[sdiy] Additive VCO

[Scott Gravenhorst]

Maybe not.  The expo converter operates on a v/oct CV and outputs a linear
current.  If the output current is pushed through a constant resistance, it
then becomes a linear voltage.  This voltage can then be run either through
opamps, or simply through series rheostat connected pots.  Each pot then
supplies a current based on the voltage.  These pots then connect to the
summing nodes of linear voltage to current converters, one per VCO.  The
ratio of the pots to one another determines the harmonic relationship of the
VCOs.

The FatMan's 2 VCOs are connected like that, except without an expo
converter.  I imagine 16 would work.  I've had as many as 4 working like
that.  I think it will work as long as the linear voltage source is low
enough impedance.

"M.A. Koot" <makoot at gmx.net> wrote:
>Oh my...
>Stupid stupid...I just realized that placing opamp-adders ,after, the
>expo-converter is nonsense of coarse. While that would only work at one
>frequency... how dumb of me.
>I guess I'd have to build expo-converters before each Sine-source then.
>But the other questions still remain though. I hope there's someone familiar
>with this.
>
>cheers,
>Michiel
>
>
>
>> Hi everyone,
>> 
>> I'm trying to design an additive-VCO, there aren't too many around, and
>> that's why I would like to at least try it myself.
>> My initial idea is by having one expo-converter, having the output devided
>> over several Opamp-adders (to create the harmonic-offset). Those
>> Opamp-adders
>> have 2 inputs each then, one with the CVin, and one with the offset
>> voltage.
>> Each of those opamp outputs then go to seperate Sine-VCO's, one sine for
>> each opamp-output.
>> Then finaly mixing all the signals together, and that should be it.
>> The things I'm troubling with though, is how many harmonics (i.e.
>> Sine-VCO's) should I have at least to create a decent Additive VCO? I was
>> thinking of
>> about 16 Sine-VCO's. 
>> Another thing that popped up is: How "correct" do they have to be?
>> I can assume that if you want to create fairly true additive waves, with
>> Fourier in mind, they have to be pretty accurate, increasingly with the
>> harmonic-number probably.. But I wouldn't know how this would be in "real
>> life". 
>> I hope anybody could help me, does anybody maby already have some
>> experience
>> in this?.
>> 
>> Thanks, cheers,
>> Michiel
>> 
>> -- 
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>
>-- 
>+++ NEU bei GMX und erstmalig in Deutschland: TÜV-geprüfter Virenschutz +++
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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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