AMSynths AM8705 Dual ADSR (2011–2012)

A rare, hand-built homage to Roland’s System 700 envelope generator—slow to build, fast to disappear.

Overview

You don’t just patch the AM8705 Dual ADSR—you inherit a moment in synthesis history. This isn’t a generic envelope module; it’s a faithful, no-compromise replica of the Roland 705 envelope generator from the legendary System 700, a modular behemoth from 1976 that shaped the sound of electronic music in studios like BBC Radiophonic and Tangerine Dream’s private lairs. AMSynths didn’t just copy the circuit—they resurrected it, using the original design as a blueprint and upgrading only where reliability demanded it: 2N6027 unijunction transistors, TL072 op-amps, and USA-sourced 2N3904/6 transistors ensure the timing and response stay true without sacrificing modern build quality. The result? Two discrete, fully analog ADSR envelope generators that don’t just track—they breathe.

Each envelope delivers the classic Attack, Decay, Sustain, Release structure, but with a twist: the Sustain control doesn’t just set a level—it adjusts the target to which the Decay stage falls. That subtle distinction gives it a more organic, less rigid feel than many modern digital or semi-digital envelopes. You can trigger each ADSR via the 16-pin Doepfer bus or through external Gate inputs (GATE1 and GATE2), and there’s a satisfying red manual gate button that fires both envelopes simultaneously—perfect for testing patches or launching a sequence by hand. The front panel is a tactile delight: 30 mm travel slide potentiometers with custom-manufactured 2M log tapers give you smooth, precise control over each stage, and color-coded red and blue toggle switches (with matching caps) let you switch between two timing ranges: normal (up to 10 seconds) and fast (max 1 second). That dual-speed toggle is a game-changer—it means you can go from cinematic swells to snappy percussion without re-patching.

And then there’s the look. At 24HP wide, this is a statement piece. The panel is large, imposing, and built with a level of care that’s rare even in boutique Eurorack. Red and blue LEDs (for ADSR1 and ADSR2 gate status) add visual feedback without being flashy. But this module wasn’t built for show—it was built for sound and authenticity. It’s not just a tool; it’s a conversation with the past, wired into your rack.

Specifications

Key Features

Authentic Roland 705 Circuitry, Reborn

The AM8705 isn’t a reinterpretation—it’s a resurrection. Every stage of the envelope follows the original Roland 705 design, preserving the quirks and character that made those System 700 envelopes so sought after. The use of discrete transistors and UJTs (unijunction transistors) instead of modern IC-based timing circuits means the response is slightly non-linear, with a warmth and unpredictability that feels alive. When you tweak the Attack knob, you’re not just changing a voltage ramp—you’re adjusting a physical process that unfolds over time, complete with the slight drift and variation that analog components naturally exhibit. This isn’t sterile precision; it’s expressive, musical timing.

Dual Outputs for Flexible Patching

Each ADSR provides both positive and negative control voltage outputs, making it effortless to route the same envelope to multiple destinations—say, a VCF and a VCA—without needing a buffered multiple. The negative output is particularly useful for inverting modulation, creating reverse-filter effects or negative amplitude swells. It’s a small detail, but one that reflects the module’s design philosophy: serve the patch, not the interface.

Manual Gate and Visual Feedback

That red manual gate button isn’t just for show—it’s a practical tool for live performance and sound design. Want to test a filter sweep without a keyboard or sequencer? Press the button. Need to trigger both envelopes in sync for a layered effect? One press does it. The red and blue LEDs give immediate visual confirmation of gate activity, so you can see at a glance whether your envelopes are firing. In a dark studio or on a crowded rack, that feedback is invaluable.

Historical Context

The AM8705 exists because of a gap in the modern modular world: the absence of faithful, accessible recreations of classic analog envelope designs. In the early 2010s, Eurorack was expanding rapidly, but many modules prioritized novelty over heritage. Rob Keeble, the engineer behind AMSynths, had spent decades restoring and studying vintage gear—from the Minisonic 2 he built in 1975 to full Roland and ARP modular systems. When he founded AMSynths in late 2011, his goal was clear: build modules that honored the golden era of analog synthesis, not just imitate it. The AM8705 was one of the earliest products from that vision, arriving alongside the AM8109 JP-8 filter and the AM8060 Jupiter-6 filter. It wasn’t trying to compete with digital envelopes or complex DADSRs—it was offering something purer: the sound and feel of a 1970s Roland envelope, rebuilt for modern racks. At a time when many boutique manufacturers were chasing features, AMSynths was chasing authenticity.

Collectibility & Value

The AM8705 is a collector’s piece, not because it’s flashy, but because it’s rare. Only 18 units were produced between 2011 and 2012, and production ceased due to the labor-intensive build process—hard-wired LEDs and switches, a large and expensive front panel, and the need for custom slide pots made assembly slow and costly. Today, finding one for sale is uncommon, and when it does appear, prices reflect its scarcity. Expect to pay between $350 and $500 on the secondhand market, depending on condition. Units with "rack rash" or dim LEDs may go for less, but pristine examples with full brightness and original packaging can command premiums.

Buyers should inspect the slide pots for smooth operation—grittiness or dropouts indicate wear, and replacements are not standard parts. The custom 2M log pots are no longer in production, so sourcing spares could be difficult. The toggle switches and manual gate button should click cleanly; worn switches can lead to timing inconsistencies. Since the module uses discrete analog components, it’s generally reliable, but old solder joints or stress fractures from rack handling could cause intermittent issues. No firmware, no USB, no hidden failure points—just analog circuitry that either works or doesn’t. If it powers on and the envelopes trigger cleanly, it’s likely in good health.

That said, the AM8705 has been succeeded by the AM8142, a 16HP version redesigned for easier manufacturing and compatibility with AMSynths’ 100M series. The AM8142 retains the same core circuit and timing characteristics but uses a narrower panel and updated PCB layout. For most users, the AM8142 is the practical choice. But for purists and collectors, the AM8705 remains the original artifact—a hand-built homage to a golden age, now frozen in time.

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