Tuning lunetta?

madskill42 · Joined: Jun 30, 2011 Posts: 25 Location: czech rep

Hi there,

I've been building stuff from CMOS for past a week or so, and after APC (which was somehow broken after it was working for like 10 minutes, hehe), I'm building stuff with 40106 chip. It's working quite well, but I have a question about tuning.

I've searched the forum and came across this:
http://www.electronics-tutorials.ws/waveforms/generators.html

and this equation seems to be solution to tuning oscillators. But I might have it wrong, because nothing that came out of this equation is even remotely close to what is measured in spectral analyzer in Ableton.

So it the equation like this?

Frequency = 1 / (1,2 * R * C)

in which R stands for resistance in ohms and C for capacity in farads.

Another thing that bothers me is fact that breadboard is supposed to create some "parasitic" capacity which can cause tuning of breadboarded circuit sound different than mounted on PCB.

And last thing I've noticed. When I connect 10K pot instead or just resistor, and try to tune it to certain frequency, after a while signal starts to "slide" higher or down in pitch very slowly. I don't know why is this happening. Pot was standing still on table.

So, is there some way how to get precise tuned 40106 oscillators?

bubzy · Posted: Thu Jun 30, 2011 7:44 am Post subject:

welcome to electro-music Smile

im no expert on this but afaik, you will need to build a proper vco if you want to be able to "tune" it (and then when its built you will need a control voltage that you can actually 'play' the notes with) you can get rough approximations of the notes you want and probably get them to hold fairly well too by using preset resistor values. (make sure you tie the unused inputs on the 40106 to GND, this is a common problem with weird behaviour)

you will get drift on most things that arent inherently "drift proof" which is why proper VCO's have tempco's and very stable capacitor types.
check this out for a 40106 vco http://electro-music.com/forum/topic-34550.html

here also are some awesomely simple circuits, including a really easy vco (not sure of its tracking, but its so easy its worth a go)
http://electro-music.com/forum/viewtopic.php?highlight=40106+vco&t=28799