[sdiy] VCO reference voltages

[Simon Brouwer]

Oren Leavitt schreef:
>
>
> 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,

Note that if these both are derived from a non-stable reference voltage
the effect on frequency stability on the one will be compensated by that
on the other. You will only get a small difference in amplitude.

> the "rails"
> for any coarse/fine tuning controls,

A quick calculation: the voltage regulation of an LM7815 for output
current variation between 250..750 mA is 50mV (max) which is 0.33% of 15V.
Assuming 0V=middle of the audible VCO range then this corresponds to ca.
20 cents error at the top or bottom.

Using a 78L12 for local voltage reference could be a cheap option. Lightly
loaded and supplied by a stabilized voltage, line and load regulation are
hardly an issue; remains a ca. 0.008%/degC voltage drift.

-- 
Vriendelijke groet,

Simon Brouwer