I've been busy lately....

[Debby and Gene Stopp]

Hi DIY,

I don't get to post very often any more (babies, work, etc.) but I have some
spare time today and I thought I'd tell some DIY stories....

Even with babies around the DIY stuff never stops - it just slows way down.
I keep working on stuff, I know what to do next in a project, but the time
scale gets streched out. Happily, I just finished a new modular that I
started about a year and a half ago. It's in a big particle board cabinet
(painted black, like most of my stuff). This one is different than any of my
previous machines, in a couple ways:

1. It's all banana jacks
2. The panel graphics are black ink-jet printed on white paper, laminated in
clear plastic and glued to the panels

It consists of four panels, each about 12" by 16". Lower left is an
8-channel DAC with 8 gates, made from an AD7228 octal 8-bit DAC driven by
the parallel port of a 486 motherboard inside the cabinet. The floppy drive
sticks out the front. A sound card provides the MIDI in and out ports, and
the software is written by me to parse the MIDI data and drive the DAC
channels (or whatever else I want to do - it's open-ended at this time).
Right now it's just running my MIDI-to-CV program that provides CV, pitch
bend, mod amount, velocity, aftertouch, and three aux voltages. There's
jacks for the monitor/keyboard/mouse on the front as well. Also on this
panel are four VCA's, one ADSR, and a quad attenuator.

Upper left is an ASM-1.

Upper right is eight VCO/VCA pairs made from four partially-stuffed ASM-1
circuit boards. Under them is a CV mixer to control the pitch of the VCO's,
and a couple audio mixers for both the VCO's and the VCA's. Next is a quad
LFO, and next is a PAIA shepard function generator that I burned into an
Altera 7000 chip a while back.

Lower right is a quad bandpass VCF (in parallel), an Electronotes 4-pole
3080 filter, and an Electronotes Quasi-Digitial Bi-N-Tic filter. Lastly
there is a stereo 16-bit digital delay that I made from a Crystal ADC/DAC
chip set and some RAM, driven by a 4046 hi-freq. VCO. The remaining panel
space is an output mixer to 1/4" jacks and the power switch and LEDs.

Some day I'll scan up some pictures and put a web site up.

Next thing I did was to (finally) hack into my OB-8. I always wanted to add
something to this to make it more interesting, and also the keyboard had the
nasty habit of getting dirty rubber contacts if it sat for too long without
being played. Here's what's been done to it:

1. I took out the cheapo Panasonic rubber-contact keyboard and put in a nice
shiny Pratt & Read keyboard (the kind with the metal key rails and J-wire
contacts). I like the style of these old keybards, with their heavier
action. The new keyboard had a diode matrix already, so the existing 16-pin
ribbon cable plugged right into it (yay!). I had to drill a couple of holes
to fit it in. Now the key contact problem has completely disappeared, and
the keyboard has a much firmer and more substantial feel to it.

2. I did Juergen Haible's low end capacitor modification to beef up the
bass.

3. I added a noise level pot on the back (the noise level in the OB-8 is
either ON full blast or totally OFF). Now I can adjust the level when noise
is enabled.

4. I added a 2-foot long ribbon controller just above the keyboard, with a
range of about +/- 5 octaves. I used black rubberized anti-static bag
material for the resistive element, and a steel band about 1/4" wide for the
ribbon. I mounted a separate linear power supply inside the case so as not
to disturb the existing circuitry. The ribbon is buffered by a TL-082 which
simply goes straight to all 16 VCO's via a 100K 1% resistor added to each
VCO's summing node. There is no memory S/H cap, so the pitch is only
affected when you press on the ribbon. Autotune still works, as long as you
leave the ribbon alone during the tuning process. Now I can do CS-80 bends
and get the VCO's down to a couple of hertz. Cool. Killer OB-8 from hell.

Fun stuff, I thought I'd share it... now I have to find the time away from
the kids to make some sounds!

- Gene