[sdiy] VCO comparator's reference voltage - rail OK?

[Pete Hartman]

Using the rails as reference is common, but not a great practice, for the
exact reason you mention.  Noise and fluctuations will impact your
circuit's behavior.  And particularly for a VCO that's not a great result.
A precision reference (e.g. LM4040-whatever voltage, or a zener, or a
decent regulator) is going to get you better stability.

Pete

On Sun, Mar 28, 2021 at 2:42 PM Neil Harper <metadata at gmx.com> wrote:

> so now that I have my own little VCO going on the breadboard, i want to
> do a perfboard module with it for my system. so now I'm thinking about
> how this VCO will remain stable in a system where the rails might be
> fluctuating.
>
> the first issue i see is that my LM311 comparator takes a reference
> voltage drawn from my +15V rail through a resistor to set the trip
> point. if that +15V waivers, so will my trip point.. and so will my
> frequency. so should things like that be derived from an onboard
> reference instead? is this common practice?
>
> I see in schematics like the ENS-76 VCO (
> http://www.synthsource.com/ens76/vcofig6.jpg ) that the comparator
> reference is just taken from the rail (through R13, R14 divider). Same
> with Thomas Henry's VCO-1's, lots of references right off the rails.
>
>
>
>
> --
> /// Neil Harper
> /// Every Wave is New Until it Breaks
>
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