is an attack-decay or attack-release envelope generator.
I call it transient because I like that name. The design was
based on Ray Wilson's Retriggerable
AR Envelope Generator. I chose his design due to its
simplicity, and because it had the same features that I wanted. I have
redesigned some parts of the circuit, and added a few things. Both, the
trigger and gate inputs have schmitt trigger circuits added. The new
inputs are active at about +2V. The peak voltage is set at +5V. The
diodes in the attack and decay current paths have been replaced by
CD4066 bilateral switches. This removes the diode 'on' voltage at the
end of the decay stage. While the gate input is high and the attack
stage is finished, the output voltage is held at +5V by an additonal
switch. When the gate is removed, the decay stage starts immediately.
When the gate is non-existent, a trigger starts the transient in
'one-shot' mode. Then the decay stage starts as soon as the attack
stage is complete. The mode is chosen by using either the gate or
trigger input. Both inputs can be used at the same time to re-trigger
the transient if it is in the decay stage. LED indicators
are connected to each EG output. This design could easily be
converted into an ADSR. (see schematic below).
The prototype was built onto a circuit board made with a CNC milling
machine. I was able to build and test the design in an afternoon.
Initially, I blew a 4066 switch. This was caused by inadequate current
limiting at minimum attack or decay settings. I have seen some designs
not limit the current but in my case, the part was destroyed instantly.
I have now added 1K resistors in series with the attack and decay pots
to limit those currents. The maximum current through the attack
switches is about 12mA. That is beyond the data
sheet's spec, but it only happens for a very short time at the
beginning of the attack stage. If this is a concern, one could
use 1.5K resistors and the current would be kept within the
4066 maximum rating. I have also read that Fairchild 4066s have more
problems with this than other brands and that is what I was using.
Finished PCB minus 1M Spectrol Pots.
I am in the process of building a tripple version of this circuit. The PCB shown above was manufactured by CustomPCB.
I left off silkscreen and soldermask to save some money. I used mostly
surface mounted components. The
construction is on hold until my 1M Spectrol 149 potentiometers arrive
from mouser. They are non-stocked so I had to special order them.
AR/AD Transient Generator Schematic
(12-10-2005) - This schematic shows a single AR/AD circuit. The power
supply components and +5V regulator are shared with the other AR/AD
circuits in my tripple version.