[sdiy] LM331

[Jim Patchell]

    I just took a look at the data sheet sheet....here are the problems
I see....

    Tempco:+/- 150ppM/C (Max)
    Linearity:They only plot this up to 10Kz, and it starts falling
apart at around 2->3KHz
    Exponential VCO Mod:This would be difficult.  The way the capacitor
is charged, converting to exponetial would be clumbsy, at best, IMHO.
    Wave Forms:Besides the pulse output, you can get a saw off of the
cap if you buffer it with a high impeadence buffer, BUT, again, due to
the way the capacitor is charged and they way the frequency is set, the
amplitude will vary with frequency, which, IMHO, makes the saw all but
useless.

    Conclusions:I still have not found a VCO core that is better than
the Terry Michaels/AMS-1 VCO.  The only good thing I can think of to say
about the LM331 is that it would make a better VCO than say the XR2206,
XR2207, or the 8038, from a pitch accuracy stand point.

    -Jim

Scott Gravenhorst wrote:

> Has anyone used this device for a musical VCO?
> I have the appnote and the claim for this IC
> is high linearity over large freq and temperature
> ranges.  From the appnotes, the draw back seems
> to be (other than square output) a larger number
> of 'glue' parts than many other VCO designs.
> I'm curious if someone has built a simplified
> VCO with it that is linear and stable enough
> for music without all the extra stuff to make it
> survive the Martian weather systems ?
>
> =========================================================
> - Government: The other religion.
> - The media's credibility should always be questioned.
> - Lambs who lie down with lions are lunch.
>
> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
> -- Linux Rex         | RedWebMail by RedStarWare
> -- FatMan: home1.GTE.NET/res0658s/TekLab_FatMan_WebSite/index.html