The DDS AHDSR is a compact yet versatile envelope generator module designed for 5U systems. Besides the classic AHDSR envelope mode with internal Gate length selection (a ’la KORG MS-20), envelope amplitude and Decay/Release time CV modulation, the module also has a convenient AHD mode with envelope amplitude modulation, contiguous and gated Cycle mode. In both modes envelope curves can be standard Expo, Linear or Logarithmic.

Here’s a video that demonstrates some of DDS AHDSR envelopes:

Production PCBs:

Controls

Function of the 4 knobs depends on the Switch 1 position:

Center

• attack  time
• decay time
• sustain level
• release time

Up (HGAT)

• hold time
• gate time
• envelope amplitude modulation by CV
• decay/release time modulation by CV

Down (AHDA):

• attack time
• hold time
• decay time
• envelope amount modulation by CV

Switch 2

Controls envelope curve: exponential, linear and logarithmic.

Switch 3

Controls repeated mode: none, gated and contiguous.

Connections

GATE: note gate signal

TRIG: inverted note trigger signal

CV: control voltage input for envelope amplitude and Decay/Release time modulation

OUT: output control voltage

Technical characteristics

Envelope stage time: 1ms to 12 seconds

Input GATE/TRIG voltage: 0-5V or more

Input CV voltage: 0-5V

Output CV voltage: 0-5V (0-10V or -5+5V jumper selectable)

Power supply: +-12V or +-15V

Power supply current: +30mA/-5mA

Envelopes

Standard exponential:

 

Linear:

Logarithmic:

PCB description

The PCB is designed with some extras so that it could also be used for an advanced LFO project. For this reason it has one extra CV modulation input and two output LEDs, one for GATE and one for CV OUTPUT, both working in op amp feedback circuit to prevent clicking.

GATE: gate jack connector, normalled to ground

TRIG: trigger jack connector, normalled to +5V

GT/TR: gate and trig signals connector for chaining other AHDSR boards

CV1: primary CV input connector

CV2: secondary CV input connector

EXT1: first extension I/O port connector connected to PD0 (RXD) and LED op amp 1 input

EXT2: second extension I/O port connector connected to PD1 (TXD)

AVR_ISP: microcontroller flash programmer connector

+15V/GND/-15V: power connector (MOTM/Euro)

OFFSET: adding a jumper to this connector will offset output signal by -5V (for -5/+5V operation)

X2: adding a jumper to this connector will multiply output signal by 2 (for 0-10V operation)

CV_OUT: envelope CV output jack connector

LED1: first LED connector to blink with the GATE signal (optional)

LED2: second LED connector to blink with the CV OUT signal (optional)

DIY Resources

Bill of Materials

Schematics: xmod_sch

Eagle files: pcb_adsr

Firmware: xadsr_hex

Firmware source code: src_adsr

Front panel: xadsr_fpd

Ordering

To order DDS AHDSR, please send an email to pete at kvitek c o m specifying how many PCBs and pre-programmed MCUs you need, a country where to ship them, and an email address to send the PayPal invoice to.

Prices (US dollars):

• DDS AHDSR pcb $20
• Pre-programmed ATMega328p $10

California residents add 8.75% tax

Shipping:

• Continental USA — $5
• Canada – $10
• Europe, Asia and Australia  – $15

Please make sure your PayPal shipping address is correct!

Acknowledgements

This project was inspired by Electric Druid’s excellent VCADSR project and was built using Mutable Instruments wonderful AVR programming framework Avril. Front panel is created using Modular Synthesis 1U basic panel template.