AM8705 Dual ADSR


Roland 705 PCB

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 30 mm 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 three timed stages: Attack, Decay, Release. The Sustain control adjusts the level to which the Decay time reduces to. In the original the ADSR’s are triggered by an internal gate and trigger signal, or an external Gate signal.

The AM8705 can be triggered by an internal Gate signal on the 16-pin Doepfer bus or an external signal (GATE1, GATE2). The red push button (MANUAL GATE) gates both ADSR’s on together. The correct 2M log slide potentiometers were custom manufactured for this module.

AM8705 module 2011

The TIME toggle switch selects normal (max 10 seconds) timing and a shorter timing of 1 second maximum enables very 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).

Module Availability  The AM8705 was produced in small numbers (18x) in 2011, and was 24HP wide. Production ceased in 2012, mainly because it was time consuming to build with the hard wiring of the LED’s and switches. The panel was also large and expensive, but the electronics were perfect. The module was redesigned in 2018 with revised PCB’s, narrower 16HP front panel, slide switches, and PTL30 potentiometers, this will make the module cheaper to produce and enable a SDIY version.

In 2023 the module was further developed into the AM8142 to provide an accurate dual ADSR, with a 16HP panel compatible with our new range of 100M modules. The correct Attack time is retained by using custom manufactured 2M log slide pots (PTL30 with red LED’s).

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