Multi Segment Envelope
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.
Schematic Files (pdf) includes 500-1008, 500-1072 and 500-1078
CAM Files (not yet)
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.
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.
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.
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.
Multi Segment Envelope Generator by James Patchell is licensed under a Creative Commons Attribution 4.0 International License.