Various Topics

[Stopp,Gene]

Hi DIY,

First of all, thanks to Rick Jansen for keeping this list going! Thanks,
Rick!

Here's a few topics that may be of interest:

Regarding the gate input to the ASM-1 envelope generators - I have
discovered that the input structure of the ASM-1 envelope generators
does not handle negative voltages. This is something that I should have
thought of but apparently overlooked at design time. I found this out
when as I was bringing up another ASM for the first time - I was trying
to trigger the envelopes with the LFO in order to adjust the trimpots,
and they did not trigger! A quick look in the databook for the LM358
verified that the input voltage should not go below ground when the chip
is powered by a single supply. To overcome this, it is easy to add a
diode in series to the gate input (cathode towards the chip input) to
block negative voltages. Once I did this, the EG's triggered fine using
a bipolar waveform.

Regarding new project ideas -

I have had an idea for some time (ever since I visited Kevin Lightner's
house last year, in fact) to build some kind of EPROM wavetable VCO. I
have the ability to program EPROM's in the lab (yes I have a new job)
and so I was pondering the various ways of loading data into the EPROM.
I figured that if I could find the download protocol description for the
Data I/O programmer (i.e. file formats), then I could write a PC program
to create the wavetable data using various algorithms. Then I had
another idea - what if I could figure out the file format of sound
files, such as .WAV files, and then write a program to translate the
wave data from that file format into a format that can be understood by
the EPROM programmer? I found the Data I/O programmer reference
document, with all of the file formats described. Step one complete. I
then searched the web for .WAV file format descriptions, and found that.
Step two complete. Then I wrote a simple program to display the contents
of .WAV files. This worked fine, and I now have all of the raw data I
need to write a program to do the file conversion from .WAV to EPROM
data. This is as far as I have gotten.

A wavetable VCO sounds like a fun idea, since the analog portion (the
clock VCO) can be made from the basic Electronotes sawtooth VCO such as
the one used in the ASM-1. This means that the VCO can have a very wide
range (down to sub-audio) with all of the advantages of continuous sweep
(modulation, portamento, all that fun stuff). Now I just need to build a
small test bed, consisting of a ZIP socket for the EPROM plus some
address counters. It may be a good idea to add an option to split the
counter into two counter groups, the least significant addresses used to
produce the audio waveform and the most significant addresses to be
clocked slower in order to scan through the wavetable for harmonic
changes. Further fun could be had by adding bit switches between the
EPROM data lines and the DAC to allow the user to "grunge up" the
waveform by reducing the bit resolution.

Although the scanning EPROM idea has been around for a while, the
ability to load my own sounds into the EPROM by recording them on my
PC's sound card has suddenly made this an idea that may just be worth
pursuing. Maybe this idea can start a conversation on the DIY list?

I have reported on the success of my home-built 8-CV/8-Gate MIDI-CV
converter using an IBM PC parallel port with the Analog Devices 7228
DAC. This is such a great device - I encourage anybody out there who
really wants to have the satisfaction of building the hardware plus the
fun of writing various algorithms to control the DAC outputs to try
this. It's really not hard to figure out the code, and you can literally
control *any* modular parameter with *any* MIDI message. No limit to the
fun here!

Regarding MIDI-CV converters that are easier to implement - I had
purchased several of Kyle Jarger's JKJ CV-1 converters a while back, and
they are starting to show up in my DIY projects. These units are the
circuit boards taken out of their enclosures and built into my machines
and powered from the system power supplies rather than the normal power
cube. I must say that these converters are *excellent* - very nice
LFO's, MIDI sync, and smooooth curves on bend and portamento. Not the
cheapest, but not the most expensive either. They make the synths sound
like there is an actual person playing an actual monophonic keyboard,
with wheels and all.

That's it for now, looking forward to a new era in DIY to go with the
new server.....

 - Gene