AMSynths AM8171 (2024)
A modern Eurorack take on a forgotten Roland 100M sequencer switch—clean, precise, and built for rhythmic voltage choreography.
Overview
It doesn’t scream for attention like a screaming filter or a detuned oscillator stack, but the AM8171 Sequential Switch slips into your rack like a stagehand who knows every cue—quiet, essential, and absolutely irreplaceable once you’ve used it. This isn’t a throwback for nostalgia’s sake; it’s a surgical reimagining of the Roland 173 module from the System 100M, a rare bird that only saw a few hundred units made back in 1983 before Roland pulled the plug on the entire 100M line. The AM8171 resurrects that logic with modern reliability, fitting seamlessly into today’s Eurorack systems while staying true to the original’s function: routing control voltages or audio signals through four stages in sequence, advanced by a clock or trigger.
AMSynths didn’t just clone the circuit—they refined it. The original Roland 173 was part of the third and final wave of 100M modules, introduced just as analog modular was being steamrolled by the digital tsunami of the DX7 and D-50. It never got the chance to become a classic, but its design had promise: a quad analog switch that could step through stages with precision, useful for anything from rhythmic panning to morphing filter cutoffs or sequencing multiple oscillators. The AM8171 captures that potential and makes it accessible, not just as a historical curiosity but as a genuinely useful tool in modern patching workflows. It’s not flashy, but it’s the kind of module that changes how you think about movement in a patch—turning static sounds into evolving sequences with minimal effort.
Specifications
| Manufacturer | AMSynths |
| Production Years | 2024 |
| Original Price | £195 GBP |
| Module Format | Eurorack |
| Width | 12HP |
| Depth | 35mm |
| Current Draw +12V | 40mA |
| Current Draw -12V | 10mA |
| Inputs | 4x Signal Inputs, 1x Clock/Trigger Input, 1x Reset Input |
| Outputs | 1x Sequential Output, 1x Step Indicator Output (Gate per step) |
| Switching Type | Analog CMOS Switch |
| Control Voltage Range | 0–10V |
| Signal Type | DC-coupled (supports both CV and audio) |
| Stepping Modes | Forward only (sequential cycle) |
| Reset Function | Resets sequence to Step 1 on trigger |
| Step Indicator | Gate pulse per active step |
| Panel Material | Black anodized aluminum |
| Mounting Type | M3 screws, standard Eurorack |
Key Features
Four-Stage Analog Switching with Eurorack Integration
The AM8171 is built around a quad analog switch IC, faithfully replicating the signal routing behavior of the original Roland 173. Each of the four inputs can accept either control voltage or audio signals—this DC coupling is crucial, as it allows the module to sequence not just notes but modulation sources like LFOs, envelope shapes, or even sample-and-hold voltages. When clocked, the module steps through each input in order, sending the selected signal to the common output. It’s a simple concept, but in practice, it opens up complex modulation possibilities: imagine cycling through four different filter cutoff voltages on each beat, or rotating a panning control across four positions in a quadraphonic setup. The switching is clean and silent when used with CVs, and with audio, it delivers a crisp, glitch-free transition—no pops or clicks if your signals are DC-balanced.
Precision Clocking and Reset Control
Timing is everything in sequencing, and the AM8171 handles it with Eurorack-standard precision. The clock input accepts 5–10V trigger signals, making it compatible with most sequencers, drum modules, or LFOs. A dedicated reset input allows external control to force the sequence back to Step 1—handy for syncing to song position or restarting a pattern on the downbeat. The step indicator output sends a gate pulse corresponding to the active stage, which can be used to light LEDs (if panel-mounted) or trigger other events in your system, like activating a different effect on each step. This output turns the AM8171 into a kind of passive sequencer brain, capable of driving multiple processes in lockstep.
Compact and Reliable Modern Build
Where the original Roland 173 lived in a fragile, aging ecosystem, the AM8171 is built for the rigors of modern modular use. At 12HP wide and 35mm deep, it’s compact enough to fit in dense systems without hogging space. The circuit uses modern CMOS switching technology, which is more consistent and less prone to leakage than vintage discrete designs. Power draw is modest (40mA on +12V, 10mA on -12V), and the module is manufactured with attention to longevity—something AMSynths emphasizes across their lineup. The black anodized aluminum panel feels solid, with clearly labeled jacks and a layout that’s intuitive even at a glance. There’s no onboard clock source or direction control (it only steps forward), but that’s by design: this is a utility module, not a full sequencer, and its simplicity is part of its strength.
Historical Context
The AM8171 exists because the original Roland 173 never had the chance to matter. Released in 1983 as part of the final wave of System 100M modules, it arrived just as the music world was pivoting hard toward digital synthesis. The Yamaha DX7, Roland’s own D-50, and Korg’s M1 were rewriting the rules, offering preset-based, polyphonic sounds that modular systems couldn’t match in convenience. Roland discontinued the 100M line in 1984, leaving modules like the 173 as obscure footnotes. Few were made, fewer survived, and even fewer found their way into documented patches. But the concept—a simple, clocked analog switch—was sound. It filled a niche between passive switching and full sequencing, offering a way to automate signal routing without complex programming.
AMSynths, led by designer Rob Keeble, specializes in resurrecting these forgotten ideas with modern engineering. The AM8171 isn’t just a replica; it’s a refinement. Keeble’s background in vintage synth restoration and modular design (including work with Behringer on their 2600 and 2500 replicas) gives him a sharp eye for what works in practice, not just in theory. The AM8171 brings the 173’s functionality into the Eurorack era, where it finally has a home. It’s not trying to be a star—it’s a supporting player, but one that can elevate an entire performance with subtle, rhythmic motion.
Collectibility & Value
As a 2024 release, the AM8171 isn’t vintage in the traditional sense, but it’s already gaining traction among modular enthusiasts who appreciate its niche utility and historical lineage. New units sell for around £195 directly from AMSynths, and given the small production runs typical of the brand, resale prices on the used market could climb if demand outpaces availability. Condition is straightforward—being a modern module, there’s little to go wrong beyond damaged jacks or power issues from incorrect cabling. The CMOS switches are robust, but like any analog switch, they can degrade over decades if exposed to high-voltage or DC-offset signals. Buyers should check for consistent stepping and clean signal transfer across all four stages.
Failures are rare, but the most vulnerable points are the input protection circuitry and the clock/reset input conditioning. A malfunctioning clock input might ignore triggers or double-step, while a failed reset could leave the sequence stuck in a loop. These are typically repairable with basic soldering skills. For collectors of Roland 100M history, the AM8171 is one of the few ways to experience the 173’s functionality without hunting down a fragile, expensive original. It’s not a status symbol, but it’s a smart investment for anyone building a performance-oriented Eurorack system where precise, rhythmic modulation is key. If you’re after movement without complexity, this is the quiet engine that can drive it.
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