Greating good fellows,
my name is Ewen Cousin. I’m pro trumpeter and keyboardist from Nantes (France).
I made this thread advised by Sam. He told me that it would be the best to share what I’ve got.
So, let’s go! (or skip to the figure, it’s self-speaking).
I made several VCO based on the Sam’s schematics and Kerry D. Wong. Firstly with a 3904, and at last with a S9018 (easier cause the the 9V supply needed).
At some point, I decided to take measurments with different capacitors (from nF to kF), in order to know what’s ambitus I got according to the capacity I used.
I measured with a specter analyser from Max MSP (checked by ears). And also with a metronome for very low frequency (then in BPM…).
The measures are a bit sloppy of couse, “handmade”.
BUT! accurate enough to show good regular exponential curves both for minimum and maximum frequency.
And then I could apply a model with exponential regressions for both curves.
Thanks to that model, you’ll be able to know from a any capacitor you got what is its range (ambitus), and can facilitate the design for a VCO with a switch between differents ranges of pitch (like f.i. in the VCO 2 of the minibrute 2).
Here are the results (pyplot)
Hope you’ll find it useful.
