[sdiy] Voltage references in VCO

[Rob]

Hi

I am with Paul on this one. You need a very stable reference voltage for the
VCO core and for the frequency adjustment pots. The more stable these
voltages the better the VCO will be. Forget onboard LM type regulator chips,
even the 723. These can drift 1mV in a few seconds. Use a precision voltage
reference chip (0.6ppm) and buffer with some low drift Op Amps. If you can’t
get to the core (SSM/CEM chips) then precision regulator the whole VCO power
supply 
This really works.

 

Regards
Rob

www.emulatorarchive.com <http://www.emulatorarchive.com/> 

 

b) you are trying to get cleaner *power* to the VCO. This is not what the
post is about. Rather, in a VCO design, there will be a *reference voltage*
(usually +5V) that either the integration cap is tied to, or that the
exponential current pair is referenced to. There are many stable +5V
reference chips to choose from, based on price/performance.

 

Paul S.

 

----- Original Message ----- 

From: Benjamín Velasco <mailto:guatis at gmail.com>  

To: Synth <mailto:synth-diy at dropmix.xs4all.nl>  DIY List 

Sent: Monday, April 10, 2006 12:00 PM

Subject: [sdiy] Voltage references in VCO

 

Hi list!!

 A few days ago i started a topic about my LFOs affecting the frequency of
my VCOs. Searching the archives i discovered this a very common problem.
Someone here suggested to use on board voltage references in the VCO rather
than using massive decouple in all the other modules. This makes sense to me
because in my synth the only modules that need critically good supply
voltages are the VCOs. So i plan to use lm317/337 in each of my VCOs. My
question is if it is better to connect only the critical points of the VCOs
to the on board refences, or it is enough to use them for the whole module?
I use +-15V. Can i use the lm317/337 to get a cleaner +-15V from the dirty
+-15V or do I need higher voltage at the inputs of the regulators?? 

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