Yamaha CS80

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, http://www.cs80.com/vco.html

Crow
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--- In yamahacs80@yahoogroups.com, The Old Crow <oldcrow@o...> wrote:
> 
>   The URL for the scope shots being, http://www.cs80.com/vco.html
> 

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

http://www.falstad.com/fourier/

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@yahoogroups.com, "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: 
http://home.debitel.net/user/jhaible/cs80_vco.gif.  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
/**/

On Fri, 27 Aug 2004, David Rogoff wrote:

> I just found this site: 
> http://home.debitel.net/user/jhaible/cs80_vco.gif.  Apparently, the 
> weird pulse is done on purpose!
> 
>  David