Simple op amp question

[harry]

In a word... NO.

The inverting op-amp works by balancing the current in and out of the inverting
input.  So if the input sees 1mA (through the input resistor) the opamp
will feed back 1mA through the feedback resistor. If the resistors are equal
value..
that means that a positive voltage at the input will result in an equal negative
voltage
at the output.

Make the feedback resistor "zero" and there will be essentially no gain at
all...
put in whatever you like and the output will stay at zero. (or very near... of
course
its now the same gain equasion... with Rf as .00001 ohms... thats not much gain
!!!

If you use a toggle to switch the non-invering input to ground (normal) or to
the
input resistor (the side AWAY from the inverting input)... that will do what you
want.
The input impedance will change though... I know you have just learned THAT
trick.
Driven from another op-amp output, you should be OK.

But OTOH... having opamp inputs go through wires to switches might get noise
pickup. ???

H^) harry

H^) harry

"J. Larry Hendry" wrote:

> A simple op amp question:
>
> OK, I am looking at an existing circuit here and not starting something from
> scratch.  Let's say I have an op amp wired in a simple inverting fashion
> with the input resistor and feed back resistor sized the same providing
> unity gain for the sole purpose of restoring the proper phase from a
> preceeding inverting stage (like a summming amp).  It appears to me (I have
> not tried it yet) that a simple switch wired from the inverting input to the
> output (shorting out the feeback resistor) could serve as a phase reversal
> switch effectively bypassing that unity gain inverting amp.
>
> Am I thinking right?  It has been my practice to short the unused amp in a
> dual in this fashion if it is not part of the circuit.  So, I cannot see why
> this would hurt the amp.
>
> As always, thanks for the help
>
> Larry (still learning slowly) Hendry