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I decided to take the discrete VCO design I'd been leaving on the
project back-burner for a year or more and finish building the
prototype. It works, but it needs a little debugging, mostly in
stabilizing the frequency vs. power supply tolerances. When I get a
chance, I'll record the raw output of the VCO sawtooth waveform both
with and without the curious little one-shot pulse that is mixed into
the leading edge of each cycle. It is only 30 microseconds wide, but
it definitely makes an audible difference, and gives that signature
CS 'rasp' to the tone.

Here are some scope shots of the actual IG00153 VCO output to see
what I'm talking about. I'll add scope shots of my discrete VCO
later.

Crow
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The URL for the scope shots being,

Crow
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--- In yamahacs80@..., The Old Crow <oldcrow@o...> wrote:

The URL for the scope shots being,

Great stuff! I did a little web searching and found this page:



You can choose pre-defined waveforms or draw your own, either by
drawing the waveform or changing the levels of the harmonics. And
then you can hear the sound! As you'd expect (assuming you're into
fourier series and the math of music), the pulse on the sawtooth
increases the harmonics (brighter tone).

David

--- In yamahacs80@..., "Christopher_S_Rider"

with and without the curious little one-shot pulse that is mixed

into

the leading edge of each cycle. It is only 30 microseconds wide,

but

it definitely makes an audible difference, and gives that signature
CS 'rasp' to the tone.

I just found this site:
. Apparently, the
weird pulse is done on purpose!

David

Yes, I have that set of Yamaha engineering notes. In fact, that page
you indicated was my primary guideline for the discrete version. I think
the reset pulse is to guarantee a full waveform reset (full capacitor
recharge) at the higher frequencies such that the pitch doesn't start to
go flat.

That page also shows why tracking of the VCOs is such a pain; the
transposition setting resistor (Rft) has to be exact for each desired
octave, which is why there are trimmers for each one. If the Rft value
for a given octave is off even slightly, the tracking goes south.

I have my prototype CS VCO running into my production CS filter. It
sounds very nice. :) I'll record some audio clips this weekend.

In other news, I built and tested the NE11000 VC-BPF as used in the
GX-1, and it works great..except that I wired the resonance pot backward.
(The original NE11000 did not have a variable resonance control; it only
had a trimmer that was set and sealed for a Q of 4 or so).

Crow
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