My First VCO - A few questions / Need suggestions

[djex]

Alright so after a great deal of research and pulling my hair out I've finally built a simple triangle wave VCO that I constructed my self (with a little help from a few data sheet examples and the many VCO diagrams on the net). I have not build it on a breadboard yet only in a simulator so far.

Now be aware that I'm new to all this so that's why I'm here. I'm quite proud of this VCO even though it's nothing to amazing .

I need suggestions and ideas on how I can implement 1V/Octave. I tried copying the fine / coarse / 1v/octave circuit idea from a VCO I found on MFOS but I couldn't seem to get it right. Is implementing 1v/octave just a matter of adjusting the capacitor size to give a low octave (for example low C, 16.35Hz) while the CV is at 1V? Also do I have the coarse and fine adjustments implemented properly in the circuit? They seem to work the way I need them to but I'm not sure if I've done it right.

I used an online simulator for my circuit. I know its not the best thing to use and I am going to recreate it in TINA-TI but at the time it was easy to understand and see my results in real time. To access the editable circuit go to this link:

http://tinyurl.com/63hw9fq
*I used tinyurl because the original link was massive

Also I put the circuit diagram below:



One final question I have is in my simulator program and as you can see in the circuit above I'm using +/-6V DC because that's what I have set up on my bread board. I have a 12V DC wall adapter that I've been using and then I use this circuit to get my +/-:



Is there a better way to do this so I can get +/-12V DC from my adapter instead of getting +/-6V DC?

[modulus in moduli]

That simulation looks really nice with (I think) the color changing as the voltage changes!

I'm not sure this osc lends itself for an easy adaptation to v/oct. You could put an exp convertor at the point where the input voltages sum and the 100 and 22k go out. afaik this is never used because you'd probably only get a very small range where it would work well (2 oct? pure guess).

Most VCO's work by using a v/oct convertor that outputs a current in stead of a voltage. Then you would need a method to invert the current instead of inverting the voltage as you do. This can be done with a couple of transistors (see some Buchla schematics that float around on the web) or by using an OTA. The latter you can find in the Thomas Henry VCO-1. You'd need to copy everything from the input upto the integrator. If you do so, the only difference with TH-VCO-1 and yours is that TH uses a discrete schmitt-trigger where you use the opamp (I am only considering the core, not the wave-shapers that are different too).

For your second question, I don't think there is an easy way to do that, you could use a swiched mode power converter. There are some IC's for that but I don't have experience with them. That would never be as simple as your current solution though.

[adambee7]

In THs book "synthesizer for the 21st century" there is a version of the VCO-1 called the VCO LM. it uses a LM13700 instead of discrete schmitt/ca3080. i've built both and they both sound good.

[djex]

Hmm well I tried setting up the circuit I posted above on a bread board to test it but I can't seem to get it to oscillate, not sure what's wrong really. Going to try a few things today to see if I can get it working.

And adambee7 thanks for the suggestion. It looks like I'll have to buy to book if I want to take a look at the circuit diagram for it.

[adambee7]

he has a couple of really good books available. well worth having.