[sdiy] Precision voltage offset

[J. Larry Hendry]

Steal from this circuit:
http://www.wiseguysynth.com/larry/jlh-822/822_schematic_1of1.pdf
It does exactly what you want but has a selector to dial in the various
offsets (which is a lot more than you need).
But, you might find the octave switch handy.

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).

So, one LT1013, and handful of resistors and one trimmer and you are set.
There is a lengthy and detailed document explaining how the circuit works
that will help you select just what you need.
http://www.wiseguysynth.com/larry/jlh-822/822_theory.htm

Larry Hendry




----- Original Message -----
From: GothGeek Sysadmin <xyzzy at sysabend.org>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, January 25, 2002 1:29 PM
Subject: [sdiy] Precision voltage offset


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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