Voltage controlled oscillator circuit needed

[charbot]

Im looking for a  VCO circuit for a "synth stick" like project.  I want something that puts out a sine wave though.  Something pretty basic that I can experiment with and build upon.    Analog, with one knob to control pitch, one output  and a way to change the waveform. A 4 octave range would also be nice.  I've found some stuff on diy synth sites, but most seem unnecessarily complex or integrated with other synth  circuits.   this is the best of what I'VE  found:
http://www.musicfromouterspace.com/analogsynth/old_synthesizer.html
this is the main page:
http://www.musicfromouterspace.com/analogsynth/SOUNDLABMINISYNTH/soundlab.html
Lots of cool stuff.   Man, synth stuff is a whole other world....

anyway, I was hoping that someone here could give me some ideas/ suggestions.
thanks in advance.

[gez]

In the analogue domain, 'simple' and 'sine wave' don't really mix unfortunately.

There's a voltage controlled sine oscillator in the LM13700 data sheet.  No idea if the range would be suitable, but I think Ton has tried all those circuits, so perhaps he'll chip in.

An 'easier' approach might be to run the oscillator at a higher frequency and splice it up for sine shaping.  Note that easier was in inverted commas though...

[Paul Perry (Frostwave)]

Another thing... do you want the frequency to be directly proportional to the voltage, or to increase exponentially, like in an analog synth?

Personally, I find it easiest to generate a triangle (eg see the LM13700 data sheet for a VCO) and then convert to a sine by overdriving the input to another LM13700.
http://www.musicfromouterspace.com/analogsynth/NewAugustSIN_TRI_SQR_LFO.html has a LM13700 triangle to sine converter section.

[slacker]

This is pretty simple http://www.musicfromouterspace.com/analogsynth/WP20/WP20_PG12.html probably worth looking at the rest of that project as well http://www.musicfromouterspace.com/analogsynth/WP20/WP20_TOC.html.

[Dan N]

Here's something interesting:

http://electro-music.com/forum/viewtopic.php?t=17762&sid=e7e2d6ff5e913f8963490a94d2b5d167

[puretube]

yes, Gez: OTA-based state variable filters with cranked up resonance make nice, easy sinewave LFOs...

[R.G.]

The simplest way to get one that actually works, and works reliably is to
1. make a VCO that has the other properties you want, but puts out a square wave.
2. Run this into a CD4046 phase locked loop and lock it to a frequency 32x higher than the VCO
3. Use the 32X square wave to generate a sine wave by resistor approximation.

This may sound complicated, but
(a) it uses all static logic and can be tested by hand on a scope or with LEDs
(b) it produces a very low-distortion sine wave, which can be made better yet by careful filtering. The distortion with NO filtering is about 5%. The first harmonic present is the 31st. Easy to filter.
(c) the necessary tweaking is all in the front end VCO.

[Paul Perry (Frostwave)]

If you are wanting to vary the wavfeform, you can do that using the 'overdriven OTA' method. As you increase the level of the triangle wave going in, the output varies from triangle to sine to rounded square. I did this with my optical theremin - I wish I had done it with the Ring Modulator carrier!

[charbot]

Thanks, lots of good leads.  Unfortunately, this project will be on hold until I order the parts.  Ill keep ya posted..   

if anyone else is following this thread,I also found this square to sine converter: http://www.oldtemecula.com/theremin/sixthvoice/index.htm

Not as simple as others suggested, but all parts are at RS and has intensity, gain and shape control.