[sdiy] Precision voltage offset

[René Schmitz]

At 12:43 26.01.02 -0500, media at mail1.nai.net wrote:
>
>>Instead of a voltage divider and selector switch to the summing input, you
>>could have a single appropriately sized resistor and trimmer connected to
>>your reference voltage. They key is having a close match (or trimming) your
>>R-in and R-feedback so you don't compromise the accuracy of your keyboard
>>CV.  The only thing I would change here is having a fixed reference as
>>opposed to using the power supply rails like I did (me bad).
>
>Really??  I would think the rails would be rather stable.  Is the
>fluctuation audible??

In a pinch an extra regulator can be used as a reference, if you have
trimming anyway, 
initial precision isn't great, but the stability is often sufficient. (For
example all 
of the tuning voltages from my CV interface are derived from a 7805.)
However the regulator 
should just be used for that reference, and not for powering other parts of
the circuits.
It should see a constant load, and not one that changes over time.

Cheers,
 René


-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159