[sdiy] tuning oscillators

[Dave Krooshof]

As I mentioned here before, I'm taking a coarse in electronics.
And naturally my attention is in oscillators and filters. I constantly
run into very dull schemes though, as those techies seem to want
very stable oscillators, I guess they are more interested in clocks.
So all of the schems in my books (about half a metre now) seem to
use fixed parts for the frequency determing circuits.

They all start of with RC which is kind of tuneable by the R, but not that
nicely in a synth as far as I managed. The Schmittriggers are OKish, but
not my favourite soundwise (in my tests).
And it seems one needs to turn two pots to set the frequency.
Then they go into LC circuits, that bring two hardly tunable components.
To make it worse, they then go into christals, and I feel I'm drifting again,
for a christal is most untunable.

All this would have been OK when I wanted to build an organ with 12 fixed
oscillators and a fist full deviders to make octaves.
But as I want constant frequency control over several oscillators, this is
not at all the direction I need to go.

So I was wondering...
What are the basic principals to make a voltage controlled oscillator?
What would you use as a frequency dertermining unit, and what
are the principals to be able to tune it over a several oktave range?

I'd like to underline that I'm looking for concepts rather then concrete
schems, as I want to be able to understand it to the point that I can come
up with schems myself.
And between brackets, I happen to feel 12tones in a tempered scale is
kind of passe, so I'm not so much interested in 1volt/oktave standards.


Hoping for an interesting thread on the subject,

Dave Krooshof


Ps. I asked Michel Waisvisz how he dealt with this problem, and he told
me a nice story about a capacitor made of plastic bags and metal plates,
a thing you could put under your arm like the bag of ulean pipes, and
sqeezing it altered the capacity. Inspirering, isn't it?

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Dave Krooshof http://www.xs4all.nl/~krooshof
geluidstechnicus @ http://www.ahk.nl/the/theatertechniek_ov.html
webmaster: http://www.popronde.nl
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