[sdiy] Group Level Shift?

[Ken Stone]

First, you will need 6 op-amps - used in pairs - one inverting buffer
followed by a scond to re-invert.

Consider this - What is the voltage at the inverting input of the standard
op-amp inverting buffer. It is 0V - the "virtual ground" or summing node. 

It will be 0V at the summing nodes of the three input buffers.

If all three are tied together through resistors as per your suggestion, how
much interaction will there be, considering all of their other ends of these
resistors are at 0V. None. In the real world there will be a little
interaction related to slew rates, but so slight it can be ignored.

Ken

>I have 3 separate signals that I want to level shift at the same time from 
>one switch. The signals are all +/-5. I want to have a toggle switch that 
>will shift the signals to 0 > +10, -5 > +5, and 0 > -10. Of course I want to 
>do it as economically as possible. Can I do it by simply adding a bias 
>resistor to the inverting input of an op-amp, plus the signal, and using a 
>switch to connect that resistor to either - rail, + rail or nothing?
>keep in mind there would be 3 op-amps - 1 per signal. If I connect the bias 
>resistors to the center of a SPDT switch will I get bad interactions between 
>the 3 channels when the switch is in the "off" position? Should I be looking 
>at a 3PDT for this?
>Does this even make sense?
>
>Thanks
>
>M. A. Ruberto
>
>
>
_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au or sasami at cgs.synth.net
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>