AMSynths AM8125 (2014–2020)

A hand-built Eurorack VCO that clones the Roland System 100's VCO, with a few modern changes under the hood

Overview

Plug in the AMSynths AM8125 and you’re not just firing up a voltage-controlled oscillator—you’re booting a love letter to Roland’s late-’70s modular DNA. This isn’t some approximation or algorithmic emulation; it’s a surgical clone of the VCO from the Roland System 100M 120 dual oscillator module, the very circuit that powered the Jupiter-8, SH-2, and System 700. But AMSynths didn’t just photocopy the original. They rebuilt it with modern stability in mind, swapping out the unobtainable UA726 dual transistor for precision-matched SSM2210 or LS318 chips, upgrading voltage references, and refining the octave switching with 0.1% resistors. The result? A VCO that tracks across eight octaves like a metronome, but still breathes with that slightly wobbly, organic character that makes vintage Roland oscillators feel alive.

It isn't all nostalgia. The AM8125 drops the original's +/-10V reference for high-precision voltage regulators, and the frequency control circuit now uses a standard 1k tempco resistor. That makes calibration easier and long-term drift a non-issue. These fix real-world Roland quirks without dulling the edge. The waveforms are sawtooth, triangle, and PWM square. They are shaped with European transistors instead of the Japanese originals, but the topology is faithful down to the capacitor-based integrator core. It has both hard and soft sync, with a switch to toggle between them. Sync performance is rock-solid, and the waveform converters behave like their Roland ancestors: clean but never sterile, with enough character to cut through a dense patch.

Here's the catch: you only get one waveform output at a time. No simultaneous saw and square jacks. No dedicated triangle out. You pick the waveform with a switch on the front panel, and that's it. For some people that's a dealbreaker in a modular world where multing is second nature. For others it forces a commitment to one sound. The sawtooth has the slightly rounded, syrupy top end Roland is known for, the triangle is pure and smooth, and the PWM square goes from hollow to aggressive with a twist of the knob. No aliasing, no digital artifacts.

Specifications

Key Features

The Roland 100M Heart, Reborn

The AM8125 is a direct descendant of the Roland 100M 120. The original dual VCO module from 1979 was already a refinement of the System 700's design. The sawtooth core, based on a capacitor integrator and dual transistor pair, is the same architecture used in the Jupiter-8 and the SH-2. Vintage units could drift with temperature. The AM8125 uses modern matched transistors and precision references to stay locked in. The waveform converters are lifted from early Roland designs, so the square wave snaps and the triangle is free of the glitches that plague cheaper clones.

No Multing, No Problem

The AM8125 has a single-output design. You pick the waveform with a switch, and that's your voice. No stacking, no layering, no sending sawtooth to one filter and square to another. It seems limiting at first. The PWM is deep and responsive, with a CV input that lets you modulate the width from a hair's breadth to full pulse. The triangle is clean enough for FM, and the sawtooth has a slight softness on top that keeps it from getting shrill. When you want multiple waveforms, the answer isn't a mult - it's a second AM8125.

Sync That Actually Works

Sync is often an afterthought in VCO design. Here the AM8125 gives you both hard and soft sync, selectable via a front-panel switch, and both behave predictably. Hard sync locks the slave oscillator to the master's zero-crossing with a sharp reset, which suits aggressive, harmonically rich leads. Soft sync is more forgiving. It nudges the waveform instead of snapping it, which can create subtle phasing and animation without the harshness. Tracking under sync is stable, even across wide pitch sweeps, and the oscillator doesn't choke or drop octaves like some vintage designs.

Historical Context

The AM8125 arrived in 2014, as Eurorack was moving from boutique curiosity to mainstream. Most Roland-inspired modules at the time were either DIY kits or broad-stroke interpretations. AMSynths, run by designer Rob Keeble, went deeper, building exacting replicas of rare, sought-after circuits using original schematics. The AM8125 was a faithful but improved take on a VCO that had influenced decades of Roland synths but was nearly impossible to find in modular form. It wasn't competing with Doepfer or Intellijel on volume.

By 2020, Behringer had released its own System 100 clones, making the original modules more accessible. Keeble stated he had no plans to continue production of the AM8125. In forums like Muff Wiggler, owners praised its tracking, build quality, and "vintage" character, calling it "superb" and a "go-to oscillator." It never became common.

Collectibility & Value

Today the AM8125 is sought after by Roland purists and high-end Eurorack collectors. Production runs were reportedly as small as 10 units per batch, so finding one takes patience and luck. Most appear on Reverb or private forums, often priced between $400 and $600 depending on condition and included accessories. Units from the 2018 revision, which has updated control knobs, are slightly more desirable, though the circuit changes were minimal.

Failures are rare, and they're usually power-related. The module draws 60mA on +12V and 50mA on -12V, and a noisy or unstable power supply can cause drift or instability. The LED-lit slide pots hold up, but over time dust or oxidation can cause slight CV glitches. Contact cleaner fixes that. The biggest issue is availability. AMSynths ceased production and has no plans to resume, so every working unit is effectively irreplaceable. There are no service manuals publicly available, and spare parts like the custom front panel or matched transistor pairs aren't stocked.

Before purchasing, check that all waveforms are present and tracking accurately across octaves. Test both sync modes with a stable LFO or clock source. Verify that the PWM responds smoothly to CV and front-panel control. Make sure the power connector is intact. Some early units used a non-standard pinout, though later revisions standardized to the Eurorack norm.

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