# Multiple CV-Ins

johns at oei.com johns at oei.com
Thu Dec 7 19:15:42 CET 1995

```     Topher wrote...

> I was wondering. My schems for VCO's, VCF's, etc. show one resistor
(usually a 100K) on each CV-in before going to the CV summing node. Is
there a problem with connecting the CV-ins BEFORE the 100K resistor
(and just using one resistor). I was planning on using banana plugs
and stacking in places where I wanted multiple inputs and it just
occured to me that this might be a problem.

(end of Topher's message)

I will attempt to answer this as I think it addresses the simple V=IR
application in op-amps.  Somebody correct me if I'm wrong.

1. You can't sum voltages simply by connecting several voltage sources
together.  No single node can be at more than one voltage potential
and that is what stacking banana plugs would do.  (Like saying a
bucket can have 2 quarts and 3 quarts of water at the same time).

2. I think what the question refers to is a single resistor for CV
input going to a current summing node (not a CV summing node) in a
summing op-amp circuit.  This op-amp configuration sum voltages by
summing currents and converting the summed current to a voltage.  The
currents are developed by allowing a current to pass from one node (at
CV input voltage) to another node (at constant, usually 0V) through a
resistor.  You need a current for every CV, therefore you need a
resistor for every CV.  This is basic op-amp theory.

So there is no way to sum voltages by using a single resistor instead
of one resistor per CV input.

JJS

```