[sdiy] New Vco

[René Schmitz]

At 14:50 28.09.01 -0400, tomg at efm wrote:
>Hi Rene, Neat! I did a quick proto-board works ok. Seems to
>go flat about 3 octs.... and I couldn't get a saw output.

I can't imagine that, because the pulse is shaped out of the sawtooth. 
Without it the whole oscillator wouldn't work. Have you tried putting
your scope probe to the output of the integrator (pin 12 of the 4069)?  
There ought to be a 7.5Vpp sawtooth sitting on top of 7.5V DC. Maybe 
there was a flakey connection. There is not much more for the saw output, 
and I notice that your circiuits often have the sawtooth sitting on DC 
anyway, so maybe you try it without the RC stage.

To make the tuning curve better I think I'll add that Franco compensation, 
its not a big deal, but I need some time to redraw my circuits. I'll all 
let you know.

>It's not really new though...Roland used something much like it
>it 1980 for the MRS-2. It was very convoluted running to a 555
>and back to a 4052 for division.

Yes, there are practically no new circuits, though I wasn't aware of that.

>They used a much simpler version for the MRS vc-adsr.. You
>may remember I posted it a few years ago......anyway here's
>something you may want to look at.  It's good for a little over
>4 octaves....It doesn't have a true saw out ether. I can give it
>one but it cost another opamp and fet....might as well build
>Terry's vco at that point.
>
>http://people.atl.mediaone.net/efm3/vco-mrs-1a.pdf

Yes I seem to remember that one, but where is the temperature compensation?! 

Cheers,
 René



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