[sdiy] tuning oscillators

[harry]

Hi Dave...

Well, you KNOW that the list can make voltage controlled oscillators...
The basic ones are relaxation oscillators... and schmitt trigger / integrator
oscillators.

The stability of both types is excellent, as long as you do not include the
1v/oct converter.

The relaxation oscillator either charges/discharges a capacitor until a trigger
threshold is reached, when it resets to an initial state. This gives a sawtooth
wave.

The integrator ramps until one schmitt trigger threshold is reached, then
reverses
polarity until the opposite threshold is reached. This gives a triangle wave and
a square wave.

Voltage controlled OTHER waveform oscillators usually start with one of these
cores.

H^) harry

Dave Krooshof wrote:

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