[sdiy] VCO reference voltages

[Oren Leavitt]

David G. Dixon wrote:
> Does anyone here have any strong views on deriving reference voltages from
> the power supply rails in VCOs for comparator or schmitt trigger thresholds,
> etc (as opposed to using precision references)?  I know that most "DIY" VCO
> designs do so.  I'm wondering whether most commercial VCOs also do so, and
> whether it is considered "kosher", even in more expensive VCOs.
> 


Me-self:
I greatly prefer on-board voltage refs for the "critical" voltages - the 
Schmitt trigger threshold, expo converter reference current, the "rails" 
for any coarse/fine tuning controls, or for the bonus point, even the 
level shifts/offset trims in the wave-shaping circuits.
Power supplies can be interchanged/replaced or a module moved from one 
one cabinet to another, without the need to recalibrate.

If you can set the VCO to any frequency and run it off of a +-15V or a 
+-12V supply with no noticeable change in pitch (or wave shapes/offsets 
for the bonus point), you're good! :-)

I would definitely consider on-board refs good design practice for 
modular systems.

You probably could omit on-board refs if your VCO is going to spend it's 
life with one well-regulated power supply, and performance is not 
absolutely critical.

- Oren