AMSynths AM8140 Dual ADSR (2014)
A transistor-switched dual envelope that copies the snappy character of the Roland 100M in a compact 16HP Eurorack module
Overview
The AM8140 is two ADSRs and a plain analog replica of the Roland 100M's envelope generator. It isn't a reinterpretation with digital smoothing or CV tricks. It's a clone for people who want that 1970s modular feel without hunting down a fragile vintage unit. Flip the front-panel toggle to "x1" and crank the attack, and the rise is sharp and immediate. There's no mush and no softening. Switch to "x0.1" and the timing slows by a factor of ten, which opens up long pads and ambient swells.
Each of the two envelope generators is color-coded red and blue. Each uses slide potentiometers (ARP-style knobs) for Attack, Decay, Sustain, and Release. The design is "less is more": no extra modulation inputs, no loop modes, no digital brains. It's just transistor-switched analog circuitry. You get two independent, high-impedance CV sources that output both positive and negative control voltages, peaking at 7.5V. With dual polarity you can modulate a VCF's cutoff and a VCA's level at the same time without an inverter. LED indicators show gate activity on each channel.
The AM8140 is only 16HP, but it has plenty of gate options. You can trigger via the Doepfer bus (if your system uses MIDI-to-CV), the front-panel momentary push buttons, or external gate inputs. That suits a live setup where you want manual control, or a sequenced patch driven by external timing. The module's roots in the Roland 100M go beyond looks. It uses the same transistor-based phase switching as the original, a design known for its reliability and musical timing. The envelope stages transition crisply, with no digital artifacts or microcontroller lag.
Specifications
| Manufacturer | AMSynths |
| Production Years | 2014 |
| Original Price | £125 GBP (approx $161 USD) |
| Module Width | 16HP |
| Power Supply | Eurorack standard ±12V |
| Envelope Type | ADSR (Attack, Decay, Sustain, Release) |
| Number of Envelopes | 2 (independent, identical) |
| Attack Range | 1 ms to 30 seconds (switchable x1 / x0.1) |
| Decay Range | 1 ms to 30 seconds (switchable x1 / x0.1) |
| Release Range | 1 ms to 30 seconds (switchable x1 / x0.1) |
| Sustain Control | Variable level (0 to max) |
| Output Voltage | ±7.5V maximum |
| Output Polarity | Positive and negative CV outputs per envelope |
| Gate Inputs | Gate 1, Gate 2 (3.5mm jacks) |
| Manual Trigger | Red and Blue momentary push buttons |
| Gate Source | External gate, manual button, or Doepfer bus |
| LED Indicators | Red and Blue LEDs for gate activity per envelope |
| Panel Style | Grey powder-coated with white silk-screen |
| Knobs | ARP-style slide potentiometers (red and blue) |
| Jack Type | Erthenvar 3.5mm sockets |
Key Features
Transistor-Switched Analog Design
The AM8140 uses no microcontrollers or digital logic to manage envelope stages. Discrete transistors switch between Attack, Decay, and Release phases, which mirrors the Roland 100M's original architecture. The envelope behaves like a true analog circuit: smooth, continuous, and with a slight organic variance that digital envelopes often lack. You can hear the slight imperfection in the curve, especially at short attack times, where it doesn't snap instantly but rises with a subtle warmth. Because it's built with fast-switching transistors, there's no latency or digital stepping, which suits percussive patches where timing is critical.
Switchable Timing Modes (x1 / x0.1)
One toggle switch per envelope shifts the timing range by a factor of ten - normal (x1) or slow (x0.1). In x1 mode, the AM8140 handles snappy plucks, tight basses, and fast staccato lines, with attack times as quick as 1 ms. In x0.1, releases stretch out to 30 seconds, good for slow filter sweeps or evolving drone textures. The switch preserves the curve, so the envelope's shape stays consistent across ranges. Budget envelope modules often distort the response when they scale, and this one doesn't.
Dual Polarity Outputs & Flexible Triggering
Each envelope provides both positive and negative CV outputs, which cuts down on external inverters. To open a filter while closing a VCA, patch both outputs directly. Triggering works through external gate inputs, manual buttons, or the Doepfer bus (for systems using MIDI-to-CV conversion), and all of them feed the same signal path. The manual buttons are firm and responsive, handy for live tweaking or testing patches without a sequencer. The red/blue LEDs show whether a gate signal arrived.
Historical Context
The AM8140 appeared in 2014, part of a wave of boutique Eurorack builders focused on analog accuracy. The Eurorack market was expanding rapidly at the time, but many modules leaned on digital convenience or cost-cutting analog designs. AMSynths, led by Rob Keeble, a seasoned engineer with deep roots in vintage synth restoration, took a different path: exact analog replication. The AM8140 was one of the first modules to faithfully recreate the Roland 100M's dual envelope generator, a module that powered countless late-'70s and early-'80s synth patches but had become rare and fragile. AMSynths cloned the transistor-based circuitry rather than approximating it with modern parts, so it behaved like the original. It wasn't the first dual ADSR on the market, but it was among the first to put timing accuracy and analog purity ahead of features. Its release coincided with a growing demand for "modular authenticity", a backlash against overly digital modules, and it earned respect in niche circles for getting the details right.
The 2014 run was small, in line with AMSynths' low-volume, hand-built approach. A revised version with PTL30 sliders was prototyped in 2018 but canceled in 2020 when Behringer released their own 100M series clones at a fraction of the price. The AM8140 still kept a loyal following among purists who valued its build quality and exacting design. The Behringer 140 uses different potentiometer values and altered timing curves. The AM8140 sticks to the original Roland specs as closely as possible within Eurorack's ±12V constraints.
Collectibility & Value
As of 2026, the AM8140 is sought after by collectors of boutique Eurorack gear, especially those focused on Roland 100M replication. Original units from the 2014 run are the only ones available, as no reissues followed the 2018 prototype's cancellation. Prices vary significantly by condition and provenance. A fully functional unit with clean sliders and no panel wear typically sells for $250 - $350 on the used market. Units with scratched panels or stiff sliders, common due to the age of the Erthenvar pots, can be found for $180 - $220, but they need servicing. The most common failure point is the slide potentiometers, which can develop crackling or dead zones after years of use. Contact cleaner sometimes helps, but full replacement is often necessary and can cost $60 - $80 in parts and labor. The Erthenvar jacks are sturdy, but their solder joints can fatigue if the module was frequently plugged/unplugged.
When buying, check both envelopes independently. Some units show timing drift between channels if one transistor has aged unevenly. Also verify that the x0.1 switch works correctly, since a faulty switch can limit the module to only fast or only slow timings. The original manual trigger buttons are mechanical and rarely fail, but make sure they click cleanly and reset without sticking. AMSynths kept limited records and didn't serialize modules, so provenance is hard to verify. Buy from trusted sellers or those who can demonstrate full functionality. For a 100M-style system, the AM8140 remains a better-timed alternative to the Behringer 140, especially for fast percussive work.
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