[sdiy] PLL-controlled VCO

[James Patchell]

Anything is possible...

You are probably going to find it easier to build a relatively drift free 
VCO...rather than doing this, however...you should find that even a VCO 
that has an expo converter compensated with a Q81 type tempco will be more 
than drift free enough...or you can even build a VCO with an expo converter 
like the ones I did:

http://www.oldcrows.net/~patchell/synthmodulesII/200-1007.pdf

         I haven't check them in a couple of months...but they have been 
rock solid steady (I have three of them in a system...excellent tracking, 
and about +/- 2 cents across 8 octaves).

         I know where you are coming from...making pitch stable oscillators 
is not an easy task.  However...I think you are going to find that using a 
PLL is going to be very challenging.

         Although...you can play a lot of fun games with the loop filter to 
get some interesting effects...

At 03:06 AM 5/13/2005 +0100, Andrew Wyld wrote:
>Hi there,
>
>I am wondering if it is possible to use an arbitrarily weird VCO in a PLL.
>Basically I want to use a square wave from a computer (specifically a
>horribly cannibalized Commodore 64) to drive an analogue VCO, making a
>drift-free synth that can be sequenced and controlled completely from the
>computer console, but still sounds like an analogue synth.
>
>I'm figuring I can do this if I do some kind of horrible gating operation on
>the VCO.  What would people suggest I read up on / look up on the net / etc?
>
>Thanks!
>
>Andrew Wyld
>
>postmaster at ripe-fruit.co.uk
>http://www.ripe-fruit.co.uk/
>
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         -Jim
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