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

Roman Sowa modular at go2.pl
Sun Mar 28 22:38:42 CEST 2021

I'm sure your VCO already has some reference voltage, so use the same 
for comparator trip point. Otherwise how would you set up reference expo 
current? That is if your VCO uses expo converter at all.
Good practice is to supply all part of circuitry with supply voltage 
dependency on frequency. Reference sources are so cheap and popular it's 
no brainer.

Old schematics used supply rail for everything, because power supplies 
back then were commonly good and stable. If you look at any synth 
service manual it says in 1st step to adjust supply voltages with 1mV 
precision. This is hard to imagine today as in eurorack the power supply 
can be anything, plus combined with a lot of noise. So that calls for 
good regulation on the module itself.


W dniu 2021-03-28 o 21:39, Neil Harper pisze:
> 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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