Multi Segment Envelope Generator

First Posted June 29, 2014
Updated July 2, 2014

This multi segment envelope generator is similar to one I did many years ago now.  The difference is that this one will only do 4 segments, mostly because I felt that was all that was needed.  And another difference, is due to advances in micro controllers, this one uses an ATmega328 for the logic rather than a 22V10 PAL.  The ATmega328 has many advantages over the 22V10.  Mostly the fact that it does not require an expensive programmer and the development software is FREE .  And it is very easy to change the code.

AVR Project

CAD Files

PCB files

Schematic Files (pdf) includes 500-1008, 500-1072 and 500-1078

CAM Files (not yet)

The most interesting feature of this circuit is the OTA.  Well, not really an OTA, it is what is known as a Blackmer VCA.  The one in this circuit is what I would call a degenerate Blackmer VCA.  It is only useful for circuits such as this because it will induce a lot of distortion into any signal you pass through it.  But, for an envelope generator, it is just perfect.  But why use it rather than a normal OTA?  Control feed through is close to being none existent for this type of ciruict.  Because if there was control feed through, the window comparator that determines when a segment is done most likely would not work.  In fact, I know it won't, because when I used a CA3280 as the control element, I discovered that I had nothing but trouble with control feed through.  Even using unmatched transistors is possible without much sacrifice in performance.

The micro controller that is one this board is the ATmega328.  The reason for this has to do with the fact that I want as few different parts floating around here as possible.  The first version of the code is about 325 bytes long, and there is 32000 bytes to put it in.  But hey, think of it as pleanty of room for future expansion.  There is also an ISP connector on the board so that it will be easier to change the code if desired.  There are many things that can be done in the code to customize how the module will function.

There are also two companion boards that can go along with this one.  The 500-1072, which has 4 jacks on it and is used to output the state of the EV cycle.  Normally, the release signal will be high.  Once triggered, the ATTACK, SEG1, SEG2, and back to RELEASE will go high in sequence.
Hey, where is the PICTURE?
The other companion board is the 500-1078, which has 3 pots and 3 jacks.  You don't need to use these boards, but the allow you to wire the module with just ribbon cables.

It gone JIM!

Creative Commons License
Multi Segment Envelope Generator by James Patchell is licensed under a Creative Commons Attribution 4.0 International License.