[sdiy] Precision voltage offset

[Jim Patchell]

    If nobody can point you to one...I can draw one up for you.  It is not
difficult.

    The main problem with a precision voltage source is having a stable voltage
reference.  While the LM336 is not the best reference in the world, it is
pretty cheap and works good.  This is the part that I generally use, and it has
a moderately low tempco.

    You could also use a zener diode as well, if you want real cheap, for a
voltage reference, but, it is more difficult to adjust.  If use a zener diode,
you want to use either 5.1 or 5.6 (I don't remember exactly which voltage) as
it is in this range that the tempco is close to zero.  Somebody on the list
that is much younger than I am might remember which zener voltage has the
lowest tempco....

    Also, depending on how precise you want to be able to set the voltage...you
might want to consider a ten turn pot with a dial...I have noticed that some
list members use such things to set their VCO's, I finally am starting to use
these as well.  The other option is to have a coarse and fine adjust pots.

    -Jim

GothGeek Sysadmin wrote:

> I've been looking around for some circuit examples and have had little luck
> and I just dont have the knowledge to do this without working from example.
> ( I can build anything, designing on the other hand is more problematic,
> unless I can work the Lego approach or its digital )
>
> I'm trying to offset a CV by a set amount.  Offset it down in fact.  The
> idea here is to offset F0 to 0 volts so I can use a standard Midi/CV with
> my Moog without having to patch it to a keyboard and use its transpose
> feature.  ( yes, I'm on the same quest I mailed about a month or 2 ago ).
>
> If someone has a circuit for this, would be great. Give me something to do
> tommorrow unstead of watching whatever marathon is on TV and cursing about
> eMagic logic...
>
> --
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