[sdiy] tony clark's 8 step envelope

[Tony Clark]

> http://www.wiseguysynth.com/larry/ahmw2004/14.jpg
> 
> This thing looks incredible. Any info on it Tony?

   Hi Mark,

   Sure, there's a bit of a write up on TGS here:

http://www.the-gas-station.com/messages.cfm?type=normal&thread_id=57125&lastdays=60&

   And also on my DIY web page:

http://www.physicsenterprises.andrews.edu/~clark/emusic/diy/

   But I'll repost here just so it's all in the archive...

   I call it the SVG, or Sequential Voltage Generator.  I designed it to 
be a full 8-stage envelope generator with individual time and level 
controls, but it does a few more things than that (more on that later).
   Pretty much every EG has two phases, the attack phase (when gated) and 
the release phase (when the gate is released), since the SVG can't really 
be discussed in the typical ADSR frame, I'll simply refer to either the 
attack phase or the release phase.
   First, the length (number of stages) is selectable (and CV controlled).  
It is marked by the RED led.  Also, the release stage is selectable 
(CV'd) and is marked by the YELLOW led.  The current active stage is 
marked by a GREEN led.  This alone allows you to set up any combination 
of attack and release stages.  You could define up to 7 attack and 1 
release stages, or 2 attack and 3 release stages, or any combination 
thereof.
   It operates pretty much like any EG.  When gated, it starts at stage 1 
and increments until it reaches the stage BEFORE the defined release 
stage.  It will sustain on this stage until the gate is released, at 
which point it will cycle the release stages until the End stage is 
reached.  As with most any EG, should you release the gate while in the 
attack phase, it automatically jumps to the release phase.  And it will 
also restart if gated during the release phase.
   Unlike most EGs, the end level does not have to be zero, so in order 
to facilitate the conventional start-from-zero, there is a reset mode.  
You can have the SVG reset on the attack phase, and also have it reset on 
the release phase.  This way the SVG can always start from zero, 
regardless of what the end stage is set to.
   The next fun feature is the loop modes.  You can loop either the 
attack or release phases (or both!).  In the EG mode, if the attack phase 
is set to loop and a gate is held, instead of sustaining at the last 
stage (before the defined release stage), it will loop back to stage 1 
and keep cycling until the gate is released.  If the release phase is set 
to loop, then once the gate is released, then that portion will 
continually loop until gated again.

   Trigger mode is similar to the EG mode except it is a one-shot and 
ignores the release phase.  If you pulse the SVG, it cycles from stage 1 
to the end stage.  If you keep it gated, it will loop.

   Sequencer mode is where things get a bit more interesting.  In this 
mode, the internal timing circuitry is separated from the panel speed 
controls, so that now the speed pots operate as lag!  But there's more!  
As with the trigger mode, the SVG ignores the release stage setting and 
runs from stage 1 to the defined end stage but does a continual loop.  
However, if you turn the loop modes on, then the release stage breaks up 
the SVG into two sequencer sections that can be toggled between by 
gating!
   The SVG also allows you to select between using the internal timing 
circuitry (and control it with a CV) or use an external clock to drive 
it.  If you use the internal clock and gate the external clock mode, you 
can use this to start and stop the SVG sequence.

   That's the basics.  There's more fun to be had though.  Since I 
included a common inputs to the level and speed circuitry, you can 
transpose the level and speed of the whole SVG.  It should also easily 
accept an audio signal into the level input so that you could use the SVG 
as a sequencable lag processor.  And once I have the expansion panel 
built, could also be used as a sequential switch.

   Speaking of expansion panels, I should note that there are so many 
connections and inputs built into the SVG that I am having to make an 
expansion panel to put all of the extra jacks onto! (things like 
individual stage level and speed inputs).  There are a total of 47 CV and 
18 gate inputs (distributed amongst the jacks, switches, and pots).  
Since I build everything to be CV and gate controlled, literally every 
feature on the SVG can be externally controlled, from the release and end 
stages, to gating the reset and loop modes.

   It's a beast of a module, and I'm still working some of the bugs out 
of the logic system.  For those of you who think I'm nuts already for 
using SMT, the SVG is controlled by good old 74xxx logic!  While it'd be 
fun to do this stuff with a microcontroller, you absolutely can NOT get 
better timing.  The only downside I've discovered is in power 
consumption.  Definately a cabinet warmer.  :)

   Anyhoo, that's pretty much it.  There's still some work to do, but it 
is a fun module.  I had loads of fun just setting it in sequencer mode 
and then driving the end stage with an S&H noise source.

   Another thing for anyone interested, it WILL work as a standard ADSR 
and only requires 3(!) of the 8 stages to do so.  Simply set END stage to 
3, Release stage to 3, set level stage 1 to max, set level stage 3 to 
min.  Stage 1 speed is attack, stage 2 speed is decay, stage 2 level is 
sustain, and stage 3 speed is release.

   Cheers,

   Tony

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