[sdiy] Voltage references in VCO

[Magnus Danielson]

From: "Benjamín Velasco" <guatis at gmail.com>
Subject: [sdiy] Voltage references in VCO
Date: Mon, 10 Apr 2006 13:00:11 -0400
Message-ID: <3f2ffabc0604101000y1e0f5446sf5422ac8f5e6609 at mail.gmail.com>

> 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??

You need a higher voltage to drop down from.

For a VCO you want to "mirror" the voltage of one side to the other, typical
stabilize the -15 V to be a mirror of the +15V. This is done in the Oberheim
SEM. The SEM modules is feeded with +/- 18.5 V from normal voltage regulators.

Most VCOs isn't sensitive in themselfs to voltage (it's a bit complex formula
exercise behind that) but their 1V/Oct scaling is. If that is important, let
the VCO supply use a voltage reference of your choice.

Usually you don't have to do all this thought. It usually works well enought,
but if you feel like it... hey, go for it!

Cheers,
Magnus