4046 VCO experiment

[Jim Patchell]

Scott Gravenhorst wrote:

> Harry, Martin and all,
>
> Thanks for the help andsuggestions.  It seems that the 4046 VCO
> really isn't suited for this sort of application.  It hasn't
> performed in a linear fashion for me, at least not over a large
> enough range to be a musical VCO.  Great little PLL though.
>
> I now have 3 options on the table:
>
> AD654, XR2206 and 566.
>
> I like the AD654 because it has a built in V/I converter.  The 566
> can probably work with an external V/I converter.  Looking at XR2206,
> I think it has one built in too.  Now I am determining how close to
> "unobtainium" each of these is.  I've already had trouble ordering
> the 566, I got my order bounced from 2 places for zero on hand, I
> still have one order pending.
>

    A couple of days ago I posted a message that listed the linearities
of selected (and ancient) VCO chips.  Even over 1 decade, the XR2206
would not make a good musical VCO (I already forgot the number that I
posted, but it was about 2% over 10:1, much worse over 1000:1, something
like 5-8%).  I don't really understand why some of these oscialators are
so bad.  And I can understand why one would want a single chip,
inexpensive solution to a VCO (I really wish the CEM3340 was still in
production).

    The thing that amazed me was that the 8038 was the best of the lot
(with a 0.2% linearity).

    Has anybody tried the off the shelf V->F converters?  I seem to
remember that some of these are down in the 0.01% linearity range.

>
> <sigh>
>
> If worse comes to worst, I may just clone the FatMan VCO.  At least
> I can get the parts for it.
>
> -- Scott Gravenhorst : On The Edge, but the Edge of What?
> -- Linux Rex, Linux Vobiscum  |  RedWebMail by RedStarWare
> -- FatMan: www.teklab.com/~chordman
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> -- The 21st century does NOT start in the year 2000!!!

-Jim