[sdiy] Nonlinear Feedback Filter Testing

[Scott Gravenhorst]

I finally got to where I could plug a synth into it.
In my case, a FatMan.

Even without hooking up a CV (yet), I was able to 
get very interesting sounds.  Right now, I'm getting
an airy flute with a kind of attack chiff in the middle
to upper register.  The lower register sounds bassoon
like, reedy and resonant, also a bit brass like.  To be
sure, nothing like that ever came out of my FatMan
before.  I am driving it with the FatMan's main output,
not as a substitute filter.  This means that the synth's
amplitude dynamics are part of the chaos equations.  The 
FatMan is set up to do 2 saw waves, one an octave over 
the other, slightly detuned.

I also added a cutoff control and a triangle LFO.

http://home1.GTE.NET/res0658s/Electronics/nonlinear_filter.gif

is the most up to date schematic.  I am using nonlinear element
'C' with 1N4148 diodes and a 1K resistor.  So far, I like 
this one the best.  There seems (so far) little difference
soundwise between the ones I've tried.  This one works the
best for generating harmonics thru a wide range of input
conditions.

I'll be going to All Electronics tomorrow to look for
little hardware doodads for mounting and stuffing this
into the box.

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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