AMSynths AM8705 Dual ADSR (2011–2012)
A rare, hand-built copy of Roland's System 700 envelope generator - slow to build, fast to disappear.
Overview
The AM8705 Dual ADSR is a faithful replica of the Roland 705 envelope generator from the System 700, a modular from 1976 that shaped the sound of electronic music in studios like BBC Radiophonic and Tangerine Dream's private lairs. AMSynths used the original design as a blueprint and changed only what reliability demanded. That means 2N6027 unijunction transistors, TL072 op-amps, and USA-sourced 2N3904/6 transistors, which keep the timing and response true to the original. The module holds two discrete, fully analog ADSR envelope generators.
Each envelope has the classic Attack, Decay, Sustain, Release structure, with one wrinkle. The Sustain control doesn't just set a level - it adjusts the target the Decay stage falls to. That gives it a more organic, less rigid feel than many modern digital or semi-digital envelopes. Each ADSR can be triggered from the 16-pin Doepfer bus or from external Gate inputs (GATE1 and GATE2). A red manual gate button fires both envelopes at once, handy for testing patches or starting a sequence by hand. The front panel has 30 mm travel slide potentiometers with custom-manufactured 2M log tapers. Color-coded red and blue toggle switches, with matching caps, select between two timing ranges: normal (up to 10 seconds) and fast (max 1 second). So you can go from slow swells to snappy percussion without re-patching.
The module is 24HP wide, and the panel is large. Red and blue LEDs show gate status for ADSR1 and ADSR2. The build is careful, even by boutique Eurorack standards, but it was made for sound first.
Specifications
| Manufacturer | AMSynths |
| Production Years | 2011–2012 |
| Original Price | $199 |
| Format | Eurorack |
| Width | 24HP |
| Depth | Not specified |
| Current Draw | Not specified |
| Number of Envelope Generators | 2 |
| Envelope Type | ADSR (Attack, Decay, Sustain, Release) |
| Trigger Sources | Internal (Doepfer bus), External Gate (GATE1, GATE2) |
| Manual Trigger | Red push button (triggers both ADSRs) |
| Timing Range | Normal (up to 10 seconds), Fast (up to 1 second) |
| Potentiometer Type | 30 mm travel, 2M log slide pots (custom manufactured) |
| Output | Positive and negative control voltage per ADSR |
| LED Indicators | Red (ADSR1 gate), Blue (ADSR2 gate) |
| Toggle Switches | Color-coded red and blue for timing selection |
| Based On | Roland 705 module (System 700) |
| Discontinued | Yes |
Key Features
Authentic Roland 705 Circuitry, Reborn
Every stage of the envelope follows the original Roland 705 design, quirks included, which is a big part of why those System 700 envelopes were so sought after. The module uses discrete transistors and UJTs (unijunction transistors) instead of modern IC-based timing circuits. The response is slightly non-linear as a result, with some unpredictability. Turn the Attack knob and you adjust a physical process that unfolds over time, with the slight drift and variation analog components naturally show.
Dual Outputs for Flexible Patching
Each ADSR gives both positive and negative control voltage outputs. You can send the same envelope to several destinations, say a VCF and a VCA, without a buffered multiple. The negative output is useful for inverting modulation, such as reverse-filter effects or negative amplitude swells.
Manual Gate and Visual Feedback
The red manual gate button is a practical tool for live performance and sound design. Press it to test a filter sweep without a keyboard or sequencer. One press triggers both envelopes in sync for a layered effect. The red and blue LEDs confirm gate activity at a glance, which helps in a dark studio or on a crowded rack.
Historical Context
The AM8705 came out of a gap in the modular market: few 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. He founded AMSynths in late 2011 with the goal of building modules that honored the golden era of analog synthesis. The AM8705 was one of the earliest products, arriving alongside the AM8109 JP-8 filter and the AM8060 Jupiter-6 filter. It wasn't meant to compete with digital envelopes or complex DADSRs. It offered the sound and feel of a 1970s Roland envelope, rebuilt for modern racks.
Collectibility & Value
The AM8705 is a collector's piece because it's rare. Only 18 units were produced between 2011 and 2012. Production ceased because the build was labor-intensive: hard-wired LEDs and switches, a large and expensive front panel, and custom slide pots made assembly slow and costly. Finding one for sale is uncommon, and prices reflect that. 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, and pristine examples with full brightness and original packaging can command premiums.
Check 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 spares could be hard to find. The toggle switches and manual gate button should click cleanly, since worn switches can cause timing inconsistencies. The module uses discrete analog components and is generally reliable, but old solder joints or stress fractures from rack handling could cause intermittent issues. There's no firmware and no USB, so it's analog circuitry that either works or doesn't. If it powers on and the envelopes trigger cleanly, it's likely in good health.
The AM8705 has been succeeded by the AM8142, a 16HP version redesigned for easier manufacturing and compatibility with AMSynths' 100M series. The AM8142 keeps the same core circuit and timing characteristics but uses a narrower panel and an updated PCB layout. For most users, the AM8142 is the practical choice.
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