National AN-299 VCO idea (was: Re: [sdiy] Exponential converter information)

[James Patchell]

You are misunderstanding how they are compensating for the drift...they 
actually are using a heater/temp sensor...using one transistor for 
both...in a servo loop to control the temperature of the die.  The tempco 
of the polystyrene cap is -100ppM as I recall...the servo loop itself still 
has a +100ppM drift...this is what they are canceling out...

The servo temp controller loop does work...although...it consumes a lot of 
power.  If you want good tempco cancelation...you really need to look at 
the expo converter I did....

This is one I did with an MAT-04 
http://www.oldcrows.net/~patchell/synthmodulesII/200-1007.pdf

and a 
CA3046:http://www.oldcrows.net/~patchell/synthmodules/100-1007.pdf  this 
one has an explanation of how the temperature compensation works.

With the MAT-04 I get about 8 octaves of control to within +/- 2 
cents....the CA3046 gives me +/-2 cents over 7 octaves about...

And they are rock solid with respect to temperature...with the equipment I 
have...I cannot measure any scale drift.


At 07:48 AM 6/19/2005 -0700, synth at oldmail.charlielamm.com wrote:
>Nice links....I esp. like this one:
>
>http://www.national.com/an/AN/AN-299.pdf#page=1
>
>Has anyone actually messed around with this? i.e., can you really use a
>LM3046 and the temp dependence of a polystyrene cap as they show here, to
>cancel temp drift of a VCO?
>
>Maybe if you get a bunch of caps and try each one?
>
>Seems like a lot of work.....put in a cap, heat it up, see if it goes out
>of tune....but it's an interesting idea.....
>
>
>On Sun, 19 Jun 2005, Ray Wilson wrote:
>
> > Some links:
> >
> > http://www.national.com/an/AN/AN-311.pdf
> > http://www.national.com/an/AN/AN-286.pdf#page=4
> > http://www.national.com/an/AN/AN-299.pdf#page=1
> >
> > I hope you find them useful.
> >
> > Ray
> >
> >
> > ----- Original Message -----
> > From: "Aaron Bader" <sparked at zadzmo.org>
> > To: <synth-diy at dropmix.xs4all.nl>
> > Sent: Saturday, June 18, 2005 1:22 PM
> > Subject: [sdiy] Exponential converter information
> >
> >
> > >
> > > Can anyone suggest a good tutorial on exponential circuits? I can find
> > > schematics aplenty, particularly as part of some larger vco/vca circuit,
> > > but nothing that attempts to explain what exactly is going on in detail.
> > > --
> > >
> > > "Not a bird not a leaf not a sound/And well after the close of time"
> > > --Front 242
> > >
> > > Public Key: http://sparked.zadzmo.org/
> > >
> >

         -Jim
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