[sdiy] more on which VCO (low fi "electro" ones)

[Linium]

On Sunday 13 June 2004 00:10, Scott Gravenhorst wrote:
> If you look at VCOs that can track a CV, you'll find that they generally
> exist in two flavors: triangle and sawtooth.  They track a CV because they

I have yet to go in the "inside" of vco design, but i am following the recent 
discussions here, slowy accumulating informations. 
 
> have linear ramps.  It is this fact that makes them musically useful.  An
> example of a nonlinear VCO would be a multivibrator that uses a simple
> resistor to charge the integrating cap.  Here, you have an exponential
> curve instead of a ramp and while this will sound different from a ramp, it
> will not be musically useful in that it won't track the CV linearly.  In
> less than an octave it will be "out of tune" with a standard scale.
>
Aren't the OB8/X/Xa said to have unperfect saw wav, a little curved cause of 
the not linear charging ramp of the capacitors ? Would this explain the 
fattnes for wich they are reputed ?

> I think what you're after isn't really called "low-fi", rather you want is
> to screw up the waveform so that it's no longer a ramp or a triangle.  But
> you also want the sound's pitch to track a CV so that it's musically
> useful.  
I said "low-fi" because i like when the VCO drift, it sounds like "Board of 
Canada", like an old vynil or tape that suffered from time ;)
Well in fact i have built my own DAC for my soundcard, so now i can produce 
any DC voltage with 16 bits resolution and use my computer with Puredata to 
create an array that would store the voltage necessary to play any kind of 
detuned or not exactly exponential VCO core.
But in fact, detuned effect alone could be obtained with a simple modulator on 
a perfect VCO, just that if it is a tradoff for reviving some kind of ancient 
vco core technology i am ready to cope with it.  May be It offers more 
experimentation playground, the last thing would be that some weird VCO 
exist, possibly with funny or unusual, if not unconstant waveform along 
pitch, and that the sound is interesting enough :)

The way this is done in the modular world is to use a good VCO
> into waveshapers and filters.  Waveshapers come in many varieties and many
> members here have schematics for all kinds of them posted.  Hardsynch is
> another method for screwing up a waveform and maintaining musical
> usefulness and it sounds interesting.  Pulses and squares are easy to make
> with comparators and they sound characteristically buzzy.  Filters can then
> further contour the waveshape to give you an infinite variety of different
> timbres.
>
I have the Wavefolder from Oakley wich is a waveshapper, well i need to repair 
it since a long time, but then it will try it again.
Theses days i have been setting up a dual moog rogue VCO clone, and i 
experimented a little with sync, yes it is a nice effect (that i knew only in 
the digital world until this afternoon) to get buzzy screwy  fat tones. :)

Linium