using half of the AS662 OTA chip, and it retains both linear and exponential response modes—rare in modern modules, where exponential is often the default. This duality means you can use it for precise amplitude shaping (linear) or classic synth envelope behavior (exponential), depending on your patch. The three audio inputs and three CV inputs per section offer serious routing flexibility, letting you mix multiple sources before filtering, or modulate the VCA with multiple envelopes or LFOs. The normalization from VCF out to VCA in is a smart default, reducing cable clutter for basic subtractive patches, but it’s easy to break if you want parallel or feedback routing.
Dual PCB Design for Reliability and Serviceability
Under the hood, the AM8120 uses a dual-PCB layout: the front board holds the jacks and slide pots, while the main board carries the core circuitry. This isn’t just for modularity—it makes servicing easier. If a jack gets loose or a pot wears out, you’re not desoldering through a dense main board. The use of SMD op-amps for signal and CV mixing keeps the front board compact, while the main board packs in the filter, VCA, and LED drivers with careful routing. The 80mm-wide PCB is densely populated with 1/8W resistors and SMD components, but the layout is clean and well-documented. Trimmers for signal and CV calibration are accessible via the front, though they require a small screwdriver—no need to disassemble the whole module for alignment.
Historical Context
The Roland 100M system was a modular dream in the late ’70s—compact, patchable, and designed for studio integration. But it never got the full expansion it deserved. The 120 module, a VCF/VCA combo, was prototyped in 1978 but never released. AMSynths didn’t just resurrect it—they reimagined it for a world where Eurorack dominates and Roland’s legacy is both revered and reverse-engineered. By pulling the filter design from the Jupiter-8, they sidestepped the limitation of the original 100M’s single filter type and gave users a more versatile tone-shaping tool. This isn’t nostalgia for nostalgia’s sake; it’s a thoughtful evolution. At a time when Behringer was reissuing the entire 100M line, AMSynths carved out a niche with modules that honor the past but improve on it—like adding Q compensation where Roland didn’t, or using modern components for better reliability.
The AM8120 also reflects a broader trend in Eurorack: the rise of “replicant” modules that blend accuracy with practicality. Unlike some clones that prioritize exact circuit replication at the expense of usability, the AM8120 makes smart concessions—like using the AS662D instead of the original BA662, which is harder to source. It’s a module for people who love Roland’s sound but don’t want to wrestle with 40-year-old engineering trade-offs. And in a market flooded with overdesigned filters, it’s refreshing to see a module that does two things very well instead of ten things passably.
Collectibility & Value
The AM8120 isn’t a vintage item yet, but it’s already a collector’s favorite among Roland purists and Eurorack minimalists. Assembled units typically sell for £220–£250, while the kit version goes for £150—reasonable for a dual-function module with this level of authenticity. Given AMSynths’ limited production runs and the module’s niche appeal, prices are likely to hold steady, if not appreciate slightly among synth historians. Condition matters: since it uses slide pots and SMD components, units with damaged sliders or cold solder joints can be a hassle to repair. Look for clean panels, smooth pot action, and consistent LED brightness.
Failures are rare but not unheard of. The most common issue reported is misalignment of the VCA’s linear and exponential modes—something that requires trimming the internal LIN1, LIN2, EXP1, and EXP2 trimmers. This isn’t user-serviceable without removing the panel, so buying from a trusted seller or testing before purchase is wise. The AS662 and AS3109 chips are still in production, so replacements aren’t a concern. For DIY builders, the kit is well-documented, but the SMD components on the main board demand decent soldering skills. If you’re not comfortable with fine-pitch work, stick to the pre-assembled version.
What makes the AM8120 a standout buy is its balance: it’s not just a Roland tribute, but a functional upgrade. If you’re building a Roland-heavy Eurorack system—especially with Behringer’s 100M modules—the AM8120 fills a gap they left open. It’s also a solid choice for anyone who values clean, musical filtering without the quirks of more esoteric designs. Just don’t expect miracles: it won’t scream like a Moog or swirl like a SEM. It’s Roland through and through—understated, reliable, and always in tune.
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