Update : dec. 31st, 2010

Envelope generator

ADSR

En français
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Description

This new version of the ADSR module provides a control voltage that makes possible shaping the envelope of a continuous sound. It is mainly used to control the gain of a VCA module or drive the cut off frequency of a VCF module. As usual it is not restricted to these two obvious applications and can be extended to the control of many others modules.
This module has a GATE input. The GATE signal determines the start and duration of the envelope signal. Four parameters can be set using potentiometers :

  • Attack duration : 1ms to 1s (short option) 5ms to 10s (long option)
  • Decay duration :  1ms to 1s (short option) 5ms to 10s (long option)
  • Sustain level : 0 to 10V
  • Release duration :  1ms to 1s (short option) 5ms to 10s (long option)
The direct ADSR signal is available on one output within 0 to 10V range and the inverted ADSR signal is available on a second output either within 0 to -10V range or 10V to 0V range.

A push button is available to manually generate a direct GATE signal. The intensity of the output signal can be visualised by means of a simple LED.

The power draw of this module is rather low : 10mA +15V rail, 3.6 mA -15V rail.

The heart of this circuit is based on an original idea by Jonathan Jacky (1980, see references at the end of this page).

The PCB provides jumpers to select the short ADSR versus long ADSR option (a DPDT switch can be added to toggle between).

Also, the power connector is now optional, it can be either a Synthesizers.com 6 pins MTA connector or a MOTM 4 pins MTA96 connector.
The module was designed to work with a +15V/0V/-15V PSU but can be used without modifications with a +12V/0V/-12V PSU, however the output levels will be lower (around 8V instead of 10V)

Schematic



The schematic of this module is rather simple and uses very common components. The 555 core of the schematic is based on an original idea by Jonathan Jacky  that was published in Electronics ("Two-chip generator shapes synthesizer's sounds" Electronics #11, September 1980 : 137-138). This core has inspired other DIYers (Tom G.-EFM, René Schmitz  ).

Q1 and Q2 operate as a Schmitt trigger and turn any input signal as a suitable GATE signal.
D1 protects the circuit from negative voltages. The trigger threshold is 2V. Diodes D2 to D4 are used to dispatch the charge and discharge current of the timing capacity C7/C8 (10µF/35V tantalum) through the potentiometers P1,P2 & P4. The 7555 chip (U1) is wired as a monostable timer. One OPA (TL074) is used to buffer the SUSTAIN voltage and avoids interference with the DECAY settings (otherwise the DECAY time would be affected by the SUSTAIN level). Two OPAs are used as a simple voltage follower and a voltage inverter, respectively. The fourth OPA drives the control LED.


Printed circuit board and component layout

PCB design



Component  layout




Download the schematic as a PDF file
Download the PCB as PDF file

Components and building guide

reference
value
quantity
U1
7555 (or any other CMOS version of the NE555, DO NOT USE A NE555 !)
1
U2
TL074
1
Q1, Q2, Q3
BC547C or equivalent (mind the pinout !)
3
D1,D2,D3,D4
1N4148
4
R1,R2,R8
10 ohms
3
R13,R16
100 ohms
2
R14
120 ohms
1
R15
680 ohms
1
R20,R21,R22
1K
3
R12
4.7K
1
R4
10K
1
R7,R9,R10,R11
22K
4
R5
47K
1
R18,R19
100K
2
R17*
150K* optional, sets the start level for inverted output (see text)
1
R6
1M
1
R3
1.2M
1
P1,P2,P3
1M log
3
P4
10k lin
1
C4,C5
10n polyester film
2
C3,C6
100nF ceramic or polyester film
3
C7
1µF 35V tantalum 1
C8
10µF 35V tantalum 1
C1,C2
22µF 35V polarised 2
LD1
LED, low current
1
JK1,JK2,JK3
female jack socket
3
SW1
push button (push to make)
1
R17 : sets the range of the inverted output, if you use a 150K for R17 the inverted output will start from 10V (quiet state) to 0V (full range). If you don't install R17 (leave its place empty) then the range will be 0V (quiet state) to -10V (full range).

Wiring


SHORT/LONG toggle switch option

Front panel
Panel design


Silkscreening


Download the silkscreen mask as a PDF file

Download the silkscreen mask as a JPEG file

Settings and trimming


This circuit does not require any trimming.

References

  • Randall Kirschman, Electronics, Jul.1980,
  • Jonathan Jacky, Electronics, Sept.1980,
  • Örley Gàbor, Electronic Design, Aug. 1980,


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