[sdiy] monolithic VCO chips for FM??

[James Patchell]

Depends on what you are trying to do with the oscillator...if it is going 
into a modular setup...that will not be good.

You would hope that all of the oscillators in the modular would respond to 
the output of any pitch controller you plug into it.  If you have 
oscillators that deviate from the ideal in the midst of their tuning range, 
you will only be able to use them with your own voltage sources...i.e...you 
make sure that that the voltages deviate the same way...but then your 
friend brings over his resistor divider keyboard....oooppss....now it is 
out of tune...drat.

Having oscillators that are precise, in a modular setup, is 
essential.  Like I have said before, I have seen the ASM-1 type oscillator 
do 8 octaves to +/- 1 cent (which is the limit to what I can measure).  I 
personally feel that sort of performance, or better, is definitely needed.

Of course...this just reminds me I need to get my butt in gear and finish 
up my VCO test set which will make testing VCO's a lot less of a drag.... :-)

And no Harry, I don't wear a dress when I test VCO's.....(heading off 
comments :-)


At 06:23 PM 8/22/2004 -0400, WeAreAs1 at aol.com wrote:

>In a message dated 8/22/04 8:44:41 AM, patchell at cox.net writes:
>
><< This I find very amazing...(i.e. BS)....If you look at the data sheet for
>the XR2206, sweep linearity is only 8%....this is no where close to
>flat....the ASM-1 oscillator is somewhere around 0.01%.... >>
>
>The real-world test for VCO accuracy is:  Build two of them and see how well
>they track when tuned exactly in unison.  One VCO that has poor linearity 
>will
>sound pretty much OK if you play it by itself - kind of like the way a guitar
>string sounds OK even if the intonation up the neck is slightly off (or the
>way a solo violinist usually sounds pretty much in tune, even when they are
>not).  But two of those same VCO's tuned toegther... that will immediately 
>show
>your ears if and where any tuning/linearity problems exist.  Let's get two of
>those XR2206 VCO's up on the bench and see how they perform, then we'll 
>really
>know how "amazing" they are (using Jim's definition of "amazing").  Or better
>yet, let's get one of them and one well-calibrated ASM-1 VCO playing 
>together,
>and see how close they stay in tune over  multiple octaves.
>
>Michael Bacich

         -Jim
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