[sdiy] Voltage references in VCO

[Magnus Danielson]

From: "Rob" <rob at emulatorarchive.com>
Subject: RE: [sdiy] Voltage references in VCO
Date: Tue, 11 Apr 2006 22:28:31 +0100
Message-ID: <00a101c65dae$ec023c60$0702a8c0 at study>

Hi,

> I agree with you that hacking my already built Vcos may be too complicated For
> this Vcos I just want to get rid of the LFO Noise so ill try first using the
> onboard regulators for my VCOs to get +-12V from the +-15V.

It is probably not very difficult at all:

1) The ref current resistor from voltage reference, assuming scaled for +15V
   you want a third of the original resistance if using a 5V reference.
2) The voltage comparator from voltage reference.
3) Hook up the output of an op-amp which has it's pos input at the voltage ref
   and the neg input at a voltage divider giving 5/12 of ratio or something
   thereabout, whichever makes you happy. For the negative side, just do the
   same thing but with two resistors one hooked to the +12V side and the other
   to the -12V side, the middle point is the neg input to that op-amp and the
   pos input hooked to ground. Since only one or two 100k pots is being fed so
   we are running 250-500 uA.

I think I see an additional cost of:

1 Voltage ref, 5V preferably
4 additional resistors (+/- 12V or whatever generation)
1 changed resistor
2 dropped resistors (the normal 15V to 5V divisor for voltage comparator)
1 added double-opamp of choice

You should be able to mod up your oscillators fairly quickly.

> Will a 10V ref from analog do the job? (perhaps changing some resistor
> values). For example the AD587 or REF01

Well, that should work well. But I would I would use a 5V.

Cheers,
Magnus