AM8140 Dual ADSR

Overview This module is a replica of the envelope generator in the Roland 100M which I first built in 2009. It contains two traditional fast ADSR envelope generators that use transistors to switch between phases. This type of ADSR was widely available in the 1970’s in analog modular and mono synths. Each envelope outputs both a positive and negative control voltage, with the maximum output level is 7.5V.

EuroRack Module: 16HP wide
User Manual:  AM8140 User Manual

Description  The AM8140 contains two identical and independent envelope generators (one RED and one BLUE) with slide potentiometers controlling Attack, Decay, Sustain and Release. The potentiometer knobs are ARP style in BLUE and RED. The timing of the envelope generators can be individually switched using a front panel slide switch to normal (x1) and slow (x0.1), thereby giving a range of timings from 1 ms to 30 seconds. Each envelope generator can be gated on and off from:

  • The Doepfer power bus (connected to a MIDI CV module), this is common to both generators
  • Panel mounted momentary push buttons (RED and BLUE)
  • Gate 1 and 2 Input signals

Red and Blue LED indicators show when the respective gate signal is on for each ADSR.

Module Availability  The AM8140 was produced in small numbers in 2014. A revised version using PTL30 sliders was developed in 2018 but cancelled when Behringer introduced 100M replica modules in 2020. In 2023 AMSynths introduced the AM8141 ADSR and Gate Delay module based on the Roland 141 prototype module – more details are here.

B140 – Short Attack

Behringer 140 The Behringer version of the 140 is a single PCB with the hardware on the front and the electronic components on the rear, which makes it easier to service and modify. There are two ADSR envelope generators and a LFO. The timing in the Behringer user manual matches the Roland values, which are:

  • Attack Time – 1.5ms to 7.5s
  • Decay Time – 4ms to 15s
  • Release Time – 4ms to 15s

Actual attack times are slightly shorter (1ms and 7.2s), and the maximum attack voltage is slightly higher than the maximum sustain by about 100mV, which creates a “droop”. Behringer have used 500MA pots for the Attack and 1MA for Decay and Release. These are half the size of the originals, and the timing is increased accordingly by using a 4.7uF capacitor rather than 3.3uF. This should create faster timings than the original, the maths say 70% of the Roland module.

Unfortunately the attack curve of the B140 is incorrect, as pointed out by Tony Oakley on Modwiggler here. This affects the top portion of the attack curve and you can see it in the picture of the shortest attack, along with the “droop” via the decay phase onto a lower sustain voltage. Whilst this doesn’t look like much, in actual use the attack sounds sluggish, as the slope is coming in at a later point (80%).



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