[sdiy] Voltage references in VCO

[clark at andrews.edu]

> 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??

   Hi Ben,

   You don't need to go to the extremes of using onboard power regulators.
     Instead, what you should be using are buffered voltage references
such as the LM4040.  You could also go cheap and use a precision zener,
but they probably won't be as temperature stable as a good voltage
reference.
   Also, you only need to tie critical points to these buffered
references.  Op-amps are extremely good at rejecting power supply
variations, so these you can typically tie directly to the incoming
power rails.  It's only things like the expo converter, front panel
controls, trim-pots that are used as set voltages, that should be tied
to a stable reference point.
   Do keep in mind to use a reference voltage that is at least 1.5 volts
under the incoming power rails.

   Cheers,

   Tony

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