[sdiy] new guy - how did you start

[Cornutt, David K]

I had one of those Science Fair things too.  My dad got
me one when the first Shack opened here, I think in 1969.
Mine was a 50-in-1 box and the "feature" items in the
center were a galvometer and a solar cell.  (I don't think
they were putting ICs into any of them at this point.  I
do remember seeing the newer 100-in-1 ones several years
later and being jealous because they had an INTEGRATED
CIRCUIT!  What actually was that IC, anyway?  A 555?)

In college I got more seriously interested in circuits.
One of my required courses was a class in digital logic
design.  Because the 300-level class wasn't offered the
quarter that I wanted to take it, I took the 500-level
graduate class instead.  The instructor was an old pro 
from a local NASA contractor and the class rocked.  We 
got to play with 6809 proto kits and we built
all kinds of stuff out of TTL logic.  At that same time
I was working for a local company that built video equipment,
and that was where I learned to use a scope.  That encouraged
me to buy one of those Shack reverb kits with the SAD1024s.
Unfortunately, school eventually got to be a lot of work
and I never finished it.  (Several years later, as I was cleaning
stuff out in preparation for moving from Florida to New Jersey,
I found that board.  Five years of exposure to salt air had
corroded the PC board and the part leads badly.  I pitched the 
whole thing, including the 1024s.  Sigh.)

After college I moved to Florida and for a while I
was playing keyboards in a bar band.  (The Juno-106
I bought for that was my first keyboard; I still have
it and play it frequently.)  I also played a bit of
guitar and I wanted a way to make weird noises.  I
came up with the idea of using a logic inverter with
a Shottky input to wave-shape a guitar signal into a
square wave.  I rigged it up on a proto board with
C-cells for the power, a 741, TTL logic (!), voltage 
dividing resistors to center the signal around the TTL 
turn voltage, and non-polar caps to isolate the inputs 
and outputs.  The thing had no business actually 
working, but incredibly it did; it tracked the guitar
fairly well (notwithstanding the tendency to want to
jump to a harmonic as the note faded away, which was
actually kind of cool).  It lacked an envelope follower,
but when the guitar was silent the output went to a
constant logic state and the caps kept the DC out of
the output, so it would stay silent as long as one
didn't brush the strings.  By adding a binary counter
to the inverter's output, I could make it a sub-harmonic
generator (I selected the desired harmonic by moving a
wire on the proto board).  I ran the output through a
volume pedal so I could control the mix of direct and
synthesized signal.  It was actually fun to play, and
it produced effects kind of like a ring mod if you
played chords into it in just a certain way.  This was
the first really interesting and successful circuit I
ever came up with on my own.  In fact, lately I've been
thinking about building another, better one.

(But the band wouldn't let me bring it to a gig, lest
we get PBR bottles thrown at us. :-)