AM8705 Dual ADSR


AM8705 Mark 1 module from 2011

Overview  This module is a Dual ADSR replica from the mighty Roland 700 modular analog synthesizer. The AM8705 contains two identical traditional ADSR format envelope generators with variable Attack, Decay, Sustain and Release. The module uses 30mm travel slide potentiometers and has toggle switches to switch between 2 different set of timings – slow or fast.

Description  The AM8705 follows the original circuit design with only a few upgrades: 2N6027 UJT, TL072 Op Amps and USA transistors (2N3904/6). The module contains two envelope generators each with 3 timed stages: Attack, Decay, Release. The Sustain control adjusts the level to which the Decay time reduces to. Both ADSR’s are triggered together by an internal gate signal from the standard Doepfer 16 pin bus, or a front panel push button (MANUAL GATE), or individually via a gate signal connected to the front panel Gate jacks (GATE1, GATE2).

The standard duration of each stage is 10 seconds, but each ADSR can be switched using the TIME toggle switch into a fast timing 1/10 the duration. This enables fast envelopes to be generated. Two identical control voltages are available for each ADSR, making it easy to patch an ADSR into both a VCF and VCA simultaneously.

There is a Red gate LED for ADSR1 and a Blue gate LED for ADSR2. The toggle switches have colour coded caps (Blue and Red) and the single gate switch is a Red push button.

Module Availability  The AM8705 was produced in small numbers (18x) in 2011, and was 24U wide. Production ceased in 2012,  mainly as it was time consuming to build this module with some hard wiring required of the LED’s and switches. The panel is also too large and expensive, but the electronics were perfect. The module is being redesigned in 2018 with revised PCB’s, 16U front panel and PTL potentiometers, this will make the module cheaper to produce and enable a SDIY version.

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