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

[David G Dixon]

I always use a reference in VCOs, and in most other things as well.  When
I'm wanting something pretty decent, I use REF02 (very low tempco).
Otherwise, LM336Z5.  Never the rails in a VCO for pitch-related voltages. 

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Neil
Harper
Sent: Sunday, March 28, 2021 12:39 PM
To: synth-diy at synth-diy.org
Subject: [sdiy] VCO comparator's reference voltage - rail OK?

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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