AMSynths AM8120 (2023)
A Eurorack version of Roland's unreleased 1978 modular prototype - a VCF and VCA in one dense module
Overview
The AMSynths AM8120 is a Eurorack build of Roland's 100M 120 module, a concept Roland sketched out in 1978 but never brought to market. Take the guts of a Roland 121 filter and a 130 VCA and fuse them into one compact unit, and you're close. It put two essential voice-path elements together, and AMSynths has built it as the prototype was meant to be.
It fills a gap in the 100M lineup. The original System 100M offered discrete filter and VCA modules, but never combined them. The 120 prototype aimed to streamline the signal path, and AMSynths kept that intent while updating the build for modern reliability. The module uses a dual PCB layout. A front board handles the jacks and potentiometers, with SMD op-amps for CV mixing. A main board carries the analog parts: filter, VCA, and LED drivers. It's dense but not overcrowded, and the surface-mount components keep noise low.
The filter is based on the AS3109 OTA design and offers both 12dB and 24dB/octave slopes. Q compensation is handled by half of an AS662 OTA chip, same as the original 130 VCA. That means no volume drop as resonance climbs, and resonance can be modulated via CV. The filter is trimmed to just reach self-oscillation, which gives a clean sine wave without going unstable. It's not as gnarly as a Moog ladder or as plasticky as some later Roland filters. It sits in the clean-but-analog pocket of Roland's late '70s modular era.
The VCA uses the other half of the AS662 chip and offers both linear and exponential response modes. It's a no-frills, high-headroom amplifier that doesn't color the sound much, which suits the end of a signal chain. The VCF output is normalized into the first VCA input, so you can run the two in series with a single patch cable, or break the chain and use them independently. Normalization is often an afterthought in modern Eurorack.
Specifications
| Manufacturer | AMSynths |
| Production Years | 2023–present |
| Module Width | 16HP |
| Depth | 35mm |
| Current Draw | +12V: 40mA, -12V: 30mA |
| Filter Type | OTA-based 12dB and 24dB/octave low-pass |
| Filter Chip | AS3109 |
| VCA Type | OTA-based voltage-controlled amplifier |
| VCA Chip | AS662 (dual OTA, shared with Q compensation) |
| Q Compensation | Yes, via AS662 |
| Self-Oscillation | Yes, trimmed to threshold |
| VCA Response | Switchable linear and exponential |
| Normalization | VCF output to VCA input |
| Panel Material | Powder-coated aluminum, Pantone Mid Grey 5U |
| PCB Design | Dual PCB: front (jacks, pots) and main (circuitry) |
| Manual | Available as PDF from AMSynths website |
| Mounting Hole Spacing | Standard Eurorack 84HP compatible |
| Input Impedance | 100kΩ (audio), 10kΩ (CV) |
| Output Impedance | 600Ω |
| Weight | 280g |
Key Features
A Filter That Doesn’t Collapse at High Resonance
Vintage OTA filters tend to lose level as resonance increases, sometimes dramatically. The AM8120 handles this with active Q compensation, using the second half of the AS662 OTA. It's a dynamic correction that keeps output consistent across the whole resonance range. You can crank the resonance without riding the VCA or boosting downstream. CV control of resonance is normalized but can be overridden with a patch cable. Modulate it with an LFO or envelope and it responds smoothly, with no jumps or dropouts.
VCA with Dual Response and Smart Normalization
The VCA is a fully functional, high-fidelity amplifier with switchable response curves. Linear mode suits CV-controlled level changes like tremolo or ducking. Exponential suits envelope shaping, with a natural attack and decay curve. The normalization from VCF output to VCA input encourages a classic subtractive signal flow without locking you into it. Break the chain and you have two independent modules. Use it and you save a cable.
Build Quality That Feels Like a Restoration, Not a Reissue
The front panel is powder-coated aluminum with white silkscreening, designed in Front Panel Designer and refined in Illustrator for alignment. The potentiometers are smooth, the jacks are sturdy Neutrik clones, and the internal layout avoids spaghetti wiring. The SMD op-amps on the front board reduce noise and crosstalk, and the circuit uses modern equivalents where it matters, like the SSM2212 in the expo converter (though that's in their VCOs, not this module). It isn't "vintage accurate" in the sense of using 1978-spec components. It's "spiritually accurate," with the same sonic character and improved stability and reliability.
Historical Context
The late 1970s were a pivotal time for Roland. They had just launched the System 100, their first foray into modular synthesis, and were experimenting with new configurations. The 100M line was modular, semi-modular, and sometimes plain experimental, as the 111 (VCO + VCF) and 120 (VCF + VCA) prototypes show. They were attempts to rethink how a modular system could flow. The 120, in particular, felt like a bridge between the raw flexibility of modular and the streamlined design of what would become the Jupiter-4 and eventually the Jupiter-8.
But Roland never released the 120. Maybe they thought the market wanted discrete modules. Maybe the engineering wasn't quite there. It remained a footnote until AMSynths decided to finish the job. This isn't a clone of a mass-produced classic. It also stands in contrast to Behringer's 100M reissues, which are faithful but sometimes lack the refinement of the originals. The AM8120 improves on the prototype idea rather than just replicating it.
Collectibility & Value
As a modern module, the AM8120 isn't "vintage" in the traditional sense, but it's becoming a sought-after piece among 100M enthusiasts and Roland purists. It was released in 2023 in limited production runs, and while it's not rare yet, it's not on every rack. New units typically sell for around £280-£320 directly from AMSynths, depending on availability. On the secondhand market, prices hover in the £300-£350 range, with mint-condition units sometimes fetching more.
Maintenance is minimal. There are no known failure points beyond standard connector wear or potentiometer cleaning. The dual PCB design means more solder joints, but the build quality is high, and service technicians observe that failure rates are low. If you're buying used, check that the normalization works. Some early units had a jumper issue, but that was resolved in later batches. Also verify that the resonance CV input responds smoothly and that the VCA switches cleanly between linear and exponential modes.
For collectors, the AM8120 is a no-brainer if you're building a 100M-style system. For players, it's a versatile, reliable module that does two jobs well. It won't appeal to those who want aggressive distortion or extreme resonance, but it suits clean, musical filtering with a touch of vintage warmth.
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