Quadrature VCO schematic posted

[Chris MacDonald]

Hi Magnus!

> Ah, nice. But being a bit picky, this is just an quadrature
> oscillator core, but I don't see any CV input. I personally see
> exactly what treatment which would be appropriate to have a CV input,
> but for other less oriented in the field would be confused by having
> this called an "VCO".

I see what you are saying, I just thought that the inclusion of the
frequency potentiometer at the top of the drawing was enough to suggest
"VCOness".  I have amended the drawing and link to say "Variable
Frequency Quadrature Sinewave Oscillator". 

Since I haven't expanded the frequency control beyond what is seen in
the schematic, I didn't want to add any circuitry to the drawing that I
hadn't actually tested.  Sorry to disappoint, I guess the addition of a
full-featured CV section is "left as an exercise for the reader."  :)
 
> In essence this is just an state-variable filter brougth up to self
> oscillation and the diode setup ensures the stabilization of the
> amplitude. If you compare this to the SEM/ASM-1 filter you are close.

Exactly.  Sorry, that's what I was trying to say in my first post.  In
fact, Mini Modular owners could probably add a "quadrature oscillator
mod" to their filter by adding a DPDT switch, an opamp, five diodes,
three resistors, and a trimmer.  

Here's a link to the Bode patent if you are interested (thanks to Mike
I. for mentioning the patent). 

http://www.delphion.com/details?pn=US04145670__
 
Best,

-Chris

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