SV: Re: Re: [sdiy] Polyester or Polypropylene for VCO?

[simon.oo.o at xs4all.nl]

Hi Karl,

karl dalen zei:
> Here we go.
>
> Now, if  we add a tiny DC voltage to Iref
> summing point we offset the VCO what if we
> use the Expo CV voltage as the offset voltage?
>
> Constant multiplication of a varying linear voltage! Ugh!

Linear detuning means that the frequency is increased by a constant
amount, for example, instead of 100 Hz or 5000 Hz you want 100.1 or 5000.1
Hz.

The output current of the expo converter (and thus the VCO frequency) is
*proportional* to the ref current. So increasing the ref current by 0.1%
gets you 100 -> 100.1 Hz, but then you also get 5000 -> 5005 Hz!

The same happens if you add a small offset voltage to the expo CV.

So, for linear detuning you have to add a tiny current to the *output* of
the expo converter.
The tapped capacitor is Jürgens clever idea to implement this in the SEM
VCO while being able to use realistic component values.


Vriendelijke groet,

Simon Brouwer
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